How does carbon cycle through the biosphere

Illustration adapted from P. Sellers et al. Plants and phytoplankton are the main components of the fast carbon cycle. Phytoplankton microscopic organisms in the ocean and plants take carbon dioxide from the atmosphere by absorbing it into their cells. Using energy from the Sun, both plants and plankton combine carbon dioxide CO 2 and water to form sugar CH 2 O and oxygen. The chemical reaction looks like this:. Four things can happen to move carbon from a plant and return it to the atmosphere, but all involve the same chemical reaction.

Plants break down the sugar to get the energy they need to grow. Animals including people eat the plants or plankton, and break down the plant sugar to get energy.

Plants and plankton die and decay are eaten by bacteria at the end of the growing season. Or fire consumes plants. In each case, oxygen combines with sugar to release water, carbon dioxide, and energy. The basic chemical reaction looks like this:. In all four processes, the carbon dioxide released in the reaction usually ends up in the atmosphere.

The fast carbon cycle is so tightly tied to plant life that the growing season can be seen by the way carbon dioxide fluctuates in the atmosphere. In the Northern Hemisphere winter, when few land plants are growing and many are decaying, atmospheric carbon dioxide concentrations climb.

During the spring, when plants begin growing again, concentrations drop. It is as if the Earth is breathing. The ebb and flow of the fast carbon cycle is visible in the changing seasons.

As the large land masses of Northern Hemisphere green in the spring and summer, they draw carbon out of the atmosphere. This graph shows the difference in carbon dioxide levels from the previous month, with the long-term trend removed. This cycle peaks in August, with about 2 parts per million of carbon dioxide drawn out of the atmosphere.

In the fall and winter, as vegetation dies back in the northern hemisphere, decomposition and respiration returns carbon dioxide to the atmosphere. Left unperturbed, the fast and slow carbon cycles maintain a relatively steady concentration of carbon in the atmosphere, land, plants, and ocean. But when anything changes the amount of carbon in one reservoir, the effect ripples through the others. See Milutin Milankovitch. Ice ages developed when Northern Hemisphere summers cooled and ice built up on land, which in turn slowed the carbon cycle.

Meanwhile, a number of factors including cooler temperatures and increased phytoplankton growth may have increased the amount of carbon the ocean took out of the atmosphere.

The drop in atmospheric carbon caused additional cooling. Similarly, at the end of the last Ice Age, 10, years ago, carbon dioxide in the atmosphere rose dramatically as temperatures warmed.

Levels of carbon dioxide in the atmosphere have corresponded closely with temperature over the past , years. Antarctic ice-core data show the long-term correlation until about Today, changes in the carbon cycle are happening because of people. We perturb the carbon cycle by burning fossil fuels and clearing land.

When we clear forests, we remove a dense growth of plants that had stored carbon in wood, stems, and leaves—biomass. By removing a forest, we eliminate plants that would otherwise take carbon out of the atmosphere as they grow.

We tend to replace the dense growth with crops or pasture, which store less carbon. We also expose soil that vents carbon from decayed plant matter into the atmosphere. Humans are currently emitting just under a billion tons of carbon into the atmosphere per year through land use changes. The burning of fossil fuels is the primary source of increased carbon dioxide in the atmosphere today.

Without human interference, the carbon in fossil fuels would leak slowly into the atmosphere through volcanic activity over millions of years in the slow carbon cycle. By burning coal, oil, and natural gas, we accelerate the process, releasing vast amounts of carbon carbon that took millions of years to accumulate into the atmosphere every year.

By doing so, we move the carbon from the slow cycle to the fast cycle. In , humans released about 8. Emissions of carbon dioxide by humanity primarily from the burning of fossil fuels, with a contribution from cement production have been growing steadily since the onset of the industrial revolution.

About half of these emissions are removed by the fast carbon cycle each year, the rest remain in the atmosphere. Since the beginning of the Industrial Revolution, when people first started burning fossil fuels, carbon dioxide concentrations in the atmosphere have risen from about parts per million to parts per million, a 39 percent increase.

This means that for every million molecules in the atmosphere, of them are now carbon dioxide—the highest concentration in two million years. Methane concentrations have risen from parts per billion in to 1, parts per billion in , the highest concentration in at least , years. All of this extra carbon needs to go somewhere. So far, land plants and the ocean have taken up about 55 percent of the extra carbon people have put into the atmosphere while about 45 percent has stayed in the atmosphere.

Eventually, the land and oceans will take up most of the extra carbon dioxide, but as much as 20 percent may remain in the atmosphere for many thousands of years. The changes in the carbon cycle impact each reservoir. Excess carbon in the atmosphere warms the planet and helps plants on land grow more.

Excess carbon in the ocean makes the water more acidic, putting marine life in danger. Carbon dioxide, methane, and halocarbons are greenhouse gases that absorb a wide range of energy—including infrared energy heat emitted by the Earth—and then re-emit it.

The re-emitted energy travels out in all directions, but some returns to Earth, where it heats the surface. Without greenhouse gases, Earth would be a frozen degrees Celsius 0 degrees Fahrenheit. With too many greenhouse gases, Earth would be like Venus, where the greenhouse atmosphere keeps temperatures around degrees Celsius Fahrenheit. Rising concentrations of carbon dioxide are warming the atmosphere. The increased temperature results in higher evaporation rates and a wetter atmosphere, which leads to a vicious cycle of further warming.

Because scientists know which wavelengths of energy each greenhouse gas absorbs, and the concentration of the gases in the atmosphere, they can calculate how much each gas contributes to warming the planet. The rest is caused by small particles aerosols and minor greenhouse gases like methane. Warmer temperatures evaporate more water from the oceans, expand air masses, and lead to higher humidity.

Cooling causes water vapor to condense and fall out as rain, sleet, or snow. Carbon dioxide, on the other hand, remains a gas at a wider range of atmospheric temperatures than water.

Carbon dioxide molecules provide the initial greenhouse heating needed to maintain water vapor concentrations. When carbon dioxide concentrations drop, Earth cools, some water vapor falls out of the atmosphere, and the greenhouse warming caused by water vapor drops.

Likewise, when carbon dioxide concentrations rise, air temperatures go up, and more water vapor evaporates into the atmosphere—which then amplifies greenhouse heating. So while carbon dioxide contributes less to the overall greenhouse effect than water vapor, scientists have found that carbon dioxide is the gas that sets the temperature. Carbon dioxide controls the amount of water vapor in the atmosphere and thus the size of the greenhouse effect. Rising carbon dioxide concentrations are already causing the planet to heat up.

At the same time that greenhouse gases have been increasing, average global temperatures have risen 0. With the seasonal cycle removed, the atmospheric carbon dioxide concentration measured at Mauna Loa Volcano, Hawaii, shows a steady increase since At the same time global average temperatures are rising as a result of heat trapped by the additional CO 2 and increased water vapor concentration.

The degree to which temperatures go up beyond that depends in part on how much more carbon humans release into the atmosphere in the future. About 30 percent of the carbon dioxide that people have put into the atmosphere has diffused into the ocean through the direct chemical exchange. Dissolving carbon dioxide in the ocean creates carbonic acid, which increases the acidity of the water. Or rather, a slightly alkaline ocean becomes a little less alkaline. Some of the excess CO 2 emitted by human activity dissolves in the ocean, becoming carbonic acid.

Increases in carbon dioxide are not only leading to warmer oceans, but also to more acidic oceans. Ocean acidification affects marine organisms in two ways. First, carbonic acid reacts with carbonate ions in the water to form bicarbonate. However, those same carbonate ions are what shell-building animals like coral need to create calcium carbonate shells. With less carbonate available, the animals need to expend more energy to build their shells. As a result, the shells end up being thinner and more fragile.

Second, the more acidic water is, the better it dissolves calcium carbonate. In the meantime, though, more acidic water will dissolve the carbonate shells of marine organisms, making them pitted and weak. Warmer oceans—a product of the greenhouse effect—could also decrease the abundance of phytoplankton, which grow better in cool, nutrient-rich waters.

On the other hand, carbon dioxide is essential for plant and phytoplankton growth. An increase in carbon dioxide could increase growth by fertilizing those few species of phytoplankton and ocean plants like sea grasses that take carbon dioxide directly from the water.

However, most species are not helped by the increased availability of carbon dioxide. Plants on land have taken up approximately 25 percent of the carbon dioxide that humans have put into the atmosphere.

Only some of this increase occurred as a direct result of fossil fuel emissions. With more atmospheric carbon dioxide available to convert to plant matter in photosynthesis, plants were able to grow more. This increased growth is referred to as carbon fertilization. Models predict that plants might grow anywhere from 12 to 76 percent more if atmospheric carbon dioxide is doubled, as long as nothing else, like water shortages, limits their growth.

Plants also need water, sunlight, and nutrients, especially nitrogen. There is a limit to how much carbon plants can take out of the atmosphere, and that limit varies from region to region. So far, it appears that carbon dioxide fertilization increases plant growth until the plant reaches a limit in the amount of water or nitrogen available.

Some of the changes in carbon absorption are the result of land use decisions. Agriculture has become much more intensive, so we can grow more food on less land.

In high and mid-latitudes, abandoned farmland is reverting to forest, and these forests store much more carbon, both in wood and soil, than crops would. In many places, we prevent plant carbon from entering the atmosphere by extinguishing wildfires. This allows woody material which stores carbon to build up.

All of these land use decisions are helping plants absorb human-released carbon in the Northern Hemisphere. Changes in land cover—forests converted to fields and fields converted to forests—have a corresponding effect on the carbon cycle.

In some Northern Hemisphere countries, many farms were abandoned in the early 20th century and the land reverted to forest. As a result, carbon was drawn out of the atmosphere and stored in trees on land.

In the tropics, however, forests are being removed, often through fire, and this releases carbon dioxide. As of , deforestation accounted for about 12 percent of all human carbon dioxide emissions.

The biggest changes in the land carbon cycle are likely to come because of climate change. Carbon dioxide increases temperatures, extending the growing season and increasing humidity.

Both factors have led to some additional plant growth. However, warmer temperatures also stress plants. With a longer, warmer growing season, plants need more water to survive. Scientists are already seeing evidence that plants in the Northern Hemisphere slow their growth in the summer because of warm temperatures and water shortages. Dry, water-stressed plants are also more susceptible to fire and insects when growing seasons become longer. Why do some smaller nations have larger per capita emission estimates than industrialized nations like the US?

Often it is difficult to attribute emissions to a source. Many small island nations have military bases that are used for re-fueling or have large tourist industries. Who do you assign the emissions to; the US whose military planes are re-fueling on the Wake Island with aviation and jet fuel or the Wake Island? The accounting practices used within the UN Energy Statistics Database assign this fuel consumption to the Wake Island thus elevating the Wake Island's per capita estimate.

The same is true for tourist nations like Aruba who are assigned the fuels used in the commercial planes carrying tourists back to their native countries. Although this distorts the per capita emission estimates it makes it easier from an accounting standpoint than trying to trace each plane or ship to its final destination. One should be cautious in using only the per capita CO 2 emission estimates.

No, they are two different but related issues. The greenhouse effect issue concerns the warming of the lower part of the atmosphere, the troposphere the layer in which temperature drops with height; it is about kilometers thick, varying with latitude and season , by increasing concentrations of the so-called greenhouse gases carbon dioxide, methane, nitrous oxide, ozone, and others in the troposphere.

This warming occurs because the greenhouse gases, while they are transparent to incoming solar radiation, absorb infrared heat radiation from the Earth that would otherwise escape from the atmosphere into space; the greenhouse gases then re-radiate some of this heat back towards the surface of the Earth.

The ozone hole issue concerns the loss of ozone in the upper part of the atmosphere, the stratosphere, resulting from increasing concentrations of certain halogenated hydrocarbons such as chlorinated fluorocarbons, known as CFCs. Through a series of chemical reactions in the stratosphere, the halogenated hydrocarbons destroy ozone in the stratosphere. This is of concern because the ozone blocks incoming ultraviolet radiation from the Sun, and portions of the ultraviolet radiation spectrum have been found to have adverse biological effects.

The greenhouse effect and ozone hole issues are, however, related. For example, CFCs are involved in both issues: CFCs, in addition to destroying stratosphere ozone, are also greenhouse gases.

It has traditionally been thought there is not much mixing of the troposphere and stratosphere. But there is recent evidence of transport of stratospheric ozone into the troposphere see "Ozone-rich transients in the upper equatorial Atlantic troposphere," by Suhre et al. So ozone depletion in the stratosphere could result in reduced concentrations of this greenhouse gas in the troposphere.

Conversely, global climate change could also affect ozone depletion through changes in stratospheric temperature and water vapor see "The effect of climate change on ozone depletion through changes in stratospheric water vapour," by Kirk-Davidoff et al.

Should we be concerned with human breathing as a source of CO 2? While people do exhale carbon dioxide the rate is approximately 1 kg per day, and it depends strongly on the person's activity level , this carbon dioxide includes carbon that was originally taken out of the carbon dioxide in the air by plants through photosynthesis - whether you eat the plants directly or animals that eat the plants. Thus, there is a closed loop, with no net addition to the atmosphere.

Of course, the agriculture, food processing, and marketing industries use energy in many cases based on the combustion of fossil fuels , but their emissions of carbon dioxide are captured in our estimates as emissions from solid, liquid, or gaseous fuels.

How does the oxygen cycle relate to the greenhouse effect and global warming? With recent developments it is now feasible to measure variations in the oxygen content of the atmosphere at the parts per million ppm level. Regular measurements of changes in atmospheric oxygen O 2 are currently being made at a number of locations around the world using two independent techniques, one based on interferometry and one based on stable isotope mass spectroscopy.

Oxygen measurements can inform us about fundamental aspects of the global carbon cycle. Oxygen is generated by green plants in photosynthesis and converted to carbon dioxide CO 2 in animal and human respiration. Variations in atmospheric O 2 are controlled largely by fluxes of carbon e.

Keeling, R. Najjar, M. Bender, P. Global Biogeochemical Cycles Moore, B. III, and B. The lifetime of excess atmospheric carbon dioxide. Seasonal and interannual variations in atmospheric oxygen and implications for the global carbon cycle.

Nature Broecker, W. Diminishing Oxygen. How long does it take for the oceans and terrestrial biosphere to take up carbon after it is burned? With over billion metric tons of carbon in the atmosphere and an annual exchange with the biosphere and oceans equal to around billion metric tons, an average atom of carbon spends only about 4 years in the atmosphere before it goes into the oceans or the terrestrial biosphere.

We can think of this as the average residence time for a carbon atom in the atmosphere. However, the oceans and terrestrial biosphere not only take up carbon from the atmosphere e. The time it takes for a carbon atom to make it out of this recycling system and to get into the deep ocean is about years.

The figure below, provided by Ken Caldiera of the Carnegie Institution for Science, shows how an instantaneous doubling of pre-industrial carbon dioxide from parts per million to parts per million would be removed from the atmosphere-biosphere system.

How much CO 2 is emitted as a result of my using specific electrical appliances? For this answer, we refer you to an excellent article, "Your Contribution to Global Warming," by George Barnwell, which appeared on p.

The article, assuming that your electricity comes from coal, calculates CO 2 emissions corresponding to the use of various electrical appliances. For example, one hour's use of a color television produces 0. In general, the coefficient is about 2. You can calculate the kWh of electricity by multiplying the number of watts W the appliance uses times the number of hours h it is used, then dividing by This use of electricity would produce an emission of 1.

Why do certain compounds, such as carbon dioxide, absorb and emit infrared energy? Molecules can absorb and emit three kinds of energy: energy from the excitation of electrons, energy from rotational motion, and energy from vibrational motion.

The first kind of energy is also exhibited by atoms, but the second and third are restricted to molecules. A molecule can rotate about its center of gravity there are three mutually perpendicular axes through the center of gravity. Vibrational energy is gained and lost as the bonds between atoms, which may be thought of as springs, expand and contract and bend.

The three kinds of energy are associated with different portions of the spectrum: electronic energy is typically in the visible and ultraviolet portions of the spectrum for example, wavelength of 1 micrometer, vibrational energy in the near infrared and infrared for example, wavelength of 3 micrometers , and rotational energy in the far infrared to microwave for example, wavelength of micrometers.

The specific wavelength of absorption and emission depends on the type of bond and the type of group of atoms within a molecule. What makes certain gases, such as carbon dioxide, act as "greenhouse" gases is that they happen to have vibrational modes that absorb energy in the infrared wavelengths at which the earth radiates energy to space.

In fact, the measured "peaks" of infrared absorbance are often broadened because of the overlap of several electronic, rotational, and vibrational energies from the several-to-many atoms and interatomic bonds in the molecules. Gray and Gilbert P. Haight, Jr. Benjamin, Inc. Is it possible to separate the carbon and oxygen from CO 2 as is possible with other molecules? The problem in separating the carbon and oxygen from CO 2 is that CO 2 is a VERY stable molecule, because of the bonds that hold the carbon and oxygen together, and it takes a lot of energy to separate them.

Most schemes being considered now involve conversion to liquid or solids. One present concept for capturing CO 2 , such as from flue gases of boilers, involves chemical reaction with MEA monoethanol amine. Other techniques include physical absorption; chemical reaction to methanol, polymers and copolymers, aromatic carboxylic acid, or urea; and reaction in plant photosynthetic systems or synthetic versions thereof. Overcoming energetic hurdles is a major challenge; if the energy needed to drive these reactions comes from burning of fossil fuels, there may not be an overall gain.

One aspect of the current research is the use of catalysts to promote the reactions. In green plants, of course, chlorophyll is such a catalyst! One area of current research is looking at using cellular components to imitate photosynthesis on an industrial scale. I am curious about the global warming potential of water vapor. Do you know if estimates are done of this in the same way as global warming potentials are calculated for other greenhouse gases? I am also interested in why no mention is ever made of the enhanced greenhouse effect caused by anthropogenic emissions of water vapor.

Are the anthropogenic emissions not significant? Water vapor is indeed a very potent "greenhouse" gas, in terms of its absorbing and re-radiating outgoing infrared radiation. It is commonly not mentioned as an important factor in global warming, because it is not clear that the atmospheric concentration as compared with CO 2 , methane, etc.

Some Richard Lindzen at MIT, prominently have argued that the uncertain potential feedbacks involving water vapor represent a serious shortcoming in models of climate warming. See the following online resource for a good discussion of this issue:. If so, are there current or impending regulation specific to their use? In essence it passes through this kind of use rather than being emitted immediately and there is no extra CO 2 produced".

Could you tell me, please, if I have 1 gallon of fuel in my car, how many units? Is there any difference if the car 4 or 6 or 8 cylinders or in respect of horse power in percentage?

And also our human body forms Inorganic Carbonate or Shells. How does carbon cycle through the biosphere? Feb 11, Explanation: All living things are made of carbon.

Related questions What is a biotic factor which would affect the net primary production of a plant? In the carbon cycle, what happens to carbon that is released during combustion?