A new record minimum for arctic sea ice
Arctic sea ice reached a new record minimum during the first half of November, according to data from the National Snow and Ice Data Center (Figure 1). The record low ice extent this month is the first extended period of record minimum arctic sea ice since 2007. The new record minimum suggests that the gains in ice seen over the past two years were probably a temporary fluctuation due to normal year-to-year variability in the weather, and that the long-term arctic sea ice decline observed since the 1970s is continuing.
Figure 1. Arctic sea ice extent up to November 16, 2009, compared to the record low year of 2007 and the average from 1979 - 2000. Sea ice extent over the past ten days has fallen below the record minimum observed in 2007. Image credit: National Snow and Ice Data Center.
What caused the new record low?
The record low was due to very warm air invading the Arctic during October, in combination with the unusually warm ocean temperatures that have prevailed in the region over the past few decades. The warm air temperatures were primarily the result of an intense series of low pressure systems in the Arctic Ocean, north of Siberia, that worked in concert with a very strong high pressure system north of Alaska to drive warm air from Central Asia poleward over the past six weeks. The strong storms and unusual pressure pattern brought winds of about 5 mph above average to large regions of the Arctic Ocean, which helped break up existing ice and kept ice from freezing as much as usual. With all that warm air flowing into the Arctic, the cold air that was there had to go somewhere else, and that "somewhere else" was North America. The U.S. recorded its 3rd coldest October on record in 2009, thanks to cold air flowing out of the Arctic. The temperature and sea level pressure patterns over the Northern Hemisphere for October (Figure 2) were highly anomalous, with temperatures up to 27°F (15°C) above average over the Arctic Ocean, and sea level pressures up to 11 mb above average. The atmospheric circulation pattern has shifted over the past two weeks, with the result that warm air from Central Asia is no longer being pumped into the Arctic so vigorously, nor is cold air from the Arctic streaming southward into North America. As a result, temperature anomalies in the Arctic are beginning to decline, and sea ice extent later this month will probably rise above the record minimums observed in 2007.
Figure 2. Departure of surface air temperature and surface pressure from average for October 2009. Surface temperatures in the Arctic were up to 27°F (15°C) above average over the Arctic Ocean, due to sea ice loss. The strongest anomalies occurred where sea ice was missing from its usual position, though the entire Arctic was affected. The clockwise flow of air around the anomalously strong high pressure system north of Alaska (labeled "H" in the right-hand image) helped drive a flow of very warm air from Central Asia into the Arctic, and a very cold flow of air out of the Arctic southward into North America. Image credit: NOAA/ESRL.
How will the November sea ice loss affect next summer's sea ice loss?
A record 19% of the Arctic sea ice cover this summer in the Arctic was over 2 years old, far below the 1981 - 2000 average of 52%. In the summer of 2009, NASA researcher Ron Kwok and colleagues from the University of Washington in Seattle published satellite data showing that mean winter arctic ice thickness declined by 48% between 1980 and 2008. The loss accelerated over the past five years, with the ice losing 0.68 meters (2.2 feet) of thickness between 2004 and 2008, finishing at 6.2 feet thick. This remarkable thinning was confirmed in May 2009 by the Catlin Arctic Survey, a 9-week, 435 km expedition across the Canadian Arctic led by polar scientist Professor Peter Wadhams of the University of Cambridge. Wadhams' expedition found that most of the route had first year ice just 5.9 feet (1.8 meters) thick. With El Niño conditions crossing from the moderate to strong category over the past two weeks in the Eastern Pacific, the prospects for a much warmer than usual winter in the Arctic have increased, likely setting the stage for continued record or near-record minimum sea ice extent and thickness into next spring. The arctic sea ice will be very vulnerable to a new record minimum next summer if warmer than average temperatures are seen over the Arctic.
Sea ice loss causes stronger storms in the Arctic
The stronger storms over the Arctic Ocean this fall were due, in part, to the loss of sea ice. In a 2009 article titled, Extraordinary September Arctic sea ice reductions and their relationships with storm behavior over 1979-2008, Simmonds and Keay found that September storms over the East Arctic intensified by about 1 mb over the past 30 years and had grown about 50 miles larger in diameter, thanks to all the extra heat energy supplied by more open water due to recent losses in Arctic sea ice. These stronger storms may create a positive feedback loop that will lead to even more sea ice loss: reduced sea ice drives stronger storms, whose winds break up sea ice, creating even more warm water to feed stronger storms with stronger winds, and so on. Now that the arctic sea ice is 48% thinner than 30 years ago, this effect will increase in importance, since thinner ice breaks up more readily in strong winds.
Expect an ice-free Arctic by 2030
In a press release put out by the Catlin Arctic Survey, Professor Wadhams said, "The Catlin Arctic Survey data supports the new consensus view--based on seasonal variation of ice extent and thickness, changes in temperatures, winds and especially ice composition--that the Arctic will be ice-free in summer within about 20 years, and that much of the decrease will be happening within 10 years". In their 2009 report on this year's Arctic sea ice minimum, National Snow and Ice Data Center Director and Senior Scientist Dr. Mark Serreze said, "It's nice to see a little recovery over the past couple years, but there's no reason to think that we're headed back to conditions seen back in the 1970s. We still expect to see ice-free summers sometime in the next few decades". At the December 2008 American Geophysical Union (AGU) meeting, the world's largest climate change conference, sea ice expert Dr. Wieslaw Maslowski of the Navy Postgraduate School blamed 60% of the melting during the past decade on heat brought in by ocean currents, and projected that summertime arctic sea ice would completely disappear by 2016. Dr. Jim Overland of NOAA's Pacific Marine Environmental Laboratory was more conservative, projecting a 2030 demise of arctic sea ice. He thought we would be "hanging around where we are for a while", and thought it would take two more unusual summers like the "perfect storm" of 2007 to push the system to an ice-free state.
There were 88 presentations on arctic sea ice at the 2008 AGU conference. None of the presenters expressed the view that the current long-term decline in arctic sea ice was almost entirely natural, or that we can expect the decline to reverse this century. Sea ice experts do blame part of the decline on natural variability in the weather, but we wouldn't be where we are now without the warming caused by human-emitted greenhouse gases. One view (Stroeve et al., 2007) is that human-emitted greenhouse gases are responsible for 47 - 57% of the arctic sea ice loss since 1979. Heat-absorbing black soot from fires and pollution settling on the white ice is thought to also be a significant contributor.
The consensus I heard at the AGU conference among arctic sea ice experts was that the summertime sea ice will be gone by 2030. If they are correct, we can expect a period of significantly accelerated global climate change to begin 10 - 20 years from now. Arctic sea ice is one of the critical components maintaining the stability of our current climate. Once the the ice is gone, the climate will become unstable, with highly unpredictable results. It is true that Earth's past has many examples of warmer climates that evolved due to natural causes where life flourished, and we shouldn't fear the new, stable climate we will eventually arrive at centuries from now. However, life on Earth is adapted to the current climate. The changes that will occur during the transition will be extremely disruptive to Earth's ecosystems and the humans that rely on them for life. If one were to rate the destructive capability of climate change the way we rate hurricanes, I would rate current climate change at the "Invest" or "tropical disturbance" stage--the climate change storm is just beginning to organize. But the coming climate change storm is destined to hit our children with the full fury of intensifying hurricane.
Kwok, R., and D. A. Rothrock. 2009, "Decline in Arctic sea ice thickness from submarine and ICESat records: 1958-2008", Geophys. Res. Lett., 36, L15501, doi:10.1029/2009GL039035
Simmonds, I., and K. Keay (2009), Extraordinary September Arctic sea ice reductions and their relationships with storm behavior over 1979.2008, Geophys. Res. Lett., 36, L19715, doi:10.1029/2009GL039810.
Stroeve, J., M.M. Holland, W. Meier, T. Scambos, and M. Serreze, Arctic sea ice decline:Faster than forecast", GRL 34 L09501, doi:1029/2007GL029703, 2007.
The road to Copenhagen
By some accounts, the future of the world will be at stake this December, when the crucial U.N. Climate Change Conference will be held December 7 - 18 in Copenhagen, Denmark. At that meeting, the leaders of the world will gather to negotiate an agreement to replace the 1997 Kyoto Protocol. The new agreement will be the world's road map for dealing with climate change, and the stakes are huge. Dr. Ricky Rood, author of Wunderground's climate change blog, will be there, and Wunderground has given the University of Michigan a grant to send a student who will also blog for us. I have a number of posts I'm planning in the run-up to Copenhagen, including:
- Impact of arctic sea ice loss on Northern Hemisphere winter weather
- The Manufactured Doubt industry
- What global warming skeptics say about arctic sea ice
- Is higher CO2 more beneficial for Earth's ecosystems?
I'll also have an end-of-hurricane season summary on November 30, plus posts on whatever breaking weather stories occur. My next post will be Friday, when I plan to summarize the global weather last month, which was the 2nd - 6th warmest October on record.