Carbon sink
A carbon sink is a natural or artificial reservoir that absorbs and stores carbon dioxide (CO2) and other greenhouse gases (GHGs) from the atmosphere. The significance of carbon sinks lies in their role in mitigating climate change; they help to reduce the amount of CO2, a major contributor to global warming, by absorbing more of it than they emit. The most notable carbon sinks include oceans and terrestrial ecosystems, such as forests and soils. Through processes like photosynthesis, forests capture carbon, while oceans dissolve atmospheric CO2, storing it over long periods.
Despite their vital function, carbon sinks can also be sources of GHG emissions, especially when human activities such as deforestation disrupt their ability to absorb carbon. The loss of trees not only releases stored carbon back into the atmosphere but also reduces the overall capacity of ecosystems to sequester CO2. Efforts to enhance carbon sinks, such as reforestation and sustainable forestry practices, are crucial for slowing climate change. International agreements like the Paris Agreement support initiatives aimed at protecting and restoring these critical ecosystems, emphasizing the importance of maintaining and expanding carbon sinks to combat climate change effectively.
Subject Terms
Carbon sink
Definition
A sink is a process or mechanism that removes or absorbs 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. Carbon sinks were referenced in the 1997 Kyoto Protocol, which promoted their use to offset carbon, and the 2016 Paris Climate Agreement, which called for the preservation of carbon sinks as a means of reducing global emissions.
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.
Significance for Climate Change
CO2 is the most important GHG, and the amount of CO2 in the atmosphere has increased by about 35 percent in the industrial era, mainly by human activities. In 2021, carbon dioxide levels in the atmosphere were almost 50 percent higher than before the Industrial Revolution. 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 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. By reducing the rate of deforestation or by planting more trees (afforestation or reforestation), Earth’s carbon sinks can be expanded. Under the ’s (CDM), and projects are eligible to earn carbon credits. This provides an incentive to increase the planting of trees and hence to enhance Earth’s reserve of carbon sinks. The Paris Climate Agreement also included climate action regarding forest conservation and restoration. The Agreement supported "Reducing Emissions from Deforestation and forest Degradation” (REDD+), a framework created by the UNFCCC Conference of Parties that concerns activities in the forest sector. This framework included goals of reducing emissions from deforestation, sustainable management of forests, and the enhancement of forest carbon stocks in developing nations.
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