Document: JAM-3-66-29

Global soil respiration in a warmer world.

RAICH, J.W.* ¹, C.S.POTTER ² and D.BHAGAWATI ¹

Iowa State University, Ames, IA, 50011, USA ¹
NASA-Ames Research Center, Moffett Field, CA, 94035, USA ²

Abstract:
Carbon dioxide emissions from soils generally increase with temperature. Thus, there exists the potential for a positive feedback in which global warming would stimulate soil CO₂ emissions, thereby exacerbating further warming. We used a previously published model to estimate global soil carbon dioxide emissions for each month from 1980-1994, based on monthly precipitation and air temperature data. This period included the warmest years yet recorded. Estimated annual soil-CO₂ emissions ranged from 81-84 Pg C, suggesting that variations in soil respiration rates contribute to interannual variations in atmospheric carbon dioxide levels. Lower-than-average rainfall decreased estimated soil respiration rates in some years. Overall, however, there was an overriding effect of temperature on predicted soil-CO₂ emissions. For each 0.1 degree increase in temperature, the predicted global annual soil respiration rate increased by an average of 0.7 Pg carbon. A mean global temperature increase of 1 degree Centigrade would therefore be expected to cause an increase in soil respiration rates that exceeds annual CO₂ inputs from fossil-fuel combustion. Evaluation of the impact of these predicted changes on the terrestrial C budget requires integration of our data with estimates of changes in net primary productivity. Our preliminary model results suggest two working hypotheses. In wet years, increasing temperatures are predicted to generate a net loss of C from terrestrial ecosystems. In dry years, soil respiration rates are predicted to decrease faster than NPP, and therefore generate net C storage on land.

Keywords: carbon dioxide, climate change, terrestrial carbon cycle

This abstract is being presented at: 4:30 PM in session:
Oral Session #66: Large Scale Climate Change.