UC-San Diego professor links global warming hiatus to rainfall


Charlie Pearce

Shang-Ping Xie, climate, atmospheric science and physical oceanography professor at UC-San Diego, says a decadal cooling of the Pacific Ocean could be the cause of a recent global warming hiatus. 

Kate Dannenmaier

While global average temperature has remained steady over the past 15 years, a visiting professor said at a talk Friday that there are warmer temperatures in store for us.

Shang-Ping Xie, University of California-San Diego climate, atmospheric science and physical oceanography professor, said his research indicated the decadal cooling of the Pacific Ocean seems to be a major cause of the current global warming hiatus. According to Xie, the cooling of the Pacific could not be linked to a carbon dioxide increase and is an example of enhanced climate variability.

“This led us to believe that the decadal cooling we saw over the past 15 years is largely due to natural variability,” Xie said. “If that is true, what’s going down is going to come up. So, when the pacific decadal isolation swings into a positive phase, we are going to see global warming coming back.”

Yuko Okumura, a research associate at the Institute for Geophysics in the Jackson School of Geosciences, organized Xie’s talk. Okumura said she thinks some people may still be skeptical about global warming because of the hiatus. According to Okumura, the natural variability caused by the interactions of the ocean and the atmosphere tends to overshadow the impact of human-caused climate change.

“It’s really hard to communicate the impact of natural variability superimposed on global warming due to anthropogenic forcing, and it’s [a] difficult concept to understand,” Okumura said. 

Judd Partin, a research scientist at the University’s geophysics institute who studies past climate change, said he thought Xie gave a great explanation of the hiatus in global warming. He said that, until the talk, he had not known sea surface temperatures can control
rainfall patterns. 

“The warmer sea temperatures lead to higher precipitation and vice versa,” Partin said.

Xie said the heat waves, warm temperatures and droughts seen in the southern United States seem to have resulted from the hiatus event because all of the precipitation and temperature patterns can be traced back to tropical Pacific cooling.

“People rely on imported water — 80, 90 percent in Southern California at least,” Xie said. “If the rainfall shifts away or something, it’s going to have tremendous consequences. Maybe it’s fairer to say global warming is not really a temperature issue but, rather, a water issue. Rainfall is going to increase somewhere and decrease somewhere else.”