No more pause: Warming will be non-stop from now on
Enjoy the pause in global warming while it lasts, because it’s probably the last one we will get this century. Once temperatures start rising again, it looks like they will keep going up without a break for the rest of the century, unless we cut our greenhouse gas emissions.
The slowdown in global warming since 1997 seems to be driven by unusually powerful winds over the Pacific Ocean, which are burying heat in the water. But even if that happens again, or a volcanic eruption spews cooling particles into the air, we are unlikely to see a similar hiatus, according to two independent studies.
Masahiro Watanabe of the University of Tokyo in Japan and his colleagues have found that, over the past three decades, the natural ups and downs in temperature have had less influence on the planet’s overall warmth. In the 1980s, natural variability accounted for almost half of the temperature changes seen. That fell to 38 per cent in the 1990s and just 27 per cent in the 2000s.
Instead, human-induced warming is accounting for more and more of the changes from year to year, says Watanabe. With ever-faster warming, small natural variations have less impact and are unlikely to override the human-induced warming.
“The implication is that we will get fewer hiatus periods, or hiatus periods that last for a shorter period,” says Wenju Cai at the CSIRO in Melbourne, Australia, who wasn’t involved in the work.
According to another recent study, the current hiatus may be our last for a while. Matthew England and his colleagues at the University of New South Wales in Sydney, Australia, tried to quantify the chance of another pause. “It’s looking to us that it’s probably going to be the last one that we’ll see in the foreseeable future,” says England.
Using 31 climate models, they showed that if emissions keep rising, the chance of a hiatus – a 10-year period with no significant warming – drops to virtually zero after 2030. The current hiatus will probably be followed by rapid warming as the heat trapped in the ocean escapes back into the atmosphere, so we are unlikely to get another decade of no warming before 2030. England believes it could be another century or more before the next hiatus.
But that could change if we slow greenhouse gas emissions now. If we can reach peak global emissions by 2040, the temperature rise will slow by the end of the century, and hiatus periods will become more likely.
Hiatuses can also be triggered by volcanic eruptions that spew particles into the air, reflecting sunlight away from Earth, as happened after the 1991 Mount Pinatubo eruption. But even if a volcano erupts it will make little difference. “After 2030, the rate of global warming is likely to be so fast that even large volcanic eruptions on the scale of Krakatoa are unlikely to drive a hiatus decade,” says team member Nicola Maher.
Journal references: Watanabe: Nature Climate Change, DOI: 10.1038/nclimate2355; Maher: Geophysical Research Letters, DOI: 10.1002/2014GL060527