Thursday, November 17, 2016

Less Gloomy Outlook for Subtropical Rainfall

A new study found that rainfall over land in the subtropics -- including in the southeastern U.S. -- will not decline as much as it does over oceans in response to increased greenhouse gases.  The study challenges our previous understanding of the drying that will occur in subtropical regions and suggests its impact on people living in these regions could be less severe than initially thought.

Image shows the clear difference in the rate of global surface warming (left panel) and the rate of subtropical rainfall decline (indicated by the brown shading in the right panel) when forced with an instantaneous increase of CO2. This is the main evidence to show that the subtropical rainfall decline is unrelated to the global surface warming. (Credit: Jie He, Ph.D., Princeton University and Brian J. Soden, Ph.D., University of Miami Rosenstiel School of Marine and Atmospheric Science) Click to Enlarge.
"The lack of rainfall decline over subtropical land is caused by the fact that land will warm much faster than the ocean in the future -- a mechanism that has been overlooked in previous studies about the subtropical precipitation change," said Jie He, a postdoc in Princeton University's Program in Atmospheric and Oceanic Sciences, and former UM Rosenstiel School graduate student, who was the lead author of the study.

In the new study, He and UM Rosenstiel School Professor Brian Soden used an ensemble of climate models to show that the rainfall decreases occur faster than global warming, and therefore another mechanism must be at play.  They found that direct heating from increasing greenhouse gases is causing the land to warm faster than the ocean and that the associated changes in atmospheric circulation are driving the rainfall decline over the oceans, rather than land.

Read more at Less Gloomy Outlook for Subtropical Rainfall

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