In the mid 1800s, some scientists and explorers ? having not yet found a way through the forbidding sea ice sheathing much of the Arctic Ocean ? posited that there was an ?open polar sea? beyond those barricades, nourished by warm waters sweeping north past Scandinavian coasts. (I have the marvelous 1867 book ?The Open Polar Sea? on my book shelf; you can read it online here.)
Now, it has become almost routine in summers to have broad stretches of the Arctic Ocean largely free of ice. Global warming from the human-driven buildup of heat-trapping greenhouse gases is seen by virtually all Arctic scientists as playing a growing role in driving the shift in summers toward a largely open sea at the top of the world, with plenty of variations along the way.
As the National Snow and Ice Data Center announced yesterday, Sept. 16 marked the end of the 2012 ice retreat, which far surpassed the ice melt in 2007 ? at the time considered a jaw-dropping outlier by many researchers. Here?s one snippet from the center?s helpful release:
The six lowest seasonal minimum ice extents in the satellite record have all occurred in the last six years (2007 to 2012). In contrast to 2007, when climatic conditions (winds, clouds, air temperatures) favored summer ice loss, this year?s conditions were not as extreme. Summer temperatures across the Arctic were warmer than average, but cooler than in 2007. The most notable event was a very strong storm centered over the central Arctic Ocean in early August. [The NASA video above shows how the storm winds centered on the ice pack. Here's my post on that storm.] It is likely that the primary reason for the large loss of ice this summer is that the ice cover has continued to thin and become more dominated by seasonal ice. This thinner ice was more prone to be broken up and melted by weather events, such as the strong low pressure system just mentioned. The storm sped up the loss of the thin ice that appears to have been already on the verge of melting completely.
Justin Gillis has a news story describing the findings and some interpretations. [5:02 p.m. | Updated |Here's Brad Plumer's ice exploration in the Washington Post.*] There?s much more coverage, of course, and plenty of messaging from green groups.
The first question is why was this year so surprisingly extreme, even along a trend toward more open water? (Other questions will be addressed in the next few days.) Overall, as I?ve said for years, it?s the trend that matters most. Otherwise you can end up in endless seesaw debates about what?s going on ? with this recent Skeptical Science graph demonstrating the importance of a longer view:
In the next 24 hours, I?ll be posting fresh excerpts from an extended and fascinating discussion of ice patterns since 2007 involving some of the world?s top ice researchers ? both modelers and field scientists like those I accompanied in 2003 on their annual North Pole expedition undertaken to monitor the vital signs of the ocean beneath the drifting sea ice.
The pace of ice loss ? both its extent and the amount of the older, thicker ice that survives from summer to summer ? has been faster than most models predicted and clearly has, as a result, unnerved some polar researchers by revealing how much is unknown about ice behavior in a warming climate.
Even with this year?s extreme loss, there?s still a wide range of predictions among polar scientists of how soon the northernmost ocean will be ?ice free? in late summer. Peter Wadhams, a British oceanographer who?s charted ice conditions for many years, is an outlier in predicting 2015 or so (he has joined an assortment of people calling for emergency geo-engineering efforts to chill the Arctic).
But most of the dozen or so ice scientists I?ve consulted of late (and several dozen since 2000) remain closer in their views to Cecilia Bitz of the University of Washington, who recently agreed with my notion (as a longtime, but lay, observer) that there?s ?a 50-50 chance it will take a few decades.? (Keep in mind that almost all Arctic sea ice researchers add a big caveat when talking of an ?ice-free Arctic Ocean,? noting that a big region of thick floes north and west of Greenland will almost surely persist in summers through this century, which is one reason some scientists have proposed targeting polar bear conservation efforts there.)
It?s clear to a range of scientists that the enormous loss of old, thick ice carried on currents from the Arctic out past Greenland into the Atlantic Ocean in recent years is a major factor that has led to sharp summer melting. (With the ocean cloaked mainly in relatively thin floes, formed over a single winter, the chances rise each summer of a big melt-off under the 24-hour sun and influxes of warmer seawater.) The forces driving that ice exodus are complicated, as you?ll hear from the scientists contributing below.
This animated, three-dimensional graph, created by an amateur Arctic watcher, Andy Lee Robinson, using data from the Piomas model of scientists at the University of Washington, gives an incredibly interesting view of how the reduction in overall ice volume has proceeded:
I asked Robinson, who is an engineer, graphics and programming expert and musician, to explain the steps and sources behind the graph. Click here for my Slideshare posting of his detailed reply.
While you wait for the exchange with ice researchers, I encourage you to explore the developing string of posts by Judith Curry of Georgia Tech, who led one of several research groups recently reporting links between summer ice loss and severe winter weather in temperate regions of the Northern Hemisphere (her relevant paper is here). Her first post explored this question: ?How should we interpret the record low minimum sea ice extent?? Her second asked: ?Whence an ?ice free? Arctic? Does an ?ice free? Arctic matter??
[5:02 p.m. | Updated | In exploring Curry's last question, also look back to what meteorologist Judah Cohen wrote about retreating sea ice, expanding Siberian snow and winter weather in a 2010 Times Op-Ed and on Dot Earth.]
Also, you can start by exploring an illustrated view of the array of factors ? from sea-bottom topography to warm water ? that may be in play in the changing Arctic Ocean provided by James Morison of the University of Washington. Morison has been studying Arctic sea ice and waters for decades and runs an annual expedition to the North Pole to drop instruments through the ice into the ocean below (the one I got to go on in 2003). He stresses this is informed speculation at this point, putting him in good company considering the many ideas in circulation and the persistent uncertainties in the system.
4:37 p.m. | Postscript | The scope of what?s unfolding, and the fascinating and persistent science and policy questions, make me think I need to update and expand my prize-winning book on the once and future Arctic, ?The North Pole Was Here.? Thoughts welcome. The first chapter is online here.
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