Hundreds of Antarctic Peninsula Glaciers Accelerating as Climate Warms; UN Issues Global Ice and Snow Report

6 June 2007

Rates of surface-elevation change in Antarctica based on radar-altimeter data (black), mass-budget calculations (red), and satellite gravity measurements (blue). Rectangles depict the time periods of observations (horizontal) and the upper and lower estimates of mass balance (vertical).Click to enlarge. Source: UNEP Global Outlook for Ice and Snow

Hundreds of glaciers on the Antarctic Peninsula (AP) are flowing faster, further adding to sea level rise according to new research published this week in the Journal of Geophysical Research. Climate warming, which is already causing increased summer snow melt and ice shelf retreat of the Antarctic Peninsula, is the most likely cause.

Using radar images acquired by European ERS-1 and -2 satellites, scientists from British Antarctic Survey (BAS) tracked the flow rate of more than 300 previously unstudied glaciers. They found a 12% increase in glacier speed from 1993 to 2003. These observations, echoing recent findings from coastal Greenland, indicate that the cause is the melting of the lower glaciers, which flow directly into the sea.

As the lower glaciers thin, the buoyancy of the ice can lift the glaciers off their rock beds, allowing them to slide faster.

We attribute this widespread acceleration trend not to meltwater-enhanced lubrication or increased snowfall but to a dynamic response to frontal thinning. We estimate that as a result, the annual sea level contribution from this region has increased by 0.047 ± 0.011 mm between 1993 and 2003. This contribution, together with previous studies that assessed increased runoff from the area and acceleration of glaciers resulting from the removal of ice shelves, implies a combined AP contribution of 0.16 ± 0.06 mm yr^-1. This is comparable to the contribution from Alaskan glaciers, and combined with estimated mass loss from West Antarctica, is probably large enough to outweigh mass gains in East Antarctica and to make the total Antarctic sea level contribution positive.

In February this year, the United Nations Intergovernmental Panel on Climate Change (IPCC) reported that they could not provide an upper limit on the rate of sea-level rise from Antarctica in coming centuries because of a lack of understanding of the behaviour of the large ice sheets.

These new results give scientists a clearer picture about the way that climate warming can affect glaciers both in the Arctic and Antarctic. Furthermore, they pave the way for more reliable projections of future sea level rise, and provide a better basis for policy decisions.

The Antarctic Peninsula has experienced some of the fastest warming on Earth, nearly 3°C over the last half-century. Eighty-seven percent of its glaciers have been retreating during this period and now we see these glaciers are also speeding up. It’s important that we use tools such as satellite technology that allow us to monitor changes in remote and inaccessible glaciers on a regional scale. Understanding what’s happening now gives us our best chance of predicting what’s likely to happen in the future.

—Dr Hamish Pritchard, Lead Author

Separately, the UN Environment Program released a comprehensive new report—The Global Outlook for Ice and Snow—showing that the amount of ice and snow, especially in the Northern Hemisphere, has decreased substantially over the last few decades, mainly due to human-made global warming.

The declines in snow cover, sea ice, glaciers, permafrost and lake ice will affect hundreds of millions of people, according to the report, with impacts including significant changes in the availability of water supplies for drinking and agriculture, rising sea levels affecting low lying coasts and islands and an increase in hazards such as subsidence of currently frozen land.

The report covers all parts of the cryosphere (the world of ice): snow, land ice, sea ice, river and lake ice, and frozen ground. More than 70 scientists from around the world contributed to The Global Outlook for Ice and Snow, which was compiled in part to support the International Polar Year (IPY) running from 2007 to 2008.

The peer-reviewed report builds on and in some areas extends the work of the Intergovernmental Panel on Climate Change (IPCC) whose fourth assessment reports were issued between February and May this year.

The report also flags up areas in need of further scientific clarity which the IPY, a major international science initiative of the World Meteorological Organization and the International Council for Science of which UNEP is a partner, aims to resolve.

These include the likely fate of the Antarctica and Greenland ice sheets where 98 to 99% of the world’s freshwater ice on the Earth’s surface is held.  Even just a 20% melting of Greenland and a 5% melting of Antarctica would result in a four to five meter sea level rise.

Resources:

• “Widespread acceleration of tidewater glaciers on the Antarctic Peninsula” H. D. Pritchard and D. G. Vaughan; Journal of Geophysical Research, Vol. 112, F03S29, doi:10.1029/2006JF000597, 2007

• The Global Outlook for Ice and Snow