Will the North pole be ice-free in Summer?
Scientists are investigating how the Arctic sea ice is affected by climate change. The North Pole lies under a thick sea ice cover. A feature, today still regulated by the laws of nature, but which some day could be utterly obsolete, since sea ice in the Arctic is also melting due to global warming. How fast this is happening, and what the consequences of the melting will be for our weather, is being studied by the oceanographer Prof. Rüdiger Gerdes, head of the Sea ice physics section at the Alfred Wegener Institute.
What is the sea ice extent in the Arctic today, and how thick is it?
During winter, sea ice covers the entire Arctic and parts of the North Pacific and the Nordic Seas. In total it comprises 12 to 14 million square kilometres - roughly 40 times the size of Germany. In summer the ice cover retreats naturally and the North Pacific and parts of the Arctic Ocean become ice-free. The ice then covers an area between four and a half and 7 million square kilometres. The sea ice thickness varies. North of Greenland and Canada, the ice can be more than five meters thick. Towards the central North Polar Sea and Siberia, it becomes thinner and is only about a meter or two thick.
How has the situation developed in recent decades? Has the extent of Arctic sea ice already decreased?
Since 1978, we have continuously recorded the sea ice extent, using satellites. These measurements show a pronounced negative trend. In figures: the Arctic ice cover during September decreased by an average of eleven percent per decade. However, the ice is not shrinking uniformly or continuously, and the cover can vary significantly from year to year. In summer 1996, the ice cover reached a record high for the whole period covered by satellite measurements. The lowest extent ever was recorded in summer 2007. It is noteworthy that the summer ice extent did not recover very much in 2008 and 2009. The long-term trend is clear: The ice cover in the Arctic is definitely declining.
The future climate is likely to be even warmer. How will global warming affect the Arctic sea ice? Will the North Pole at some point in summer be ice-free?
The warming will lead to a further decrease in ice extent and thickness. This trend will be reinforced by feedback processes: the more the ice retreats, the more ocean is exposed. And since the ocean absorbs solar energy more efficiently than sea ice, it will warm up. This heating then leads to an even more rapid retreat of the Arctic sea ice. At which point in time we can expect an ice-free Arctic during summer, is currently still difficult to predict. Climate models do not give us a clear answer on this. Some indicate that the North Pole will be ice-free by the year 2080, or even later. Other models suggest that this could be as early as 2040. But there are also voices which see an even earlier ice free Arctic- within the next few years. But this is not necessarily credible.
What consequences could a loss of Arctic sea ice have for the animal and plant life there?
Many consequences. In summer, more light penetrates the ocean so that more energy is available for the phytoplankton, which will grow more. This is important for the consumers in the food web and thus for higher organisms like fish that feed directly or indirectly on the plankton. On the other hand, species that live on the underside of the sea ice and which rely on it year-round are likely to be severely affected. These are small crustaceans such as copepods and krill. They have a key position in the food web because they eat algae and are then eaten themselves by fish, birds or seals. While plankton growth may increase, krill stocks might decline - which causes shifts in the entire ecosystem. Moreover, with the increased inflow of relatively warm and saline Atlantic water masses, a new community of species is carried into the Arctic Ocean, and these could prevail in some regions
When the sea ice in the Arctic melts, will it have an effect on the sea level?
Not directly. In fact, since sea ice floats it displaces as much water as it weighs. When this ice melts, the sea level doesn’t change. However, there might be an indirect effect - not on global sea level, but on its regional distribution. For where the ice melts, changes in ocean currents may occur and consequently affect the regional distribution of the water level. But, exactly how the ocean currents will change with a decreasing sea ice cover, is not easy to predict. Should there, however, be a real impact on the large scale circulation in the Atlantic, which includes the Gulf Stream, this could indeed lead to a significant rise in sea level along the coasts of North America and Europe.
Could the melting Arctic sea ice also influence our weather?
Possibly, for as long as the ocean is covered with ice, it is well insulated and won’t release much heat into the atmosphere during winter. But once the ice disappears, the water will lose heat to the atmosphere. This appears to affect the air pressure patterns. In the past few years, we have observed that the air pressure patterns are gradually shifting. Formerly the so-called North Atlantic Oscillation was the dominant pattern - an area of high pressure over the Azores and a low-pressure area over Iceland. This Iceland low brings warm and moist air to central Europe. In recent years, however, this area of low pressure has moved further east into the Siberian region. Thus large parts of Europe are increasingly subjected to cold and dry northerly winds. And that means: In the future, the winters could be drier and colder.