Global warming’s effect on rainfall distribution so far has been limited by an unexpected source: airborne pollutants, according to a new study by researchers at the University of Hawaii’s International Pacific Research Center and the Scripps Institution of Oceanography.

But as greenhouse gases increase, they will overwhelm the influence of aerosols — that is, airborne dust, soot and other pollutants, the researchers say. Their paper was published online Sunday in the journal Nature Geoscience.

“Under global warming, rainfall will change from the present distribution … increasing in some places and decreasing in some others,” lead author Shang-Ping Xie, a professor of climate science at Scripps, said in an email Monday. “For example, rainfall may increase in Hawaii but decrease in California in 2100 compared to the present, even though temperature increases in both places. A grand challenge of climate science is to figure out the spatial pattern of future rainfall change from the present.”

The research suggests that the opposing effects of greenhouse gases and aerosols have not allowed much change in rainfall so far, he said.

“Larger shifts in rainfall patterns are in store as the greenhouse gas effect intensifies and becomes more dominant,” Xie said.

Using three state-of-the-art climate models, the researchers found that despite having very different geographical distributions, greenhouse gases and aerosols have similar regional effects on rainfall over the ocean. Greenhouse gases warm and aerosols generally cool surface temperatures,

“This came as a big surprise to us,” Xie said. “It took a while for the results to sink in.”

The researchers say the results of their study suggest the need for further innovative model experiments, which in turn may help to refine regional climate projections. The other researchers are Baoqiang Xiang, with the International Pacific Research Center at UH-Manoa, and Bo Lu of the National Climate Center, China Meteorological Administration, Beijing.