Why are biogeochemical cycles important to ecosystems? What are some examples of biogeochemical cycles? How is evaporation related to humidity? How can condensation heat the atmosphere? How can condensation be observed? What are some examples of precipitation? What is precipitation?
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. In the far north, where an increase in temperature has the greatest impact, the forests have already started to burn more, releasing carbon from the plants and the soil into the atmosphere.
Tropical forests may also be extremely susceptible to drying. With less water, tropical trees slow their growth and take up less carbon, or die and release their stored carbon to the atmosphere.
This is of particular concern in the far north, where frozen soil—permafrost—is thawing. Permafrost contains rich deposits of carbon from plant matter that has accumulated for thousands of years because the cold slows decay.
When the soil warms, the organic matter decays and carbon—in the form of methane and carbon dioxide—seeps into the atmosphere. Current research estimates that permafrost in the Northern Hemisphere holds 1, billion tons Petagrams of organic carbon.
If just 10 percent of this permafrost were to thaw, it could release enough extra carbon dioxide to the atmosphere to raise temperatures an additional 0. Many of the questions scientists still need to answer about the carbon cycle revolve around how it is changing. The atmosphere now contains more carbon than at any time in at least two million years. Each reservoir of the cycle will change as this carbon makes its way through the cycle.
What will those changes look like? What will happen to plants as temperatures increase and climate changes? Will they remove more carbon from the atmosphere than they put back? Will they become less productive? How much extra carbon will melting permafrost put into the atmosphere, and how much will that amplify warming? Will ocean circulation or warming change the rate at which the ocean takes up carbon?
Will ocean life become less productive? How much will the ocean acidify, and what effects will that have? Time series of satellite data, like the imagery available from the Landsat satellites, allow scientists to monitor changes in forest cover. Deforestation can release carbon dioxide into the atmosphere, while forest regrowth removes CO 2. This pair of false-color images shows clear cutting and forest regrowth between and in Washington State, northeast of Mount Rainier.
Dark green corresponds to mature forests, red indicates bare ground or dead plant material freshly cut areas , and light green indicates relatively new growth. As of early , two types of satellite instruments were collecting information relevant to the carbon cycle.
Two Landsat satellites provide a detailed view of ocean reefs, what is growing on land, and how land cover is changing. It is possible to see the growth of a city or a transformation from forest to farm. This information is crucial because land use accounts for one-third of all human carbon emissions. Future NASA satellites will continue these observations, and also measure carbon dioxide and methane in the atmosphere and vegetation height and structure. All of these measurements will help us see how the global carbon cycle is changing through time.
They will help us gauge the impact we are having on the carbon cycle by releasing carbon into the atmosphere or finding ways to store it elsewhere. They will show us how our changing climate is altering the carbon cycle, and how the changing carbon cycle is altering our climate.
Most of us, however, will observe changes in the carbon cycle in a more personal way. For us, the carbon cycle is the food we eat, the electricity in our homes, the gas in our cars, and the weather over our heads.
We are a part of the carbon cycle, and so our decisions about how we live ripple across the cycle. Likewise, changes in the carbon cycle will impact the way we live. As each of us come to understand our role in the carbon cycle, the knowledge empowers us to control our personal impact and to understand the changes we are seeing in the world around us.
Atmosphere Land. EO Explorer. At the time of publication, it represented the best available science. The Slow Carbon Cycle Through a series of chemical reactions and tectonic activity, carbon takes between million years to move between rocks, soil, ocean, and atmosphere in the slow carbon cycle. The Fast Carbon Cycle The time it takes carbon to move through the fast carbon cycle is measured in a lifespan. These maps show net primary productivity the amount of carbon consumed by plants on land green and in the oceans blue during August and December, In August, the green areas of North America, Europe, and Asia represent plants using carbon from the atmosphere to grow.
In December, net primary productivity at high latitudes is negative, which outweighs the seasonal increase in vegetation in the southern hemisphere. As a result, the amount of carbon dioxide in the atmosphere increases.
Changes in the Carbon Cycle Left unperturbed, the fast and slow carbon cycles maintain a relatively steady concentration of carbon in the atmosphere, land, plants, and ocean. Effects of Changing the Carbon Cycle All of this extra carbon needs to go somewhere.
Ocean About 30 percent of the carbon dioxide that people have put into the atmosphere has diffused into the ocean through the direct chemical exchange. Land Plants on land have taken up approximately 25 percent of the carbon dioxide that humans have put into the atmosphere. Studying the Carbon Cycle Many of the questions scientists still need to answer about the carbon cycle revolve around how it is changing. References Angert, A.
Drier summers cancel out the CO2 uptake enhancement induced by warmer springs. Proceedings of the National Academy of Science, 31 , Archer, D. Carbon cycle: Checking the thermostat. Nature Geoscience, 1, Behrenfeld, M. Climate-driven trends in contemporary ocean productivity. Nature, , Berner, R. The long-term carbon cycle, fossil fuels and atmospheric composition. Bonan, G. Forests and climate change: Forcings, feedbacks, and the climate benefit of forests.
Click for larger image Carbon Cycle - Sedimentation:. Biochemical Cycles. Elmhurst College. Carbon Cycle. Phosphorus Cycle. Chemistry Department. Nitrogen Cycle. Virtual ChemBook. Click for larger image. Carbon Cycle Carbon Cycle - Photosynthesis: Photosynthesis is a complex series of reactions carried out by algae, phytoplankton, and the leaves in plants, which utilize the energy from the sun.
Carbon Cycle - Sedimentation: Carbon dioxide is slightly soluble and is absorbed into bodies of water such as the ocean and lakes. It is not overly soluble as evidenced by what happens when a can of carbonated soda such as Coke is opened. Some of the dissolved carbon dioxide remains in the water, the warmer the water the less carbon dioxide remains in the water.
0コメント