Definition (Encyclopedia of Global Warming)
A sink is a process or mechanism that removes or absorbs carbon dioxide (CO2) and other greenhouse gases (GHGs) from the atmosphere. The 1992 U.N. Framework Convention on Climate Change (UNFCCC) defines a sink as any process, activity, or mechanism that removes or absorbs a GHG, aerosol, or precursor of a GHG from the atmosphere.
Sinks, to be so called, must be net sinks—that is, if they also release GHGs into the atmosphere, they must remove more GHGs than they emit. Otherwise, they would count as sources of GHG emissions. The most common sinks are carbon sinks, which include oceans and terrestrial ecosystems such as forestry and soil. Carbon sinks remove carbon from the atmosphere and store them; in the latter respect, they are also referred to as reservoirs.
Forests act as carbon sinks through the process of photosynthesis. Oceans act as sinks when atmospheric CO2 dissolves in ocean surface waters and is stored there. This continues until the surface waters are saturated, at which point the rate of CO2 uptake declines. The CO2 remains in the surface until the oceans turn over, which happens in cycles of about one thousand years. During this overturning, the surface waters move downward, carrying with them the dissolved carbon. This enables the oceans to continue to absorb carbon from the atmosphere.
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Significance for Climate Change (Encyclopedia of Global Warming)
CO2 is the most important anthropogenic GHG, and the amount of CO2 in the atmosphere has increased by about 35 percent in the industrial era, mainly by human activities. However, the increase in CO2 in the atmosphere is less than the increase in CO2 emissions. This is because, of approximately 400 billion metric tons of carbon released into the atmosphere by human activity in the past two hundred years, only about 40 percent has remained in the atmosphere. The rest has been absorbed by carbon sinks, especially land and oceans. Without these carbon sinks, the amount of CO2 in the atmosphere, one of the major causes of anthropogenic climate change, would be considerably higher than it currently is.
Terrestrial ecosystems—land and vegetation—currently act as a net global sink for carbon. They are, however, also potentially major sources of GHG emissions. Over the years, deforestation has contributed an estimated 30 percent to GHG concentration. When trees are cut down, the atmosphere is affected in two ways: The trees, which also act as reservoirs of CO2,, release carbon into the atmosphere, and the CO2 that would otherwise have been removed from the atmosphere by these trees remains in the atmosphere. These two effects of deforestation on the whole make the warming of the climate worse.
Modifying carbon sinks to enhance their carbon uptake would have the effect of slowing the rate of climate change....
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Further Reading (Encyclopedia of Global Warming)
Binkley, C. S., et al. “Carbon Sink by the Forest Sector: Options and Needs for Implementation.” Forest Policy and Economics 4 (2002): 65-77. Assesses the mitigation potential of forest carbon sinks and identifies some of the outstanding issues that need to be addressed in order to maximize this potential.
Field, Christopher B., and Michael R. Raupach, eds. The Global Carbon Cycle: Integrating Humans, Climate, and the Natural World. Washington, D.C.: Island Press, 2004. Chapters 12-16 contain a description of the carbon cycle as it relates to the uptake of carbon by oceans and land.
Missfeldt, Fanny, and Erik Haites. “The Potential Contribution of Sinks to Meeting Kyoto Protocol Commitments.” Environmental Science and Policy 4 (2001): 269-292. Analyzes the potential of sinks to help industrialized countries meet their emission-reduction targets under the Kyoto Protocol, the costs of using sinks, and the potential impact the use of sinks could have on industrialized and developing countries.
Nabuurs, G. J., et al. “Forestry.” In Climate Change, 2007—Mitigation of Climate Change: Contribution of Working Group III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, edited by Beth Metz et al. New York: Cambridge University Press, 2007. Assesses the climate change mitigation potential of the forestry sector, analyzing various forest...
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