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Animation: The Global Carbon Cycle and the Greenhouse Effect

by Pearson
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Human activities have altered the global carbon cycle. In particular, humans have created two new fluxes of carbon into the atmosphere. When forests are cleared for agriculture or timber production, some of the carbon stored in the trees and soil is released to the atmosphere. Deforestation also decreases one of the significant sinks of this carbon, because less photosynthesis is occurring to remove carbon from the air. Fossil fuels contain an abundance of carbon. The burning of fossil fuels in automobiles and for industrial uses releases several gigatons of carbon to the atmosphere each year. If carbon inputs to the atmosphere exceed outputs, carbon will accumulate in the atmosphere. In recent decades, inputs have indeed exceeded outputs, and so the concentration of carbon dioxide in the atmosphere has been rising. These data indicate how the concentration of carbon dioxide in the atmosphere has changed since 1950 at an observatory at Mauna Loa, Hawaii. Most scientists agree that the rise in carbon dioxide shown in the graph has contributed to global warming, an increase in Earth's temperature, in recent decades. A greenhouse gas such as carbon dioxide acts like the glass panes in a greenhouse: It lets solar energy in, but does not let heat out. In addition to carbon dioxide, other greenhouse gases include water vapor, nitrous oxide, and methane. Solar radiation reaching the Earth consists of a mixture of wavelengths, including visible light, shorter wavelength ultraviolet light, and longer wavelength infrared light. Most of this radiation travels through the atmosphere to the surface of the Earth. Here, the land and oceans absorb many of the shorter wavelengths (in the visible and ultraviolet spectra); others are simply reflected from the surface. Earth's surface then reflects much of the absorbed radiation in the form of longer wavelength infrared, also called radiant heat. Although much of this radiant heat is lost to space, some of it is trapped by the greenhouse gases, leading to global warming.
Human activities have altered the global carbon cycle. In particular, humans have created two new fluxes of carbon into the atmosphere. When forests are cleared for agriculture or timber production, some of the carbon stored in the trees and soil is released to the atmosphere. Deforestation also decreases one of the significant sinks of this carbon, because less photosynthesis is occurring to remove carbon from the air. Fossil fuels contain an abundance of carbon. The burning of fossil fuels in automobiles and for industrial uses releases several gigatons of carbon to the atmosphere each year. If carbon inputs to the atmosphere exceed outputs, carbon will accumulate in the atmosphere. In recent decades, inputs have indeed exceeded outputs, and so the concentration of carbon dioxide in the atmosphere has been rising. These data indicate how the concentration of carbon dioxide in the atmosphere has changed since 1950 at an observatory at Mauna Loa, Hawaii. Most scientists agree that the rise in carbon dioxide shown in the graph has contributed to global warming, an increase in Earth's temperature, in recent decades. A greenhouse gas such as carbon dioxide acts like the glass panes in a greenhouse: It lets solar energy in, but does not let heat out. In addition to carbon dioxide, other greenhouse gases include water vapor, nitrous oxide, and methane. Solar radiation reaching the Earth consists of a mixture of wavelengths, including visible light, shorter wavelength ultraviolet light, and longer wavelength infrared light. Most of this radiation travels through the atmosphere to the surface of the Earth. Here, the land and oceans absorb many of the shorter wavelengths (in the visible and ultraviolet spectra); others are simply reflected from the surface. Earth's surface then reflects much of the absorbed radiation in the form of longer wavelength infrared, also called radiant heat. Although much of this radiant heat is lost to space, some of it is trapped by the greenhouse gases, leading to global warming.