Climate models project that the global average temperature will rise about 1 degree C by mid-century, if we continue with business as usual and emit greenhouse gases.

The global average, though, does not tell us anything about what will happen to regional climates.

Analysing global model warming projections in models used by the Intergovernmental Panel on Climate Change, a team headed by meteorologist Shang-Ping Xie at the University of Hawaii finds that ocean temperature patterns in the tropics and sub-tropics will change in ways that will significantly alter rainfall patterns.

Scientists have mostly assumed that the surfaces of oceans will warm rather evenly in the tropics. This assumption has led to “wetter-gets-wetter” and “drier-gets-drier” regional rainfall projections.

Xie’s team has gathered evidence that, although ocean surface temperatures can be expected to increase mostly everywhere by mid-century, the increase may differ by up to 1.5degreesC depending upon the region.

“Compared to the mean projected rise of 1degreesC, such differences are fairly large and can have a pronounced impact on tropical and subtropical climate by altering atmospheric heating patterns and therefore rainfall,” explains Xie.

“Our results broadly indicate that regions of peak sea surface temperature will get wetter, and those relatively cool will get drier,” adds Xie, according to the University of Hawaii at Manoa.

The study is slated for publication in the Journal of Climate this month.