Reduced Tropical Climate Land Area Under Global Warming

Regions along the edges of the tropics host vast populations and ecosystems which are sensitive to climate change. Here we examine the extent of tropical land areas in the ERA5 and MERRA-2 reanalyses and in high-emission scenarios of 45 models participating in phases 5 and 6 of the Coupled Model Intercomparison Project (CMIP5/6). Based on the definition of tropical climate land areas as regions where the diurnal temperature range exceeds the seasonal temperature range, we find a net reduction of tropical land area with global warming. This change is primarily due to an increased seasonal temperature range driven by enhanced summer warming, which in turn is largely driven by reduced evaporative cooling. The reduction of tropical climate area is consistent with a narrowing of the tropical rain belt and with an equatorward and poleward expansion of the subtropical dry zones. Understanding the links between these trends requires further study.