WASHINGTON // Arctic sea ice has shrunk to its smallest surface area since record-keeping began, taking the world into "uncharted territory" as climate change intensifies, US scientists say.
Satellite images show the ice cap has melted to 3.4 million square kilometres as of September 16, the predicted lowest point for the year.
That's the smallest Arctic ice cover since record-keeping began in 1979, according to the National Snow and Ice Data Centre.
"We are now in uncharted territory," the centre's director, Mark Serreze, said. "While we've long known that as the planet warms up, changes would be seen first and be most pronounced in the Arctic, few of us were prepared for how rapidly the changes would actually occur."
Arctic sea ice expands and contracts seasonally, with the lowest extent usually occurring in September.
This year's minimum followed a season already full of records for shrinking ice, with the lowest ever extents recorded on August 26 and again on September 4.
And in the last two weeks, the ice cover melted by more than 200,000 square miles, a large margin for the end of the summer.
"The strong late season decline is indicative of how thin the ice cover is," said Walt Meier, a scientist at the centre. "Ice has to be quite thin to continue melting away as the sun goes down and fall approaches."
Scientists use Arctic sea ice extent as a gauge of the overall climate. Despite year-to-year fluctuations from natural weather variations, the ice cap has shown a clear trend towards shrinking over the past 30 years, according to the centre.
"This year's minimum will be nearly 50 per cent lower than the 1979 to 2000 average," it said.
The centre said the Arctic is shifting in composition. Whereas most of the ice previously stayed frozen through several summers, much of it now melts and refreezes each season.
"Twenty years from now in August, you might be able to take a ship right across the Arctic Ocean," said the scientist Julienne Stroeve.
Climate models predict "ice-free conditions" before 2050, she said, but added the decline appears to be happening faster than predicted.
The centre warned that increased heat and moisture from the melting Arctic ice cover could have global climate implications.
"This will gradually affect climate in the areas where we live," he said. "We have a less polar pole - and so there will be more variations and extremes."
