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Arctic icemelt is a natural cycle

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The skeptic argument...

Arctic icemelt is a natural cycle

"In 2007, the Northern Hemisphere reached a record low in ice coverage and the Northwest Passage was opened. At that point, we were told melting was occurring faster than expected. What you were not told was that the data that triggered this record is only available back to the late 1970s. We know the Northwest Passage had been open before." (Matt Rogers)

What the science says...

Arctic sea ice has been retreating over the past 30 years. The rate of retreat is accelerating and in fact is exceeding most models' forecasts.

Global warming affects Arctic sea ice in various ways. Warming air temperatures have been observed over the past 3 decades by drifting buoys and radiometer satellites (Rigor 2000, Comiso 2003). Downward longwave radiation has increased, as expected when air temperature, water vapor and cloudiness increases (Francis 2006). More ocean heat is being transported into Arctic waters (Shimada 2006).

As sea ice melts, positive feedbacks enhance the rate of sea ice loss. Positive ice-albedo feedback has become a dominant factor since the mid-to-late 1990s (Perovich 2007). Older perennial ice is thicker and more likely to survive the summer melt season. It reflects more sunlight and transmits less solar radiation to the ocean. Satellite measurements have found over the past 3 decades, the amount of perennial sea ice has been steadily declining (Nghiem 2007). Consequently, the mean thickness of ice over the Arctic Ocean has thinned from 2.6 meters in March 1987 to 2.0 meters in 2007 (Stroeve 2008).

Global warming has a clearly observed, long term effect on Arctic sea ice. In fact, although climate models predict that Arctic sea ice will decline in response to greenhouse gas increases, the current pace of retreat at the end of the melt season is exceeding the models’ forecasts by around a factor of 3 (Stroeve 2007).

Figure 1: September Arctic Sea Ice Extent (thin, light blue) with long term trend (thick, dark blue). Sea ice extent is defined as the surface area enclosed by the sea ice edge (where sea ice concentration falls below 15%).

What caused the dramatic ice loss in 2007?

The sudden drop in sea ice extent in 2007 exceeded most expectations. The summer sea ice extent was 40% below 1980's levels and 20% below the previous record minimum set in 2005. The major factor in the 2007 melt was anomalous weather conditions.

An anticyclonic pattern formed in early June 2007 over the central Arctic Ocean, persisting for 3 months (Gascard 2008). This was coupled with low pressures over central and western Siberia. Persistent southerly winds between the high and low pressure centers gave rise to warmer air temperatures north of Siberia that promoted melt. The wind also transported ice away from the Siberian coast.

In addition, skies under the anticyclone were predominantly clear. The reduced cloudiness meant more than usual sunlight reached the sea ice, fostering strong sea ice melt (Kay 2008).

Both the wind patterns and reduced cloudliness were anomalies but not unprecedented. Similar patterns occurred in 1987 and 1977. However, past occurances didn't have the same dramatic effect as in 2007. The reason for the severe ice loss in 2007 was because the ice pack had suffered two decades of thinning and area reduction, making the sea ice more vulnerable to current weather conditions (Nghiem 2007).

Conclusion

Recent discussion about ocean cycles have focused on how internal variability can slow down global warming. The 2007 Arctic melt is a sobering example of the impact when internal variability enhances the long term global warming trend.

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Further viewing

The following animation shows how the oldest thickest sea ice has been progressively flushed from the Arctic Ocean over the last two decades. The colours are an indication of the age of the sea ice. Lighter colours are older sea ice - white is 10 years old.

Comments

Comments 1 to 13:

Mizimi at 05:32 AM on 6 September, 2008
So the sudden drop in sea ice in 2007 was due to weather conditions, not climate change ( excepting weather is the end product of the climate process).
How many times do we need to remind ourselves "one swallow does not a summer make"?
Sea ice is a part of the negative feedback system that keeps climate (reasonably) stable. Melting requires heat
(334J/gm if I remember rightly)and this mostly affects local sea temperature. It also keeps plankton et al very happy and bloomimg nicely, (they like it cool)which is good because they lock up a bit more CO2 and
the food chain speeds up.
Quietman at 05:34 AM on 7 September, 2008
John
Well written. I like this one much better than the original.
jecht8 at 02:05 AM on 22 December, 2008
This whole piece is somewhat humorous. To even use arctic ice as evidence of a global warming trend as caused by CO2 over merely 3 decades of evidence is utterly ridiculous. Anthropogenic GW advocates will cite that the Northwest Passage has opened the for the first time since records began in 1978. Since records began. Sorry, but if a norweigan sailor by the name of Roald Amundsen could navigate the passage in 1906, then you're going to have to accumulate another century of evidence of so-called Anthropogenic Global Warming before the case is made. Remember people, satellite data is only available after satellites were invented...
GFW at 18:36 PM on 19 April, 2009
What jecht8 either doesn't know or acknowledge is that it took Amundsen 3 years to make the trip because only bits opened up at a time. Also, he took an extremely shallow water route sticking close to the mainland shore.

When we speak of the NW passage opening now, we're talking about being able to go pretty much full speed, just steering around a few bergs - and it's the more northern, deep water route.
cold beer please at 22:51 PM on 7 May, 2009
Two recent Arctic Ice updates:

Beginning in early January 2009, sensor drift caused an underestimation of ice that grew until the error was finally caught in the mid-February. Internet visitors who look to the NSIDC for data sent emails to the center and, it became clear that there was a significant problem—sea-ice-covered regions were showing up as open ocean. (See NSIDC)

MORE . . . (May 4, 2009)

Ice in the Arctic is often twice as thick as expected, report surprised scientists who returned last week from a major scientific expedition. The scientists - a 20-member contingent from Canada, the U.S., Germany, and Italy - spent one month exploring the North Pole as well as never-before measured regions of the Arctic. Among their findings: Rather than finding newly formed ice to be two metres thick, "we measured ice thickness up to four metres," stated a spokesperson for the Alfred Wegener Institute for Polar and Marine Research of the Helmholtz Association, Germany's largest scientific organization.
http://network.nationalpost.com/np/blogs/fpcomment/archive/2009/05/04/lawrence-solomon-deep-arctic-ice-surprises-scientific-expedition.aspx

More info to come from Polar 5.
Argus at 09:27 AM on 27 February, 2010
The Arctic seems to be warming up. Reports from fishermen, seal hunters and explorers … all point to a radical change in climate conditions, and hitherto unheard-of high temperatures in that part of the earth's surface. … Ice conditions were exceptional. In fact so little ice has never before been noted. The expedition all but established a record, sailing as far north as 81 degrees 29 minutes in ice-free water. … Many old landmarks are so changed as to be unrecognizable. Where formerly great masses of ice have been were found, there are now often moraines... At many points where glaciers formerly extended far into the sea, they have entirely disappeared.
- - -
The above alarming excerpts were taken from an October report to the US Weather Bureau. October 1922, that is, not 2009. So it has happened before, and will happen again. We should not think that everything is so special for our time: the contents of this site strike me as very centered around here and now. It is 10 years this, 30 years that, highest since record began in 1978, and so on. That is a very short time perspective. Somehow the lack of perspective in the climate discussions remind me of the 2000+ year old quote attributed to Socrates that most people would place in our time frame:
"The children now love luxury; they have bad manners, contempt for authority; they show disrespect for elders and love chatter in place of exercise. Children are now tyrants, not the servants of their households. They no longer rise when elders enter the room. They contradict their parents, chatter before company, gobble up dainties at the table, cross their legs, and tyrannize their teachers."

It is presumptuous to think that mankind rules the earth's climate. There are other, more powerful, forces in play. But we think we can raise or lower the average temperature of the earth at will! 0.33 degrees up, or why not 4 degrees. Or raise the oceans, 38 centimeters up, or why not 6 meters, or whatever ! Invent a figure, and people will bow to you in awe. Ridiculous. Anything could happen, and probably will, but we are not in control.
Riccardo at 09:41 AM on 27 February, 2010
Argus,
yes, you can claim whatever you wish untill you look at the data. Which tell a different story.
By the way, in the '20s the arctic was already warming.
Argus at 20:50 PM on 27 February, 2010
Well Riccardo, who was warming it so much then, when human CO2 emissions were only a fraction (less than 1/10) of what it is now? The cows and their methane outlets? What explanation do you have in your 'data'?
Riccardo at 23:45 PM on 27 February, 2010
Argus,
it should come as no surprise that climate has changed before. Indeed, one has to look at how climate works, i.e. that there are several possible forcings other than CO2.
In particular, in the first half of last century there has been a reduced volcanic activity (grey line) concomitant to an increase of total solar irradiance (top panel). The result is an increase in temperature till about 1950, overall and in the Arctic as well.
Argus at 02:51 AM on 28 February, 2010
Thank you very much for acknowledging that there are other forcings than CO2, and that climate changes similar to what we are experiencing now, have occurred before. It seems to me that 99% of what is presented here is focussed on CO2 only, as if there were no other explanation to anything at all happening on this planet.
Also, thanks for the links! I am continually reading up on more facts presentations and connected debates within this great site (and some others). I am slowly learning, and by now I know a lot more than the average person in the street, but I also recognize how little I know compared to those who have studied this field seriously for years.
Riccardo at 03:23 AM on 28 February, 2010
Argus,
I'm glad you now realize that we all think that there's not just CO2. It's an important point to make clear as did our host writing a post on it. It is only by looking at all the important factors that scientists can be so confident on the causes of recent and past climate variations.
Please keep reading and asking, it won't take that much time :)
Tom Dayton at 03:44 AM on 28 February, 2010
Argus, a good overview is cce's The Global Warming Debate. It will give you a good base from which you can more efficiently and effectively pursue particular topics here.
cloneof at 03:13 AM on 2 June, 2010
Is the graph from Stroeve 2007? I find it quite hard to read a graph that I don't know the source from.