Global mean temperatures have been flat for 15 years despite an increase of heat-trapping greenhouse gases and new research by scientists at Scripps Institution of Oceanography found that cooling in the eastern Pacific Ocean is behind the recent hiatus in global warming.
Partially funded by NOAA’s Climate Program Office, Scripps climate scientists Yu Kosaka and Shang-Ping Xie used innovative computer models to simulate regional patterns of climate anomalies, enabling them to see global warming in greater spatial detail. The models revealed where warming was most intense and where on the planet there had been either less warming or even cooling trends.
“Climate models consider anthropogenic forcings like greenhouse gases and tiny atmospheric particles known as aerosols, but they cannot study a specific climate event like the current hiatus,” Kosaka said in prepared remarks. “We devised a new method for climate models to take equatorial Pacific Ocean temperatures as an additional input. Then amazingly our model can simulate the hiatus well.”
Simulated temperature trend patterns (right) created by climate modelers at Scripps Institution of Oceanography, UC San Diego, showed strong agreement to observed boreal summer temperatures (left) for 2002-2012. JJA stands for June July August. Image courtesy of Nature
“Specifically the model reproduced the seasonal variation of the hiatus, including a slight cooling trend in global temperature during northern winter season,” said Xie, also in a statement. “In summer, the equatorial Pacific’s grip on the Northern Hemisphere loosens, and the increased greenhouse gases continue to warm temperatures, causing record heat waves and unprecedented Arctic sea ice retreat.”
According to the scientists, when the natural climate cycle that governs ocean cooling reverses and the Pacific waters begin warming again, the increase in global temperatures will resume “with vigor.” The study authors said it is not known if the current cooling phase will last as long as the last one, which lasted from roughly 1940 to the early 1970s, and added that predicting equatorial Pacific conditions more than a year in advance is “beyond the reach of current science.”
“That speaks to the challenge in predicting climate for the next few years,” said Xie. “We don’t know precisely when we’re going to come out of [the hiatus] but we know that over the timescale of several decades, climate will continue to warm as we pump more greenhouse gases into the atmosphere.”
“These compelling new results provide a powerful illustration of how the remote eastern tropical Pacific guides the behavior of the global ocean-atmosphere system, in this case exhibiting a discernible influence on the recent hiatus in global warming,” Dan Barrie, program manager at CPO, said in a statement.
The study, “Recent global-warming hiatus tied to equatorial Pacific surface cooling,” was published online in the journal Nature on Aug. 28. Along with CPO, the National Science Foundation, the National Basic Research Program of China supported the research.
To learn more, visit: http://scripps.ucsd.edu/news/13251