[ccebook.cn]The World in 2010

Science
On thin ice
Nov 13th 2009
An imminent answer to an Arctic riddle
For the past three years, the vast cap of shining-white ice covering the Arctic has melted away in summer to
an area that would have been unbelievable just a decade ago. At the end of the winter, the frozen seas cover
15.7m square kilometres (6.1m square miles), an area more than one and a half times that of the United
States. By September the ice regularly used to melt to 7m square kilometres. But since a great collapse in
2007 the figure has been closer to 4.3m square kilometres. Every summer an extra area of ice six times the
size of California has been disappearing. As well as this reduction in area, scientists believe that, hidden
beneath the surface, the ice is growing ever thinner, setting up the Arctic for another sudden, catastrophic
collapse. The big question now is when the ice will disappear totally each summer. There will be an answer in
2010.
Another year of observations, better computer models and—the Holy Grail of ice scientists—maps of the
thickness of the ice from a new European satellite called -Cryosat-2 should reveal in 2010 how long the Arctic
ice has left. Estimates range from 2013—terrifyingly soon—to 2050 for the first year when the Arctic is free of
ice in summer.
When that happens, it will be the biggest and fastest change to the Earth’s surface ever made by human
influence. The ice, poised between freezing and melting, is an especially sensitive indicator of the planet’s
temperature. When it disappears, it will be a disaster for all the Arctic life that depends on ice, from the polar
bears that walk on it to the tiny creatures that live within it.
And it will be a disaster for the planet. That great dome of ice reflects sunlight back into space throughout the
24 hours a day of polar summer sunshine. When it turns sea-dark and soaks up the sun, global warming will
really take off.
Alun Anderson: former editor-in-chief of New Scientist; author of “After the Ice” (Harper-Smithsonian/Virgin Books)