Magazine article Geographical

A Continent in Pieces: Temperatures Are Rising Rapidly in Parts of Antarctica, but the Overall Picture of the Way in Which the Frozen Continent and Its Inhabitants Are Responding to Climate Change Is Still Incomplete

Magazine article Geographical

A Continent in Pieces: Temperatures Are Rising Rapidly in Parts of Antarctica, but the Overall Picture of the Way in Which the Frozen Continent and Its Inhabitants Are Responding to Climate Change Is Still Incomplete

Article excerpt

The science is emphatic--parts of Antarctica are among the most rapidly warming regions on Earth. According to scientists at the British Antarctic Survey (BAS), air temperatures at some weather stations are 'rising at four to six times the global average rate'. On the Antarctic Peninsula, the air temperature has increased by as much as 3 [degrees]C in the past 50 years, while a recently compiled temperature record for Byrd Station in West Antarctica revealed a linear increase in annual temperature between 1958 and 2010 that amounted to a total rise of about 2.4 [degrees]C.

The impact of this temperature rise is being felt across the continent. On the small scale, it has led to an increase in the growth of moss and the activity of soil microbes on the Antarctic Peninsula. On a larger scale, it's causing the volume of ice in the Antarctic Ice Sheet to decline.

The ice sheet losses are mainly from the northern Antarctic Peninsula and the Amundsen Sea sector of West Antarctica--primarily from the acceleration of outlet glaciers. In all, the average rate of ice loss from Antarctica has increased five-fold in the two decades, from 30 gigatonnes a year between 1992 and 2001, to 147 gigatonnes a year between 2002 and 2011 (some estimates put the current rate as high as 250 gigatonnes a year).

Scientists are now highly confident that the Antarctic Ice Sheet is in a state of net mass loss and that its contribution to sea level is also likely to have increased in the past two decades.

FLORAL ENCROACHMENT

One of the more unusual pieces of evidence that the Antarctic is changing can be seen on the Antarctic Peninsula, where Professor Lloyd Peck, individual merit scientist at the BAS, and colleagues have documented plants growing where there was ice 25 years ago. And looking out to sea, the picture becomes even more stark. Along the Antarctic Peninsula alone, Peck and colleagues estimate that an area of more than 5,100 square kilometres that was covered by sea ice before the 1980s is now open water in summer. The US National Snow and Ice Data Centre (NSIDC) has also noted similar decreases in sea ice around the Bellingshausen/Amundsen sea.

Elsewhere on the continent, 87 per cent of the 244 marine glaciers have retreated over the past 50 years, Peck says. 'We know we can never convince the die-hard sceptic, and no one event can be directly attributed to climate change--but we can say we understand how the Southern Ocean works, we understand how the wind and weather patterns work, and the warming of the Antarctic Peninsula is entirely consistent with a global warming effect,' he says.

The Pine Island Glacier on the West Antarctic Ice Sheet is also being followed closely. The glacier has sped up 73 per cent since 1974 and thinned throughout 1995-2008, with the ice shelf at the glacier's end currently melting at a rate of about 80 cubic kilometres a year, 50 per cent faster than it was during the early 1990s.

The cause of the rapid melt is 'grounding line retreat'. The grounding line is the point where the bottom of the glacier comes into contact with the ground, and recent studies suggest that warm ocean water is eating away at the glacier at this point, making it more unstable. There's also evidence, from a study published a few years ago in Nature Geoscience, that an increase in the strength of ocean currents beneath the glacier is causing it to melt more rapidly.

The neighbouring Thwaites, Smith and Kohler glaciers are also speeding-up, thinning and contributing to increasing mass loss.

LIMITED DATA

And yet the picture across Antarctica isn't straightforward, and nor is it complete. 'It's pretty obvious, but Antarctica doesn't have the density of people you have in Europe, where people can walk down the street and see different butterflies that weren't there before,' says Peck. 'We just don't have the coverage to monitor species' range within the sea, so we don't have the data you can get in other parts of the planet. …

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