Summary/Abstract
Tropical climate land areas host about 40% of the world’s population and 80% of the world’s biodiversity. Changes in the extent of tropical climate land areas, which generally border semi-arid climate zones, can therefore carry vast ecological and socio-economic implications. Tropical climate land areas are generally defined as regions where the daily temperature range exceeds the seasonal temperature range. Based on this definition, the authors find a net decrease in tropical climate land area in climate model projections of greenhouse-gas-induced global warming. The net reduction in tropical land area is driven primarily by increased seasonal temperature range, due to enhanced summer warming, which in turn is largely driven by drying. The reduction in tropical climate land area in a warming climate agrees with a narrowing of the tropical rain belt and with “Subtropical widening”, that is, a poleward and equatorward expansion of the subtropical dry zones. However, understanding the links between these trends requires further study.