Model estimates of CO₂ emissions from soil in response to global warming

Abstract

ONE effect of global warming will be to accelerate the decomposition of soil organic matter, thereby releasing CO₂ to the atmosphere, which will further enhance the warming trend^1–7. Such a feedback mechanism could be quantitatively important, because CO₂ is thought to be responsible for ∼55% of the increase in radiative forcing arising from anthropogenic emissions of gases to the atmosphere⁸, and there is about twice as much carbon in the top metre of soil as in the atmosphere⁹. Here we use the Rothamsted model for the turnover of organic matter in soil³ to calculate the amount of CO₂ that would be released from the world stock of soil organic matter if temperatures increase as predicted, the annual return of plant debris to the soil being held constant. If world temperatures rise by 0.03 °C yr⁻¹ (the increase considered as most likely by the Intergovernmental Panel on Climate Change⁸), we estimate that the additional release of CO₂ from soil organic matter over the next 60 years will be 61 × 10¹⁵ gC. This is ∼19% of the CO₂ that will be released by combustion of fossil fuel during the next 60 years if present use of fuel continues unabated.