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Report: Most Antarctic Peninsula Warming Human-Caused

The debate over whether global warming is natural or manmade is an artificial one: scientists know that both factors can affect the planet’s temperature. The real question is which factor is doing the heavy lifting — and a new report in Nature released Wednesday says that on the Antarctic Peninsula, at least, human-generated greenhouse gases have almost certainly been by far the most important driver of warming over the past half-century.

Scientists are intrigued with this corner of the world because it’s warming faster than anyplace else on Earth. The planet as a whole has heated up by about 1.3°F since 1900, but on the peninsula, it has shot up by a whopping 5° in just 50 years, forcing massive ice shelves to disintegrate and penguin colonies to collapse.

Antarctic Peninsula
 

Heat trapping greenhouse-gas emissions are the obvious culprit, since they’ve increased dramatically over that same 50 years, but scientists prefer hard evidence to presumption, so a team from the British Antarctic Survey has been drilling into ancient ice to see how the current warming stacks up against what happened in the ancient past. If the kind of warming happening now also happened before we started burning fossil fuels, it would cast doubt on the human contribution.

What the scientists discovered, however, removed any doubt. “We found that the peninsula has been warming for the past 600 years,” said lead author Robert Mulvaney, of the British Antarctic Survey, in an interview. “But the rate of warming has been much faster during the past century, and fastest over the past 50 years.”

The currently skyrocketing temperatures, in short, are very likely the result of human-caused warming, which is superimposed on a natural climate variation. “Asking whether it’s natural or caused by humans is silly,” said Eric Steig, of the University of Washington, who wrote a Nature commentary on the new research. “We’ve changed the atmosphere so dramatically that it has to be mostly human. The only question,” he said in an interview, “is how large the human influence is relative to other things.”

Given the rapid rise in recent decades, the answer seems to be “pretty large,” but emissions from the burning of fossil fuels may only be part of the human contribution. Another is almost certainly the infamous ozone hole that opened up over Antarctica in the 1980s, and which is still there. The loss of stratospheric ozone has changed the local energy balance in the atmosphere, which in turn has changed wind patterns, bringing warmer air to the Peninsula. “The ozone hole alone would have caused some warming,” Steig said.

The disintegration of ice shelves is clearly caused by warmer air, according to Steig. “It’s clear from satellite images that the breakups are preceded by the appearances of large ponds on the ice surface,” he said. “The meltwater then drills down, turns the ice into Swiss cheese.”

Warm water, by contrast, is the problem in other parts of Antarctica — at the Ronne-Fitchner Ice Shelf, for example, to the east of the Peninsula, or along the Antarctic coast to the west. In both cases, however, the melting of ice that reaches the sea allows ice further inland to flow faster, boosting the overall transfer of ice from the continent to the ocean and adding to the rise in sea level. (The same thing is happening in Greenland).

Unlike some other scientists, Mulvaney declined to comment on whether the warming will continue. “I cannot say for sure,” he said. But he did say that when he started doing Antarctic research several decades ago, he was a climate skeptic. “Not any more,” Mulvaney said. “You can’t keep doing this year to year and decade to decade and not become a very strong believer.”

“You can look at one particular location and say ‘oh, it’s happened before,’ “ Steig said. “But this is one of the very few times you can say it’s warming all over the planet.”

Comments

By Eric Steig (98195)
on August 23rd, 2012

A correction: I did not say that “We’ve changed the atmosphere so dramatically that it has to be mostly human.”

What I said was that we’ve changed the atmosphere so much that there has to be *some* influence on Antarctic Peninsula temperatures.

As Lemonick’s article correctly notes, the question is how much human influence, relative to other things?

The reality is that this new paper doesn’t provide a quantitative answer to this.  For some more thoughts, check out the write-up on this at RealClimate.org, which I’ll finish in the next day or so.

Reply to this comment

By mlemonick
on August 23rd, 2012

Dr. Steig’s correction is most welcome. I try to get things 100% right 100% of the time, but when I fall short, I want to hear about it right away.

Reply to this comment

By Eamon (Ponte Vedra Beach, FL 32082)
on August 24th, 2012

This article is yet another bit of pseudo-science seeking to promote a preconceived agenda.  Consider the following, whether in its corrected form or as it appeared in the article:

—-“Asking whether it’s natural or caused by humans is silly,” said Eric Steig, of the University of Washington, who wrote a Nature commentary on the new research.—-

The principal reason this is a silly question is…humans are, in fact, part of nature—even when their actions are adversely affecting all around them.  Then we have this completely unscientific gem, apparently misquoted rather notably by a purportedly professional writer:

——“We’ve changed the atmosphere so dramatically that it has to be mostly human. The only question,” he said in an interview, “is how large the human influence is relative to other things.——

Whichever version of the quote is used, it is just a vague, unsubstantiated statement.  This article does not even mention any of the other things, such as the massive increase in the release of methane into the atmosphere.  Methane has a FAR more potent influence, but I don’t have to back that up with anything specific because, apparently, that does not even matter around these parts.  This article and the unsubstantiated theory it presents are just another caricature of actual science and actual reporting.  The other planets in the solar system are going through similar changes and…that’s right…human beings are playing a rather non-existent role.  Ciao

Reply to this comment

By mlemonick
on August 24th, 2012

Eamon points out, quite rightly, that humans are part of nature, so you can argue that everything we do is natural.

Somehow, though, when I try to think about the natural atomic bomb that destroyed Hiroshima and Nagasaki, the natural thalidomide that led to terrible birth defects, the natural chemical leak that devastated Bhopal, in India….it somehow doesn’t work for me.

The “massive increase in the release of methane” is news to me, and, I’m pretty sure, to most atmospheric scientists, since in another story we posted this week, it’s pretty well documented that there’s been a slight DECREASE in methane concentrations over the past several decades. Methane does have a more potent influence molecule for molecule, than CO2, but there are still far fewer methane molecules in the atmosphere.

Finally, the statement about other planets is based on a poor understanding of the facts. Here’s a good explanation of why this urban legend should have died out long ago:  http://www.skepticalscience.com/global-warming-other-planets-solar-system.htm

 

Reply to this comment

By Mel Tisdale
on August 26th, 2012

The argument regarding whether global warming is human in origin or not is a diversion. An excellent diversion, but a diversion none-the-less. It matters not, until it comes to laying blame, of course. But the day that happens is some way away, perhaps so far away it might never happen.

Imagine Fred and Reg, the look-outs in the crow’s nest of the Titanic:
Fred: Hey Reg, is that an ice-berg dead ahead?
Reg: Yeah, looks like it Fred, dead ahead, too. Better warn the Captain.
Fred: I can see clearer now. Its o.k. Reg, its one of those natural ones, so no problem.
Reg, What do you mean?
Fred: Natural ones are no danger, Reg. Those man-made ones are the dangerous ones, if it was one of them, it could sink us and that’s a fact.
And, as they say, the rest is history.

We know what to do about climate change and arguing its origin only serves to delay action, much to the glee of the fossil fuel industry.

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