The sensitivity of terrestrial carbon storage to climate change

Abstract

THE high correlation found between atmospheric CO₂ concentration and temperature during the past 160,000 years^1,2 implicates CO₂ as an important driving force behind changes in palaeoclimate. Changes in biological processes and circulation patterns in the oceans are believed to drive glacial-to-interglacial changes in CO₂ and thus in climate. Here we estimate the role of the terrestrial biosphere in controlling atmospheric CO₂ levels during climate perturbations. By considering the coupling between vegetation distributions and climate, we perform simulations to calculate the global geographical distribution of vegetation during the last glacial maximum, 18 kyr ago. The known changes in sea level at this time, together with the simulated climate-driven spatial arrangement of vegetation, result in a mass transfer of carbon from the terrestrial biosphere to the atmosphere ranging from 30 x 10⁹ tonnes (30 Gt, corresponding to 15 p.p.m. CO₂) to –50 Gt (25 p.p.m.). Thus, although the biosphere may have contributed to the decrease in atmospheric CO₂ of 80 p.p.m. known to have occurred at 18 kyr (refs 1,2), it does not seem to have been a dominant factor. For simulations run with twice the present-day CO₂ levels, strong negative feedbacks appear which remove 235 Gt of carbon (128 p.p.m. CO₂) from the atmosphere.