Molly Docherty, contributor
3 August: wide open (Images: NASA)
Now you see it, now you don't. These images, captured two weeks apart by NASA's Terra satellite on 17 July (below) and 3 August (above), show a dramatic retreat of sea ice in the Arctic's North-West Passage.
17 July: frozen shut (Images: Jesse Allen/ Land Atmosphere Near real-time Capability for EOS/NASA Earth Observatory)
The region's ice cover is now significantly lower than expected, says the Canadian Ice Service, with coverage on July 30th estimated at 33 per cent, compared to the 1981-2010 median of 79 per cent. Despite the melt, this part of the North-West passage may not yet be navigable.
Melting will continue as we head towards September, when annual ice cover is at its lowest.
At the current rate, 2012 is likely to see the greatest ice shrinkage since satellite records began, exceeding 2007's record low. Annual variations in ice levels are normal, but recent years have shown a worrying decline, the majority of which has been attributed to greenhouse gas emissions (Environmental Research Letters, DOI: 10.1088/1748-9326/7/3/034011).
Increasing temperatures and diminishing Arctic sea ice could have far-reaching implications, and have been linked to changes in the behaviour of salmon and bears. Extreme Arctic melts can leave shorelines vulnerable to erosion, and may even be responsible for the colder winters experienced in Northern Europe and North America of late.
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