New tool to monitor climate change

by Michael Richardson

Some of the most dramatic signs of climate change are taking place in the vast and frigid polar caps, where relatively few humans live. We would know much less about them than we do but for recent advances in satellite technology and remote sensing.

A European Space Agency satellite scheduled for launch April 8 promises to add to the growing body of scientific knowledge, based on observable facts, about the way in which rising surface temperatures are interacting with ice and ocean in the north and south polar regions, raising sea levels around the world.

The ESA satellite is due to be carried into polar orbit about 700 km above Earth on a rocket from the Baikonur Cosmodrome in Kazakhstan. It will carry an advanced all-weather microwave radar altimeter. This sensor is specially configured to measure changes in the elevation, and thus the thickness, of ice on land and floating on the sea.

The vast majority of ice on land is stored in the ice sheets of Antarctica (88 percent) and Greenland (11 percent). The total is enough to raise the average global sea level by nearly 65 meters.

If all goes well, the CryoSat (the name comes from the Greek kryos, meaning icy cold) will beam back information for at least the next three years that should enable scientists to predict more accurately how much sea levels will rise this century and beyond — information that will be vital in preparing densely populated low-lying parts of Japan and other Asian nations for any potential disruptions to come.

The ESA spacecraft is capable of detecting changes of as little as one centimeter per year in the thickness of the polar ice sheets and sea ice.

At the same time as final preparations are being made to put the ESA satellite into space, a team of Americans is in Greenland carrying out the most extensive airborne survey of polar ice ever flown.

Using a long-range jet packed with sensors and later a smaller, more maneuverable aircraft, the team from the National Aeronautics and Space Administration (NASA), the U.S. space agency, has at its first priority to survey Arctic sea ice, which reaches its maximum extent each year in March or April. In recent years, it has shown a pronounced shrinking and thinning trend.

High- and low-altitude flights by NASA will also survey Greenland’s ice sheet and outlet glaciers over the next few weeks. In addition, they will carry out some new observations not currently possible from satellites, including use of radar to peer below the surface to “see” snow, ice and bedrock characteristics at different depths to help understand ice sheet behavior and the way in which glaciers, huge but slow-moving rivers of ice, flow from the interior of ice sheets to the sea.

Both aircraft will carry laser altimeters similar to those on a NASA satellite that ceased to function last year. The altimeter measures changes in the surface elevation of the ice by reflecting light pulses from the ground back to the aircraft and converting the readings into elevation maps. Another laser altimeter operates at higher altitudes and can survey large areas quickly.

The NASA mission started in 2009 and will continue until 2015. It covers both the Arctic and Antarctic zones. Since the aircraft follow repeat routes in their annual surveys, the surface topography maps of the latest year can be compared to previous years to show changes in the extent and thickness of polar ice.

The last major report in 2007 by the international panel of scientists and officials advising the United Nations on climate change projected that the rise in sea level by 2099 could be in the range of 18 to 59 cm. However, the panel cautioned that this estimate should not be considered a maximum and did not include the full effects of changes in the rate of ice-sheet melting in Antarctica and Greenland.

Since late 2005, the cut-off date for research assessed by the panel, further studies of ice sheet accumulation and loss have been made using not only satellite altimetry but also gravity measurements from spacecraft (available since 2003) and estimates of the difference between net snowfall and discharge of ice into the sea.

These confirm that both Greenland and Antarctica are losing ice mass and contributing to the rise of sea levels — Greenland at a rate of 120 billion tons per year and Antarctica 100 billion tons per year. This is enough to raise the sea level by around 60 ml annually, or 3 cm in five years.

With the overall rate of discharge from ice sheet outlet glaciers into the sea accelerating, the latest assessment of scientists at the Australian government’s Antarctic Division is that the rise in sea level by the end of this century will probably be less than 2 meters but may be as much as 80 cm.

The polar regions are a key source of information about our planet. Yet even today they are sparsely sampled.

They need to be monitored in much greater detail to detect new developments, improve understanding of the processes at work, and distinguish between climate change caused by natural variability and that caused by human influence.

Michael Richardson is a visiting senior research fellow at the Institute of South East Asian Studies in Singapore.