Experts have warned of a “planetary emergency” due to the unforeseen global consequences of Arctic ice melt, including methane gas released from permafrost regions currently under ice.

Columbia University and the environmental activist group Greenpeace held separate events to discuss US Government data showing that the Arctic sea ice has shrunk to its smallest surface area since record-keeping began in 1979.

Satellite images show the Arctic ice cap melted to 3.4 million square kilometres as of September 16, the predicted lowest point for the year, according to data from the National Snow and Ice Data Center in Boulder, Colorado.

“Between 1979 and 2012, we have a decline of 13 per cent per decade in the sea ice, accelerating from six per cent between 1979 and 2000,” said oceanographer Wieslaw Maslowski with the US Naval Postgraduate School, speaking at a Greenpeace event.

“If this trend continues, we will not have sea ice by the end of this decade,” said Maslowski.

While these figures are worse than the early estimates, they come as no surprise to scientists, said Nasa climate expert James Hansen, who also spoke at the Greenpeace event.

“We are in a planetary emergency,” said Hansen, decrying “the gap between what is understood by scientific community and what is known by the public”.

Scientists say the earth’s climate has been warming because carbon dioxide and other human-produced gases hinder the planet’s reflection of the sun’s heat back into space, creating a greenhouse effect.

Environmentalists warn that a string of recent extreme weather events around the globe, including deadly typhoons, devastating floods and severe droughts, show urgent action on emission cuts is needed.

The extreme weather include the drought and heatwaves that struck the US in summer. One consequence of the melt is the slow but continuous rise in the ocean level that threatens coastal areas.

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