Explainer The Subtle Art of Covering Climate Cycles By JOHN UPTON
The planet is enduring an extraordinary jolt. A 13-year warming lull was recently followed by an unprece- dented jump in global temperatures. The temperature spike is co- inciding with a surge in worldwide efforts to slow global warming, and it appears to be helping to change the minds of Americans about global warming during a precariously optimistic time for global cli- mate diplomacy. It’s also presenting reporting challenges for journalists. What exactly is happening, and what’s the clearest way to report it? A key concept is that scientists now recognize the importance of slow natural changes in temperature patterns on a “decadal scale” — cycles that can take decades or longer to flip from one extreme to the other. The so-called “warming pause” from 2001 to 2014 is now understood by scientists to have been caused by natural variation — even as the planet heated unnaturally.
What we know, and what we don’t
Not only was 2015 globally the warmest on record, it beat the previ- ous record — which was set one year prior — by the greatest margin ever seen.
Like most trends that are af- fected by multiple factors, those of global surface temperatures can seem confounding. Even some scientists disagree about recent patterns. But all of the leading scientists who re- search them agree about the details that matter to us the most: the planet is warming inexorably, and it is doing so unsteadily.
To Paul Rogers, an environmental journalist at KQED and the
San Jose Mercury News, the most important line to include is that the ten hottest years on record have been since 1998. “It’s simple and stunning,” he said. That was despite the warming slowdown. “That fact cuts through the complexities of the science and the pol- itics for the public.”
Ocean cycles complicate warming trajectory
Climate scientists blame ocean cycles for the bumps and plateaus in an upward overall temperature trajectory that’s caused by worsening greenhouse gas pollution.
Ocean cycles caused by trade winds in the Pacific are to blame for unevenness in an overall upward global temperature trajectory, scientists say.
Graphic courtesy of National Centers for Environmental Information, NOAA
Journalists need to abandon the notion that a graph of global warming curls steadily upward. It looks more like steps. “Some- times it’s steeper,” said Gerald Meehl, a National Center for At- mospheric Research scientist. “Sometimes it’s slower.” From 2001 to 2014, there was a slowdown in warming at the surface of the earth — thermometers at the planetary sweet-spot we call home stopped detecting the type of warming that had been recorded since the 1970s, and before the 1940s. That 13-year period has been called a “global warming hiatus,” or a “pause,” though neither phrase is accurate. Global warming never paused.
So how to best report it? There are basic facts that can be in- cluded in any story dealing with the recent burst of worldwide heat — or with the lull in warming that came before it.
From 2001 until 2014, extra heat that was being trapped on Earth by rising levels of greenhouse gas pollution was being churned into the oceans. That’s because Pacific trade winds, which loop the southern and northern boundaries of the world’s biggest water body, gusting westward along the equator to weave a figure eight, were blowing more strongly than usual. For those 13 years, the oceans absorbed an unusually large propor- tion of the extra warmth that green- house gases were trapping on Earth. The surface temperatures were mod- erated because temperatures in the oceans were increasing. Nearly half of the dramatic ocean warming caused by climate change so far has occurred since 1997, Lawrence Liv- ermore National Laboratory re- ported in Nature Climate Change in January.
The acceleration of ocean warming raised sea levels by corrod- ing ice sheets and expanding the seas.
Then, in 2014, a long-running ocean cycle changed phase, slackening the trade winds. That phase is usually called the Pacific Decadal Oscillation (PDO), or the Interdecadal Pacific Oscillation (IPO).
The most powerful El Niño on record, which arrived a year later in 2015, also ratcheted down wind strengths, fostering heat waves at the planet’s surface and fueling temperature records that have stunned scientists.
“Earth got so hot last month that federal scientists struggled to find words,” the
Associated Press reported this spring
(
http://j.mp/RecordHotFeb), after two successive monthly temper- ature records followed two successive yearly temperature records. “Astronomical,” “staggering” and “strange” were among the words
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