News•February 27, 2015

Looming Warming Spurt Could Reshape Climate Debate

Humanity is about to experience a historically unprecedented spike in temperatures.

That’s the ominous conclusion of a vast and growing body of research that links sweeping Pacific Ocean cycles with rates of warming at the planet’s surface — warming rates that could affect how communities and nations respond to threats posed by climate change.

Papers in two leading journals this week reaffirmed that the warming effects of a substantial chunk of our greenhouse gas pollution have been avoided on land for the last 15 to 20 years because of a phase in a decades-long cycle of ocean winds and currents. With Pacific trade winds expected to slacken in the years ahead, the studies warn that seas will begin absorbing less of global warming’s energy, and that some of the heat they’ve been holding onto will rise to the surface.

Extreme heat can exacerbate drought.
Credit: Kecko/Flickr

“Their results make sense to me, and are consistent with other evidence,” National Center for Atmospheric Research scientist Kevin Trenberth, who has published research dealing with the relationship between Pacific Decadal Oscillation (PDO) phases and surface warming, but who was not involved with either of the new studies, said. “The PDO clearly plays a key role — and very high PDO values in recent months appear to signal a change.”

The growing body of research helps explain why ocean temperatures have been rising faster than anticipated, and, perhaps more compellingly, why land temperatures rose less than models had projected after the turn of the century — a mystery, sometimes dubbed the warming “hiatus,” “pause” or “faux pause,” that confounded science until just the last couple of years.

“The hiatus is associated with the negative PDO phase — with strong subtropical trade winds that pile the warm water up in the tropical western Pacific, and bury some warm water in the subtropics,” Trenberth said. “If you turn that off, then the waters warm more generally and over a shallower layer, with consequences for the atmosphere above.”

Amid the questions left unanswered by the research, however, are whether communities are prepared for looming assaults of increasingly intense heat waves after the warming slowdown reverses, and how the expected spikes in surface temperatures could affect policy debates dealing with climate action and clean energy.

“A future speedup in warming is likely to affect public opinion about climate change if it results in changes at the local level that people recognize,” Utah State University assistant professor Peter Howe, who has researched public perceptions of climate change, said. “I would also caution, though, that perceptions and experiences of local climate conditions appear to be related to some extent by pre-existing beliefs about global warming.”

Surface air temperature (SAT) has risen fastest during the positive phases of a Pacific Ocean cycle that's sometimes called the IPO.
Credit: England, M. H. et al. Recent intensification of wind-driven circulation in the Pacific and the ongoing warming hiatus. Nature Clim. Change 4, 222–227 (2014).

Along with rising tides caused by rising temperatures, intense heat and heat waves are the clearest signs so far that human activity is altering the climate. A suite of modeling studies have independently concluded that heat waves that ravaged Australia in 2013 would have been almost impossible without the warming effects of our greenhouse gas pollution. Scientists have also directly linked record-breaking heat in Europe with global warming.

Meanwhile, California’s record-breaking heat last year, which some research links more closely with ocean cycles than with global warming, substantially worsened the drought-inducing effects of low rainfall and snowfall rates. That’s a problem that will continue to worsen fire risks throughout the American West, and much of the rest of the world, as temperatures start to really spike. That could threaten the survival of entire ecosystems, including the spectacular high-altitude forests of the American Southwest.

Cities and communities around the world are already taking steps to protect their citizens from the rising threats of extreme heat waves, which often take the heaviest tolls in cities, where concrete urban landscapes produce islands of intense heat. Steps taken by public health departments in places such as Milwaukee, for example, include better planning for heat emergencies, such as providing places where vulnerable residents can cool down. Steps being taken in other American cities, such as Louisville, Ky., aim to reimagine the built environment in ways that can reduce the heat island effect.

Residents of tropical countries can be even more vulnerable than those in the U.S. to the looming warming burst.

The Indian city of Ahmedabad during an annual kite festival
Credit: sandeepachetan.com travel photography/Flickr

“Temperatures are rising in India,” Nehmat Kaur, a Natural Resources Defense Council official who helped develop heat action plans and early warning systems for the oppressively hot Gujarati city of Ahmedabad, said. “Cities in India are taking notice of that, and taking measures to safeguard vulnerable communities.”

But experts agree that more could be done. And a renewed urgency in boosting the resilience of cities, farms and infrastructure to the effects of extreme heat may be required as temperatures rise at a hastening pace in the coming years.

“The public health community is starting to talk a lot more about climate generally,” Georgetown University Law Center adjunct professor Sara Pollock Hoverter, who specializes in climate change and climate resilience, said. “I think that all of us need to do more.”

In one of this week’s papers, four British researchers used a suite of climate models to conclude that there’s a 25 percent probability that a 15-year warming slowdown, such as the recent one, would extend by five more years. “Therefore,” they wrote in their paper, published Monday in Nature Climate Change, “we should not be surprised if the current hiatus continues until the end of the decade.” During the five years that follows such a slowdown, they found there was a 60 percent chance that surface temperatures would leap by 0.36°F — which is double the normal background rate of warming that would be expected given current levels of greenhouse gas pollution. That could worsen heat waves, compound droughts and exacerbate other impacts of climate change.

Seperately, three American researchers used computer models to tease apart the warming roles of heat-trapping air pollution, sunlight-reflecting air pollution and other forces that affect global temperatures from the effects of natural variation caused by long-term Atlantic and Pacific ocean cycles.

“Our interpretation is it’s this low-frequency internal variation in the Pacific that’s contributing substantially to the slowdown of the last 10 or 15 years,” Penn State meteorology professor Michael Mann, one of the authors of the study, published this week in Science, said. “In our analysis, it very much looks like we’re at a turning point, so it's likely to turn around and go in the other direction in the decade ahead.”

Many climate debates have been muddied in recent years by false or confused claims that global warming stopped around 1998, in spite of the steady succession of record-breaking globally hot years — including last year’s unprecedented global temperatures.

“When it comes to this argument that global warming has somehow slowed down or stopped, that climate change isn’t a problem, this is just another piece of evidence adding to the pile of evidence that’s accumulating that this is a temporary blip,” Mann said. “We are likely to see the flip side in the decades ahead. At that point, will the same contrarians in the climate debate who argued that global warming has stopped turn around and say global warming is accelerating?”

Anthony Leiserowitz, a researcher who leads the Yale Project on Climate Change Communication, said a sudden ramp-up in global warming rates could affect decisions made by policy makers. That could lead to a redoubling of the lackluster efforts so far to reduce climate pollution caused by fossil fuel burning, deforestation and agriculture, and help prompt communities to take more meaningful steps to adapt to the changes already underway.

Kids keep cool during a New York summer.
Credit: Vasilios Sfinarolakis/Flickr

A flip from a global warming slowdown to a warming speedup wouldn’t necessarily be enough, Leiserowitz cautions, to change the minds of people who stubbornly doubt the existence or importance of the climate crisis.

“It’s fair to say that the vast majority of the public is completely unaware of the word ‘hiatus,’ or the word ‘pause,’ or any of the arguments that have been going on for a few years now between the scientific community and the deniers,” Leiserowitz said. “The vast majority of, well, at least Americans, rarely hear about climate change in the media.”

Research by Leiserowitz and others has shown that people can link extreme weather events, such as heat waves, with climate change — but he said they often need help in understanding the relationship.

“There have been a number of studies that have shown that some people will change their views of climate change based on extreme weather,” Leiserowitz said. “It’s not enough to simply experience a heat wave — it then needs to be contextualized. It needs to be interpreted by thought leaders and trusted people in a community and by the media and scientists saying, ‘This is an indication of global warming.’”

The looming warming spike could be one of the clearest indications yet of global warming — an indicator that will coincide with the ongoing fall in the price of renewable energy. Perhaps it will also coincide with a renewed international commitment to U.N. climate talks, following decades of failures and inaction — inaction that led us to this precarious moment in the industrialized planet’s climate history.