The Economist's Climate Deep Dive off the Shallow End
Posted April 12, 2013 in Solving Global Warming
The Economist is a well-regarded magazine. Its writers aren’t loony science deniers, like those on the Wall Street Journal’s editorial page, or the broadcasters on Fox News. Generally speaking, their climate coverage wins high marks.
But an article the magazine published recently—“A Sensitive Matter”—has misled or at least grabbed the attention of a lot of people; I have been asked about it by several of my NRDC colleagues, leaders of other environmental organizations, and (through Facebook) a high school classmate, turned investment banker. It raises reasonable-sounding questions about how quickly our world is actually warming and how accurate models are that predict climate changes going forward. Is global warming actually accelerating as forecast? Or, are things slowing down, at least a little? And what does this mean for policy?
It really would be nice if there were solid reasons to think, as the Economist article suggests, that the pace of climate change will be at the low end of the range of mainstream forecasts. That would give us more time to cut carbon pollution, reverse deforestation, plug methane leaks, and reduce the other major drivers of climate change.
No such luck.
As it turns out, the article is a more sophisticated, but no more valid, version of the long-standing climate denier claim that global warming has stopped since [1970, 1977, 1988, 1998]. The Skeptical Science website provides an excellent illustration, reproduced here, of what happens if you cherry pick the starting point of a trend analysis of data that includes significant natural variability, as our climate does. The Economist doesn’t go this far, but it does engage in equally dubious cherry picking of the scientific literature, including some genuine scientific uncertainties, to reach a false conclusion, as Dana Nuccitelli and Michael Mann point out in an excellent response posted yesterday.
At issue, in the article anyway, is a concept called “climate sensitivity”—how much the climate reacts to changes in greenhouse gas levels. Will a doubling of the carbon dioxide in the earth’s atmosphere, from preindustrial levels to 560 parts per million, result in a temperature increase of “just” 2 degrees Celsius or is a full 4.5 degrees or more in the offing? No one is exactly sure. The best estimate from scientists, combining multiple lines of research, is about 3 degrees, the Economist story notwithstanding.
So how do we explain the apparent lack of increase in the earth’s surface temperatures over the last 15 years? Over this period the amount of heat-trapping pollution in our atmosphere has continued to rise: Carbon dioxide levels have now reached 395 parts per million and their climbing fast. If carbon dioxide is trapping as much heat as we thought, where has it gone off to?
As it turns out, the answer is pretty deep. Deep in the ocean, that is.
About 90 percent of the excess heat trapped by increases in greenhouse gases ends up in the ocean. Our atmosphere is very thin, after all, and it just doesn’t have that much capacity to store heat. The ocean’s heat capacity, by contrast, is vast. Surface air temperatures should be thought of as responding to the temperature of the ocean, rather than the other way around. The ocean also has distinct layers, which mix slowly. Much of the natural variability of our climate from year to year comes from heat sloshing around among different parts of the ocean.
The starting point for the claimed global warming hiatus should be the tip off. 1998 was a very hot year—one of the three hottest on record, and well above the trend line at that time. That year, an El Niño—a warm Pacific current that can cause extreme climate variations—moved a lot of heat from the ocean to the surface. And since then, that heat has been seeping back. Still it was difficult to account for all the additional heat because it has accumulated deep in the sea, at depths well below 700 meters, where there have been few measurements until recently. This was documented in an important paper (subscription required; good summary here) published last month by Balmaseda, Trenberth, and Källén, and explained in this handy graph.
The results shouldn’t surprise us. In 2011, researchers at the National Center for Atmospheric Research showed in repeated simulations of climate change over the last century that frequently there are pauses in surface warming as heat dives into the deeper parts of the ocean, similar to what Balmaseda et. al. have observed.
In climate science, there are some legitimate disagreements about which models best predict climate change. But let’s be clear: We can’t afford to assume that we will be lucky. Anything above 2 degrees is the global warming red zone, beyond which we tread at our rapidly escalating peril.
It’s magical thinking to believe that because the rise in surface temperatures may have paused for a few years that we’ve gotten a free pass or a breather on climate change. That we need not push hard for cuts in carbon emissions from fossil-fuel-fired power plants. That we need not scale up renewable energy and energy efficiency at a rapid clip.
Already, the earth’s temperature is more than 1 degree Celsius higher than it was 70 years ago. The Economist article acknowledges that, even as it creates confusion and unjustified hope that we dodged a bullet.
The earth’s missing heat can be found deep in the ocean. Let’s not bet the planet that it won’t come back to haunt us.
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