Greenhouse Gases and Aerosols Have Similar Effects on Rainfall, Study Shows

Despite their many differences, greenhouse gases and aerosols play a similar role on spatial patterns of rainfall change, according to a new study published in the journal Nature Geoscience.

The discovery is based on experiments carried out using three different state-of-the-art climate models and was led by researchers from the University of Hawaii at Manoa's International Pacific Research Center (IPRC) and Scripps Institution of Oceanography.

According to the study's authors, each model revealed similar regional effects on rainfall over the ocean, despite the fact that aerosols and greenhouse gases are concentrated in different regions of the world.

These results, the scientists said, represented a far different reality than they had anticipated.

"This came as a big surprise to us," lead-author Shang-Ping Xie, a professor of climate science and first Roger Revelle Chair in Environmental Science at Scripps, said in a statement. "It took a while for the result to sink in."

However, once it did, Xie said the implications became obvious.

"The result means that it is hard to tell apart the greenhouse and aerosol effects," he explained.

For example, whether aerosol- or greenhouse gas-induced, the researchers found that changes in rainfall are mediated by spatial patterns in sea surface temperature.

"Although much of the aerosol research has focused on microphysical processes, over the ocean the climate response to aerosols appears to be insensitive to details of the micro-processes in clouds," Xie said. "The climate changes induced by greenhouse gases and by aerosols share a common set of ocean-atmospheric feedback structures, explaining the spatial resemblance between the two types of response."

According to co-author Baoqiang Xiang, a postdoctoral fellow at the IPRC, more innovative model experiments are needed if they are to "probe the ocean-atmosphere interaction mechanisms that mediate these rainfall patterns and to determine what forms the foundation."

Doing so, Xiang explains, "will allow us to develop more reliable regional climate projections."