ESA’s Cryosat satellite to measure Earth’s ice mass in 2004
Between 1978 and 1996, according to a study by the internationally respected Worldwatch Institute based on worldwide quantities, the Arctic ice, which covers an area about the size of the USA, has already shrunk by six percent. 34.000 square kilometers of ice – an area the size of North Rhine-Westphalia – changes its aggregate state every year and flows away. According to the latest scientific findings, the ice at the poles is melting faster than expected, so that a drastic rise in sea level is imminent worldwide. In mid-April 2004, the ESA satellite will reveal how much ice has actually already melted at the poles.
Pine Island Glacier
These are cold, stark numbers; but their implications are hard to foresee. Since 1993, ice on the southern and eastern edges of the Arctic has been receding at an average rate of one meter per year. The situation of the continuously shrinking glaciers in the Antarctic is downright catastrophic. After analyzing satellite data, Andrew Shepherd of the Climate Physics Group at University College London and his colleagues conclude that more than 30 cubic kilometers of ice melted and flowed into the sea between 1992 and 2000. The main reason for this, according to researchers, is the accelerated movement of the Pine Island Glacier, which makes up about ten percent of the Antarctic ice sheet. As a result, ten times as much water flows into the sea as is renewed inland by snowfall. If this trend continues, it will take another 600 years for the major part of the glacier to float. However, this has had dramatic effects on sea levels.
Fifty percent fewer glaciers in 100 years
Meanwhile, the first scientists fear that by 2050 almost a quarter, and by 2100 even half of the glacier mass on Earth could disappear. Rougher flats were left only in Alaska, Patagonia and the Himalayas. According to the experts, in the foreseeable future the climatic repercussions that favor the disappearance of the ice masses on Earth could be fatal. The more polar ice disappears, which reflects large amounts of solar energy and thus keeps the Earth cool, the more the ice will melt. This is precisely the trend that can be observed worldwide: While the Columbia Glacier in Alaska has shrunk by 13 kilometers since 1982, 100 of the 150 glaciers in the American Montana Glacier National Park have melted completely since 1850. The remaining 50 will disappear in the next 30 years.
The computer model created by the Australian scientist Bill Budd from the center of the Antarctic Research Network is also highly dramatic. According to this model, the atmosphere in Antarctica has warmed by 2.5 degrees Celsius over the past 50 years. And as a result of the increase in greenhouse gases, global warming will continue, which in turn will lead to the dissolution of almost all ice floes over the next five centuries.
The results of Robert Harris and David Chapman from the University of Utah are also alarming. In 1998, both researchers took on the Sisyphean task of digging 430 boreholes to measure the warming on the mainland of the Northern Hemisphere. They compared the data obtained with the weather records of the past 100 years. Their findings: The average temperature increase since then has been 1.1 degrees Celsius.
So far no long-term observations covering the whole area
The land ice of Gronland and the ice of the Antarctic continent, unlike sea ice, consists of glacial ice formed from fallen snow. This ice is up to four kilometers thick and in some cases several hundred thousand years old. It contains 95 percent of the world’s sub-water resources. In Antarctica alone (the following figures apply only to the South Pole) there are about 11.5 million cubic kilometers of ice. About 84 percent of the world’s glacial ice is found there. If Antarctica was completely thawed, this would result in a 72-meter rise in sea level.
Satellite image Victoria Land – Antarctica
In all this, so far there are only punctual, but no coherent, especially long-term direct observations of changes in ice masses. Although long-term observations can only be carried out with the help of satellites because of the enormous size of the Arctic and Antarctic, research probes have so far only been able to determine the extent of the ice, but not its thickness. In fact, data from U.S. weather satellites show that the extent of sea ice in the Arctic has decreased by about nine percent at the margins over the last thirty years. However, sea ice is only a one to four meter thick layer of frozen seawater covering the Arctic Ocean and the Sudocean around the Antarctic continent. Observations of the surface extent do not yet allow any conclusions about the volume. This requires thicknesses of sea ice. These have been carried out only very sporadically in the Arctic by U.S. Navy nuclear submarines. Although these spatially limited quantities also indicate a decrease in thickness since the 1950s, they do not allow any conclusions to be drawn about the development of the total ice masses. Although sea ice cover in Antarctica has actually increased slightly over the last thirty years, the reality is that ice melt is eating away at the volume of the floes. For the time being, it is not the area that is decreasing, but the volume. However, the total volume of ice around the globe is still completely unknown.
Cryosat to fill data gap
It is precisely this information gap that the European small satellite Cryosat, which was specially designed to observe the Earth’s entire ice supply, is expected to fill in three years from now. During a scientific workshop at the Alfred Wegener Institute for Polar and Marine Research (AWI) in Bremerhaven at the end of May this year, 25 German scientists from the universities of Dresden, Freiburg, Trier, Darmstadt, Munster, Munchen and representatives of the ESA discussed and coordinated the mission’s tasks.
The Cryosat radar altimeter mission was designed to provide a better estimate of the total sea and land ice masses. This is the first mission in ESA’s so-called Earth Opportunity Missions program, which aims to solve limited, purely scientific problems with relatively small and inexpensive satellites.
The Cryosat satellite is equipped with a new type of radar altimeter (SIRAL: Synthetic Aperture Interferometric Radar Altimeter), which aims to achieve a measurement accuracy of one to three centimeters for the thickness of the sea ice and the height of the land ice masses. Radar altimeters can be used to determine the height of the Earth’s surface. Radar waves are transmitted to the earth and the time of flight is measured until they are reflected back to the satellite. In addition, this altimeter can accurately measure the steeply inclined edges of the ice sheets, which have so far been difficult to measure from satellites. The high spatial resolution of the satellite makes it possible to distinguish even individual ice floes.
When Cryosat is launched, probably in April 2004, observations of ice thickness increase or decrease will be available for the three to six years of the mission. Cryosat is built by Astrium GmbH in Friedrichshafen on Lake Constance. German scientists were significantly involved in the planning, conception and implementation of the mission. The total budget of the mission amounts to 100 million euros. Separate polar expeditions will follow in order to regularly compare the Cryosat data with measurement data from the polar regions and to control their accuracy. Due to the logistical capabilities of the Alfred Wegener Institute with land stations, research aircraft and the icebreaker Polarstern, German groups will ame important functions within the overall mission.