Sea ice melted this year to a record low because of global warming, prompting fears the entire polar ice cap may disappear within decades. Satellite images show
that the northern area of ocean covered by ice this month was the lowest ever seen.
For four summers in a row the area covered by sea ice in the Arctic has shrunk below even the long-term decline, which began in th late 1970s. A gradual loss of
sea ice has been happening for 25 years but scientists say it is accelerating because of climate change and "positive feedback" causing a vicious cycle of melting and warming.
The latest figures came yesterday from Nasa and Colorado University, which described the loss of September ice as a "stunning reduction". Sea ice coverage this
month fell about 20 per cent below the long-term average.
For the past four years loss of summer sea ice in the Arctic has been equivalent
to 500,000 square miles - about twice the size of Texas or Iraq. Since the 1990s melt and retreat trends have accelerated. The only common thing is that Arctic temperatures over ice, ocean and surrounding land have increased in recent decades.
Four years in a row with such low ice extents has never been seen before in the
satellite record. The loss of Arctic sea ice is likely to make global warming worse because more ocean is exposed to the warming effects of the sun.
Something called a positive feedback loop happens when warming begins a chain of
events that causes further warming. The Arctic is very susceptible to this. Sea
ice is white and reflects a lot of the sun's energy back into space. Dark, open
ocean absorbs a lot more energy. A warming Arctic leads the planet to absorb more energy. That, in turn, could cause global average temperatures to rise still
more.
Average surface temperatures in the Arctic this summer were between 2C and 3C warmer than average across the Arctic Ocean. Something has fundamentally changed.
The start of the melting period in spring occurs earlier than average. Ice that has remained stable for many years - so called multiyear ice -has begun to melt.