Module 19: The Respiratory System

Transport of carbon dioxide in the blood, learning outcomes.

  • Explain how carbon dioxide is transported from body tissues to the lungs

Carbon dioxide molecules are transported in the blood from body tissues to the lungs by one of three methods: dissolution directly into the blood, binding to hemoglobin, or carried as a bicarbonate ion. Several properties of carbon dioxide in the blood affect its transport. First, carbon dioxide is more soluble in blood than oxygen. About 5 to 7 percent of all carbon dioxide is dissolved in the plasma. Second, carbon dioxide can bind to plasma proteins or can enter red blood cells and bind to hemoglobin. This form transports about 10 percent of the carbon dioxide. When carbon dioxide binds to hemoglobin, a molecule called carbaminohemoglobin is formed. Binding of carbon dioxide to hemoglobin is reversible. Therefore, when it reaches the lungs, the carbon dioxide can freely dissociate from the hemoglobin and be expelled from the body.

Third, the majority of carbon dioxide molecules (85 percent) are carried as part of the bicarbonate buffer system . In this system, carbon dioxide diffuses into the red blood cells. Carbonic anhydrase (CA) within the red blood cells quickly converts the carbon dioxide into carbonic acid [latex]\left(\text{H}_{2}\text{CO}_{3}\right)[/latex]. Carbonic acid is an unstable intermediate molecule that immediately dissociates into bicarbonate ions [latex]\left(\text{HCO}^{-}_{3}\right)[/latex] and hydrogen (H + ) ions. Since carbon dioxide is quickly converted into bicarbonate ions, this reaction allows for the continued uptake of carbon dioxide into the blood down its concentration gradient. It also results in the production of H + ions. If too much H + is produced, it can alter blood pH. However, hemoglobin binds to the free H + ions and thus limits shifts in pH. The newly synthesized bicarbonate ion is transported out of the red blood cell into the liquid component of the blood in exchange for a chloride ion (Cl − ); this is called the chloride shift . When the blood reaches the lungs, the bicarbonate ion is transported back into the red blood cell in exchange for the chloride ion. The H + ion dissociates from the hemoglobin and binds to the bicarbonate ion. This produces the carbonic acid intermediate, which is converted back into carbon dioxide through the enzymatic action of CA. The carbon dioxide produced is expelled through the lungs during exhalation.

[latex]\text{CO}_2+\text{H}_2\text{O}\longleftrightarrow\underset{\left(\text{carbonic acid}\right)}{\text{H}_2\text{CO}_3}\longleftrightarrow\underset{\left(\text{bicarbonate}\right)}{\text{HCO}_3+\text{H}^+}[/latex]

The benefit of the bicarbonate buffer system is that carbon dioxide is “soaked up” into the blood with little change to the pH of the system. This is important because it takes only a small change in the overall pH of the body for severe injury or death to result. The presence of this bicarbonate buffer system also allows for people to travel and live at high altitudes: When the partial pressure of oxygen and carbon dioxide change at high altitudes, the bicarbonate buffer system adjusts to regulate carbon dioxide while maintaining the correct pH in the body.

Carbon Monoxide Poisoning

While carbon dioxide can readily associate and dissociate from hemoglobin, other molecules such as carbon monoxide (CO) cannot. Carbon monoxide has a greater affinity for hemoglobin than oxygen. Therefore, when carbon monoxide is present, it binds to hemoglobin preferentially over oxygen. As a result, oxygen cannot bind to hemoglobin, so very little oxygen is transported through the body (Figure 1).

 Percent oxygen saturation of hemoglobin at an oxygen pressure of 100 millimeters of mercury decreases as percent carbon monoxide increases. In the absence of carbon monoxide, hemoglobin is 98 percent saturated with oxygen. At twenty percent carbon monoxide, hemoglobin is 77 percent saturated with oxygen. At forty percent carbon monoxide, hemoglobin is 68 percent saturated with oxygen. At sixty percent carbon monoxide, hemoglobin is 40 percent saturated with oxygen. At eighty percent carbon monoxide, hemoglobin is 20 percent saturated with oxygen.

Figure 1. As percent CO increases, the oxygen saturation of hemoglobin decreases.

Carbon monoxide is a colorless, odorless gas and is therefore difficult to detect. It is produced by gas-powered vehicles and tools. Carbon monoxide can cause headaches, confusion, and nausea; long-term exposure can cause brain damage or death. Administering 100 percent (pure) oxygen is the usual treatment for carbon monoxide poisoning. Administration of pure oxygen speeds up the separation of carbon monoxide from hemoglobin.

In Summary: Transport of Carbon Dioxide in the Blood

Carbon dioxide can be transported through the blood via three methods. It is dissolved directly in the blood, bound to plasma proteins or hemoglobin, or converted into bicarbonate.

The majority of carbon dioxide is transported as part of the bicarbonate system. Carbon dioxide diffuses into red blood cells. Inside, carbonic anhydrase converts carbon dioxide into carbonic acid [latex]\left(\text{H}_{2}\text{CO}_{3}\right)[/latex], which is subsequently hydrolyzed into bicarbonate [latex]\left(\text{HCO}^{-}_{3}\right)[/latex] and H + . The H + ion binds to hemoglobin in red blood cells, and bicarbonate is transported out of the red blood cells in exchange for a chloride ion. This is called the chloride shift.

Bicarbonate leaves the red blood cells and enters the blood plasma. In the lungs, bicarbonate is transported back into the red blood cells in exchange for chloride. The H + dissociates from hemoglobin and combines with bicarbonate to form carbonic acid with the help of carbonic anhydrase, which further catalyzes the reaction to convert carbonic acid back into carbon dioxide and water. The carbon dioxide is then expelled from the lungs.

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StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-.

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StatPearls [Internet].

Physiology, carbon dioxide transport.

James Doyle ; Jeffrey S. Cooper .

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Last Update: July 4, 2023 .

  • Introduction

Carbon dioxide is an important side product of the citric acid cycle (Krebs cycle). This oxidized carbon represents an end product of metabolism that, ultimately, needs to be removed using transport to the lungs and subsequent expiration out into the surrounding environment. Together with renal regulation, this complex process of carbon dioxide production, transport, and elimination is the principal means by which the body regulates the blood’s pH. Disorders in this delicate process can result in acid-base derangements and may be acute or chronic.

  • Cellular Level

Carbon dioxide production occurs in cells, mainly during the citric acid cycle in the cytoplasm and mitochondria, respectively. During these successive biochemical reactions, the energy stored in the reduced carbon bonds of fats, sugars, and proteins is gradually liberated in a series of stepwise reactions until the carbon atom is fully oxidized and bound to two oxygen atoms. This final product is carbon dioxide. Like other molecules, carbon dioxide always moves down its concentration gradient from sites of production in the mitochondria and cytosol through the phospholipid membrane and into the extracellular space. However, carbon dioxide diffuses readily, much quicker than oxygen. As the cells produce carbon dioxide, it dissolves into the water of the cytoplasm and continues to build up until it reaches a partial pressure greater than 40 to 45 mmHg. This buildup sets up a concentration gradient down which carbon dioxide can diffuse. From that extracellular space, carbon dioxide molecules freely diffuse through the capillary walls, rapidly equilibrating and increasing the partial pressure of carbon dioxide in the blood from about 40 mmHg on the arterial side of a capillary to 45 to 48 mmHg on the venous side. [1]  

Once the venous blood returns to the lungs, the carbon dioxide diffuses out of the bloodstream, through the capillaries, and into the alveoli, from where it is expelled, during which time oxygen simultaneously binds with hemoglobin to be carried back to the tissues.

There are three means by which carbon dioxide is transported in the bloodstream from peripheral tissues and back to the lungs: (1) dissolved gas, (2) bicarbonate, and (3) carbaminohemoglobin bound to hemoglobin (and other proteins). As carbon dioxide diffuses into the bloodstream from peripheral tissues, approximately 10% remains dissolved either in plasma or the blood's extracellular fluid matrix to a partial pressure of about 45 mmHg. [2]  Most of the carbon dioxide diffusing through the capillaries and ultimately into the red blood cells combines with water via a chemical reaction catalyzed by the enzyme carbonic anhydrase, forming carbonic acid. Carbonic acid almost immediately dissociates into a bicarbonate anion (HCO3-) and a proton. Thus, bicarbonate is the primary means by which carbon dioxide is transported throughout the bloodstream according to the equation CO2 + H2O --> H2CO3 --> H+ + HCO3-.  

As carbon dioxide continues to be produced by tissues, this reaction is continually driven forward in the periphery, according to Le Chatelier's principle. The proton formed by this reaction is buffered by hemoglobin, while the bicarbonate anion diffuses out of the red blood cell and into the serum in exchange for a chloride anion through a special HCO3-/Cl- transporter. Thus, venous blood has both a higher concentration of bicarbonate and a lower concentration of chloride, thanks to this so-called chloride shift. In the lungs, this process reverses as both the HCO3-/Cl- exchanger and carbonic anhydrase enzyme reverse directions; this results in an influx of bicarbonate into red blood cells, an efflux of chloride ions, and the generation of first carbonic acid and then carbon dioxide. The carbon dioxide diffuses out of the red blood cells, through the capillary walls, and into the alveolar spaces when exhaled. [1]  Finally, the remaining 10% of the carbon dioxide that diffuses into the bloodstream and, subsequently, into the red blood cells binds to the amino terminus of proteins, predominantly hemoglobin, to form carbaminohemoglobin. [2]  Of note, this site differs from the one to which oxygen binds. Multiple physiologic phenomena ensure that this continuous cycle runs with maximal efficiency.

Oxygen delivery and carbon dioxide removal intrinsically link through processes described by the Bohr and Haldane effects. While not detailed here, the Bohr effect states that the increase of carbon dioxide in the blood in peripheral tissues causes a right shift in the oxygen-hemoglobin dissociation curve and, consequently, increased oxygenation of the tissues. Once the carbon dioxide-enriched blood reaches the lungs, however, the reverse of this reaction will also occur. As the influx of oxygen increases hemoglobin saturation, the carbon dioxide is more likely to become detached and diffused into the alveoli for exhalation; this is called the Haldane effect. [3]

Specifically, the Haldane effect describes the difference in carbon dioxide carrying capacity in oxygenated blood compared with deoxygenated blood. At a consistent partial pressure of carbon dioxide, the Haldane effect states that oxygenated (arterial) blood will carry less carbon dioxide than deoxygenated (venous) blood due to a combination of an impaired ability of hemoglobin to buffer the excess carbon dioxide as well as a decreased capacity for carbamino carriage. [2] As oxygen binds to hemoglobin, the hemoglobin becomes more acidic, which has two effects. First, it reduces the binding affinity of the hemoglobin for carbon dioxide, making the carbon dioxide more likely to dissociate from the hemoglobin and diffuse out of the red blood cell into the alveolar space. Second, acidic hemoglobin can release a proton that will combine with bicarbonate to form carbonic acid. Again, Le Chatelier's principle drives the following reaction forward as blood passes through the alveoli: H+ + HCO3- --> H2CO3 --> CO2 + H2O. The carbon dioxide produced here continually diffuses into the alveoli and is exhaled, ensuring favorable kinetics for the reaction to proceed. Thus, the Haldane effect increases the quantity of carbon dioxide that can be eliminated during a given timeframe. Graphically, the Haldane effect is represented by a right shift that occurs in the carbon dioxide dissociation curve (see graph). [4]

In peripheral tissues, where oxygen content is low, carbon dioxide binds to hemoglobin to form carbaminohemoglobin. As blood returns to the lungs and the partial pressure of oxygen increases, the carbon dioxide dissociation curve shifts right (seen by the arrow showing the offloading of carbon dioxide as oxygenation increases), lowering the total carbon dioxide content in the bloodstream. Thus, although the partial pressure of carbon dioxide decreases from 45 or 46 mmHg on the venous side to 40 mmHg on the arterial side, the total amount of carbon dioxide in the bloodstream decreases by a much greater percentage.

  • Clinical Significance

Clinically, transportation and elimination of carbon dioxide become especially crucial in regulating the pH of the blood. Should the partial pressure of carbon dioxide increase or decrease, the body’s pH will decrease or increase, respectively. This change can occur as a primary disorder, such as in the case of an individual who becomes apneic and develops acidosis because of the increased partial pressure of carbon dioxide, or as a compensatory reaction, such as in a person with diabetes who develops ketoacidosis and hyperventilates to decrease carbon dioxide levels and prevent the pH from dropping too low. [5]

  • Review Questions
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  • Comment on this article.

Haldane Effect. The carbon dioxide dissociation curve shows a graphical representation of the Haldane effect. Contributed by James Doyle, BS

Disclosure: James Doyle declares no relevant financial relationships with ineligible companies.

Disclosure: Jeffrey Cooper declares no relevant financial relationships with ineligible companies.

This book is distributed under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0) ( http://creativecommons.org/licenses/by-nc-nd/4.0/ ), which permits others to distribute the work, provided that the article is not altered or used commercially. You are not required to obtain permission to distribute this article, provided that you credit the author and journal.

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22.5 Transport of Gases

Learning objectives.

By the end of this section, you will be able to:

  • Describe the principles of oxygen transport
  • Describe the structure of hemoglobin
  • Compare and contrast fetal and adult hemoglobin
  • Describe the principles of carbon dioxide transport

The other major activity in the lungs is the process of respiration, the process of gas exchange. The function of respiration is to provide oxygen for use by body cells during cellular respiration and to eliminate carbon dioxide, a waste product of cellular respiration, from the body. In order for the exchange of oxygen and carbon dioxide to occur, both gases must be transported between the external and internal respiration sites. Although carbon dioxide is more soluble than oxygen in blood, both gases require a specialized transport system for the majority of the gas molecules to be moved between the lungs and other tissues.

Oxygen Transport in the Blood

Even though oxygen is transported via the blood, you may recall that oxygen is not very soluble in liquids. A small amount of oxygen does dissolve in the blood and is transported in the bloodstream, but it is only about 1.5% of the total amount. The majority of oxygen molecules are carried from the lungs to the body’s tissues by a specialized transport system, which relies on the erythrocyte—the red blood cell. Erythrocytes contain a metalloprotein, hemoglobin, which serves to bind oxygen molecules to the erythrocyte ( Figure 22.5.1 ). Heme is the portion of hemoglobin that contains iron, and it is heme that binds oxygen. One hemoglobin molecule contains iron-containing Heme molecules, and because of this, each hemoglobin molecule is capable of carrying up to four molecules of oxygen. As oxygen diffuses across the respiratory membrane from the alveolus to the capillary, it also diffuses into the red blood cell and is bound by hemoglobin. The following reversible chemical reaction describes the production of the final product, oxyhemoglobin (Hb–O 2 ), which is formed when oxygen binds to hemoglobin. Oxyhemoglobin is a bright red-colored molecule that contributes to the bright red color of oxygenated blood.

In this formula, Hb represents reduced hemoglobin, that is, hemoglobin that does not have oxygen bound to it. There are multiple factors involved in how readily heme binds to and dissociates from oxygen, which will be discussed in the subsequent sections.

This diagram shows a red blood cell and the structure of a hemoglobin molecule.

Function of Hemoglobin

Hemoglobin is composed of subunits, a protein structure that is referred to as a quaternary structure. Each of the four subunits that make up hemoglobin is arranged in a ring-like fashion, with an iron atom covalently bound to the heme in the center of each subunit. Binding of the first oxygen molecule causes a conformational change in hemoglobin that allows the second molecule of oxygen to bind more readily. As each molecule of oxygen is bound, it further facilitates the binding of the next molecule, until all four heme sites are occupied by oxygen. The opposite occurs as well: After the first oxygen molecule dissociates and is “dropped off” at the tissues, the next oxygen molecule dissociates more readily. When all four heme sites are occupied, the hemoglobin is said to be saturated. When one to three heme sites are occupied, the hemoglobin is said to be partially saturated. Therefore, when considering the blood as a whole, the percent of the available heme units that are bound to oxygen at a given time is called hemoglobin saturation. Hemoglobin saturation of 100 percent means that every heme unit in all of the erythrocytes of the body is bound to oxygen. In a healthy individual with normal hemoglobin levels, hemoglobin saturation generally ranges from 95 percent to 99 percent.

Oxygen Dissociation from Hemoglobin

Partial pressure is an important aspect of the binding of oxygen to and disassociation from heme. An oxygen–hemoglobin dissociation curve is a graph that describes the relationship of partial pressure to the binding of oxygen to heme and its subsequent dissociation from heme ( Figure 22.5.2 ). Remember that gases travel from an area of higher partial pressure to an area of lower partial pressure. In addition, the affinity of an oxygen molecule for heme increases as more oxygen molecules are bound. Therefore, in the oxygen–hemoglobin saturation curve, as the partial pressure of oxygen increases, a proportionately greater number of oxygen molecules are bound by heme. Not surprisingly, the oxygen–hemoglobin saturation/dissociation curve also shows that the lower the partial pressure of oxygen, the fewer oxygen molecules are bound to heme. As a result, the partial pressure of oxygen plays a major role in determining the degree of binding of oxygen to heme at the site of the respiratory membrane, as well as the degree of dissociation of oxygen from heme at the site of body tissues.

The top panel of this figure shows a graph with oxygen saturation of the y-axis and partial pressure of oxygen on the x-axis.

The mechanisms behind the oxygen–hemoglobin saturation/dissociation curve also serve as automatic control mechanisms that regulate how much oxygen is delivered to different tissues throughout the body. This is important because some tissues have a higher metabolic rate than others. Highly active tissues, such as muscle, rapidly use oxygen to produce ATP, lowering the partial pressure of oxygen in the tissue to about 20 mm Hg. The partial pressure of oxygen inside capillaries is about 100 mm Hg, so the difference between the two becomes quite high, about 80 mm Hg. As a result, a greater number of oxygen molecules dissociate from hemoglobin and enter the tissues. The reverse is true of tissues, such as adipose (body fat), which have lower metabolic rates. Because less oxygen is used by these cells, the partial pressure of oxygen within such tissues remains relatively high, resulting in fewer oxygen molecules dissociating from hemoglobin and entering the tissue interstitial fluid. Although venous blood is said to be deoxygenated, some oxygen is still bound to hemoglobin in its red blood cells. This provides an oxygen reserve that can be used when tissues suddenly demand more oxygen.

Factors other than partial pressure also affect the oxygen–hemoglobin saturation/dissociation curve. For example, a higher temperature promotes hemoglobin and oxygen to dissociate faster, whereas a lower temperature inhibits dissociation (see Figure 22.5.2 , middle ). However, the human body tightly regulates temperature, so this factor may not affect gas exchange throughout the body. The exception to this is in highly active tissues, which may release a larger amount of energy than is given off as heat. As a result, oxygen readily dissociates from hemoglobin, which is a mechanism that helps to provide active tissues with more oxygen.

Certain hormones, such as androgens, epinephrine, thyroid hormones, and growth hormone, can affect the oxygen–hemoglobin saturation/disassociation curve by stimulating the production of a compound called 2,3-bisphosphoglycerate (BPG) by erythrocytes. BPG is a byproduct of glycolysis. Because erythrocytes do not contain mitochondria, glycolysis is the sole method by which these cells produce ATP. BPG promotes the disassociation of oxygen from hemoglobin. Therefore, the greater the concentration of BPG, the more readily oxygen dissociates from hemoglobin, despite its partial pressure.

The pH of the blood is another factor that influences the oxygen–hemoglobin saturation/dissociation curve (see Figure 22.5.2 ). The Bohr effect is a phenomenon that arises from the relationship between pH and oxygen’s affinity for hemoglobin: A lower, more acidic pH promotes oxygen dissociation from hemoglobin. In contrast, a higher, or more basic, pH inhibits oxygen dissociation from hemoglobin. The greater the amount of carbon dioxide in the blood, the more molecules that must be converted, which in turn generates hydrogen ions and thus lowers blood pH. Furthermore, blood pH may become more acidic when certain byproducts of cell metabolism, such as lactic acid, carbonic acid, and carbon dioxide, are released into the bloodstream.

Hemoglobin of the Fetus

The fetus has its own circulation with its own erythrocytes; however, it is dependent on the mother for oxygen. Blood is supplied to the fetus by way of the umbilical cord, which is connected to the placenta and separated from maternal blood by the chorion. The mechanism of gas exchange at the chorion is similar to gas exchange at the respiratory membrane. However, the partial pressure of oxygen is lower in the maternal blood in the placenta, at about 35 to 50 mm Hg, than it is in maternal arterial blood. The difference in partial pressures between maternal and fetal blood is not large, as the partial pressure of oxygen in fetal blood at the placenta is about 20 mm Hg. Therefore, there is not as much diffusion of oxygen into the fetal blood supply. The fetus’ hemoglobin overcomes this problem by having a greater affinity for oxygen than maternal hemoglobin ( Figure 22.5.3 ). Both fetal and adult hemoglobin have four subunits, but two of the subunits of fetal hemoglobin have a different structure that causes fetal hemoglobin to have a greater affinity for oxygen than does adult hemoglobin.

This graph shows the oxygen saturation versus the partial pressure of oxygen in fetal hemoglobin and adult hemoglobin.

Carbon Dioxide Transport in the Blood

Carbon dioxide is transported by three major mechanisms. The first mechanism of carbon dioxide transport is by blood plasma, as some carbon dioxide molecules dissolve in the blood. The second mechanism is transport in the form of bicarbonate (HCO 3 – ), which also dissolves in plasma. The third mechanism of carbon dioxide transport is similar to the transport of oxygen by erythrocytes ( Figure 22.5.4 ).

This figure shows how carbon dioxide is transported from the tissue to the red blood cell.

Dissolved Carbon Dioxide

Although carbon dioxide is not considered to be highly soluble in blood, a small fraction—about 7 to 10 percent—of the carbon dioxide that diffuses into the blood from the tissues dissolves in plasma. The dissolved carbon dioxide then travels in the bloodstream and when the blood reaches the pulmonary capillaries, the dissolved carbon dioxide diffuses across the respiratory membrane into the alveoli, where it is then exhaled during pulmonary ventilation.

Bicarbonate Buffer

A large fraction—about 70 percent—of the carbon dioxide molecules that diffuse into the blood is transported to the lungs as bicarbonate. Most bicarbonate is produced in erythrocytes after carbon dioxide diffuses into the capillaries, and subsequently into red blood cells. Carbonic anhydrase (CA) causes carbon dioxide and water to form carbonic acid (H 2 CO 3 ), which dissociates into two ions: bicarbonate (HCO 3 – ) and hydrogen (H + ). The following formula depicts this reaction:

Bicarbonate tends to build up in the erythrocytes, so that there is a greater concentration of bicarbonate in the erythrocytes than in the surrounding blood plasma. As a result, some of the bicarbonate will leave the erythrocytes and move down its concentration gradient into the plasma in exchange for chloride (Cl – ) ions. This phenomenon is referred to as the chloride shift and occurs because by exchanging one negative ion for another negative ion, neither the electrical charge of the erythrocytes nor that of the blood is altered.

At the pulmonary capillaries, the chemical reaction that produced bicarbonate (shown above) is reversed, and carbon dioxide and water are the products. Much of the bicarbonate in the plasma re-enters the erythrocytes in exchange for chloride ions. Hydrogen ions and bicarbonate ions join to form carbonic acid, which is converted into carbon dioxide and water by carbonic anhydrase. Carbon dioxide diffuses out of the erythrocytes and into the plasma, where it can further diffuse across the respiratory membrane into the alveoli to be exhaled during pulmonary ventilation.

Carbaminohemoglobin

About 20 percent of carbon dioxide is bound by hemoglobin and is transported to the lungs. Carbon dioxide does not bind to iron as oxygen does; instead, carbon dioxide binds amino acid moieties on the globin portions of hemoglobin to form carbaminohemoglobin , which forms when hemoglobin and carbon dioxide bind. When hemoglobin is not transporting oxygen, it tends to have a bluish-purple tone to it, creating the darker maroon color typical of deoxygenated blood. The following formula depicts this reversible reaction:

Similar to the transport of oxygen by heme, the binding and dissociation of carbon dioxide to and from hemoglobin is dependent on the partial pressure of carbon dioxide. Because carbon dioxide is released from the lungs, blood that leaves the lungs and reaches body tissues has a lower partial pressure of carbon dioxide than is found in the tissues. As a result, carbon dioxide leaves the tissues because of its higher partial pressure, enters the blood, and then moves into red blood cells, binding to hemoglobin. In contrast, in the pulmonary capillaries, the partial pressure of carbon dioxide is high compared to within the alveoli. As a result, carbon dioxide dissociates readily from hemoglobin and diffuses across the respiratory membrane into the air.

In addition to the partial pressure of carbon dioxide, the oxygen saturation of hemoglobin and the partial pressure of oxygen in the blood also influence the affinity of hemoglobin for carbon dioxide. The Haldane effect is a phenomenon that arises from the relationship between the partial pressure of oxygen and the affinity of hemoglobin for carbon dioxide. Hemoglobin that is saturated with oxygen does not readily bind carbon dioxide. However, when oxygen is not bound to heme and the partial pressure of oxygen is low, hemoglobin readily binds to carbon dioxide.

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Watch this video to see the transport of oxygen from the lungs to the tissues. Why is oxygenated blood bright red, whereas deoxygenated blood tends to be more of a purple color?

Chapter Review

Oxygen is primarily transported through the blood by erythrocytes. These cells contain a metalloprotein called hemoglobin, which is composed of four subunits with a ring-like structure. Each subunit contains one atom of iron bound to a molecule of heme. Heme binds oxygen so that each hemoglobin molecule can bind up to four oxygen molecules. When all of the heme units in the blood are bound to oxygen, hemoglobin is considered to be saturated. Hemoglobin is partially saturated when only some heme units are bound to oxygen. An oxygen–hemoglobin saturation/dissociation curve is a common way to depict the relationship of how easily oxygen binds to or dissociates from hemoglobin as a function of the partial pressure of oxygen. As the partial pressure of oxygen increases, the more readily hemoglobin binds to oxygen. At the same time, once one molecule of oxygen is bound by hemoglobin, additional oxygen molecules more readily bind to hemoglobin. Other factors such as temperature, pH, the partial pressure of carbon dioxide, and the concentration of 2,3-bisphosphoglycerate can enhance or inhibit the binding of hemoglobin and oxygen as well. Fetal hemoglobin has a different structure than adult hemoglobin, which results in fetal hemoglobin having a greater affinity for oxygen than adult hemoglobin.

Carbon dioxide is transported in blood by three different mechanisms: as dissolved carbon dioxide, as bicarbonate, or as carbaminohemoglobin. A small portion of carbon dioxide remains. The largest amount of transported carbon dioxide is as bicarbonate, formed in erythrocytes. For this conversion, carbon dioxide is combined with water with the aid of an enzyme called carbonic anhydrase. This combination forms carbonic acid, which spontaneously dissociates into bicarbonate and hydrogen ions. As bicarbonate builds up in erythrocytes, it is moved across the membrane into the plasma in exchange for chloride ions by a mechanism called the chloride shift. At the pulmonary capillaries, bicarbonate re-enters erythrocytes in exchange for chloride ions, and the reaction with carbonic anhydrase is reversed, recreating carbon dioxide and water. Carbon dioxide then diffuses out of the erythrocyte and across the respiratory membrane into the air. An intermediate amount of carbon dioxide binds directly to hemoglobin to form carbaminohemoglobin. The partial pressures of carbon dioxide and oxygen, as well as the oxygen saturation of hemoglobin, influence how readily hemoglobin binds carbon dioxide. The less saturated hemoglobin is and the lower the partial pressure of oxygen in the blood is, the more readily hemoglobin binds to carbon dioxide. This is an example of the Haldane effect.

Interactive Link Questions

When oxygen binds to the hemoglobin molecule, oxyhemoglobin is created, which has a red color to it. Hemoglobin that is not bound to oxygen tends to be more of a blue–purple color. Oxygenated blood traveling through the systemic arteries has large amounts of oxyhemoglobin. As blood passes through the tissues, much of the oxygen is released into systemic capillaries. The deoxygenated blood returning through the systemic veins, therefore, contains much smaller amounts of oxyhemoglobin. The more oxyhemoglobin that is present in the blood, the redder the fluid will be. As a result, oxygenated blood will be much redder in color than deoxygenated blood.

Review Questions

Critical thinking questions.

1. Compare and contrast adult hemoglobin and fetal hemoglobin.

2. Describe the relationship between the partial pressure of oxygen and the binding of oxygen to hemoglobin.

3. Describe three ways in which carbon dioxide can be transported.

Answers for Critical Thinking Questions

  • Both adult and fetal hemoglobin transport oxygen via iron molecules. However, fetal hemoglobin has about a 20-fold greater affinity for oxygen than does adult hemoglobin. This is due to a difference in structure; fetal hemoglobin has two subunits that have a slightly different structure than the subunits of adult hemoglobin.
  • The relationship between the partial pressure of oxygen and the binding of hemoglobin to oxygen is described by the oxygen–hemoglobin saturation/dissociation curve. As the partial pressure of oxygen increases, the number of oxygen molecules bound by hemoglobin increases, thereby increasing the saturation of hemoglobin.
  • Carbon dioxide can be transported by three mechanisms: dissolved in plasma, as bicarbonate, or as carbaminohemoglobin. Dissolved in plasma, carbon dioxide molecules simply diffuse into the blood from the tissues. Bicarbonate is created by a chemical reaction that occurs mostly in erythrocytes, joining carbon dioxide and water by carbonic anhydrase, producing carbonic acid, which breaks down into bicarbonate and hydrogen ions. Carbaminohemoglobin is the bound form of hemoglobin and carbon dioxide.

This work, Anatomy & Physiology, is adapted from Anatomy & Physiology by OpenStax , licensed under CC BY . This edition, with revised content and artwork, is licensed under CC BY-SA except where otherwise noted.

Images, from Anatomy & Physiology by OpenStax , are licensed under CC BY except where otherwise noted.

Access the original for free at https://openstax.org/books/anatomy-and-physiology/pages/1-introduction .

Anatomy & Physiology Copyright © 2019 by Lindsay M. Biga, Staci Bronson, Sierra Dawson, Amy Harwell, Robin Hopkins, Joel Kaufmann, Mike LeMaster, Philip Matern, Katie Morrison-Graham, Kristen Oja, Devon Quick, Jon Runyeon, OSU OERU, and OpenStax is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License , except where otherwise noted.

22.5 Transport of Gases

Learning objectives.

By the end of this section, you will be able to:

  • Describe the principles of oxygen transport
  • Describe the structure of hemoglobin
  • Compare and contrast fetal and adult hemoglobin
  • Describe the principles of carbon dioxide transport

The other major activity in the lungs is the process of respiration, the process of gas exchange. The function of respiration is to provide oxygen for use by body cells during cellular respiration and to eliminate carbon dioxide, a waste product of cellular respiration, from the body. In order for the exchange of oxygen and carbon dioxide to occur, both gases must be transported between the external and internal respiration sites. Although carbon dioxide is more soluble than oxygen in blood, both gases require a specialized transport system for the majority of the gas molecules to be moved between the lungs and other tissues.

Oxygen Transport in the Blood

Even though oxygen is transported via the blood, you may recall that oxygen is not very soluble in liquids. A small amount of oxygen does dissolve in the blood and is transported in the bloodstream, but it is only about 1.5% of the total amount. The majority of oxygen molecules are carried from the lungs to the body’s tissues by a specialized transport system, which relies on the erythrocyte—the red blood cell. Erythrocytes contain a metalloprotein, hemoglobin, which serves to bind oxygen molecules to the erythrocyte ( Figure 22.25 ). Heme is the portion of hemoglobin that contains iron, and it is heme that binds oxygen. Each hemoglobin molecule contains four iron-containing heme molecules, and because of this, one hemoglobin molecule is capable of carrying up to four molecules of oxygen. As oxygen diffuses across the respiratory membrane from the alveolus to the capillary, it also diffuses into the red blood cell and is bound by hemoglobin. The following reversible chemical reaction describes the production of the final product, oxyhemoglobin (HbO 2 ), which is formed when oxygen binds to hemoglobin. Oxyhemoglobin is a bright red-colored molecule that contributes to the bright red color of oxygenated blood.

In this formula, Hb represents reduced hemoglobin, that is, hemoglobin that does not have oxygen bound to it. There are multiple factors involved in how readily heme binds to and dissociates from oxygen, which will be discussed in the subsequent sections.

Function of Hemoglobin

Hemoglobin is composed of subunits, a protein structure that is referred to as a quaternary structure. Each of the four subunits that make up hemoglobin is arranged in a ring-like fashion, with an iron atom covalently bound to the heme in the center of each subunit. Binding of the first oxygen molecule causes a conformational change in hemoglobin that allows the second molecule of oxygen to bind more readily. As each molecule of oxygen is bound, it further facilitates the binding of the next molecule, until all four heme sites are occupied by oxygen. The opposite occurs as well: After the first oxygen molecule dissociates and is “dropped off” at the tissues, the next oxygen molecule dissociates more readily. When all four heme sites are occupied, the hemoglobin is said to be saturated. When one to three heme sites are occupied, the hemoglobin is said to be partially saturated. Therefore, when considering the blood as a whole, the percent of the available heme units that are bound to oxygen at a given time is called hemoglobin saturation. Hemoglobin saturation of 100 percent means that every heme unit in all of the erythrocytes of the body is bound to oxygen. In a healthy individual with normal hemoglobin levels, hemoglobin saturation generally ranges from 95 percent to 99 percent.

Oxygen Dissociation from Hemoglobin

Partial pressure is an important aspect of the binding of oxygen to and disassociation from heme. An oxygen–hemoglobin dissociation curve is a graph that describes the relationship of partial pressure to the binding of oxygen to heme and its subsequent dissociation from heme ( Figure 22.26 ). Remember that gases travel from an area of higher partial pressure to an area of lower partial pressure. In addition, the affinity of an oxygen molecule for heme increases as more oxygen molecules are bound. Therefore, in the oxygen–hemoglobin saturation curve, as the partial pressure of oxygen increases, a proportionately greater number of oxygen molecules are bound by heme. Not surprisingly, the oxygen–hemoglobin saturation/dissociation curve also shows that the lower the partial pressure of oxygen, the fewer oxygen molecules are bound to heme. As a result, the partial pressure of oxygen plays a major role in determining the degree of binding of oxygen to heme at the site of the respiratory membrane, as well as the degree of dissociation of oxygen from heme at the site of body tissues.

The mechanisms behind the oxygen–hemoglobin saturation/dissociation curve also serve as automatic control mechanisms that regulate how much oxygen is delivered to different tissues throughout the body. This is important because some tissues have a higher metabolic rate than others. Highly active tissues, such as muscle, rapidly use oxygen to produce ATP, lowering the partial pressure of oxygen in the tissue to about 20 mm Hg. The partial pressure of oxygen inside capillaries is about 100 mm Hg, so the difference between the two becomes quite high, about 80 mm Hg. As a result, a greater number of oxygen molecules dissociate from hemoglobin and enter the tissues. The reverse is true of tissues, such as adipose (body fat), which have lower metabolic rates. Because less oxygen is used by these cells, the partial pressure of oxygen within such tissues remains relatively high, resulting in fewer oxygen molecules dissociating from hemoglobin and entering the tissue interstitial fluid. Although venous blood is said to be deoxygenated, some oxygen is still bound to hemoglobin in its red blood cells. This provides an oxygen reserve that can be used when tissues suddenly demand more oxygen.

Factors other than partial pressure also affect the oxygen–hemoglobin saturation/dissociation curve. For example, a higher temperature promotes hemoglobin and oxygen to dissociate faster, whereas a lower temperature inhibits dissociation (see Figure 22.26 , middle ). However, the human body tightly regulates temperature, so this factor may not affect gas exchange throughout the body. The exception to this is in highly active tissues, which may release a larger amount of energy than is given off as heat. As a result, oxygen readily dissociates from hemoglobin, which is a mechanism that helps to provide active tissues with more oxygen.

Certain hormones, such as androgens, epinephrine, thyroid hormones, and growth hormone, can affect the oxygen–hemoglobin saturation/disassociation curve by stimulating the production of a compound called 2,3-bisphosphoglycerate (BPG) by erythrocytes. BPG is a byproduct of glycolysis. Because erythrocytes do not contain mitochondria, glycolysis is the sole method by which these cells produce ATP. BPG promotes the disassociation of oxygen from hemoglobin. Therefore, the greater the concentration of BPG, the more readily oxygen dissociates from hemoglobin, despite its partial pressure.

The pH of the blood is another factor that influences the oxygen–hemoglobin saturation/dissociation curve (see Figure 22.26 ). The Bohr effect is a phenomenon that arises from the relationship between pH and oxygen’s affinity for hemoglobin: A lower, more acidic pH promotes oxygen dissociation from hemoglobin. In contrast, a higher, or more basic, pH inhibits oxygen dissociation from hemoglobin. The greater the amount of carbon dioxide in the blood, the more molecules that must be converted, which in turn generates hydrogen ions and thus lowers blood pH. Furthermore, blood pH may become more acidic when certain byproducts of cell metabolism, such as lactic acid, carbonic acid, and carbon dioxide, are released into the bloodstream.

Hemoglobin of the Fetus

The fetus has its own circulation with its own erythrocytes; however, it is dependent on the pregnant person for oxygen. Blood is supplied to the fetus by way of the umbilical cord, which is connected to the placenta and separated from maternal blood by the chorion. The mechanism of gas exchange at the chorion is similar to gas exchange at the respiratory membrane. However, the partial pressure of oxygen is lower in the maternal blood in the placenta, at about 35 to 50 mm Hg, than it is in maternal arterial blood. The difference in partial pressures between maternal and fetal blood is not large, as the partial pressure of oxygen in fetal blood at the placenta is about 20 mm Hg. Therefore, there is not as much diffusion of oxygen into the fetal blood supply. The fetus’ hemoglobin overcomes this problem by having a greater affinity for oxygen than maternal hemoglobin ( Figure 22.27 ). Both fetal and adult hemoglobin have four subunits, but two of the subunits of fetal hemoglobin have a different structure that causes fetal hemoglobin to have a greater affinity for oxygen than does adult hemoglobin.

Carbon Dioxide Transport in the Blood

Carbon dioxide is transported by three major mechanisms. The first mechanism of carbon dioxide transport is by blood plasma, as some carbon dioxide molecules dissolve in the blood. The second mechanism is transport in the form of bicarbonate (HCO 3 – ), which also dissolves in plasma. The third mechanism of carbon dioxide transport is similar to the transport of oxygen by erythrocytes ( Figure 22.28 ).

Dissolved Carbon Dioxide

Although carbon dioxide is not considered to be highly soluble in blood, a small fraction—about 7 to 10 percent—of the carbon dioxide that diffuses into the blood from the tissues dissolves in plasma. The dissolved carbon dioxide then travels in the bloodstream and when the blood reaches the pulmonary capillaries, the dissolved carbon dioxide diffuses across the respiratory membrane into the alveoli, where it is then exhaled during pulmonary ventilation.

Bicarbonate Buffer

A large fraction—about 70 percent—of the carbon dioxide molecules that diffuse into the blood is transported to the lungs as bicarbonate. Most bicarbonate is produced in erythrocytes after carbon dioxide diffuses into the capillaries, and subsequently into red blood cells. Carbonic anhydrase (CA) causes carbon dioxide and water to form carbonic acid (H 2 CO 3 ), which dissociates into two ions: bicarbonate (HCO 3 – ) and hydrogen (H + ). The following formula depicts this reaction:

Bicarbonate tends to build up in the erythrocytes, so that there is a greater concentration of bicarbonate in the erythrocytes than in the surrounding blood plasma. As a result, some of the bicarbonate will leave the erythrocytes and move down its concentration gradient into the plasma in exchange for chloride (Cl – ) ions. This phenomenon is referred to as the chloride shift and occurs because by exchanging one negative ion for another negative ion, neither the electrical charge of the erythrocytes nor that of the blood is altered.

At the pulmonary capillaries, the chemical reaction that produced bicarbonate (shown above) is reversed, and carbon dioxide and water are the products. Much of the bicarbonate in the plasma re-enters the erythrocytes in exchange for chloride ions. Hydrogen ions and bicarbonate ions join to form carbonic acid, which is converted into carbon dioxide and water by carbonic anhydrase. Carbon dioxide diffuses out of the erythrocytes and into the plasma, where it can further diffuse across the respiratory membrane into the alveoli to be exhaled during pulmonary ventilation.

Carbaminohemoglobin

About 20 percent of carbon dioxide is bound by hemoglobin and is transported to the lungs. Carbon dioxide does not bind to iron as oxygen does; instead, carbon dioxide binds amino acid moieties on the globin portions of hemoglobin to form carbaminohemoglobin , which forms when hemoglobin and carbon dioxide bind. When hemoglobin is not transporting oxygen, it tends to have a bluish-purple tone to it, creating the darker maroon color typical of deoxygenated blood. The following formula depicts this reversible reaction:

Similar to the transport of oxygen by heme, the binding and dissociation of carbon dioxide to and from hemoglobin is dependent on the partial pressure of carbon dioxide. Because carbon dioxide is released from the lungs, blood that leaves the lungs and reaches body tissues has a lower partial pressure of carbon dioxide than is found in the tissues. As a result, carbon dioxide leaves the tissues because of its higher partial pressure, enters the blood, and then moves into red blood cells, binding to hemoglobin. In contrast, in the pulmonary capillaries, the partial pressure of carbon dioxide is high compared to within the alveoli. As a result, carbon dioxide dissociates readily from hemoglobin and diffuses across the respiratory membrane into the air.

In addition to the partial pressure of carbon dioxide, the oxygen saturation of hemoglobin and the partial pressure of oxygen in the blood also influence the affinity of hemoglobin for carbon dioxide. The Haldane effect is a phenomenon that arises from the relationship between the partial pressure of oxygen and the affinity of hemoglobin for carbon dioxide. Hemoglobin that is saturated with oxygen does not readily bind carbon dioxide. However, when oxygen is not bound to heme and the partial pressure of oxygen is low, hemoglobin readily binds to carbon dioxide.

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Watch this video to see the transport of oxygen from the lungs to the tissues. Why is oxygenated blood bright red, whereas deoxygenated blood tends to be more of a purple color?

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The Carbon Cycle

The Carbon Cycle

The carbon cycle is a fundamental and complex process in Earth’s system, influencing climate, ecosystems, and life itself. It involves the movement of carbon , a key element for life, through the atmosphere, oceans, soil, rocks, and living organisms. This cycle plays a critical role in regulating the Earth’s climate by controlling the concentration of carbon dioxide, a major greenhouse gas, in the atmosphere.

Carbon Cycle Definition

The carbon cycle is the series of processes through which carbon atoms continually travel from the atmosphere into organisms, the oceans, and the Earth and then back into the atmosphere. This cycle maintains the balance of carbon on Earth, making it available to living organisms and regulating the Earth’s climate.

Main Carbon Reservoirs

The carbon cycle involves several key reservoirs where carbon is stored in different forms:

  • Atmosphere : Carbon mainly occurs as carbon dioxide gas.
  • Oceans : Carbon occurs as dissolved carbon dioxide, carbonate, and bicarbonate ions.
  • Terrestrial Ecosystems : Plants and soils store carbon in organic forms through photosynthesis.
  • Fossil Fuels : Coal, oil, and natural gas store carbon.
  • Rocks and Sediments : Carbonate rocks like limestone and organic-rich sediments store large amounts of carbon.

Carbon Cycle Steps

The carbon cycle involves a series of steps through which carbon exchanges between the atmosphere, hydrosphere, lithosphere, and biosphere. Here’s an outline of these steps:

  • Carbon Dioxide in the Atmosphere : The cycle begins with carbon dioxide (CO 2 ) present in the atmosphere .
  • Photosynthesis : Plants, algae, and phytoplankton absorb CO 2 from the atmosphere or water. Through photosynthesis , they convert carbon dioxide and water into glucose (a form of sugar) and oxygen.
  • Consumption : Animals and other organisms consume plants, transferring carbon through the food chain. Organisms incorporate carbon into their bodies in various organic forms.
  • Respiration : Both plants and animals release carbon back into the atmosphere as CO 2 through the process of respiration, which is the breakdown of glucose for energy .
  • Decomposition : When plants, animals, and other organisms die, decomposers like bacteria and fungi break down their bodies. This process releases carbon into the soil or water.
  • Sedimentation and Burial : Over long periods, some carbon in the soil or in water bodies becomes buried and incorporated into sediments. This carbon eventually forms fossil fuels (coal, oil, and natural gas) or sedimentary rocks like limestone.
  • Release from Rocks and Fossil Fuels : Geological processes and human activities release carbon from rocks and fossil fuels. Weathering of rocks, volcanic activity, and burning fossil fuels release carbon dioxide back into the atmosphere.
  • Carbon in the Oceans : Oceans absorb a significant amount of CO 2 from the atmosphere. Marine organisms use some of this carbon. Some reacts and forms carbonate and bicarbonate ions. Some carbon gets stored in deep ocean waters or ocean sediments.
  • Exchange Between Ocean and Atmosphere : There is a constant exchange of carbon dioxide between the ocean surface and the atmosphere, helping to regulate atmospheric CO 2 levels.

Why Is the Carbon Cycle Important?

The carbon cycle is crucial for several key reasons:

  • Support for Life : Carbon is a fundamental building block of life. The carbon cycle ensures that carbon is recycled and reused throughout the biosphere, making it available to living organisms. Through processes like photosynthesis and respiration, the carbon cycle supports the growth of plants and animals, which are essential for the food chain and ecosystem balance.
  • Regulation of Climate : Carbon dioxide is one of the most significant greenhouse gases in the Earth’s atmosphere. The carbon cycle helps regulate the concentration of CO 2 . This balance maintains Earth’s temperature and climate stability. Disruptions in the carbon cycle lead to climate change.
  • Ocean Health : The carbon cycle affects the health of the oceans. The oceans absorb carbon dioxide absorbed and help regulate the Earth’s temperature. However, excessive CO 2 absorption causes ocean acidification, which affects marine life, particularly organisms with calcium carbonate shells or skeletons.
  • Soil Fertility : Carbon in the form of organic matter is a key component of healthy soil, influencing soil structure, fertility, and the ability to support plant life. The decomposition of organic matter releases nutrients necessary for plant growth and sustains the productivity of ecosystems.
  • Energy Resources : The carbon cycle forms fossil fuels. These fuels are a major energy source, although their use significantly impacts the carbon cycle and the climate.
  • Global Carbon Budget Understanding : The carbon cycle provides a framework for understanding the global carbon budget. This is much carbon is stored in various reservoirs, how quickly it moves between these reservoirs, and how human activities affect this movement. This understanding is crucial for developing strategies to mitigate climate change and manage carbon resources.

The Fast and Slow Carbon Cycles

There are really two carbon cycle. When people talk about the carbon cycle, generally they refer to the fast carbon cycle. However, there is also a slow cycle that occurs over geological spans of time.

  • Fast Carbon Cycle : This involves the rapid exchange of carbon between the atmosphere and living organisms. Photosynthesis by plants and phytoplankton absorbs atmospheric carbon dioxide, converting it into organic matter. When these organisms respire, decay, or are consumed, carbon releases back into the atmosphere or ocean relatively quickly, typically within a few years or decades.
  • Slow Carbon Cycle : This process takes much longer, spanning hundreds to millions of years. It involves the movement of carbon through geological processes. Carbon in rocks and sediments eventually releases back into the atmosphere through volcanic activity, weathering of rocks, and the movement of tectonic plates .

Interconnection with the Water Cycle

The carbon and water cycles are closely interconnected. For instance, carbon dioxide in the atmosphere dissolves in water bodies, influencing the acidity of oceans and affecting marine life. Similarly, the process of photosynthesis in plants, a key part of the carbon cycle, depends on water availability.

Major Natural Influences on the Fast Carbon Cycle

Several natural processes significantly influence the carbon cycle:

  • Volcanic Eruptions: Volcanoes release huge volumes of carbon dioxide into the atmosphere.
  • Photosynthesis : Plants and phytoplankton convert carbon dioxide from the atmosphere into organic matter, significantly influencing the amount of carbon in the atmosphere and biosphere.
  • Respiration and Decomposition : Living organisms release carbon dioxide back into the atmosphere through respiration, and decomposers release carbon from dead matter.
  • Oceanic Absorption and Release : Oceans absorb and release large quantities of carbon dioxide, acting as major reservoirs and regulators of atmospheric carbon.
  • Rock Weathering : The chemical breakdown of rocks on the Earth’s surface captures atmospheric carbon dioxide, contributing to long-term carbon storage in the form of carbonate minerals.
  • Wildfires : Natural wildfires release significant amounts of carbon dioxide and other greenhouse gases by burning biomass.
  • Soil Carbon Dynamics : Soil processes, including the formation and breakdown of organic matter, play a critical role in storing and releasing carbon.
  • Orbital Fluctuations: Orbital fluctuations, also known as Milankovitch cycles, significantly impact the carbon cycle over long geological timescales. These cycles involve changes in the Earth’s orbit and tilt, which influence the amount and distribution of solar energy the Earth receives. Solar energy, in turn, drives carbon storage or release from ice, the ocean, and plants.

Major Human Influences on the Carbon Cycle

Human activities, particularly the burning of fossil fuels and deforestation, significantly impact the fast carbon cycle. These activities increase the amount of carbon dioxide in the atmosphere, contributing to global warming and climate change.

  • Burning of Fossil Fuels : The combustion of coal, oil, and natural gas for energy and transportation releases large amounts of carbon dioxide into the atmosphere.
  • Deforestation and Land Use Changes : Clearing forests for agriculture, urbanization, and other purposes reduces the number of trees available to absorb CO 2 through photosynthesis, and also releases carbon stored in trees and soil.
  • Industrial Processes : Certain industries, such as cement production, release CO 2 through chemical reactions and the burning of fossil fuels.
  • Agriculture : Agricultural practices, including the use of fertilizers and livestock farming, produce greenhouse gases like methane and nitrous oxide, which affect the carbon cycle.
  • Waste Management : Decomposition of organic waste in landfills produces methane (CH 4 ), a potent greenhouse gas, while incineration of waste materials can release CO 2 .
  • Archer, David (2010). The Global Carbon Cycle . Princeton: Princeton University Press. ISBN 9781400837076.
  • Falkowski, P.; Scholes, R. J.; et al. (2000). “The Global Carbon Cycle: A Test of Our Knowledge of Earth as a System”. Science . 290 (5490): 291–296. doi: 10.1126/science.290.5490.291
  • Friedlingstein, P., Jones, M., et al. (2019). “Global carbon budget 2019”. Earth System Science Data . 11(4): 1783–1838. doi: 10.5194/essd-11-1783-2019
  • Heede, R. (2014). “Tracing anthropogenic carbon dioxide and methane emissions to fossil fuel and cement producers, 1854–2010”. Climatic Change . 122 (1–2): 229–241. doi: 10.1007/s10584-013-0986-y
  • Walker, James C. G.; Hays, P. B.; Kasting, J. F. (1981). “A negative feedback mechanism for the long-term stabilization of Earth’s surface temperature”. Journal of Geophysical Research . 86 (C10): 9776. doi: 10.1029/JC086iC10p09776

Related Posts

The movement of carbon around Earth's atmosphere explained

Science The movement of carbon around Earth's atmosphere explained

Most of the earth's carbon is trapped in limestone for millions of years at a time.

We hear a lot about the amount of carbon in our atmosphere increasing, but the actual number of carbon atoms on our planet has not changed since the Earth first formed - it's just that more carbon is spending more time as gas.

The increase in the atmosphere happens when carbon is released as a gas - like when a dead thing decays, a fossil fuel is burnt or a volcano erupts. But that's only a tiny part of the whole story of the movement of carbon.

Individual atoms of carbon constantly move from one form to another - in air, water, living things and rock. The movement is managed by different chemical and physical processes, from photosynthesis, respiration, combustion and plate tectonics, to plain old dissolving and off-gassing.

And the one thing that all of these carbon paths have in common is that they all pass through the atmosphere, because they all at some stage turn carbon into a gas, and gases float.

Together those paths that carbon can take make up a cycle. But unlike the simple water cycle (evaporation - clouds - rain - evaporation), the carbon cycle takes place in all parts of the planet and across all time scales.

In fact, the cycle takes place in such different time scales - from a fraction of a second to many millions of years - that there are really two carbon cycles, the quick and the slow.

The quick and slow carbon cycles

The quick carbon cycle

Considering the spectacular capacity of humans to pump CO2 out of fossil fuels and limestone, the biological contribution that we - and all other animals - make to the carbon cycle by eating, breathing and dying is pathetically small compared to what plants get up to.

When plants photosynthesise, they suck CO2 from the air, add water and make sugars and more plant out of it.

  • Carbon dioxide + water + light energy = sugar + oxygen

When plants or animals break that sugar back down for energy through respiration (the opposite of photosynthesis) they release CO2 back into the atmosphere.

  • Sugar + oxygen = carbon dioxide + water + energy

There's enough CO2 moving in and out of plants this way that the level of atmospheric CO2 drops every year during the northern spring (when plant growth and photosynthesis are at a max globally) and increases during autumn as photosynthesis drops right back.

It's like watching the planet take its annual breath.

Most of the carbon that's stored in plants - and in anything that eats them - is released back into the atmosphere by respiration when the organisms die and are eaten by microbes.

But organic processes are not known for being tidy, and bits of plant and animal remains can stay in the soil for hundreds of years, making it another serious carbon storage site.

Soil holds about 1550 billion tonnes of carbon this way - about three times as much as the total carbon stored in all the plants (550 billion tonnes) and animals (2 billion tonnes) alive today.

Clearing land exposes the carbon in that soil to decay, releasing about 1.5 billion tonnes of carbon back into the atmosphere.

Those numbers seem big until you look at the amount of carbon stored in the ocean - a massive 38,000 billion tonnes. Because CO2 is soluble, it's constantly dissolving in and being released from the ocean surface, helping keep the levels in both sea and sky in reasonable balance.

The twin systems of photosynthesis and respiration, and the movement of carbon in and out of the ocean are the main drivers of the natural "quick" carbon cycle.

Luckily, plants and the ocean both absorb slightly more carbon dioxide than they release each year, which helps make up for the excess delivered when we burn fossil fuels, clear land and make cement.

The slow carbon cycle

As well as cycling through living things and the upper surfaces of the planet, atmospheric carbon can end up deep underground.

Over very long periods of time and under enormous pressure the carbon from ancient buried swamps becomes coal, phytoplankton becomes oil and gas, and humble seashells from things like long-dead coral become limestone.

In fact, the vast majority of carbon on the planet is stashed away in these long-term underground stores - 99.9 per cent of it is stored in rock, including around 80 per cent as limestone.

Under natural conditions, it can take millions of years to release that slow cycle carbon back into the atmosphere as CO2, through geological and chemical processes like crashing tectonic plates and the odd belching volcano. But we can speed the process up with the lighting of a match.

Burning fossil fuels (oil, gas and coal) and heating limestone (calcium carbonate, CaCO3) to make cement instantly shoot long hidden carbon back into the atmosphere as CO2.

This adds up to about an extra 6 billion tonnes of carbon each year. Luckily our plants and oceans can suck up about half that, but it still leaves an annual increase that's not showing any signs of slowing despite our slackest attempts to reduce carbon emissions.

Let's hope the work being done to stuff CO2 back into its box via carbon sequestration can provide the missing arrow in the carbon cycle, the one that balances out those anthropogenic emissions.

Thanks to Dr Evelyn Krull, former Research Team Leader - Biochar and Carbon Sequestration, CSIRO Land and Water

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The Two-Way

The Two-Way

International, watch: how carbon dioxide travels around the globe.

Eyder Peralta headshot

Eyder Peralta

We're a few days late on this, but it's too cool not to share.

Here's a NASA video made from a new model that shows how carbon dioxide moves throughout Earth:

NASA explains what you just watched :

"Plumes of carbon dioxide in the simulation swirl and shift as winds disperse the greenhouse gas away from its sources. The simulation also illustrates differences in carbon dioxide levels in the northern and southern hemispheres and distinct swings in global carbon dioxide concentrations as the growth cycle of plants and trees changes with the seasons. "Scientists have made ground-based measurements of carbon dioxide for decades and in July NASA launched the Orbiting Carbon Observatory-2 (OCO-2) satellite to make global, space-based carbon observations. But the simulation — the product of a new computer model that is among the highest-resolution ever created — is the first to show in such fine detail how carbon dioxide actually moves through the atmosphere."
  • carbon dioxide

carbon dioxide travel through

Exchanging Oxygen and Carbon Dioxide

The primary function of the respiratory system is to take in oxygen and eliminate carbon dioxide. Inhaled oxygen enters the lungs and reaches the alveoli. The layers of cells lining the alveoli and the surrounding capillaries are each only one cell thick and are in very close contact with each other. This barrier between air and blood averages about 1 micron ( 1 / 10,000 of a centimeter, or 0.000039 inch) in thickness. Oxygen passes quickly through this air-blood barrier into the blood in the capillaries. Similarly, carbon dioxide passes from the blood into the alveoli and is then exhaled.

Oxygenated blood travels from the lungs through the pulmonary veins and into the left side of the heart, which pumps the blood to the rest of the body (see Function of the Heart ). Oxygen-deficient, carbon dioxide-rich blood returns to the right side of the heart through two large veins, the superior vena cava and the inferior vena cava. Then the blood is pumped through the pulmonary artery to the lungs, where it picks up oxygen and releases carbon dioxide.

carbon dioxide travel through

To support the absorption of oxygen and release of carbon dioxide, about 5 to 8 liters (about 1.3 to 2.1 gallons) of air per minute are brought in and out of the lungs, and about three tenths of a liter (about three tenths of a quart) of oxygen is transferred from the alveoli to the blood each minute, even when the person is at rest. At the same time, a similar volume of carbon dioxide moves from the blood to the alveoli and is exhaled. During exercise, it is possible to breathe in and out more than 100 liters (about 26 gallons) of air per minute and extract 3 liters (a little less than 1 gallon) of oxygen from this air per minute. The rate at which oxygen is used by the body is one measure of the rate of energy expended by the body. Breathing in and out is accomplished by respiratory muscles .

Gas Exchange Between Alveolar Spaces and Capillaries

Three processes are essential for the transfer of oxygen from the outside air to the blood flowing through the lungs: ventilation, diffusion, and perfusion.

Ventilation is the process by which air moves in and out of the lungs.

Diffusion is the spontaneous movement of gases, without the use of any energy or effort by the body, between the alveoli and the capillaries in the lungs.

Perfusion is the process by which the cardiovascular system pumps blood throughout the lungs.

The body's circulation is an essential link between the atmosphere, which contains oxygen, and the cells of the body, which consume oxygen. For example, the delivery of oxygen to the muscle cells throughout the body depends not only on the lungs but also on the ability of the blood to carry oxygen and on the ability of the circulation to transport blood to muscle. In addition, a small fraction of the blood pumped from the heart enters the bronchial arteries and nourishes the airways.

Heart–Lung Connections

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carbon dioxide travel through

Introduction

Selective permeability, carrier proteins, attribution:, works cited:.

  • Lodish, H., Berk, A., Zipursky, S. L., Matsudaira, P., Baltimore, D., and Darnell, J. (2000). Overview of membrane transport proteins. In Molecular cell biology (4th ed., section 15.2). New York, NY: W. H. Freeman. Retrieved from http://www.ncbi.nlm.nih.gov/books/NBK21592/ .

Additional references:

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Carbon is the chemical backbone of life on Earth. Carbon compounds regulate the Earth’s temperature, make up the food that sustains us, and provide energy that fuels our global economy.

A diagram of the carbon cycle with arrows showing the movement of carbon through a landscape with plants and animals, mountains and a volcano, a river leading to the ocean, and an industrial area. Carbon moves in and out of our atmosphere, ocean, waterways, and soil through burning fossil fuels, precipitation, fires, vegetation, volcanoes, and organic processes.

The carbon cycle. (Image credit: NOAA)

Most of Earth’s carbon is stored in rocks and sediments. The rest is located in the ocean, atmosphere, and in living organisms. These are the reservoirs through which carbon cycles.

This graph shows the monthly mean carbon dioxide measured at Mauna Loa Observatory, Hawaii, the longest record of direct measurements of CO2 in the atmosphere.

Carbon dioxide concentrations are rising mostly because of the fossil fuels that people are burning for energy. 

Carbon storage and exchange

Carbon moves from one storage reservoir to another through a variety of mechanisms. For example, in the food chain, plants move carbon from the atmosphere into the biosphere through photosynthesis. They use energy from the sun to chemically combine carbon dioxide with hydrogen and oxygen from water to create sugar molecules. Animals that eat plants digest the sugar molecules to get energy for their bodies. Respiration, excretion, and decomposition release the carbon back into the atmosphere or soil, continuing the cycle.

The ocean plays a critical role in carbon storage, as it holds about 50 times more carbon than the atmosphere. Two-way carbon exchange can occur quickly between the ocean’s surface waters and the atmosphere, but carbon may be stored for centuries at the deepest ocean depths.

Rocks like limestone and fossil fuels like coal and oil are storage reservoirs that contain carbon from plants and animals that lived millions of years ago. When these organisms died, slow geologic processes trapped their carbon and transformed it into these natural resources. Processes such as erosion release this carbon back into the atmosphere very slowly, while volcanic activity can release it very quickly. Burning fossil fuels in cars or power plants is another way this carbon can be released into the atmospheric reservoir quickly.

A research vessel ploughs through the waves, braving the strong westerly winds of the Roaring Forties in the Southern Ocean in order to measure levels of dissolved carbon dioxide in the surface of the ocean.

New research utilizes airborne measurements of carbon dioxide to estimate ocean uptake.

Changes to the carbon cycle

Human activities have a tremendous impact on the carbon cycle. Burning fossil fuels, changing land use, and using limestone to make concrete all transfer significant quantities of carbon into the atmosphere. As a result, the amount of carbon dioxide in the atmosphere is rapidly rising; it is already greater than at any time in the last 3.6 million years . The ocean absorbs much of the carbon dioxide that is released from burning fossil fuels. This extra carbon dioxide is lowering the ocean’s pH, through a process called ocean acidification . Ocean acidification interferes with the ability of marine organisms (including corals , Dungeness crabs , and snails ) to build their shells and skeletons.

An aerial view of Century City section of Los Angeles, California.

Global carbon emissions are projected to bounce back to after an unprecedented drop caused by the response to the coronavirus pandemic, according to an annual report by the Global Carbon Project. 

EDUCATION CONNECTION

Take a bite of dinner, breathe in air, or a drive in a car — you are part of the carbon cycle. The resources in this collection provide real world examples of the changes occurring in the cycle. There is much to learn about this essential topic and some of the resources highlight exciting career opportunities in this field of study.

During Year of Extremes, Carbon Dioxide Levels Surge Faster than Ever

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Carbon dioxide is accumulating in the atmosphere faster than ever — accelerating on a steep rise to levels far above any experienced during human existence, scientists from NOAA and  Scripps Institution of Oceanography at the University of California San Diego announced today.

Scientists at Scripps Oceanography, which initiated the CO 2 monitoring program known as the  Keeling Curve at Mauna Loa in 1958 and maintains an independent record, calculated a May monthly average of 426.7 ppm for 2024, an increase of 2.92 ppm over May 2023’s measurement of 423.78 ppm. May is historically the month when CO 2 reaches its highest level in the Northern Hemisphere.

When combined with 2023’s increase of 3.0 ppm, 2022 to 2024 has seen the largest two-year jump in the May peak of the Keeling Curve in the NOAA record. For Scripps, the two-year jump tied a previous record set in 2020.  From January through April, NOAA and Scripps scientists said CO2 concentrations increased more rapidly than they have in the first four months of any other year. The surge has come even as one  highly regarded international report has found that fossil fuel emissions, the main driver of climate change, have plateaued in recent years.

“Not only is CO 2  now at the highest level in millions of years, it is also rising faster than ever.  Each year achieves a higher maximum due to fossil-fuel burning, which releases pollution in the form of carbon dioxide into the atmosphere,” said Ralph Keeling, director of the Scripps CO 2  program that manages the institution’s 56-year-old measurement series. “Fossil fuel pollution just keeps building up, much like trash in a landfill.” 

Keeling also noted that other measurements recorded in recent months yielded another troubling superlative when the March 2024 reading achieved the  highest 12-month increase for both Scripps and NOAA in Keeling Curve history. 

Like other greenhouse gases, CO2 acts like a blanket, preventing heat from radiating from the atmosphere into space. The warming atmosphere fuels extreme weather events, such as heat waves, drought and wildfires, as well as heavier precipitation and flooding.

 “Over the past year, we’ve experienced the hottest year on record, the hottest ocean temperatures on record and a seemingly endless string of heat waves, droughts, floods, wildfires and storms,” said NOAA Administrator Rick Spinrad. “Now we are finding that atmospheric CO 2 levels are increasing faster than ever. We must recognize that these are clear signals of the damage carbon dioxide pollution is doing to the climate system, and take rapid action to reduce fossil fuel use as quickly as we can.

Levels measured at NOAA’s Mauna Loa Atmospheric Baseline Observatory by NOAA’s  Global Monitoring Laboratory surged to a seasonal peak of just under 427 parts per million (426.90 ppm) in May. That’s an increase of 2.9 ppm over May 2023, and the fifth-largest annual growth in NOAA’s 50-year record.

The record two-year growth rate observed from 2022 to 2024 is likely a result of sustained high fossil fuel emissions combined with El Niño conditions limiting the ability of global land ecosystems to absorb atmospheric CO 2 , said John Miller, a carbon cycle scientist with the Global Monitoring Laboratory. The absorption of CO 2 is changing the chemistry of the ocean, leading to   ocean acidification  and lower levels of dissolved oxygen, which interferes with the growth of some marine organisms.

For most of the past half century, continuous daily sampling by both NOAA and Scripps at Mauna Loa provided an ideal baseline for establishing long-term trends. In 2023, some of the measurements were obtained from  a temporary sampling site atop the nearby Mauna Kea volcano, which was established after lava flows cut off access to the Mauna Loa Observatory in November 2022. With the access road still buried under lava, staff have been accessing the site once a week by helicopter to maintain the NOAA and Scripps in-situ CO 2 analyzers that provide continuous CO 2 measurements.

Scripps geoscientist Charles David Keeling initiated on-site measurements of CO 2 at NOAA’s Mauna Loa weather station in 1958. Keeling was the first to recognize that CO 2 levels in the Northern Hemisphere fell during the growing season, and rose as plants died in the fall. He documented these CO 2 fluctuations in a record that came to be known as the  Keeling Curve . He was also the first to recognize that, in addition to the seasonal fluctuation, CO 2 levels rose every year.

NOAA climate scientist Pieter Tans spearheaded the effort to begin NOAA’s own measurements in 1974, and the two research institutions have made complementary, independent observations ever since.

While the Mauna Loa Observatory is considered the benchmark climate monitoring station for the northern hemisphere, it does not capture the changes of CO 2 across the globe. NOAA’s  globally distributed sampling network  provides this broader picture, which is very consistent with the Mauna Loa results. Similarly, the Scripps CO 2 program operates  14 global sampling stations. 

The Mauna Loa data, together with measurements from sampling stations around the world, are incorporated into the  Global Greenhouse Gas Reference Network , a foundational research dataset for international climate scientists and a benchmark for policymakers attempting to address the causes and impacts of climate change.

Measurements by the Scripps CO 2 program are supported by the US National Science Foundation, by the Eric and Wendy Schmidt Fund for Strategic Innovation, and by Earth Networks, a technology company that is collaborating with Scripps to expand the global GHG monitoring network.

In-kind support for field operations is also provided by NOAA, the National Science Foundation, Environment Canada, and the New Zealand National Institute for Water and Atmospheric Research.

-- Adapted from NOAA

Learn more about research and education at UC San Diego in: Climate Change

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How pulling carbon out of the ocean may help remove it from the air

Taking carbon dioxide from the ocean could increase its natural ability to remove emissions from the atmosphere, like wringing out a sponge to make it more absorptive.

Aboard a World War II Navy barge bristling with metal cages, tanks, and an orderly maze of pipes and wires tied up in the Port of Los Angeles, a group of scientists is on a quest to answer a simple question: is there a way to coax the ocean into swallowing more carbon dioxide? The answer could hold the key to a cooler future.

The world’s oceans already act as a vast carbon sink, offsetting approximately one-quarter of the CO2 emissions that human activity generates each year. But as they face challenges like acidification and rising temperatures, they’re becoming less effective at taking up the planet-warming gas.  

Engineers at Captura , a startup spun out from the California Institute of Technology, have devised a process that’s meant to revive that drawdown. Working like a large-scale desalination plant, it takes in ocean water, keeps a tiny portion aside, and zaps it with electricity using a special machine. The electrical charge splits the water into two parts: one acidic and the other alkaline.

The acid part goes into the remaining onboard ocean water, where it triggers a reaction causing CO2 to bubble out into storage tanks. The alkaline part is then added back to the seawater to neutralize the acidity before it is returned to the ocean, ready to absorb the same amount of CO2 that was removed.

“What we do is basically removing carbon dioxide from the seawater and then returning the decarbonated water to the ocean so it can suck more of the greenhouse gas out of the air,” says Captura’s CEO Steve Oldham. “It’s like wringing out a sponge to boost its absorption power."

The power of the ocean

Captura is part of a small yet expanding cohort of companies including California startups Equatic and Calcarea , as well as the Dutch venture SeaO2 , seeking to harness the power of the ocean to naturally concentrate CO2.

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In addition to phasing out fossil fuels, climate science experts are increasingly convinced that vast quantities of CO2 will need to be taken away from the atmosphere in order to avoid runaway climate change. The notion is contentious, as removing CO2 on a large scale hasn’t been fully tested; a recent U.N. panel labeled the approach "unproven."

But with millions of dollars in venture capital funding and lucrative contracts to offset the emissions of some of the world’s biggest companies, these firms are trying to prove otherwise.

A large barge with monitoring equipment at a research facility

Pulling CO2 out from the ocean, where it is present at a concentration 150 times as high as in the atmosphere, is more efficient than capturing it from the air, where it makes up less than 0.05 percent of the total volume, believes Edward Sanders, COO of Equatic, which also runs a test vessel in the Port of Los Angeles.

He says that the technology also avoids using land, and systems can be integrated with desalination plants, wastewater treatment facilities, and other water-processing facilities and even coupled with offshore wind energy to facilitate access to oceanic storage sites.

According to Oldham, leveraging the ocean’s carbon-sucking power also doesn't require building expensive machinery to interact with the air, ultimately helping reduce overall costs. "The ocean really does all the work itself,” he says.

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Both Captura and Equatic are confident that they will be able to pull CO2 for less than $100 a ton by the end of the decade—a significantly lower cost compared to direct air capture, which currently ranges between $250–600 per ton and is not anticipated to decrease anytime soon.

Uncharted territory

After almost a year of testing with the barge, which is designed to capture 100 tons of CO2 per year, Captura is expanding its operations by building a 1,000-ton-per-year facility in Norway. Equatic is also stepping up , establishing an even larger 3650-ton-per-year plant in Singapore. Both are set to be up and running by next year.

Companies say data collected there and at the Port of Los Angeles will help in the design of large-scale commercial facilities that sequester millions of tons of carbon annually.

But even hitting that target would be just a drop in the bucket. The IPCC estimates up to 12 gigatons of CO2, or about a quarter of the current global annual emissions, would need to be removed from the air every year to make a meaningful dent in the carbon debt.

To facilitate this, Captura, Equatic, and the others must erect thousands of new facilities that extract CO2 from seawater around the world. That buildout would entail billions of dollars in capital investment. More importantly, it would take massive quantities of carbon-free energy to power decarbonization plants.

Critics argue these resources would be better spent reducing fossil fuel use and electrifying the economy. “Removing already-emitted carbon is laughably small, incredibly expensive, and full of engineering obstacles,” says Jonathan Foley, executive director of Project Drawdown, a nonprofit organization focused on climate solutions. “Limited research on this should continue, but our time and resources should focus on cutting emissions as quickly as possible.”

Sanders points out that Equatic’s process yields green hydrogen as a byproduct, which can be used to partially power the process and cut the net power requirement. He notes that further energy efficiency could be achieved by tapping energy during off-peak times – typically late at night or early in the morning – when demand is lower and costs are reduced.

Questions also remain about the environmental impact of the technology. Lisa Levin, a marine ecologist at UC San Diego's Scripps Institution of Oceanography, warns that processing huge volumes of seawater could have unforeseen consequences on ocean ecosystems.

"We're in uncharted territory here,” she says. “Nobody knows what’s going to happen when you manipulate the ocean chemistry at such a large scale.”

Levin claims that there are risks to marine life as well. "Whenever large volumes of water are drawn in, they bring along everything within it—including plankton, fish larvae, and other small animals," she explains.

Sanders says the Equatic’s process is designed to have minimal impact on the local ecosystem, adding that the company has commissioned an environmental impact assessment to understand the potential implications of implementing the technology at scale. “We do not want to cause greater harm to the planet in the process,” he maintains.

Oldham echoes the sentiment, stressing that Captura’s process does not add anything to ocean waters that’s not already there. "We won't risk disrupting the ocean with things we haven’t fully understood," he asserts. "We simply can't afford it."

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Pennsylvania landowners may soon have to accept carbon dioxide burial on their land—whether they want it or not

A mid a divided state Legislature, Pennsylvania Democrats and Republicans are finding rare common ground in a bill designed to usher in a new industry for capturing climate-altering carbon dioxide and burying it underground.

Among other provisions,  Senate Bill 831  would create an enforcement structure for carbon capture within the state, set a low bar for gaining consent from landowners near sites where carbon is injected into the ground and, in some cases, spare the fossil fuel industry from seismic monitoring—that is, watching for earthquakes, a known risk.

The bill, sponsored by state Sen. Gene Yaw, a Republican representing north central Pennsylvania who has  personal ties  to the fossil fuel industry, cleared the Republican-controlled Senate on a 30-20 vote in April. It now moves to the House of Representatives, which is controlled by Democrats.

But a coalition of environmental groups said the bill is riddled with problems. Landowners could be left in the dark when the collected carbon is pumped into the ground near their properties, they said. Additionally, carbon dioxide could eventually leak into the atmosphere, posing a risk to both the environment and public health: In  Satartia, Mississippi , a pipeline carrying carbon dioxide ruptured, sending 49 people to the hospital complaining of labored breathing, stomach disorders, and mental confusion. 

“Our concerns with this were pretty significant,” said Jen Quinn, legislative and political director at the Pennsylvania chapter of the Sierra Club.

In introducing the legislation, Yaw  pitched the bill  as a proposal to direct state regulators to take over responsibility for the permitting process for carbon dioxide injection wells from the U.S. Environmental Protection Agency. 

In reality, the bill, as written, would go much further than that. It would allow operators to inject carbon dioxide into underground geologic formations with permission from just 60% of the nearby landowners. It would allow operators to apply for a waiver ceding liability for these wells to the state after 10 years of a well’s completion. And it would allow operators to forgo seismic monitoring of the storage fields into which the carbon dioxide pumped into the earth, if they can prove that the field does not “pose significant risk.” 

Several of these provisions, Quinn said, are “setting the bar very low.” 

A  report  by the Ohio River Valley Institute, a nonprofit environmental think tank, showed that no state sets the landowner consent bar at less than 60%. 

The report also argued that waiving operators’ liability over their carbon storage fields will lead to negligence: Operators that know they won’t be held responsible for any mess in the long run won’t be incentivized to run a clean operation, the report said. 

Capital & Main reached out to Sen. Yaw, author of SB 831, and did not hear back by publication time. However, he  said in a press release  that the bill is a “proactive step” to building out the state’s carbon capture industry. 

Environmentalists have long splintered over carbon capture and sequestration, known as CCS. The practice of collecting carbon dioxide from power plants and storing it underground has been  criticized  as costly, dangerous and largely unproven. While  some say  it is a useful tool among many for addressing the climate crisis, others call CCS a  boondoggle  that could offer a lifeline to the fossil fuel industry, which has  rallied   around  the technology.

Environmentalists worry that in Pennsylvania, which has centuries of oil and gas drilling under its belt, the state’s geology could prove treacherous. “This idea that they’re going to go all in on carbon capture and try to inject this stuff in the same places where it’s like Swiss cheese . . . is just plain stupid,” said Karen Feridun, co-founder of the grassroots Better Path Coalition, a staunch opponent of burying carbon in the earth.

The state is  dotted  with orphaned and abandoned oil and gas wells, including many that likely have yet to be located. The wells create pathways underground through which gases can travel and potentially seep into waterways or leak into the atmosphere, undoing the progress of capturing the carbon in the first place. A  2009 report  by the state’s Department of Conservation and Natural Resources said that the state’s legacy oil and gas fields could “constitute a leakage pathway for reservoir gases, including injected CO2.”

“The safest course of action would be to avoid the oldest of these oil fields,” the report added. 

Feridun said she also anticipates that an influx of carbon dioxide injection wells will come with a maze of pipelines to transport the carbon.

Because the bill would permit operators to get consent from only 60% of property owners atop an injection site, some landowners would be left without a voice in the process, the southwestern Pennsylvania-based Center for Coalfield Justice warned in an  online petition  opposing the bill. The petition urges signatories to send a message to their representatives with language such as: “If 40% of people within a carbon storage field don’t want carbon injected beneath their feet — the project can move forward anyway.” 

Ethan Story, advocacy director at the Center for Coalfield Justice, believes few Pennsylvanians are aware of the bill and what it could mean to them. “Landowners, in addition to elected officials in some communities, are very unaware and uneducated on this proposal,” he said. “The immediate reaction from a majority of the community members that we have talked to and presented this information to has been met with great pause.”

SB 831 has been met with a different reaction in the state Legislature, where it’s earned—and sometimes lost—votes from Democrats and Republicans alike. 

Affirmative votes in the Senate came from a handful of Democrats, including state Sens. Jay Costa from Pittsburgh and Christine Tartaglione from Philadelphia. Those who opposed the bill included Sen. Doug Mastriano, a far-right Republican from south central Pennsylvania who made headlines in 2022 with a failed gubernatorial run and his full embrace of various hard-line policies, including a firm  pro-fossil fuel stance .

Carbon capture “is, to a degree, cutting across what we would probably classify as traditional ideological divisions,” said Sean O’Leary, senior researcher, energy and petrochemicals, at the Ohio River Valley Institute, a nonprofit think tank.

One of carbon capture’s most crucial endorsements in the state came from Gov. Josh Shapiro. Shapiro, a Democrat, ran on an  all-of-the-above strategy  for tackling the climate crisis. He has now thrown his weight behind the technology as the state has pursued federal funding for hydrogen hubs. Carbon capture was also recently included in two of the governor’s  climate proposals .

“Carbon capture is crucial to Pennsylvania’s energy future,” Shapiro spokesperson Manuel Bonder told Capital & Main. “We are glad to see a bipartisan group of senators agree with the governor that we need to invest in carbon capture and sequestration.

“The Administration looks forward to continuing to work with leaders in both parties to ensure bipartisan legislation contains appropriate environmental, public health, and safety protections as it moves through the legislative process,” Bonder added. 

Shapiro’s support for carbon capture could be key to getting SB 831 over the goal line in the Democratically controlled state House, despite warnings from environmentalists. It also has the  backing  of the Pennsylvania State Building & Construction Trades Council, which makes campaign contributions to members on both sides of the aisle and which has  supported  fossil fuel and renewable projects alike.

The bill currently sits in the House Consumer Protection, Technology and Utilities Committee, where a handful of more straightforward climate bills—including one that would improve school district access to solar energy and another that would legalize community solar projects across the commonwealth—have advanced with unanimous support before winning votes on both sides of the aisle on the full floor.

Capital & Main reached out to Democratic Rep. Rob Matzie, chair of the House Consumer Protection, Technology and Utilities Committee, for comment on the bill. Matzie did not respond by publication time. In the past, he has championed bills that proved to be a boon for fossil fuels, including  one  subsidizing a Shell Chemical Appalachia LLC plastics plant in southwestern Pennsylvania. When Shapiro released his carbon capture-infused energy plan, Matzie  signaled his support : “These proposals will create good energy jobs, promote opportunities for technologies that will deliver power while reducing their carbon footprint, and—most importantly—maintain our status as a net exporter of energy,” he said in a news release in March.

It’s an open question whether some of the provisions of SB 831 that are stoking environmentalists’ concern will make it through the House. But Democratic Rep. Emily Kinkead has offered an  alternative proposal that incorporates provisions to protect environmental justice communities that have long been scarred with the detritus of the oil and gas industry. It would also offer heightened protections for landowners situated near carbon sequestration projects. Kinkead, from Pittsburgh, circulated a memo describing the bill on March 25 but has yet to introduce formal legislation. 

Kinkead told Capital & Main she’s not certain such legislation will pass, but she hopes it will at least offer a starting point for negotiations to amend SB 831. 

“I think the goal of my bill is, at the very least, to demonstrate that we don’t have to do it exactly the way that it’s outlined,” she said. “We can incorporate some better practices.” 

If SB 831 passes the House without amendments, O’Leary, the Ohio River Valley Institute senior researcher, fears immediate repercussions for residents. At least one company—Omaha, Nebraska-based  Tenaska —is already planning carbon dioxide injection in the fracking-heavy southwestern part of Pennsylvania. The company  envisions  using 80,000 acres stretching across Pennsylvania, Ohio and West Virginia for up to 20 injection wells that would extend as far as 10,000 feet horizontally underground. This will require a  yet unknown number of pipelines . Those who oppose burying carbon under their land, but fall into the 40% minority, will be out of luck. 

— Audrey Carleton, Capital & Main

This piece was originally published by Capital & Main , which reports from California on economic, political, and social issues.

This post originally appeared at fastcompany.com

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Pennsylvania landowners may soon have to accept carbon dioxide burial on their land—whether they want it or not

Subscribe to our Energy E-Alert.

" "

Energy Transition

/ article, boosting demand for carbon dioxide removal.

By  Karan Mistry ,  Amy Sims ,  Thomas Baker ,  Paulina Ponce de León Baridó ,  Alex Dewar , and  Habib Azarabadi

The math behind carbon emissions and the need to curtail their impact on the world’s climate is both straightforward and alarming. Even if we deploy a wide range of carbon abatement solutions, there will likely still be a large amount of residual emissions in 2050 that will need to be removed to meet global emission targets. (For this discussion, we define residual emissions as being either overly expensive or infeasible to abate at any cost.)

As our latest report explains, scaling carbon dioxide removal (CDR) enough to reduce as much projected residual CO 2 emissions as possible will require combined effort from the world’s governments and regional governing bodies, using a full range of policy drivers including carbon pricing mechanisms, regulatory requirements, and financing incentives. And promoting the most durable forms of CDR—those, like direct air capture and sequestration, that remove CO 2 for centuries or more—will be necessary to ensure its permanent removal from the atmosphere.

How could these demand drivers work? And what is required to make sure they will be enough to bring residual emissions down to the fullest extent possible?

A Critical Need to Expand Demand for Carbon Reduction

According to the Intergovernmental Panel on Climate Change (IPCC), the use of CDR to counterbalance hard-to-abate residual emissions is unavoidable if net zero CO 2 is to be achieved. Our analysis suggests that between 6 and 10 gigatons per annum (Gtpa) of residual CO 2 emissions are likely to remain unabated globally in 2050. Across sectors, residual CO 2 emissions are expected to be concentrated in the industrial (~40%), energy supply (~30%), and transport (~20%) sectors.

Since many carbon reduction technologies are still nascent, there is uncertainty whether they will develop and scale to the degree needed. As a result, there is no consensus on the expected volume of residual emissions that will need to be removed for the world to reach net zero emissions on an annual basis. Therefore, CDR will be needed to help close the emissions gap. (See “An Overview of CDR Methods.”)

An Overview of CDR Methods

  • Direct Air Carbon Capture and Sequestration (DACCS)
  • Biomass with Carbon Removal and Storage (BiCRS)
  • Bioenergy Carbon Capture and Storage (BECCS)
  • Enhanced Weathering / CO 2 Mineralization

Voluntary CDR purchases grew from 600 kilotons (kt) in 2022 to 4.5 megatons (Mt) purchased in 2023, according to CDR.fyi. Last year, BCG estimated that the voluntary market for durable CDR would continue to expand significantly—from around 60 Mt to as much as 750 Mt per annum (Mtpa) by 2040, depending on how CDR costs decline. However, this is far below the multi-gigaton per annum scale that will be needed to limit global temperature rise.

In short, the voluntary market cannot induce enough CDR demand to meet requirements—in part because, unlike other climate technologies such as solar and wind power, CDR produces no product or service that creates its own demand. Instead, CDR could be considered a public good, and it is likely that only changes in government regulation and policy will lift the barriers to scaling the CDR demand needed.

Measures to Drive CDR Demand

Our analysis shows that governments have five primary direct and indirect ways to boost demand for durable CDR, which vary significantly in terms of the amount of demand created.

Direct demand drivers include the integration of durable CDR into carbon pricing mechanisms, regulatory requirements to decarbonize, and government procurement of CDR. Indirect drivers include enabling policies, such as financial incentives to reduce prices, and CO 2 accounting enablers, such as requirements that must be met for a company to claim it is “net zero.” In addition to promoting the scale-up of durable CDR demand, many of these policies could also play a major role in incentivizing the maximum emissions reductions possible. (See Exhibit 1.)

carbon dioxide travel through

We estimate that the expansion of existing and proposed policies to incorporate durable CDR could lead to around 0.5 to 2.5 Gtpa of CO 2 in durable CDR demand in 2050, covering as much as 30% of global residual emissions. Two policy demand drivers in particular—carbon pricing mechanisms and standards and requirements—have the greatest potential to incentivize demand. (See Exhibit 2.)

carbon dioxide travel through

Carbon pricing

Integrating durable CDR pathways into carbon pricing mechanisms could drive the largest share of potential demand—as much as 1.25 Gtpa—because existing and proposed carbon pricing mechanisms already cover a large portion of global emissions. Both emissions trading schemes and border carbon adjustments could incentivize durable CDR demand in two ways. Durable CDR could be directly integrated into these systems, allowing participants to procure durable CDR to generate an allowance or avoid a levy. In addition, parallel removal trading systems could be created that require a minimum purchase of durable CDR, which would rise over time.

Current efforts to address emissions primarily focus on reduction—which will not be enough to fully curtail climate impacts. Carbon pricing mechanisms will be most effective in promoting both CO 2 emissions reductions and CDR demand when high-quality, durable CDR is prioritized, a larger portion of emissions across industries is covered, and the cost of durable CDR declines to between $100 and $200 per ton of CO 2 . Adopting subsidies to lower durable CDR prices in the near term would encourage CDR purchases; however, in the long term, keeping prices artificially low through subsidies could encourage emitters to remove emissions rather than reducing them, which must occur first.

Standards and regulatory requirements

New standards and requirements could encourage the decarbonization of various industries, allowing companies to use CDR as one option to decrease their emissions. This would incentivize demand when durable CDR is more economically viable than carbon reduction alternatives, and would be especially effective in sectors such as transportation and power.

  • Aviation and shipping are among the sectors that are especially difficult to abate, with limited decarbonization levers. CDR can effectively accelerate decarbonization in these sectors, both as a source of CO 2 feedstock for e-fuels production and as a direct counterbalance to fossil fuel emissions. Regional and national clean fuel mandates and standards could increase CDR demand from decarbonizing aviation and shipping by up to 600 Mtpa by 2050. (It is important to note that demand for CDR is highly impacted by whether policies specifically target pathways that require CDR or whether they are left open to alternatives that may be more economical, such as the use of sustainable aviation fuels produced from biomass feedstocks.)
  • Power industry net zero portfolio standards could drive demand through the use of bioenergy with carbon capture and storage, a negative emissions power generation technology. Purchases of CDR credits could also account for residual emissions from peaker plants as well as any other remaining fossil-based power generation, even when mitigated with carbon capture and storage. These regulations and requirements would be particularly relevant in geographies where power generation is not regulated under an ETS.

In addition to these direct demand drivers, governments could induce further demand indirectly through financial incentives and carbon dioxide accounting enablers.

  • Financial incentives could reduce the cost or risk associated with CDR production and purchasing. Examples include tax credits and feed-in tariffs, such as current investment tax credits, production tax credits, or credits for various green technologies. Rather than increasing the number of potential CDR buyers, these mechanisms would help boost the supply of CDR to increase demand from buyers who were already interested in purchasing but deterred by price or lack of supply.
  • Carbon dioxide accounting enablers would generally allow for clarity in how to use CDR to meet voluntary or policy commitments. Changes in how greenhouse gases (which include more than CO 2 ) are accounted for could indirectly increase demand. For example, standard-setting bodies such as the Science Based Targets initiative (SBTi) could clarify how companies should use CDR to meet net zero targets. International efforts like the Paris Agreement could define mechanisms for countries to count CDR as part of their own nationally determined contributions to reducing all carbon emissions. However, accounting enablers would not inherently drive CDR demand without additional voluntary or policy actions.

The Regional Outlook for CDR Demand

The scale of demand incentivized by incorporating CDR into these policy demand drivers will vary regionally, driven by the maturity of existing climate policies, the ambition of proposed policies, and the ability to finance decarbonization, with the largest gaps likely to remain in Asia Pacific.

Europe and North America are the most advanced regions in the implementation of climate policies and therefore are also the most likely to drive significant demand for durable CDR. As a result, Europe and North America could see the highest coverage of residual emissions—around 65% in Europe and 60% in North America. Some countries in Asia Pacific will face challenges in covering residual emissions with durable CDR due to the scale of projected residuals, a lack of regional consistency in the advancement of climate policy, and the high cost of decarbonization and durable CDR.

Methods for increasing CDR demand in Asia Pacific and other regions with significant residual emissions, such as Africa and South America, could include expanding the scope of existing and proposed demand drivers and creating new durable CDR demand drivers. Emissions trading schemes and border carbon adjustments, for example, could expand to cover additional industries and goods. Demand could also grow significantly if more governments were to implement sustainable fuel blending or decarbonization requirements in transport. Among new demand drivers, government procurement of enhanced rock weathering or biochar on agricultural lands has significant potential: allocating just 2% of total existing agricultural subsidies in regions with the highest capacity for ERW could generate as much as 1 Gtpa or more in durable CO 2 removals.

Taking Action

What steps need to be taken to increase the demand for durable CDR—and to ensure that there’s enough supply to meet that demand? We see three actions that could be taken in the near-term.

First, governments could set clear goals for durable CDR and encourage near-term supply and demand. These actions could include pursuing durable CDR targets, promoting government procurement of durable CDR, funding more R&D for CDR technologies, and developing policies, such as financial incentives, to encourage voluntary demand. Governments could also define frameworks for durable CDR to be integrated into both compliance and voluntary carbon markets.

Second, standard-setters could encourage procurement of high-quality durable CDR in tandem with meaningful emissions reduction measures. They could also provide market clarity by defining guidelines for when durable CDR is needed, such as encouraging its use in accounting for fossil emissions in hard-to-abate sectors.

Finally, actors across the ecosystem must continue to drive innovation in CDR methods to help expand the supply. In this report, we have focused on increasing the demand for durable CDR, but it will also be crucial for CDR supply to grow further and for costs to decrease. This will require public-private collaboration and increased investment in technology and infrastructure—including expanded R&D, pilot projects, and demonstration plants—to prove the viability, efficiency, and environmental impacts of CDR technologies such as direct air capture and ocean-based removals. Suppliers, investors, and other relevant stakeholders should focus on building a supportive ecosystem that includes financial incentives, partnerships, and streamlined regulatory processes in order to accelerate innovation and maximize CO 2 removal.

Karan Mistry

Managing Director & Partner

Los Angeles

Amy Sims | square

Project Leader

San Francisco - Bay Area

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Washington, DC

Habib Azarabadi | square

Senior Knowledge Analyst

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IMAGES

  1. Transport of CO2 from tissues to lungs

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  2. Carbon Cycle

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  3. How is Oxygen and Carbon Dioxide Transported in Human Beings?

    carbon dioxide travel through

  4. What Is The Carbon Cycle?

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  5. Most of the Carbon Dioxide That Is Absorbed by Blood

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  6. Carbon cycle

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VIDEO

  1. CARBON DIOXIDE REDUCTION THROUGH THE USEOF RU, RH AND IR COMPLEXES AS CATALYSTS

  2. Carbon dioxide effects at Horseshoe Lake in Mammoth Lakes, California

  3. The use of carbon dioxide gas for blasting in quarries is highly efficient and greatly reduces costs

  4. Carbon Removal (Working in Sustainable Technology)

  5. Carbon Dioxide Experiment #thirdfloradventures #kids #fun #joy #science

  6. Atmospheric Carbon Dioxide Tagged by Source: Australia and Asia

COMMENTS

  1. 21.9D: Carbon Dioxide Transport

    Carbon Dioxide Transport. Carbon dioxide is the product of cellular respiration, and is transported from the cells of tissues in the body to the alveoli of the lungs through the bloodstream. Carbon dioxide is carried in the blood through three different ways. About 5% of carbon dioxide is transported in the plasma of the blood as dissolved CO 2 ...

  2. Transport of Carbon Dioxide in the Blood

    Carbon dioxide can be transported through the blood via three methods. It is dissolved directly in the blood, bound to plasma proteins or hemoglobin, or converted into bicarbonate. The majority of carbon dioxide is transported as part of the bicarbonate system. Carbon dioxide diffuses into red blood cells. Inside, carbonic anhydrase converts ...

  3. Physiology, Carbon Dioxide Transport

    Carbon dioxide is an important side product of the citric acid cycle (Krebs cycle). This oxidized carbon represents an end product of metabolism that, ultimately, needs to be removed using transport to the lungs and subsequent expiration out into the surrounding environment. Together with renal regulation, this complex process of carbon dioxide production, transport, and elimination is the ...

  4. 22.17: Transport of Carbon Dioxide in the Blood

    The carbon dioxide produced is expelled through the lungs during exhalation. ... The presence of this bicarbonate buffer system also allows for people to travel and live at high altitudes: When the partial pressure of oxygen and carbon dioxide change at high altitudes, the bicarbonate buffer system adjusts to regulate carbon dioxide while ...

  5. Human respiratory system

    Robert A. Klocke. Human respiratory system - Gas Exchange, Lungs, Airways: Transport of carbon dioxide in the blood is considerably more complex. A small portion of carbon dioxide, about 5 percent, remains unchanged and is transported dissolved in blood. The remainder is found in reversible chemical combinations in red blood cells or plasma.

  6. 22.5 Transport of Gases

    The first mechanism of carbon dioxide transport is by blood plasma, as some carbon dioxide molecules dissolve in the blood. The second mechanism is transport in the form of bicarbonate (HCO 3- ), which also dissolves in plasma. The third mechanism of carbon dioxide transport is similar to the transport of oxygen by erythrocytes ( Figure 22.5.4 ).

  7. Carbon dioxide transport in blood: Video & Anatomy

    The transport of carbon dioxide in the blood occurs through three main mechanisms. First, there is a portion of carbon dioxide that is directly dissolved in the plasma, which is the liquid part of blood. The next part of carbon dioxide is bound to hemoglobin, what's called carbaminohemoglobin. Most of the amount of carbon dioxide is chemically ...

  8. 22.5 Transport of Gases

    Carbon dioxide is transported by three major mechanisms. The first mechanism of carbon dioxide transport is by blood plasma, as some carbon dioxide molecules dissolve in the blood. The second mechanism is transport in the form of bicarbonate (HCO 3- ), which also dissolves in plasma. The third mechanism of carbon dioxide transport is similar ...

  9. The Carbon Cycle

    The carbon cycle is the series of processes through which carbon atoms continually travel from the atmosphere into organisms, the oceans, and the Earth and then back into the atmosphere. ... Carbon Dioxide in the Atmosphere: The cycle begins with carbon dioxide (CO 2) present in the atmosphere. Photosynthesis: Plants, ...

  10. 39.14: Transport of Gases in Human Bodily Fluids

    The carbon dioxide produced is expelled through the lungs during exhalation. ... The presence of this bicarbonate buffer system also allows for people to travel and live at high altitudes. When the partial pressure of oxygen and carbon dioxide change at high altitudes, the bicarbonate buffer system adjusts to regulate carbon dioxide while ...

  11. CO2 Transport in the Blood

    This article provides an overview of the transport of carbon dioxide (CO 2) in the blood including the three main methods of transport, the effect of oxygen on CO 2 carriage and the impact of CO 2 on the acid-base balance of the body.. Production of CO 2. CO 2 is produced as a waste product of respiration within the mitochondria of cells. 1 CO 2 is then transported to the lungs for excretion ...

  12. The carbon cycle (article)

    Carbon dioxide— CO 2 ‍ —from the atmosphere is taken up by photosynthetic organisms and used to make organic molecules, which travel through food chains. In the end, the carbon atoms are released as CO 2 ‍ in respiration.

  13. The movement of carbon around Earth's atmosphere explained

    Carbon dioxide + water + light energy = sugar + oxygen When plants or animals break that sugar back down for energy through respiration (the opposite of photosynthesis) they release CO2 back into ...

  14. WATCH: How Carbon Dioxide Travels Around The Globe

    Eyder Peralta. We're a few days late on this, but it's too cool not to share. Here's a NASA video made from a new model that shows how carbon dioxide moves throughout Earth: YouTube. NASA explains ...

  15. Exchanging Oxygen and Carbon Dioxide

    This barrier between air and blood averages about 1 micron (1/10,000 of a centimeter, or 0.000039 inch) in thickness. Oxygen passes quickly through this air-blood barrier into the blood in the capillaries. Similarly, carbon dioxide passes from the blood into the alveoli and is then exhaled. Oxygenated blood travels from the lungs through the ...

  16. Method of Carbon Dioxide Transport in the Blood & Lungs

    The majority of the carbon dioxide in our body, around 85%, is transported as part of the blood's bicarbonate buffer system. The bicarbonate buffer system is the body's way of regulating the pH of ...

  17. What is the carbon cycle?

    The carbon cycle is nature's way of reusing carbon atoms, which travel from the atmosphere into organisms in the Earth and then back into the atmosphere over and over again. Most carbon is stored in rocks and sediments, while the rest is stored in the ocean, atmosphere, and living organisms. These are the reservoirs, or sinks, through which ...

  18. How Blood Flows Through the Heart & Body

    Blood flows through your main pulmonary artery and its branches to your lungs, where it gets oxygen and releases carbon dioxide. On the left side. Oxygen-rich blood travels from your lungs to your left atrium through large veins called pulmonary veins. These veins directly empty the blood into your left atrium.

  19. Simple diffusion and passive transport (article)

    The simplest forms of transport across a membrane are passive. Passive transport does not require the cell to expend any energy and involves a substance diffusing down its concentration gradient across a membrane. A concentration gradient is a just a region of space over which the concentration of a substance changes, and substances will ...

  20. How Exactly Does Carbon Dioxide Cause Global Warming?

    Water is indeed a greenhouse gas. It absorbs and re-emits infrared radiation, and thus makes the planet warmer. However, Smerdon says the amount of water vapor in the atmosphere is a consequence of warming rather than a driving force, because warmer air holds more water. "We know this on a seasonal level," he explains.

  21. Carbon cycle

    As a result, the amount of carbon dioxide in the atmosphere is rapidly rising; it is already greater than at any time in the last 3.6 million years. The ocean absorbs much of the carbon dioxide that is released from burning fossil fuels. This extra carbon dioxide is lowering the ocean's pH, through a process called ocean acidification.

  22. You Asked: How Does Carbon Dioxide Get So High Up Into the Atmosphere

    Carbon dioxide is a gas. The density of a gas increases as temperatures get colder. So, because temperatures decrease as we reach higher altitudes, gases become denser at higher altitudes. Denser objects tend to sink, pulled down by gravity. (In fact, the force of gravity pulling gas molecules towards the Earth's surface is what maintains our ...

  23. During Year of Extremes, Carbon Dioxide Levels Surge Faster than Ever

    Article Content. Carbon dioxide is accumulating in the atmosphere faster than ever — accelerating on a steep rise to levels far above any experienced during human existence, scientists from NOAA and Scripps Institution of Oceanography at the University of California San Diego announced today.. Scientists at Scripps Oceanography, which initiated the CO 2 monitoring program known as the ...

  24. How pulling carbon out of the ocean may help remove it from the air

    Taking carbon dioxide from the ocean could increase its natural ability to remove emissions from the atmosphere, like wringing out a sponge to make it more absorptive. By Marcello Rossi June 21, 2024

  25. Pennsylvania landowners may soon have to accept carbon dioxide ...

    The wells create pathways underground through which gases can travel and potentially seep into waterways or leak into the atmosphere, undoing the progress of capturing the carbon in the first place.

  26. Boosting Demand for Carbon Dioxide Removal

    In addition to these direct demand drivers, governments could induce further demand indirectly through financial incentives and carbon dioxide accounting enablers. Financial incentives could reduce the cost or risk associated with CDR production and purchasing. Examples include tax credits and feed-in tariffs, such as current investment tax ...

  27. Serbia seeks to beat air pollution with 'liquid trees'

    06/25/2024 June 25, 2024. Serbian scientists are helping purify the air in cities with what they call liquid trees. The tanks full of microalgae bind carbon dioxide and produce oxygen through ...

  28. Carbon-capture projects launch in Los Angeles County

    As soaring fossil fuel emissions continue to heighten global warming, multiple projects seeking to remove carbon dioxide from the air have been launched across Los Angeles County — an effort ...