In the second half of the 20th century, “the place that’s warmed the most was the Antarctic Peninsula,” said John Turner, a researcher with the British Antarctic Survey. “It’s a real hotspot of warming across the Earth.”
Now, however, Turner and a team of fellow scientists with the survey are out with a rather unexpected new finding in the journal Nature — one likely to be seized on by climate change skeptics, doubters and deniers. Since about 1998, the research finds, the Antarctic Peninsula has reversed this famous trend and cooled down again, and done so fairly significantly.
Yet Turner stresses this doesn’t mean climate change isn’t happening — only that natural variability in the region is quite large, and has recently kicked into gear for rather complex reasons. “This switch from a very very marked warming to a modest cooling is purely a local factor, and not saying anything like ‘global warming has stopped,’ ” Turner said.
Indeed, the Antarctic Peninsula has still warmed in the long run, said Eric Steig, an Antarctic researcher at the University of Washington, Seattle — whose comment on the study accompanies its publication in Nature on Wednesday. Two decades of reversal aren’t enough to change that. So it’s important to keep a sense of perspective.
“It hasn’t cooled nearly as much as it had warmed before,” Steig said.
To further put the new findings in context, it helps to understand more deeply why Antarctica is isolated not only from humanity, but also, to some extent, from the human-induced warming of the rest of the planet.
As Steig explains, this has much to do with the Southern Ocean. He pointed in particular to recent research showing that the overturning circulation of the sea in this region draws very cold water up from the depths as it circulates around the Antarctic Peninsula, and exports warmer water northward, away from the region.
“There is kind of a natural thermostat which on average prevents the warming of the rest of the globe creeping down,” Steig said.
For an admittedly anecdotal indicator of just how out of whack the Antarctic can be with the warming of the globe, consider a recent NASA documentation of how the planet’s warming was distributed, by latitude, during June this year, the warmest June ever recorded by the agency. While the midlatitudes in the Northern Hemisphere were warm and the Arctic was quite warm, down in the Antarctic, temperatures were actually cooler than usual:
So Antarctica as a whole isn’t dutifully following the rest of the globe in warming — which brings us back to the Antarctic Peninsula, and the new study from the British Antarctic Survey.
The new research suggests that the recent cooling around the Antarctic Peninsula is a phenomenon driven by changes in Antarctic winds. More specifically, there have been more easterly winds (winds blowing from the east) affecting the peninsula, Turner said, and these winds tend to carry cold air across the Weddell Sea, which is located to the east of the peninsula. That has pushed sea ice close to the eastern side of the peninsula, cooling it and preventing heat from escaping the ocean, he said.
Overall, Turner believes, what has happened is due to a combination of a stabilizing and early healing of the Antarctic ozone hole — which had helped warm the peninsula — and this simple natural wind variability.
“The Antarctic is a huge block of ice, and we have very strong winds around it, the strongest winds of any ocean region of the world,” he said. These winds are westerlies — they blow from west to east.
“The ozone hole increased [the westerlies] and it brought warm air down from the South Pacific onto the peninsula, decreasing sea ice, which impacted the penguins,” Turner continued. “[But] the ozone hole stabilized, it couldn’t get any worse, from the late 1990s, so that strength in the westerlies stopped. And then natural variability, then gave more easterly winds.”
However, some other researchers — including Steig — would be inclined to connect the recent Antarctic Peninsula cooling to much broader natural fluctuations in the planet’s climate, which are linked to the state of the tropical Pacific Ocean (though Turner isn’t convinced of this linkage).
“There’s no question things have changed in the atmospheric circulation around that region, and I think there’s also no question that a lot of that atmospheric circulation change relates to changes in the tropics,” Steig said.
Indeed, it’s tempting to connect the latest findings to another recent discovery — that the recent expansion of Antarctic sea ice, which has also been widely touted by climate change skeptics, may in fact be the result of a natural large-scale wobble of the climate system driven by the Pacific Ocean. It is this same wobble — a shifting into a negative phase of the so-called Interdecadal Pacific Oscillation, or IPO — that is also widely credited with having created the so-called global warming “pause,” or hiatus, during the 2000s. That’s the same period when the Antarctic Peninsula cooled and Antarctic sea ice increased.
“This very interesting study focuses on the Antarctic Peninsula (we looked at the entire Antarctic region) and agrees with our results,” said Gerald Meehl, a climate scientist at the National Center for Atmospheric Research in Boulder, Colo., who led the sea ice research. “Internally generated decadal climate variability produced the negative phase of the IPO with cooler sea surface temperatures in the eastern tropical Pacific starting in the late 1990s, and this had remote effects seen far from the tropical Pacific in the Antarctic region that included a cooling of the Antarctic Peninsula and an increase in Antarctic sea ice.”
Turner, however, says that the Antarctic Peninsula cooling has been strongest in summer, even as the Pacific influences the region the most strongly in winter — so he isn’t as convinced of this global “teleconnection,” as scientists call it.
“We think it’s just a coincidence that we tie in the change with the global warming hiatus,” he said.
In any case, the future looks to be one of more warming for the Antarctic Peninsula, despite the current bout of cooling. Turner and Steig agree that in the long run, despite natural variability and a recovering ozone hole, greenhouse gases are expected to win out, and eventually warm the peninsula and the broader Antarctic.
In the meantime, then, the lesson is not that the new research should be seized upon to spur doubt about climate change — but rather, that it helps advance better understanding of the crucial, and still sometimes mysterious, Antarctic system.
“We’re really trying to stress that this is a fantastic example of natural variability,” Turner said. “We have to be so careful about drawing global conclusions from what’s happening in one very small area.”