Time for an Arctic update and a bit of “original” research. There’s been quite a bit of polar news around, and a rapid freeze-up is underway in the Arctic – so rapid that some are declaring that the sea ice is “back to normal” for the time of year, based on this graph from the Arctic Regional Ocean Observing System in Norway, which shows sea ice area climbing up towards to the average for 1979-2007, within one standard deviation (the grey area). On the other hand, if you look at the equivalent graph at Cryosphere Today, you’ll see that ice area is 1.25m km2 below the average – which in CT’s case is 1979-2000. So the ice is approaching normal, only if you define “normal” as including the significant ice reductions over the last seven years. How encouraging. But this autumn’s freeze-up has been pretty rapid. Does that mean that it’s been unusually cold up there? I thought I’d take a lookâ€¦
My tool of choice for looking at climate/weather anomalies is this page at NOAA’s Earth System Reseach Lab. It allows you to plot a wide range of maps based on the NCEP/NCAR reanalysis of climate data (explained here). Have a play. If you like maps and seeing what’s going on in the atmosphere it’s fun (in a climate/weather geek sort of way). To find out whether the weather has been warm or cold in the Arctic recently, I plotted the surface temperature anomaly for the last seven days of October:
There’s a cold blue/purple bit to the north of Ellesmere Island, but most of Siberia and the seas to the north are 6 to 12 C above average for the time of the year. So it’s not unusuallly cold – it’s warm, but is it unusually warm? Here’s the same period last year:
The situation is very similar over Siberia, but last year Greenland was seeing colder temperatures (note that the scale is slightly different, because the positive anomalies were bigger in 2007 – up to +15C over the ocean…).
OK, but a week is not a long time, and weather can change rapidly – what was the whole month of October like? I looked at the monthly data for the last six years (2003-8), and stuck them together to make an animated file:
There are – as you might expect over a period when there’s been significant ice loss – large positive anomalies in all years, over large areas of the ocean (as the ice freezes it gives up heat to the atmosphere) – but there are also large positive anomalies over the surrounding land – particularly in the last three years. We’re talking about +3C to +6C over large areas of Siberia. That reminded me of something from a paper I reported on earlier this year:
The decade during which a rapid sea-ice loss event occurs could see autumn temperatures warm by as much as 9 degrees F (5 degrees C) along the Arctic coasts of Russia, Alaska, and Canada.
Looks to me like it’s already happening. Even though the sea ice area has increased rapidly this autumn, temperature anomalies remain strongly positive. Taking all the information together, it’s clear that the “normal autumn weather” over large chunks of the Arctic – especially Siberia and its methane-rich seabeds – has changed rather dramatically. It’s rapid climate change happening now.
But the Arctic’s a long way away: why should this warming worry us? The answer lies in what meteorologists call a “general circulation response”. Change the patterns of weather around the Arctic, and you get knock on effects further south as the atmosphere responds. Stu Ostro, a senior meteorologist at The Weather Channel has been following this issue, analysing changes in the behaviour and intensity of upper level high and low pressure systems. A strong upper level high pressure system is usually associated with warm temperatures below – and the highs have been getting more and more intense. Ostro’s put all his thoughts into a detailed presentation, available as a large (30MB) pdf here, recently updated to include autumn 2008. Bottom line? “The general circulation has been changing, and it’s been happening quickly.” Ostro’s pretty blunt about it: it doesn’t matter where the heat comes from, but if you put more heat into the atmosphere, it’s going to respond. We’re seeing that response now.
That brings us back to the sea ice. What’s the best way to describe what’s going on, when change is so rapid? This year’s freeze-up is close to “normal”, provided that we include in our definition of normal the ice losses of recent years. If we refer back to a period before big losses, we can see this year is way below “normal”. Ostro points out that this also applies to other weather events and weather extremes. What’s normal, when what’s normal is changing?
Meanwhile, a team at University College London have used Envisat data to calculate Arctic sea ice thickness, and report that last winter saw losses of up to half a meter over large areas (ESA, Science Daily, BBC). Plus: Arctic and Antarctic warming has been shown to be directly attributable to human causes (Nature News, Guardian, e! Science News, New Scientist).
[Update 5/11: Tamino at Open Mind demonstrates that there’s no “recovery” of sea ice during October.]
[Update 6/11: Mauri Pelto in the comments to Tamino’s post (link above) points to a recent paper (PDF) by Mark Serreze et al (The emergence of surface-based Arctic ampliï¬cation, Serreze et al,The Cryosphere Discussions, 2, 601â€“622, 2008), which essentially conducts a much more thorough version of my quick peek at the data. Here’s the punchline:
With models consistently simulating reductions of ice cover into the future, we view the emerging Arctic ampliï¬cation documented in this paper as but a harbinger of a more pronounced signal to appear in the near future with impacts that may extend well beyond the Arctic Ocean (Lawrence et al., 2008).
The Lawrence et al paper is referred to in my post.]