Tuesday, July 29, 2008
Why the melting of the Arctic sea ice may still be trouble, or not
Because we are nothing if not fair, we call your attention to this apparently reasonable post on sea-ice journalism at the Yale Forum on Climate Change & the Media. It reviews the media's coverage of the issue and finds it wanting while nevertheless holding up the majority view that melting Arctic sea ice both reflects anthropogenic global warming and threatens a feedback loop that could accelerate warming (by reducing the reflectivity, or albedo, of the far Northern Hemisphere). Since I have occasionally pointed out that Southern Hemisphere sea ice is increasing and above the baseline, I thought this assertion was particularly interesting:
One final point: While Arctic ice has been declining, Antarctic sea ice has been increasing recently. But changes at the bottom of the world are well within the range of natural variability, Alley said. In contrast, the Arctic changes under way are far outside of it.
Sadly, the post's author (Bruce Lieberman) neither adduced evidence in support nor explained why the increase in Southern Hemisphere albedo does not compensate for the decrease in the Northern (since the total global sea ice coverage was actually above the baseline average as recently as this spring). This seems like a big miss, even for a Yalie.
Anyway, if the Yale operation is serious about presenting climate change science in an intellectually honest way, it had better address the actual objections raised by the skeptics instead of the straw-man objections thought up by the activists.
NOTE (posted April 7, 2009): Via Bruce Lieberman, this email from Professor Alley:
The “simple” answer is that the ice-albedo feedback is primarily a local-regional one rather than a global one. Ice-albedo does matter globally, but not a whole lot, because most of the snow and ice hang out in the winter in small polar regions with low sun angles and often with clouds, so that not a whole lot of the total sun reaching the planet actually can bounce off the snow and ice and back to space. Ignoring ice-albedo will get you in trouble quantitatively globally, but ignoring water vapor would get you into way worse shape. Locally, however, the sea ice makes a much bigger deal. The easiest way to cause a big temperature change is to alter sea-ice coverage in a polar winter—open water is at or above freezing, and nearby air can’t escape this, whereas in the dark of a polar winter you can run to –40 over sea ice without too much trouble. Very little else in the climate system can get you 40 degrees C or more for a chnuk of a season. So probably correct, with modern ice coverage, to view ice-albedo as a positive but not overly strong feedback on global temperatures but with the potential to have very large regional effects, insofar as the absorbed heat from reduced ice can delay ice regrowth and cause corresponding anomalies not only from the direct balance of absorbed versus reflected sunlight, but also from other things including the lid-or-not on the ocean in winter.
If (big if, see below) Antarctic changes were offsetting Arctic changes in sea ice, and if some other things also are comparable (cloud cover, for example, and seasonal persistence of the anomalies—the sea ice has to be illuminated by the sun to matter), then globally you could have offsetting changes in radiative balance of the planet. For what it’s worth, though, the trends in sea-ice coverage from NSIDC (http://nsidc.org/data/seaice_index/s_plot.html and http://nsidc.org/data/seaice_index/n_plot.html) are listed as –3.4 +- 0.7 % per decade with a 1979-2000 mean of 12.2 million sq km in the Arctic, and 0.9 +- 1.3 % per decade with a 1979-2000 mean of 13.8 million sq km for the Antarctic. If one is interested in momentary radiative balance, then it may be acceptable to pick a month or three and compare northern and southern values, but any assessment of statistically significant trends shows that the southern trends are not offsetting the northern ones.
Your correspondent might locate the 1984 J. Hansen et al. paper in Climate Processes and Climate Sensitivity, to get a better feel for the amplification of feedbacks, and the strengths of various feedbacks. --Richard
My apologies for the delay in posting this email, which I received in mid-December. I only remembered that I had not corrected this post when another spate of news about the meltic Arctic sea ice cropped up in the news in early April 2009. That said, I do have a question: It seems to me that Antarctic sea ice is, on average, further from the pole than Arctic sea ice. Would that not mean that the albedo of Antarctic sea ice would have a greater impact on the reflection and absorption of heat?
6 Comments:
By 
joated, at
Tue Jul 29, 09:27:00 PM:
"This seems like a big miss, even for a Yalie."
Why, I do believe your Tiger stripes are showing!
By Anthony, at
Tue Jul 29, 09:32:00 PM:
I'll be impressed if and when they deal honestly with David Evans' objections. A former global warming alarmist, it's pretty damning stuff:
By Purple Avenger, at
Tue Jul 29, 10:17:00 PM:
All the arctic ice vanished in the early 1900's during a warm spell.
Presuming it happens now, two incidents within 100 years strikes me as well within the realm of natural variability...unless they want to blame the early 1900's incident on global warming too.
By Simon Kenton, at
Tue Jul 29, 10:34:00 PM:
For most of the Cretaceous, there were no polar ice caps. Sea level was at its highest. The Interior Cretaceous Seaway extended from the Gulf of Mexico into Canada, along the front of the Rockies. There's a reason most of our abundant coal resources are Cretaceous; it was one of the most fertile periods in the life of the Earth. There was a period in the Precambrian/Cambrian when atmospheric CO2 was about 7 times the projected concentration, and yet (mirabile dictu) it was much colder than now.
I suppose it too much to ask, that climate "scientists" and reporters read a book or two about the history of the planet? There's a bit more to natural variability than what they have observed from 1980 - 2000.
By 
, at
Wed Jul 30, 02:52:00 AM:
majority view that melting both reflects anthropogenic global warming and threatens a feedback loop that could accelerate warming (by reducing the reflectivity, or albedo, of the far Northern Hemisphere)
The majority view overlooks the effects of the addition moisture that may be added to the atmosphere when unusually large areas of the Arctic Ocean are ice free.
Remember the record cold and heavy snows in Central Asia and China last winter followed last fall's 'unprecedented' melt of Arctic sea ice?
By Nomennovum, at
Wed Jul 30, 10:15:00 AM:
The first question we should ask about melting sea ice at the north pole -- and about AGW in general -- is: Is it a bad thing?
I am willing to put my beach house at risk and say, "Let the ice melt." (Not that melting sea ice will ever put the house at risk.) Global warming (anthropomorphic or not) will be a net benefit to humanity, in my opinion.
Of course, there a a lot more questions to be asked and answered before I get to: "We've got to stop this AGW right now by turning the US and world economies upside down, or we're all gonna die!"
