Signs of Arctic illness

If the Arctic really is the “canary in the coal mine” for climate change impacts, as it’s often been labelled, then it’s a canary about which we know a little more following a spate of scientific papers coming out in the recent past.

And looking at what they say, as well as readings from instruments monitoring the canary’s health, the signs of sickness appear to be stronger and more certain than before.

There are several distinct symptoms that need monitoring here: sea-ice area and volume, air temperature and wind, water temperature and currents, and the state of the Greenland icecap.

Along with all this is the constant effort to interpret new data and see whether long-term beliefs about how Arctic weather works still hold true, or whether – as with the El Nino Southern Oscillation, for example – the sustained rise in global temperatures may change mechanisms people thought they understood.

Greenland is especially important globally because of the potential of icecap melting to raise sea levels around the world.

Andy Shepherd’s research team shed a bit of light on how higher temperatures might affect ice loss with a paper in Nature showing that paradoxically, inland glaciers flow slower at higher temperatures. Essentially, there’s so much meltwater that it runs away in channels under the ice, and doesn’t lubricate the glacier’s flow against the rock so well.

Impact of ice disappearance

However, what it means in real terms isn’t clear, as several other mechanisms are in play that could work in the opposite direction. Disappearance of ice from any part of the world will have an impact on albedo – the reflectance of solar energy back into space. But because there’s so much of it there, the Arctic ice on land and at sea is especially important.

The steady shrinking of both has clearly led to a change in albedo and so, presumably, to amplification of temperature rise. In Nature Geoscience recently, Mark Flanner from the University of Michigan and colleagues calculated what the shrinking ice cover means for radiative forcing – the impact on temperatures.

But one figure alone is enough to give pause for thought: over the course of the satellite record, the net heating from this loss of albedo – the extra absorption of solar heat by the earth - has increased by 10-20 per cent – a huge change in just over 30 years. Ice is affected by higher temperatures in the air above and in the sea below.

Warm water moves northward in the Atlantic Ocean by dint of the North Atlantic Drift, more colloquially known as the Gulf Stream. Whether the warmth affects the Arctic – and if so, whether its impact is changing – is a question that a team led by Robert Spielhagen from the University of Mainz in Germany addresses in Science.

Using a marine sediment record from Svalbard, they deduce that the temperature of Atlantic water entering the Arctic Ocean is higher than it’s been for 2,000 years. The average temperature since 1850 is 2C higher than the average before – and comfortably higher than during the Mediaeval Warm Period, for example. To quote from a paper in Nature, “...Warming of the Atlantic water layer, unprecedented in the past 2,000 years, is most likely another key element in the transition toward a future ice-free Arctic Ocean.”

And what of that transition itself?

At a briefing on the coming season’s work by the Catlin Arctic Survey, Simon Boxall, who designed one of the projects they’ll be carrying out this year, cautioned reporters (and I guess by extension everyone else) not to place too much importance on annual statistics. Some iconic ones do stand out in the annals of climate change history: 1998 with its strong El Nino spike, 2003 with its European heatwave, 2007 with its startling Arctic melt, and they make news.

His point was that although summer melt records haven’t been set since 2007, what we have had are four summers in succession where the ice has shrunk back further than at any other time since 1979.

The winter maxima are showing a similar trend. And the latest plot from the US National Snow and Ice Data Center shows that another record low, this time for the smallest winter maximum, could be on its way. Meanwhile, the ice volume, as calculated by the University of Washington’s Polar Science Center, shows not just a steady decrease over the last couple of decades, but a decrease that’s accelerated in the last few years.

If it is accelerating, then it would be good to know why. But here, science inevitably has to play catch-up.

Analyses of weather and climate depend on data, which must by definition come from the past; and you need a fair bit of data before you can start extracting rules. But the slow build-up of greenhouse gases, along with albedo changes and perhaps influences from events further south, may be altering the rules as we go along.

Fluctuating temperatures

A month ago, the Northern Hemisphere had the same kind of “upside-down” temperatures that we saw for large chunks of last winter, with the Arctic Oscillation in a “negative phase”, bringing snow to western Europe and leaving parts of the Arctic itself basking in unseasonable warmth. See this often enough, and the question of whether we’ve entered a new regular weather pattern begins to be asked.

It’s currently unanswerable. But in the words of NSIDC: “It may be that with a warmer Arctic, old rules regarding links between the atmospheric pressure patterns and sea ice extent no longer hold.”

What all this means for Greenland, and hence for sea levels globally, is less clear – and we’re not likely to have answers before the next Intergovernental Panel on Climate Change (IPCC) report in 2013/4.

Already, a fair proportion – I won’t claim to know the exact figure, but I’d estimate it’s over 90 per cent – of Arctic researchers believe that for the region as a whole, the canary is already toppling off its perch.

New York Times News Service