lightblueline

The Arctic Sea ice

The floating sea ice of the Arctic covers an area equal to that of the United States. The permanent presence of sea ice, ice sheets, and continuous permafrost are unique features of the Polar Regions. Even though it is characterized by its harsh environment and vast landscapes the Arctic serves as the home of many forms of life, including organisms living in the ice, fish and marine mammals living in the sea, birds, land animals such as polar bears, and human societies. But much more than that, its white ice cover reflects huge amounts of sunlight and thereby helps the world stay cool.
Scientists differentiate between two types of ice, which cover the ocean surface in the Arctic Region: seasonal ice that melts during summer time and the perpetual ice. The perpetual ice typically is about 10 feet thick and quite resilient towards the melting during summer time. In previous times the overall Arctic sea ice extent, or the area that is covered by at least 15 percent ice, reached its minimum by the end of the summer melt season in September. But what melted during the summer time usually grew back when the temperatures dropped in the winter. And by March the sea ice cover was at or near its maximum again. In recent years however, the Arctic sea ice has undergone dramatic changes. Satellites reveal that the significantly rising average air temperatures have caused severe declines in the ice cover thickness and extent.1

Fig. 1: Arctic-wide and annual averaged surface air temperature anomalies (60◦– 90◦N) over land for the 20th century based on the CRU TEM2V monthly data set.1

According to the latest “State of the Arctic”-report the polar ice cap has shrunk by 15-20 percent over the last 30 years and at an average rate of 9 percent per decade. But much worse than this, the downward trend seems to have accelerated dramatically within the last few years, with an increased rate of now about 14 percent per decade, excluding the possibility of just a short-term anomaly.
For the fourth consecutive year the satellite observations have revealed a quite alarming reduction of the Arctic sea ice extent. And in 2005 almost each month showed a record breaking minimum sea ice extent compared to the period of 1979-2005, with the lowest extent ever observed since the beginning of the satellite observations.1

Fig. 2: Sea ice extent in March (left) and September (right) 2005, when the ice cover was at or near its maximum and minimum extent, respectively. The magenta line indicates the median maximum and minimum extent of the ice cover for 1979–2000. In both cases, the ice extent reached a record minimum in 2005 for the period 1979–2005.1

Fig. 3: Time series of the difference in ice extent in March (maximum) and September (minimum) from the mean values for 1979–2005. Based on a least-squares linear regression, the rates of decrease in March and September were 2% per decade and 7% per decade, respectively. Recent data from March 2006 are also shown and represent a new record minimum for the period of observation. 1

Fig. 4: Daily ice extent in the summers of 2002-2005.4

Recent data from 2006 indicate a further reduction in the sea ice cover and furthermore revealed that the sea ice hasn’t recovered during winter time, leaving the Polar Region ice free for the second time in a row.
Despite that there is still some uncertainty about to which extent periodic changes in Arctic wind patterns as part of a natural variability (Arctic Oscillation) could have contributed to the ice cover changes, there is a clear consensus among the scientific community that with the build up of greenhouse gases this trend is set to accelerate in the near future.2
Latest studies even suggest that, if the greenhouse gases were left unrestricted, a tipping point may soon to be passed, with forecasts of possibly ice-free Arctic summers in as little as three decades.3

Fig. 5: a) Northern Hemisphere sea ice extent in September from one integration of the Community Climate System Model version 3 (CCSM3) with observations from the satellite era shown in red. The light blue line is a 5-yr running mean. The three lower panels show the September ice concentration (ice floes are separated by open water) in three select decades. 3

The changes in the Arctic that are now being observed are surprisingly rapid and draw a most likely very grim picture of the future.
Even though the melting sea ice cover won’t contribute directly to the sea-level rise it has dramatic adverse effects on the global environment. As the ice melts, people will soon not only be able to reach the North Pole in a sailing boat, but the Earth will loose the unique air-conditioning capacity of its Arctic sea ice cover. The dark sea that replaces the former white ice cover will absorb the sun’s heat instead of reflecting it. And as the Arctic Ocean warms positive feedback loops lead to a further ice retreat, resulting in a thinner and less extensive ice cover in the Arctic (Fig. 5) that contributes to major physical, ecological, social and economic changes, many of which have already begun. The whole complex interconnected network of arctic life and its environment are changing dramatically and in many ways never thought to be possible.
Whether it is the now endangered population of polar bears or the changing circumstances of the indigenous Arctic people, the changes we are seeing now in the Arctic are no longer a possible scenario of what might happen in future decades. These changes are already very real and happening right now! But the local environmental changes we are seeing now in the Arctic could only be forerunners of far worse changes on a global scale. Climate processes unique to the Arctic Region are highly interconnected with the global climate system. The Arctic will not just feel the impacts of a warmer environment, it will also cause a cascade of other global environmental changes. While changes in the reflectivity of the land and the ocean surface could amplify the global warming, some scientists worry that the melting Arctic sea ice could dump enough fresh water into the North Atlantic to slow down the great conveyor belt. Both scenarios are very likely to happen in the near future, if the current melting rates continue.1
As the Arctic goes, so most scientists say, so goes the planet.

References:

1 RICHTER-MENGE, J., J. OVERLAND, A. PROSHUTINSKY, V. ROMANOVSKY, L. BENGTSSON, L. BRIGHAM, M. DYURGEROV, J.C. GASCARD, S. GERLAND, R. GRAVERSEN, C. HAAS, M. KARCHER, P. KUHRY, J. MASLANIK, H. MELLING, W. MASLOWSKI, J. MORISON, D. PEROVICH, R. PRZYBYLAK, V. RACHOLD, I. RIGOR, A. SHIKLOMANOV, J. STROEVE, D. WALKER, AND J. WALSH (2006): State of the Arctic Report. NOAA.
Source: www.arctic.noaa.gov/soa2006/

2 JOHANNESSEN, O. M., E. V. SHALINE AND M. W. MILES (1999): Satellite
evidence for an Arctic sea ice cover in transformation, Science, 286,
1937– 1939.

3 HOLLAND, M. M., C. BITZ, AND B. TREMBLAY (2006): Future abrupt reductions in the summer Arctic sea ice In: Geophysical Research Letters, Vol. 33, doi:10.1029/2006GL028024.

4 RENFROW, S. AND J. SCOTT (2005): Sea Ice Decline Intensifies.
Source: http://nsidc.org/news/press/20050928_trendscontinue.html