European and US researchers who claim they’ve found a better way of measuring the melting ice cap say they’re quite sure that Greenland’s melting ice cap makes sea levels rise by half a millimeter annually.
Greenland lost an average of 195 cubic kilometers of ice per year between 2003 and 2008, the researchers say in an article published recently in the scientific journal Geophysical Research Letters. That is enough to cause an annual increase in the global sea level of half a millimetre, or 5 cm over the course of the next century.
The researchers who wrote the report are Dutch scientists from TU in Delft, who joined forces with the Center for Space Research (CSR) in Austin, Texas to develop the method for creating an accurate picture of Greenland’s shrinking ice cap. They used data from two satellites that have been orbiting the earth behind each other since mid-2002. To give you an idea of how accurate this technology is likely to be; deviations in the earth’s gravitational field cause fluctuations in the distance between the satellites, which is measured to a precision of a millionth of a meter.
As gravity is directly related to mass, the satellite information can be used to plot changes in the earth’s water balance, such as the disappearance of the ice caps. Satellite data of this kind are ideal for measuring areas such as Greenland, where the extreme conditions make local measurements very difficult. With this in mind, researchers from TU Delft and the CSR devised a method that would create a more accurate picture of the changes taking place in Greenland than had previously been possible.
Not only does the method enable scientists to plot water mass, it gives a precise idea of the loss of mass per region, thereby providing new insight into the patterns of ice loss. For example, for the first time since measurements were started, the extremely warm summer of 2007 saw a decrease in the ice mass at high altitudes (above 2,000 metres).
It also became clear that the ice loss is advancing towards the North of Greenland, particularly on the west coast. The areas around Greenland, particularly Iceland, Spitsbergen and the northern islands of Canada, seem to be particularly affected. A follow-up study will focus on the influence of these smaller glaciers on the sea level.
Another recent report which appeared in Science concluded that it’s pretty difficult to come up with a concrete number. How quickly the ice sheets are going to dynamically drain is termed the unknown of the unknown, but this report ruled out a rise of over 2 meters due to Greenland’s melting ice caps in the next century. Yet the researchers could not rule out that up to two meters in total was going to be likely. The researchers projected that anything is possible, from 80 centimeters to 2 meters.
A report recently published by the Dutch Delta commission estimated that the Dutch need to prepare for a melting ice cap in Greenland causing sea level rises of 13 to 22 cm by 2100. But these two figures do not necessarily contradict each other because whereas the first two years of the study showed a loss of 131 cubic kilometers of ice per year, during the last two years this figure had risen to 222 cubic kilometers per year, an increase of 70 percent. This sharp increase was mainly caused by the extremely warm summer of 2007, when more than 350 cubic meters of ice melted in just two months.
However, it is not yet clear whether the ice will continue to melt at this rate during the next few years, as ice loss varies greatly from summer to summer. Long-term observations are needed to compile a reliable estimate of Greenland’s contribution to the rising sea level during the next century.
By comparison, the IPCC estimates that the global average sea level will rise between 0.6 and 2 feet (0.18 to 0.59 meters) in the next century.