Arctic sea ice extent has begun its seasonal decline towards the September minimum. Ice extent through the winter was similar to that of recent years, but lower than the 1979 to 2000 average. More importantly, the melt season has begun with a substantial amount of thin first-year ice, which is vulnerable to summer melt.
From EO Newsroom
This image shows Arctic sea ice concentration on September 8, 2008, as observed by the Advanced Microwave Scanning Radiometer–Earth Observing System (AMSR-E) sensor on NASA’s Aqua satellite. The observations are collected on a pixel by pixel basis over the Arctic. The percentage of a 12.5-square-kilometer pixel covered by ice is shown in shades of dark blue (no ice) to white (100 percent ice). The gray line around the Arctic basin shows the median minimum extent of sea ice from 1979-2000. (The median of a data set is the middle value if you arrange the numbers in order from smallest to largest.)
The southern portions of the Northwest Passage through the Arctic (the western route from Europe to Asia through the islands of northern Canada) opened in early August. Then in early September, ice scientists confirmed that the waters around the Russian coastline—the Northern Sea Route— were navigable, but still treacherous, with shifting floes of thick, multi-year ice, that could coalesce rapidly. The image shows that the widest avenue through the Northwest Passage, Parry Channel, still harbored some ice, but the more circuitous, southern waterways were clear. On the other side of the Arctic Ocean, the passage around Russia’s Taymyr Peninsula, normally locked in by ice, was similarly open. According to a press release from the U.S. National Ice Center, “This is the first recorded occurrence of the Northwest Passage and Northern Sea Route both being open at the same time.”
The summer opening of the Arctic means that new uses of the Arctic are likely to emerge. International legal experts believe that “existing laws governing everything from fish stocks to bio-prospecting by pharmaceutical companies” are inadequate.
To date, the eight Arctic nations (the United States, Russia, Canada, Norway, Sweden, Iceland, Denmark and Finland) have limited discussions to existing agreements, such as the law of the sea. Environmental groups would like new laws, but others have suggested a more feasible, and adaptive response may be to strengthen the role of the existing Arctic Council to better govern a changing Arctic in a more adaptive way.
The summer of 2007 was apocalyptic for Arctic sea ice. The coverage and thickness of sea ice in the Arctic has been declining steadily over the past few decades, but this year the ice lost an area about the size of Texas, reaching its minimum on about the 16th of September. Arctic sea ice seems to me the best and more imminent example of a tipping point in the climate system. A series of talks aimed to explain the reason for the meltdown.
The disappearance of the ice was set up by warming surface waters and loss of the thicker multi-year ice in favor of thinner single-year ice. But the collapse of ice coverage this year was also something of a random event. This change was much more abrupt than the averaged results of the multiple IPCC AR4 models, but if you look at individual model runs, you can find sudden decreases in ice cover such as this. In the particular model run which looks most like 2007, the ice subsequently recovered somewhat, although never regaining the coverage before the meltback event.
So what is the implication of the meltback, the prognosis for the future? Has the tipping point tipped yet? When ice melts, it allows the surface ocean to begin absorbing sunlight, potentially locking in the ice-free condition. Instead of making his own prognosis, Overland allowed the audience to vote on it. The options were
* A The meltback is permanent
* B Ice coverage will partially recover but continue to decrease
* C The ice would recover to 1980’s levels but then continue to decline over the coming century
Options A and B had significant audience support, while only one brave soul voted for the most conservative option C. No one remarked that the “skeptic” possibility, that Arctic sea ice is not melting back at all, was not even offered or asked for. Climate scientists have moved beyond that.
For more coverage see Nature’s Great Beyond.
In 2005 on Resilience Science, Line Gordon, wrote about recent research that we may have already passed tipping points in the Arctic.
NSIDC Arctic Sea Ice News Fall 2007 is providing weekly updates on the state of Arctic sea ice, which has reached record low coverage this year (the previous record low was in 2005).
The figure shows daily ice extent for 2007, 2005 and to the 1979 to 2000 average.