How large is the global carbon sink?
The magnitude of the global carbon sink can be estimated by comparing the rate at which carbon is being emitted into the atmosphere — currently about 7 Gigatonnes a year, which we know from inventories of fossil fuel and biomass burning — with measurements of the rate of increase of carbon dioxide in the atmosphere. The difference between the two represents the rate at which carbon is being absorbed by the Earth. Over the 40 years since atmospheric carbon dioxide measurements began, it is estimated that the earth has been able to absorb about half of the carbon dioxide that has been emitted by human activities. Year-to-year fluctuations in the amount of carbon dioxide that is observed to accumulate in the atmosphere, however, indicate that the rate at which the global sink operates varies over relatively short periods of time. During the 1990s, for example, the annual rate at which carbon dioxide increased in the atmosphere ranged from 0.9 ppm a year to 2.8 ppm a year. To understand th
