El Niño is coming. Above-average sea surface temperatures have developed off the west coast of South America and seem poised to grow into a full-fledged El Niño event, in which unusually warm water spreads across the equatorial East Pacific. Models indicate a 75 percent chance of an El Niño this fall, which could bring devastating droughts to Australia or heavy rains to the U.S. South.
The debate about climate change, however, brings additional significance to this round of El Niño, which will probably increase global temperatures, perhaps to the highest levels ever. It could even inaugurate a new era of more rapid warming, offering vindication to maligned climate models and re-energizing climate activists who have struggled to break through in a polarized political environment.
For a decade, climate scientists have battled a public-relations challenge: Even though atmospheric temperatures are higher than at any time in the past 4,000 years, surface-temperature increases seem to have slowed down since 1998.
The planet has grown warmer in the past decade, but climate-change skeptics have used this so-called hiatus or pause in warming to take aim at the accuracy of the climate models, which appeared to predict more significant warming than has so far happened.
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Most climate scientists argue that the climate models have never predicted steady, uninterrupted warming. Annual global temperatures always rise and fall on either side of the longer-term average, they say, in much the same way stocks rise and fall from day to day, even during a strong market.
They believe, based on computer simulations of hiatus periods and measurements from new floating sensors, that they can account for the “missing” heat, much of which they believe is deep in the ocean, more than 700 meters below the water’s surface.
Nonetheless, the hiatus helped climate-change skeptics earn mainstream adherents last year as global temperatures hung perilously close to falling beneath even the lowest model projections. “Apocalypse perhaps a little later,” as The Economist put it.
It is hard to assess how much the hiatus has undermined the public’s confidence in climate science. There is some evidence that the number of Americans who don’t believe in global warming has increased by about 7 percentage points since the hiatus began to gain mainstream news-media attention, according to Edward Maibach, the director of the Center for Climate Change Communication at George Mason University.
In any case, it’s impossible to know how much the public would have been swayed by more significant temperature increases. One thing that is clear is that climate scientists have struggled to communicate the complexities of the climate system.
But this year’s El Niño might represent a turning point. The oscillation between El Niño and La Niña, El Niño’s cold-water cousin, is part of the reason for slower atmospheric warming.
Sea surface temperatures in the Pacific rise during El Niño and ultimately heat up the atmosphere in what Kevin Trenberth, a climate scientist at the National Center for Atmospheric Research, calls a “mini” global-warming event. The reverse happens during La Niña.
The shifts between El Niño and La Niña offer an elegant explanation for some or perhaps most of the slowdown in atmospheric warming. The hiatus is said to have begun in 1998, just after the historic El Niño of 1997 and early 1998. La Niña has often prevailed since then, cooling the atmosphere.
But if this fall’s El Niño event is strong and long enough, Trenberth believes it is “reasonable” to expect that 2015 will be the warmest year on record.
That could make a difference in the battle for public opinion. One-third of Americans do not trust climate scientists, according to Jon Krosnick of Stanford University, and form their views about climate change “based on very recent trends in warming.” Belief in warming jumps when global temperatures hit record highs; it drops in cooler years.
As El Niño returns heat from the oceans to the atmosphere, the ensuing spike in global surface temperatures could earn considerable media attention, especially if record-setting global temperatures coincide with extreme weather events typically brought by El Niño.
But El Niño has the potential to do more than offer a one-time jolt to climate activists. It could unleash a new wave of warming that could shape the debate for a decade or longer.
In this chain of events, a strong El Niño would cause a shift in a longer cycle known as the Pacific Decadal Oscillation (PDO), which favors more frequent and intense El Niños during its “warm” or “positive” phase. The oscillation has been “negative” or “cool” since the historic El Niño of 1998.
Climate scientists do not fully understand the mechanics of this phenomenon. “But the suspicion is certainly that it is related to El Niño events,” Trenberth said. “The switch to the current negative phase was probably triggered by the ’97-98 El Niño.”
The question is whether this fall’s El Niño “might kick the PDO into a positive phase,” he said. If it does, a result would be faster warming, at least doubling the rate of surface temperature increases.
A sustained period of faster warming will not convert skeptics into climate-change activists. But the accompanying wave of headlines might energize climate-change activists and refocus attention on climate change heading into the 2016 presidential election.
The timing could be uncomfortable for Republican presidential hopefuls who are skeptical of climate change, like Sen. Marco Rubio of Florida, who recently said he did not believe human activity was causing climate change. Democrats, eager to cast Republicans as anti-science or to appeal to voters in the endangered coastal city of Miami, might be likelier to re-emphasize climate change if polls show an increase in the public’s belief in global warming, which Krosnick anticipates will happen if global temperatures rise to record levels.
Even so, Krosnick doubts whether higher temperatures would compel more ambitious measures to curb carbon emissions. “It won’t vastly increase pressure on the government to do something.”
Mark McKinnon, a Republican strategist, thinks recurring catastrophic events will be necessary to soften the GOP’s position on climate change. Without Republican support, it will be hard for Congress to pass climate legislation.