Most of the reduction in subtropical rainfall expected as a result of climate change will occur over oceans, not land, reports a paper published online this week in Nature Climate Change. The study challenges our previous understanding of the drying of the subtropics, and suggests its impact on people living in these regions could be less severe than previously thought.
Subtropical rainfall changes have been previously attributed to two mechanisms that are both related to global warming: greater moisture content in air that is transported away from the subtropics, and a poleward shift in circulation. In this study, Jie He and Brian Soden use an ensemble of climate models to show that the rainfall decreases occur faster than global warming, and so another mechanism must be taking place. They find that direct local heating is causing the land to warm faster than the ocean, and that the associated changes in atmospheric dynamics are driving the rainfall decline over the oceans, rather than land.
In an accompanying News & Views article, Robin Chadwick notes that: “… improved understanding - and hence confidence - regarding why most subtropical land regions are not projected to dry should prove useful to stakeholders involved in climate change adaptation policy in these regions”.