Cloud formations over the eastern Pacific Ocean. NASA photo

A new study co-authored by a Scripps Institution of Oceanography researcher reinforces findings that a decades-long climate cycle is behind the stability of global surface air temperatures since 2000.

Event though atmospheric greenhouse gases have continued to rise during recent years, global mean surface temperature has shown no clear warming since about 2000. This slowdown in surface warming, often referred to as the global warming “hiatus,” is in sharp contrast to what computer models predict.

A National Science Foundation-supported study co-authored by Shang-Ping Xie, a climate scientist at Scripps, attributes nearly the entire difference between observations and computer models to a climate cycle known as the Inter-decadal Pacific Oscillation, or IPO. The cycle is similar to the more commonly known El Niño Southern Oscillation but significantly longer in duration, reversing phases over the course of decades.

The study found that this long-term cycle explains essentially all the difference between observed and computer-simulated global warming rates over decades since 1920, and in particular the warming hiatus since year 2000.

“The new study extends this earlier modeling study by relying on observations that go back to 1920,” said Xie, “We show that over nearly 100 years, the observed deviations in global mean temperature from the anthropogenically (human) forced climate response are nearly all due to IPO.”

The model-versus-observation discrepancy in the pace of global warming has attracted considerable attention in climate research and in news media since it has the potential to undermine the credibility of climate models and their projections of future climate changes.

“Naturally, people would ask the question: if the models cannot simulate the current global warming rate, how can we trust their projections of future climate change? This is a very reasonable question that deserves a satisfactory answer from the climate science community,” said study lead author Aiguo Dai, an associate professor at the University of Albany. “The global warming hiatus has also been used to dismiss climate science entirely by some deniers of global warming. Thus, explaining the warming hiatus has become an urgent task for climate scientists.”

The study, “Decadal modulation of global surface temperature by internal climate variability,” was published online April 13, 2015 in Nature Climate Change.

“Recent history suggests that the IPO could reverse course soon. Should that happen, we may see accelerated global warming rates in the coming decades,” said Dai.

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Chris Jennewein

Chris Jennewein is Editor & Publisher of Times of San Diego.