Fears tipping point is past

SCIENTISTS fear global warming has passed an ominous tipping point after Nasa satellite data showed the already relentless melting of the Arctic increased greatly during the northern hemisphere’s hot summer months.

One expert even speculated that summer sea ice would be gone in five years.

Greenland’s ice sheet melted nearly 19 billion tonnes more than the previous high mark, and the volume of Arctic sea ice at summer’s end was half what it was just four years earlier, according to the Nasa data.

“The Arctic is screaming,” said Mark Serreze, senior scientist at the US government’s snow and ice data centre in Colorado.

Just last year, two top scientists surprised their colleagues by projecting that the Arctic sea ice was melting so rapidly that it could disappear by the summer of 2040.

This week, after reviewing his own new data, Nasa climate scientist Jay Zwally said: “At this rate, the Arctic Ocean could be nearly ice-free at the end of summer by 2012, much faster than previous predictions.”

Scientists have been asking themselves if the record melt seen all over the Arctic this year was a blip amid relentless and steady warming, or had everything accelerated to a new climate cycle going beyond the worst-case scenarios presented by computer models.

“The Arctic is often cited as the canary in the coal mine for climate warming,” said Mr Zwally.

“Now as a sign of climate warming, the canary has died. It is time to start getting out of the coal mines.”

For the past several days, government diplomats in Bali have been debating the outlines of a new climate treaty calling for tougher limits on these gases.

What happens in the Arctic has implications for the rest of the world. Faster melting there means an eventual sea level rise and more immediate changes in winter weather because of less sea ice.

Scientists said they were surprised by the level of ice melt this year.

“I don’t pay much attention to one year... but this year the change is so big, particularly in the Arctic sea ice, that you’ve got to stop and say, ‘What is going on here?’ You can’t look away from what’s happening here,” said Waleed Abdalati, Nasa’s chief of cyrospheric sciences.

“This is going to be a watershed year.”

Previous patterns have suggested that 2007 should not have been a major melt year, according to Konrad Steffen of the University of Colorado, which gathered the latest data.

“I’m quite concerned,” he said. “Now I look at 2008. Will it be even warmer than the past year?”

Other new data, from a Nasa satellite, measures ice volume. Nasa geophysicist Scott Luthcke, reviewing it and other Greenland numbers, concluded: “We are quite likely entering a new regime.”

Melting of sea ice and Greenland’s ice sheets also alarms scientists because they become part of a troubling spiral.

White sea ice reflected about 80% of the sun’s heat away from Earth, Mr Zwally said. When there was no sea ice, about 90% of the heat went into the ocean which then heated up everything else. Warmer oceans then led to more melting.

Nasa scientist James Hansen, the lone-wolf researcher often called the godfather of global warming, will tell a meeting of researchers in California tomorrow that in some ways Earth has hit one of his so-called tipping points, based on Greenland melt data.

“We have not passed a point of no return. We can still roll things back in time — but it is going to require a quick turn in direction,” said Mr Hansen.