Interannual variability in global soil respiration, 1980–94

Abstract

We used a climate‐driven regression model to develop spatially resolved estimates of soil‐CO 2 emissions from the terrestrial land surface for each month from January 1980 to December 1994, to evaluate the effects of interannual variations in climate on global soil‐to‐atmosphere CO 2 fluxes. The mean annual global soil‐CO 2 flux over this 15‐y period was estimated to be 80.4 (range 79.3–81.8) Pg C. Monthly variations in global soil‐CO 2 emissions followed closely the mean temperature cycle of the Northern Hemisphere. Globally, soil‐CO 2 emissions reached their minima in February and peaked in July and August. Tropical and subtropical evergreen broad‐leaved forests contributed more soil‐derived CO 2 to the atmosphere than did any other vegetation type (∼30% of the total) and exhibited a biannual cycle in their emissions. Soil‐CO 2 emissions in other biomes exhibited a single annual cycle that paralleled the seasonal temperature cycle. Interannual variability in estimated global soil‐CO 2 production is substantially less than is variability in net carbon uptake by plants (i.e., net primary productivity). Thus, soils appear to buffer atmospheric CO 2 concentrations against far more dramatic seasonal and interannual differences in plant growth. Within seasonally dry biomes (savannas, bushlands and deserts), interannual variability in soil‐CO 2 emissions correlated significantly with interannual differences in precipitation. At the global scale, however, annual soil‐CO 2 fluxes correlated with mean annual temperature, with a slope of 3.3 Pg C y−1 per °C. Although the distribution of precipitation influences seasonal and spatial patterns of soil‐CO 2 emissions, global warming is likely to stimulate CO 2 emissions from soils.