On land-with the right mix of heat, light, nutrients, and water-millions of plant species thrive to feed and shelter millions of animal species. Not only do plants form the very foundations of their ecosystems, they also interact dynamically with the atmosphere to moderate climate through the exchanges of moisture, heat, and greenhouse gases. Plants' most significant influence on climate is their regulation of the global carbon cycle. Via "photosynthesis," plants take in carbon dioxide from the atmosphere and then use sunlight as energy to "fuse" carbon dioxide and water into complex molecules called "carbohydrates." The basic raw materials that feed Earth's biosphere, plants use carbohydrates as food and to make plant structures. Then, animals and humans consume plants to get these same carbohydrates that also serve as building blocks in our bodies. Both plants and animals breathe (or "respire"), thereby "burning" carbohydrates as fuel for metabolism and converting them back into separate water and carbon dioxide molecules that are eventually released back into the atmosphere. Hence, through biological respiration and decomposition of dead tissue, carbon is returned back to the atmosphere and the carbon cycle is complete.

As previously stated, scientists observe that the amount of carbon dioxide in the atmosphere has risen by 30 percent over the last 100 years, contributing to a 0.5°C increase in average global temperatures. Scientists recently discovered that these two trends have prolonged each growing season in the northern hemisphere over the last 20 years, resulting in more annual plant productivity. Some scientists theorize that increasing plant productivity will effectively act as a "storehouse" for the excess carbon dioxide in the atmosphere, and that the two trends will balance. However, new scientific data suggest that as the rate of increase in carbon dioxide accelerates, and temperatures rise, land plants could begin regulating their "evapotranspiration" (water loss due to evaporation) rates in order to conserve water. If this plant response occurs on a large scale, then computer models indicate that the greenhouse warming will be amplified over tropical land areas by as much as 50 percent over and above the current greenhouse warming trend.

The EOS Terra spacecraft will enable scientists to compare plant productivity with carbon dioxide and other important greenhouse gas levels, as well as temperature trends. These data will better enable scientists to predict how changes in the climate will impact Earth's ecosystems. The new data will also allow scientists to measure how certain human activities, such as biomass burning and deforestation (see before and after pics of deforestation), may be contributing to climate change.

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