The carbon balance of terrestrial ecosystems is likely to be strongly affected by climate change but the direction and magnitude of the resulting climate feedbacks are uncertain. Soils tain the largest reservoir of global terrestrial carbon so even small fractional changes in total soil carbon cycling could have significant impacts on the centration of atmospheric carbon dioxide. The response of soil carbon to environmental change is, therefore, a critical regulator of future climate. A widespread prediction is that the projected increase in mean global temperature will increase microbial mineralization of stable soil organic matter and release carbon from soil into the atmosphere; and that the biology (microbial functional diversity) rather than chemistry of soil may be more important in determining long-term carbon storage. This prediction, based on temperate forest and laboratory studies, is of particular cern for tropical forests because they have huge influence on the global carbon cycle, tain 30% of global soil carbon and have the highest -and most threatened- biodiversity of any terrestrial ecosystem. Here, I will use two different experimental approaches (in situ soil warming and soil translocation) in tropical forests in Panama and Peru to examine how soil chemistry and biology regulate soil carbon storage under climatic warming. I will combine experimental findings with a study of soil chemistry and biology for an additional twenty global tropical forest sites to make predictions on the future of soil carbon in global tropical forests under scenarios of climatic warming. This will be the first study of elevated temperature effects on soil carbon dynamics, and of tinental-scale patterns in soil microbial diversity, in tropical forests. I will directly address one of the greatest sources of uncertainty in global carbon cycling models by showing how microbial soil carbon cycling in tropical forests will respond to climatic warming.