DYNAMIC-RESPONSES OF TERRESTRIAL ECOSYSTEM CARBON CYCLING TO GLOBAL CLIMATE-CHANGE

Terrestrial ecosystems and the climate system are closely coupled, par ticularly by cycling of carbon between vegetation, soils and the atmos phere. It has been suggested(1,2) that changes in climate and in atmos pheric carbon dioxide concentrations have modified the carbon cycle so as to render terrestrial-ecosystems as substantial carbon sinks(3,4); but direct evidence for this is very limited(5,6). Changes in ecosyst em carbon stocks caused by shifts between stable climate states have b een evaluated(7,8), but the dynamic responses of ecosystem carbon flux es to transient climate changes are still poorly understood. Here we u se a terrestrial biogeochemical model(9), forced by simulations of tra nsient climate change with a general circulation model(10), to quantif y the dynamic variations in ecosystem carbon fluxes induced by transie nt changes in atmospheric CO2 and climate from 1861 to 2070. We predic t that these changes increase global net ecosystem production signific antly, but that this response will decline as the CO2 fertilization ef fect becomes saturated and is diminished by changes in climatic factor s. Thus terrestrial ecosystem carbon fluxes both respond to and strong ly influence the atmospheric CO2 increase and climate change.