A couple of people have recently complained about the rash of stories explaining how snow-in-December (or, your pet weather event at whatever time of year) is compatible with Global Warming. For example: Cold Spells From Climate Change? (DA) or Yes, they have now said it (TW; I’m sure those two will love being associated).
What I think is correct is to explain that Yes, X has occurred, which perhaps you might not expect given GW, but then showing that it is entirely compatible with GW. Not that it is a particularly exciting game to play, because pretty well any form of weather will be; the variation in weather is so large, compared to the slow changes under GW, that it will be a long time before any given weather event we’re used to could possibly be ruled out.
What I think rather less correct is attempting to say Y has occurred because of GW; and that is so for pretty well the same reasons. And of course it doesn’t play terribly well either: “ha, they are saying that both heatwaves and freezes are caused by GW, hence it must all be nonsense”. Of course that isn’t what the science is saying, only that both are compatible.
So before explaining such-and-such an event, the first thing you need to do is to show that there is something in need of an explanation. A cold December in Europe doesn’t fall into that category. So when the NYT (ref’d by DA) says
Over the past few weeks, subzero temperatures in Poland claimed 66 lives; snow arrived in Seattle well before the winter solstice, and fell heavily enough in Minneapolis to make the roof of the Metrodome collapse; and last week blizzards closed Europe’s busiest airports in London and Frankfurt for days, stranding holiday travelers. The snow and record cold have invaded the Eastern United States, with more bad weather predicted. All of this cold was met with perfect comic timing by the release of a World Meteorological Organization report showing that 2010 will probably be among the three warmest years on record, and 2001 through 2010 the warmest decade on record.
How can we reconcile this?
The obvious answer is: Der, this is global warming, not local, and 2010 is more than just a few weeks. Annual cycles like El Niño/Southern Oscillation, solar variability and global ocean currents cannot account for recent winter cooling is probably true, but deliberately leaving out natural variability as an explanation is at worst ignorant. But all this is just a peg to hang some bloke’s forecasts off: Model accuracy demonstrated says “Judah Cohen, AER, Inc.” who looks to have consultancy to sell. Cohen issued a real-time winter forecast for Europe for 2010, which was significantly more accurate than those issued by the European forecast centers it says, but conspicuously fails to link to the forecast. Remind you of anyone called Piers? (that’s unfair, I know). FWIW the overall idea (less sea ice => more moisture => more seasonal snow => changes to the jet stream => pick your own favourite result, it could do anything) is at least plausible; I’ve no idea if it is also true.
Meanwhile, George Monbiot has another explanation which made Timmy sad, also keyed off the sea ice, but using a different mechanism (warmer Arctic => reduced pressure gradient between Iceland and Azores => pick your own favourite result, again, possibly mediated by the jet stream if it pleases you).
Or possibly the two mechanisms are, cunningly, the same thing in disguise. But at the moment, such things are subjects for research papers, not settled science. The correct (but boring) response is to go back to the beginning, which should always be, Is there actually anything in need of explanation?
* Environmental reporters ought to be more responsible too (Eric at RC)
* Snowfalls are now just a thing of the past
* Cold winter in a world of warming? – Rasmus at RC
* Joe Romm reports Munich Re talking out of its arse but unfortunately he doesn’t realise they are doing so.
* Ben Santer on the attribution of extreme weather events to climate change – ht: CP
* NCAR’s Trenberth on the link between global warming and extreme deluges at CP
* Are recent snows from global warming? – DA