Differing Trends in the Tropical Surface Temperatures and Precipitation over Land and Oceans

In the past 50 years, sea surface temperatures (SSTs) in the tropical latitudes have trended toward a warmer ocean state. As a response, tropical land surface temperatures, as well as tropical tropospheric temperatures (as manifested in the variations in the 200-mb tropical heights), have also trended upward. Analysis of trends in the tropical precipitation fields, however, remains problematic because of the scarcity of the observed data over the tropical oceans. Using both observed data and data from atmospheric general circulation model simulations, trends in tropical precipitation over the ocean and land are analyzed. The analysis reveals that in the tropical latitudes over land, the precipitation trend differs from the trend in the surface temperature. Oceanic precipitation has an increasing trend that is consistent with increasing SSTs, whereas over the tropical land regions precipitation decreases. In contrast, land temperatures increase in phase with the trend in SSTs. It is suggested that the combination of increasing surface temperature and decreasing precipitation could produce considerably greater societal consequences compared with the traditionally argued scenario in which both temperature and precipitation increase in response to increasing SSTs.