It's getting warm at the poles!
The trend towards Arctic warming is generalised, and in some regions the temperature has risen by more than 3°C over the past 50 years. This is more than ten times faster than the rest of the planet, where the average increase was only 0.6°C over the past century.
At the other end of the world, and although warming at present only affects the Antarctic peninsula, the phenomenon, although it has recently slowing, is just as marked: 4-5°C in the past 50 years…
Early trends in the south…
Because of the effect of temperature on the distribution of living organisms in these extreme environments, such changes are not without consequences.
"On the Antarctic peninsula, only two flowering plants were seen on exceptional occasions in the past," points out Pete Convey, from the BAS (British Antarctic Survey). "But over the past thirty years, antarctic grass and pearlwort have been developing in the south, as are several species of moss. All are benefiting from a lengthening in the periods of thaw."
Other effects are seen in the marine environment, following a regional trend towards a halt to the spread of pack ice. This ice is necessary to ensure the winter development of juvenile krill (a small crustacean which looks like a shrimp and upon which an impressive range of predators are dependent) and there has been a reduction in the frequency of successful breeding years. Their predators are also suffering: Wayne Trivelpiece from the NOAA (the US National Oceanic and Atmospheric Administration) has thus seen the disappearance of the chinstrap penguin from the multi-species colony he has been studying for nearly 30 years near to the Polish Arctowski research station: "It is probably the reduction in krill fecundity which is the reason for the decline of Adélie and chinstrap penguins on the Antarctic peninsula." The same effects have been seen in South Georgia, where Keith Reid & John Croxall from the BAS have shown that the growing competition for krill between sea lions and Macaroni penguins has led to a marked decline in the latter.
… and much disquiet in the north
As made clear a few months ago by the ACIA (Arctic Climate Impact Assessment) report in Reykjavik, the effects of global warming on fauna and flora are even more pronounced in the Arctic. Terry Callaghan, from the Abisko Scientific Research Centre in Sweden, explains: "On land, amongst other phenomena, warming has caused a gradual melting of the permafrost (permanently frozen ground), with the disappearance of hundreds of pools and lakes (because they have drained into the thawed soil) and the flora and fauna which inhabit them. We have also seen a gradual spread of forest coverage to the north, to the detriment of the tundra, where millions of migrating birds have their breeding grounds."
"Because the forests are darker, the albedo (percentage of reflected solar radiation) of these areas has fallen and thus created a positive retroaction which enhances warming," adds Glenn Patrick Juday, from the University of Alaska. "At the same time, we are seeing an increase in the number of fires and massive swarms of insect pests in several regions around the Arctic landmass."
The situation is no better in the Arctic Ocean: the average surface area of pack ice (measured at the end of each summer) has shrunk in 30 years by practically a million square kilometres (around 15 to 20%). This gradual shrinkage is causing increasing problems for the species associated with sea ice, whether these are single-cell algae, the copepod crustaceans which graze on them, the fish which hide in them and so on, up the chain to that most emblematic animal of the North Pole, the polar bear.
Polar bears facing major problems
According to Andrew Derocher from the University of Alberta in Canada, and his colleagues, shrinkage of the pack ice has caused a reduction in the numbers of ringed seals as well as in their accessibility for polar bears, for whom they are the principal prey. This is of crucial importance for the female bears when it comes to building up fat reserves before fasting for several months in winter and giving birth to their young. Indeed, researchers have shown that in Hudson Bay, each week the spring thaw advances represents a 10 kg loss of weight for female bears by the time they enter the snow den where their young will be born. In addition, warming also increases the frequency of winter rains and the collapse of these dens.
Sadly, there are few prospects for an improvement in the Arctic pack ice, because climate models agree on a continuous rise in the average temperature over the 100 years to come: up to 7°C for the ocean and up to 10°C in winter. The ACIA report even suggests the possible disappearance of summer pack ice between now and 2100…
Dying of heat in the Antarctic
On the other hand, at the other end of the globe, the formidable mass of the Antarctic ice sheet may protect the Antarctic Ocean from global warming. But at a local level, and once again in the context of rising temperatures in the peninsula, a series of joint studies, headed in particular by Lloyd Peck from the BAS and Hans-Otto Pörtner from the Alfred Wegener Institute in Germany, recently put forward new reasons for concern. Their research on several marine invertebrate species has shown that the oxygen supply necessary for several vital functions, such as reproduction, is easily disturbed by a rise in water temperature. In fact, a 4°C rise would be sufficient to condemn several populations, or even some species with a limited distribution, to extinction.