The Ice Fields of Kilimanjaro

The ice fields on Mount Kilimanjaro in Tanzania are expected to melt within the next three to four decades, despite having existed for hundreds of thousands of years. Sea levels will rise by 21 feet if the Greenland ice cap were to melt, and a further 360 feet if Antarctica melted. Cities like New York, New Orleans and London will be among the first to go as sea levels rise.

Temperatures in the Antarctic Peninsula have risen 2.5 degrees over the last 50 years - five times the global average. Samples taken from Antarctic ice cores have shown carbon dioxide levels in the atmosphere during glacial periods were approximately 200 parts per million (ppm) and increased to about 270 ppm in warm periods. Now levels have reached 379 ppm and are increasing at a rate of 3 ppm a year. These levels are probably not much lower than they were during the Eocene Epoch 55 million years ago, one of the warmest episodes in Earth’s history, when there was little or no polar ice on the planet.

In 2002, the Larsen B ice shelf, which was 650 feet thick and had a surface area of 2,000 square miles, broke apart in less than a month. Researchers from the British Antarctic Survey had predicted that several ice shelves around the peninsula were doomed because of rising temperatures in the region, but were shocked by the speed with which the Larsen B broke up.

However, the break up of the ice mass itself is not expected to raise sea levels because the ice was already floating. Sea levels would only be affected if the land ice behind it began to flow more rapidly into the nearby Weddell Sea. Movement of continental glaciers into the sea had been held in check by the ice shelf.

New data has demonstrated that the collapse of the Larsen B ice shelf two years ago has in fact accelerated the flow of glaciers into the sea. Scientists using a variety of satellite data have tracked the speed of the glaciers before and after the collapse of Larsen B. Images taken by the Landsat 7 satellite between January 2000 and February 2003 reveal that four glaciers flowing into the now collapsed section of Larsen B increased in speed by between two and six times. Another study showed an eightfold increase in the speed of three glaciers between 2000 and 2003. Two other glaciers moved twice as quickly at the beginning of 2003 than they did in 2000, and nearly three times as fast by the end of the year.

How much the extra ice is raising the level of the oceans isn’t known. In other places around Antarctica, much larger glaciers are still held in check by existing ice shelves. Further warming could lead to much larger quantities of ice falling into the sea. But the picture generally in Antarctica is complicated, with temperatures in the interior actually falling over the same 50-year period. There is also some evidence that the retreat of the West Antarctic ice sheet, on the other side of the peninsula to the Larsen B shelf, has halted.

The world has barely begun to recognize the danger of setting off rapid and irreversible changes in some crucial natural systems. If these critical regions, which act like massive regulators of the Earth’s environment, are subjected to stress, they could trigger large-scale, rapid changes across the entire planet and have dramatic consequences for humans and other life forms. But not enough is known about them to be able to predict when the limits of tolerance are reached. Examples of crucial natural systems are the West Antarctic ice sheet, the Sahara desert, the forests of the Amazon basin, the Asian monsoon system and the Gulf Stream current in the North Atlantic, the ocean circulation pattern responsible for bringing warmer air to northern Europe, the collapse of which could lead to a very large regional climate shift.