Key Facts

The degree of warming observed in the Arctic is greater than that observed in the rest of the Northern Hemisphere—a phenomenon known as Arctic amplification.^2,3,4,5 The resulting effects of faster Arctic warming may be felt well beyond the Arctic Ocean.⁶

• The area of Arctic sea ice extent fell in 2007 to the lowest level recorded since satellite measurements began in 1979; 2008 and 2010 saw the second- and third-lowest levels, respectively.^7,8,9
• Decreases in the bright, reflective sea ice expose areas of dark ocean, increasing absorption of solar radiation. In turn, this warmer ocean water releases heat back into the air as the season changes to autumn.¹⁰
• Warmer air extends over adjacent land, thawing permafrost and allowing bacteria to decompose plant and other organic matter that had long been frozen—amplifying global warming by releasing more heat-trapping gases into the atmosphere.^6,10

Details

Globally temperatures are rising, but in the Arctic, near-surface air temperatures rose nearly twice as much as the world average in the decades leading up to 2010. This phenomenon is known as "Arctic amplification."^2,3,4

Sea ice extent is generally defined as the area within which at least 15 percent of the ocean surface is covered with ice.⁸ Since satellite recordkeeping began in 1979, summer sea ice extent in the Arctic has been shrinking.⁷ It reached a record low of 1.6 million square miles (4.29 million square kilometers) in September 2007;¹¹ 2008 had the second-lowest sea ice extent, and 2010 the third-lowest: 1.8 million square miles (4.6 million square kilometers).^8,9

Part of a Larger Pattern

Arctic amplification is primarily a result of reduced sea ice cover.^10,12 Open water absorbs heat from the sun during summer; in autumn, without ice to hold it in, this heat is released, raising nearby air temperatures.^4,10,13 The largest near-surface air temperature spikes correlate closely to areas with the greatest declines in sea ice cover.¹⁰ Between 2005 and 2008, for example, sea ice loss pushed autumn surface air temperatures in the central Arctic more than 9°F (5°C) above the norm—an increase similar to that projected for 2070 in the Intergovernmental Panel on Climate Change Fourth Assessment Report.^14,15,16,17

For example, warmer-than-average surface air temperatures extended into areas still covered with ice in September 2007, suggesting that a combination of sea ice loss and atmospheric circulation affects amplification.¹⁰ High- and low-pressure systems that were particularly pronounced in summer 2007 and continued into autumn created a wind flow pattern that made conditions worse.^7,10 Warm surface air traveled northward over the Chukchi Sea, where atypical surface air temperatures of 41°F (5°C) were recorded, to the north pole, where surface air temperatures over 37.4°F (3°C) were recorded—despite the presence of sea ice cover.¹⁰ The circulation of this warm air over areas of ice cover was responsible, in part, for that summer's huge ice losses.^7,10

What the Future Holds

Summer sea ice extent is expected to continue diminishing, further delaying the formation of sea ice in autumn.¹⁰ Arctic amplification should eventually start to be observed in winter (in response to reduced ice cover), and there are signs that this may already be happening.^10,18,19 When ice extent and thickness drop sufficiently, low-level warming is likely to be seen in the spring as well.¹⁰

Loss of Arctic sea ice in the summer is already associated with higher air temperatures over nearby Arctic lands. Between 1989 and 1998, one study linked a large increase in permafrost degradation to a 3.6° to 9°F (2° to 5°C) rise in air temperature over central Alaska.²⁰ And according to more recent data, temperatures in the western Arctic from August to October 2007 were higher than any in the preceding three decades: 4°F (2.3°C) above average for that time of year.⁶

Model results suggest future warming over land in the Arctic during the twenty-first century may be 3.5 times higher during periods of rapid sea ice loss, and this warming may reach 932 miles (1,500 kilometers) inland.⁶ Such warming can lead to the rapid melting of already warm permafrost, and may make colder permafrost more vulnerable.⁶ As permafrost melts, it can release methane and carbon dioxide—two potent heat-trapping gases—providing even more fuel for the warming trend.

Projections of increased—and perhaps drastic—sea ice melt in the Arctic are dependent on the amount of heat-trapping gases the world releases over the coming decades.²¹ The results of a study that ran models both with and without increases in concentrations of global warming pollution demonstrate that such emissions are a critical factor in the rate at which summer sea ice extent is likely to shrink.^13,22,23

Credits

Endnotes

1. Photo: Kathryn Hansen, NASA. Accessed October 31, 2010, at http://www.nasa.gov/ multimedia/ imagegallery/ image_1710.html ↑
2. Solomon, S., D. Qin, M. Manning, R.B. Alley, T. Berntsen, N.L. Bindoff, Z. Chen, A. Chidthaisong, J.M. Gregory, G.C. Hegerl, M. Heimann, B. Hewitson, B.J. Hoskins, F. Joos, J. Jouzel, V. Kattsov, U. Lohmann, T. Matsuno, M. Molina, N. Nicholls, J. Overpeck, G. Raga, V. Ramaswamy, J. Ren, M. Rusticucci, R. Somerville, T.F. Stocker, P. Whetton, R.A. Wood, and D. Wratt. 2007. Technical summary. In: Climate change 2007: The physical science basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, edited by S. Solomon, D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M. Tignor, and H.L. Miller. Cambridge, UK, and New York: Cambridge University Press. ↑
3. ACIA. 2004. Impacts of a warming Arctic: Arctic Climate Impact Assessment. Cambridge University Press. Online at http://www.acia.uaf.edu. ↑
4. Serreze, M.C., and J.A. Francis. 2006. The Arctic amplification debate. Climatic Change 76:241-264. ↑
5. Stroeve, J., M.M. Holland, W. Meier, T. Scambos, and M. Serreze. 2007. Arctic sea ice decline: Faster than forecast. Geophysical Research Letters 34:L09501. ↑
6. Lawrence, D.M., A.G. Slater, R.A. Tomas, M.M. Holland, and C. Deser. 2008. Accelerated Arctic land warming and permafrost degradation during rapid sea ice loss. Geophysical Research Letters 35. ↑
7. Stroeve, J., M. Serreze, S. Drobot, S. Gearheard, M. Holland, J. Maslanik, W. Meier, and T. Scambos. 2008. Arctic sea ice extent plummets in 2007. EOS Transactions American Geophysical Union 89:13-20. ↑
8. NSIDC Arctic Sea Ice News & Analysis. 2010. Updated minimum Arctic sea ice extent. National Snow and Ice Data Center. September 27. Accessed October 31, 2010, at http://nsidc.org/ arcticseaicenews/ index.html. ↑
9. Kwok, R., G.F. Cunningham, M. Wensnahan, I. Rigor, H.J. Zwally, and D. Yi. 2009. Thinning and volume loss of the Arctic Ocean sea ice cover: 2003-2008. Journal of Geophysical Research 114:C07005. ↑
10. Serreze, M.C., A.P. Barrett, J.C. Stroeve, D.N. Kindig, and M.M. Holland. 2009. The emergence of surface-based Arctic amplification. Cryosphere 3:11-19. ↑
11. Simmonds, I., and K. Keay. 2009. Extraordinary September Arctic sea ice reductions and their relationships with storm behavior over 1979-2008. Geophysical Research Letters 36. ↑
12. Screen, J.A., and I. Simmonds. 2010. The central role of diminishing sea ice in recent Arctic temperature amplification. Nature 464:1334-1337. ↑
13. Wang, M., and J.E. Overland. 2009. A sea ice free summer Arctic within 30 years? Geophysical Research Letters 36. DOI:10.1029/2009GL037820 ↑
14. Chapman, W.L., and J.E. Walsh. 2007. Simulations of Arctic temperature and pressure by global coupled models. Journal of Climate 20:609-632. ↑
15. Overland, J.E., M. Wang, and S. Salo. 2008. The recent Arctic warm period. Tellus Series A- Dynamic Meteorology and Oceanography 60:589-597. ↑
16. Schweiger, A.J., R.W. Lindsay, S. Vavrus, and J.A. Francis. 2008. Relationships between Arctic sea ice and clouds during autumn. Journal of Climate 21:4799-4810. ↑
17. Zhang, X.D., and J.E. Walsh. 2006. Toward a seasonally ice-covered Arctic ocean: Scenarios from the IPCC AR4 model simulations. Journal of Climate 19:1730-1747. ↑
18. Deser, C., R. Tomas, M. Alexander, and D. Lawrence. 2010. The seasonal atmospheric response to projected Arctic sea ice loss in the late twenty-first century. Journal of Climate 23:333-351. ↑
19. Higgins, M.E., and J.J. Cassano. 2009. Impacts of reduced sea ice on winter Arctic atmospheric circulation, precipitation and temperature. Journal of Geophysical Research 114. ↑
20. Jorgenson, M.T., Y.L. Shur, and E.R. Pullman. 2006. Abrupt increase in permafrost degradation in Arctic Alaska. Geophysical Research Letters 25:L02503. ↑
21. Serreze, M.C., and J.C. Stroeve. 2008. Standing on the brink. Nature reports climate change 2. ↑
22. Holland, M.M., and C.M. Bitz. 2003. Polar amplification of climate change in coupled models. Climate Dynamics 21:221-232. ↑
23. Overland, J.E., and M. Wang. 2007. Future regional Arctic sea ice declines. Geophysical Research Letters 34:L17705. ↑