July 2009 • Issue 424

The Arctic climate

What happens in the far north affects the whole world. Here are some important ways in which the Arctic influences the global environment.

1   The albedo effect
‘Albedo’ is a scientific word for reflectivity. As this diagram shows (see right), the Arctic sea-ice, glaciers and ice sheets reflect a lot more of the sun’s heat than bare earth or ocean surface, and thus have a cooling effect on the planet.

2   Ocean currents
Temperature variants between different seas create ocean currents which affect temperatures and climate all over the world. Low Arctic temperatures, and the effect of ice on the temperature exchange between air and ocean, play a vital role in this complex process. Major changes in temperature or in water movement      (e.g. from the melting of the Greenland ice-sheet) could have serious knock-on effects around the world (see map below).

3   Sea-level rise
While the melting and freezing of floating ice does not directly affect global sea-levels, the melting of land-based ice – such as the Greenland ice-sheet which is over three kilometres thick in places – is a different matter. If Greenland thawed completely global sea-levels could rise by up to six metres.

4   Permafrost
The permafrost (frozen soil) that covers much of the Arctic contains large amounts of the greenhouse gases carbon dioxide and methane. As Arctic soils and waters grow warmer these gases are being released. If the permafrost were to thaw completely it would release twice the amount of greenhouse gases that humanity has already released into the atmosphere.

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Facing the future
The faster than expected sea-ice melt has already led to increased Arctic warming, thanks to its reduced reflectivity. This has forced climate scientists to reassess sharply their future predictions. The picture now looks even more stark: we can expect an Arctic summer free of sea-ice within the next 20 years no matter what we do, thanks to the long-term warming effect of greenhouse gases already in the atmosphere.

However, the disappearance of the Greenland ice sheet and the calamitous release of huge amounts of greenhouse gases from the permafrost are probably not yet inevitable – if we act fast to cut global emissions.

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The changing Arctic
The Arctic is one of the areas of the planet being hit first and hardest by climate change. Here are some of the major effects so far:

1   High temperatures
Arctic temperatures are on a jagged upward trend – 2007 was the warmest year on record. While 2008 wasn’t quite as hot, autumn temperatures were still a record 5˚C higher than usual.

2   Melting sea-ice
Arctic sea ice grows and shrinks each year with the changing seasons, reaching its minimum size around September each year. Worryingly, this minimum extent has been on a gradual downward trend for the past 30 years (see satellite images right). The speed of this thaw has shocked climate scientists: it is happening faster than the most extreme predictions made by the Intergovernmental Panel on Climate Change (IPCC).

3   The Greenland ice-sheet
Greenland’s ice has been shrinking much more rapidly that expected. Latest predictions are that this will result in a 1-1.5 metres sea-level rise by the end of the century (see image below).

Sources: Arctic Climate Impact Assessment, International Polar Year, NASA/Goddard Space Flight Center, Cooperative Institute for Research in Environmental Sciences (Colorado University).

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