It’s Arctic ice time again. A paper in Nature on Arctic warming is getting some interesting and possibly somewhat misleading media pick-up. In their paper Rune Graversen and colleagues at Stockholm University use statistical analyses to try and understand what processes are important in the recent warming of the Arctic. One of their findings is that a substantial part of the warming is seen at altitude, rather that at the surface — “A remarkable result,” Graversen told National Geographic News. “I think nobody expected that.”
As that report and others (AFP, New Scientist) point out, the surprise is that this work diminishes the role of the “ice-albedo feedback” in recent Arctic warming. In theory less ice means more sunshine is absorbed, rather than reflected back into space, which means more warming, which means less ice, and so on and so on — a positive feedback that could be a powerful amplifier of climate change. But that effect would be felt most nearer the surface, not at altitude (The fact that some of the amplified warming takes place in the dark lends further weight to the argument).
Warming at altitude points to a role for increased energy transport by way of the atmosphere — warm and/or moist air moving north at greater rates than heretofore, and warming the Arctic both directly and indirectly (possibly through more water-vapour greenhousing and more clouds).
The AP’s take on this comes under the headline “Nature and Man Jointly Cook Arctic” (they’re referring to nature in its broad sense, not to our journal…) Seth Borenstein takes the line that the ice-albedo effect and anthopogenic warming are effectively synonymous, and that if warming isn’t due to the feedback but to increased atmospheric transfer of heat then it is more “natural” and less “man-made”. Unsurprisingly, a few blogs have taken up this notion.
But my reading of the paper doesn’t really support that claim. The researchers don’t say the increasing atmospheric heat transport is directly related to anthropogenic warming, but nor do they say it isn’t — and Graversen was explicit about this when talking to National Geographic News:
Nobody knows how much of this change is the result of human emissions of planet-warming gases such as carbon dioxide, but it’s likely that they play a role.
“Many models suggest an increase in energy transport when more greenhouse gases are introduced into them,” [Graversen] said.
“Changes in the circulation in the atmosphere might have had a much larger effect than previously thought, but these changes may also have been induced by greenhouse gases.”
So I’m a little surprised that the paper is being seen as evidence that the human role has been exagerrated. And I’m also a little surprised that, as far as I can see, no-one has picked up on the scariest part of it. The fact that ice-albedo feedbacks aren’t the whole story now doesn’t mean they don’t have a role to play, or that that role won’t increase in the future. In their conclusion, the authors make this point pretty explicit:
Our results do not imply that studies based on models forced by anticipated future CO2 levels are misleading when they point to the importance of the snow and ice feedbacks. It is likely that a further substantial reduction of the summer ice-cover would strengthen these feedbacks and they could become the dominant mechanism underlying a future Arctic temperature amplification.
Which is to say that, in the long run, the much discussed ice-albedo feedbacks could be the biggest factor of all — and we’ve already seen unparalleled amounts of warming before they’ve even kicked in…
Image: global view of Arctic Ocean from NASA Visible Earth / NASA JPL, University of Alaska – Fairbanks