An enhancement of seasonal precipitation range under global warming

Anthropogenic forcings, such as greenhouse gases and aerosols, are starting to show their influence on the climate as evidenced by a global warming trend observed in the past century. However, unlike estimating the temperature changes, it has been a great challenge to estimate precipitation changes because complicated dynamical and physical processes are involved. In this study, we show a clear trend of tropical precipitation changes induced by global warming in hemispherical averages. It is observed that in response to global warming, an asymmetric pattern develops between tropical precipitation changes in the northern and southern hemispheres, and this asymmetry is locked with the seasonal cycle of tropical convection. In boreal summer, the northern hemispherical average departure from tropical mean increases, while the departure of the southern hemispherical average decreases. In boreal winter, on the other hand, the trend for both hemispherical averages is reversed. This implies an enhanced seasonal precipitation range between rainy and dry seasons and an increased precipitation difference between northern and southern hemispheres. In other words, the wet season tends to be wetter and the dry season tends to be drier under future global warming. As the trend continues, by the end of 21st century, the range of seasonal cycle and hemispherical difference will have increased by approximately 16% of our current climate.