Clouds over the Pacific (image courtesy Shang-Ping Xie)

Global warming from greenhouse gases affects rainfall patterns in the world differently than that from solar heating, according to a study by an international team of scientists in the January 31 issue of Nature.

Using computer model simulations, the scientists, led by Jian Liu of the Chinese Academy of Sciences and Bin Wang of the International Pacific Research Center at the University of Hawaiʻi at Mānoa, showed that global rainfall has increased less over the present-day warming period than during the Medieval Warm Period, even though temperatures are higher today than they were then.

“Our climate model simulations show that this difference results from different sea surface temperature patterns” said UH Mānoa Professor of Meteorology Wang. “When warming is due to increased greenhouse gases, the gradient of sea surface temperature (SST) across the tropical Pacific weakens, but when it is due to increased solar radiation, the gradient increases. For the same average global surface temperature increase, the weaker SST gradient produces less rainfall, especially over tropical land.”

The team examined global precipitation changes over the last millennium and projections to the end of the 21st century, comparing natural changes from solar heating and volcanism with changes from man-made greenhouse gas emissions. Using an atmosphere-ocean coupled climate model that simulates realistically both past and present-day climate conditions, the scientists found that for every degree rise in global temperature, the global rainfall rate since the Industrial Revolution has increased less by about 40 percent than during past warming phases of the earth.

For more on the team’s research, read the UH Mānoa news release.