A record loss of sea ice in the Arctic this summer has convinced scientists that the northern hemisphere may have crossed a critical threshold beyond which the climate may never recover.
Scientists fear that the Arctic has now entered an irreversible phase of warming which will accelerate the loss of the polar sea ice that has helped to keep the climate stable for thousands of years.
They believe global warming is melting Arctic ice so rapidly that the region is beginning to absorb more heat from the sun, causing the ice to melt still further and so reinforcing a vicious cycle of melting and heating.
The greatest fear is that the Arctic has reached a “tipping point” beyond which nothing can reverse the continual loss of sea ice and with it the massive land glaciers of Greenland, which will raise sea levels dramatically.
Satellites monitoring the Arctic have found that the extent of the sea ice this August has reached its lowest monthly point on record, dipping an unprecedented 18.2 per cent below the long-term average.
Experts believe that such a loss of Arctic sea ice in summer has not occurred in hundreds and possibly thousands of years. It is the fourth year in a row that the sea ice in August has fallen below the monthly downward trend - a clear sign that melting has accelerated.
Scientists are now preparing to report a record loss of Arctic sea ice for September, when the surface area covered by the ice traditionally reaches its minimum extent at the end of the summer melting period.
Sea ice naturally melts in summer and reforms in winter but for the first time on record this annual rebound did not occur last winter when the ice of the Arctic failed to recover significantly.
Arctic specialists at the US National Snow and Ice Data Centre at Colorado University, who have documented the gradual loss of polar sea ice since 1978, believe that a more dramatic melt began about four years ago.
In September 2002 the sea ice coverage of the Arctic reached its lowest level in recorded history. Such lows have normally been followed the next year by a rebound to more normal levels, but this did not occur in the summers of either 2003 or 2004. This summer has been even worse. The surface area covered by sea ice was at a record monthly minimum for each of the summer months - June, July and now August.
Scientists analysing the latest satellite data for September - the traditional minimum extent for each summer - are preparing to announce a significant shift in the stability of the Arctic sea ice, the northern hemisphere’s major “heat sink” that moderates climatic extremes.
“The changes we’ve seen in the Arctic over the past few decades are nothing short of remarkable,” said Mark Serreze, one of the scientists at the Snow and Ice Data Centre who monitor Arctic sea ice.
Scientists at the data centre are bracing themselves for the 2005 annual minimum, which is expected to be reached in mid-September, when another record loss is forecast. A major announcement is scheduled for 20 September. “It looks like we’re going to exceed it or be real close one way or the other. It is probably going to be at least as comparable to September 2002,” Dr Serreze said.
“This will be four Septembers in a row that we’ve seen a downward trend. The feeling is we are reaching a tipping point or threshold beyond which sea ice will not recover.”
By Steve Connor