Loss of Arctic sea ice must spur action

In 1845, Captain Sir John Franklin of the British Royal Navy led 128 men on two steam ships into the Arctic, where they eventually disappeared. The voyage was the culmination of four centuries of failed attempts to navigate the Northwest Passage and remains one of the greatest tragedies of polar exploration.

Today, a far greater Arctic tragedy is unfolding: the Arctic sea-ice cap is melting. Last month, an unprecedented new low was reached after decades of decline. The ice cap's area is now probably smaller than it has been for at least 1,500 years.

Walt Meier of the US National Snow and Ice Data Centre describes today's ice cap as "crushed ice". And it is getting thinner. In the past three decades, its volume has shrunk by roughly three-quarters.

In addition to the sea-ice loss, satellite data shows that Greenland's continental ice sheet is also melting at a record rate. This ice loss, caused largely by human-induced global warming, has far-reaching environmental, geopolitical and economic consequences.

For starters, Greenland's meltwater is flowing into the ocean, raising global sea levels. As temperatures have increased, the sea level's rise has accelerated from 1cm per decade in the early 20th century to more than 3cm in each of the past two decades - an overall increase of nearly 20cm since 1900. While the numbers may seem small, the rise significantly increases the likelihood of severe flooding along vulnerable coasts worldwide.

Greenland's meltwater accounts for one-fifth of the global sea-level rise over the past decade. If its ice sheet melted completely, sea levels would rise by seven metres - meaning we cannot afford to lose even a small fraction of the ice sheet. Meanwhile, satellite data shows that Antarctica's ice sheet, which is 10 times larger than Greenland's, is losing ice as well.