D Most researchers are now willing to accept that human activities have contributed to global warming, but no one can say with any assurance whether the Antarctic ice cap is growing or shrinking in response. A satellite being planned by the National Aeronautics and Space Administration will use laser range finders to map changes in the elevation of the polar ice caps, perhaps to within 10 millimetres, and should end the speculation. E Whatever the fate of the polar ice caps may be, most researchers agree that the sea level is currently rising. That, however, is difficult to prove. Tide gauges in ports around the world have been measuring sea levels for decades but the data are flawed because the land to which the gauges are attached can itself be moving up and down. In Stockholm the data from the sea level gauge show the sea level to be falling at four millimetres a year, but that is because all Scandinavia is still rebounding after being crushed by massive glaciers during the last ice age. By contrast, the gauge at Honolulu, which is more stable, shows the sea level to be rising at a rate of one and a half millimetres a year. Unstable regions cannot be omitted from the data because that would eliminate large areas of the world. Most of the eastern seaboard of North America is still settling after a great ice sheet which covered Eastern Canada 20,000 years ago tilted it up. And then there is buckling occurring at the edges of the great tectonic plates as they are pressed against each other. There is also land subsidence as oil and underground water is tapped. In Bangkok, for example, where the residents have been using groundwater, land subsidence makes it appear as if the sea has risen by almost a metre in the past 30 years. F Using complex calculations on the sea level gauge data, Peltier and Tushingham found that the global sea level has been rising at a rate of 2mm a year over the past few decades. Confirmation came from the TOPEX satellite which used radar altimeters to calculate changes in ocean levels. Steven Nerem, working on the TOPEX data, found an average annual sea level rise of 2mm which is completely compatible with the estimates that have come from 50 years of tide gauge records. The key question still facing researchers is whether this trend will hold steady or begin to accelerate in response to a warming climate. The Intergovernmental Panel on Climate Change gives the broad prediction for the next century of a rise between 200mm and 1 metre.
9
Questions 33 - 40
Complete each sentence with the correct ending A-L from the box below.
Write the correct letter A-L in boxes 33-40 on your answer sheet.
33 34 35 36 37 38 39 40 The Dutch dykes were broken Without ice shelves, West Antarctic ice covers would contract Mercer predicted a 5-metre sea-level rise SeaRISE believed the collapse of Antarctic ice had begun Mosley-Thompson doubted the SeaRlSE theory Doubts over Antarctica's trends will soon be settled Stockholm's tide gauge shows a fall in sea level At Bangkok the sea appears to have risen one metre in 30 years A B C D E F G H I J K L because the land mass is rising. because ice stream flows are variable and unpredictable. because Europe's alpine valley glaciers were shrinking. because of a combination of wind and high tide. because of geological evidence of an earlier rise. became satellites will take laser measurements. because the temperature had risen five degrees in 1978. because there were five active streams of ice. because they are inherently unstable. because use of groundwater has caused the land to sink. because warmer, wetter air would increase snowfall. because we cannot predict the rate of change. 10
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