Yes it's cold... and it's still getting warmer
For anyone wondering about our early winter, and what it's got to do with El Nino/La Nina, Pacific and Atlantic Ocean temperatures and climate change I thought I'd jot down some notes from a chat I had with Dr Adam Scaife at the Met Office.
He is head of Seasonal to Decadal Prediction, which includes seasonal forecasting, decadal forecasting and modelling of climate variability.
After the barbecue summer fall out, the Met Office has of course stopped giving out seasonal forecasts - at least to the general public. But here's what he had to say about this week's record-breaking weather.
Why is it so cold in northern Europe so early?
"What's happened so far is consistent with El Nino/La Nina signals." Briefly put, in an El Nino year, like that of last winter, the Pacific is warm, and Europe's winters are cold and dry. In a La Nina year, which is where we are now, European winters are warmer and wetter.
But all of that is for LATE winter. In EARLY winter the situation is flipped, so cold and dry in a La Nina year - ie now. But later on this winter, possibly in January (though no one knows for sure), it should start to get warmer than it was last winter. Dr Scaife stressed that it's all very variable, so don't hold him (or me) to that.
The reason it is hard to be sure is that the El Nino/La Nina signal is strong enough only to be seen over a number of years, and not strong enough to use to determine an outcome. "In any individual year, there are lots of other fluctuations that can hide it," Dr Scaife said. Examples would be volcanic activity (strong enough for ash to reach the stratosphere), and what's going on over the Atlantic Ocean.
So what does this all mean for our understanding of climate change?
As the UK and Europe froze over, the World Meteorological Organisation (WMO) issued its annual global temperature data, posted today - and showing 2010 as almost certain to rank in the top three warmest years since the beginning of instrumental climate records in 1850.
"The feature we're seeing now and last winter, where the UK and most of Northern Europe are cold, are a result of a re-arrangement of the air. So for as many places that are cold, there are places that are anomalously warm. It's like a jigsaw with the pieces in the wrong place. So we have local anomalies, but on average it works out to zero," Dr Scaife said.
"For example, at the moment we have cold over northern Europe and Eastern US, but in Canada and the Mediterranean it's mild, so the heat is sitting in a different place. That kind of shuffling can happen locally, but the global mean temperature doesn't care about that."
And possibly feeling a little bruised by questions about the skills of Met Office seasonal forecasting (after that barbecue summer) Dr Scaife directed me to a paper he published in 2005, looking at trends in winter temperatures from the 1960s to 1990s. This work is beginning to look prescient. It talked about possible changes afoot in European climate.
The winter of 1962/63 was famously bitterly cold, but by the 1990s we had got used to warmer, wetter winters in the UK and Northern Europe. Dr Scaife's paper said that although some of this winter warming was directly attributable to climate change, the majority of European winter warming between the 1960s and 1990s appeared to be due to changes in Atlantic winds (Scaife et al, Geophysical research Letters, 2005).
"We worked out that 70% of the warming in that period was due to the change in the Atlantic winds, rather than a direct radiative effect of greenhouse gases. And in 2008, before the last two cold winters, we wrote in a second paper on that topic that future decades could see a reversal, if those winds changed back - and that is exactly what has happened," Dr Scaife told me.
Here's what he said back then: "Future decades could easily see a reversal of regional trends in European winter climate because North Atlantic Oscillation (NAO) effects can dominate the effects of global warming on Europe in winter, even on multi-decadal time scales. Indeed, this may already be underway given the recent decrease of the winter NAO" (Scaife et al, Journal of Climate, 2008)
So a vindication perhaps? Dr Scaife said his team does not yet know what causes those decade to decade natural fluctuations in Atlantic winds. But this is just one example of how a global trend in which the planet is warming, can be masked by local, natural changes.
And finally, he said the key point about recent global temperature change is the rate at which it's happening: "Obviously there were bigger temperature variations in the past, but they took a long time to build up, over many thousands of years*. It's the rate of change in just 50 years (a degree or so of warming) that's different."
* Update on 13/12/2010. Please note there was an error in the reporting of this quote. We initially quoted Dr Scaife as saying: "Obviously there were bigger temperature variations in the past, but they took a long time to build up, over thousands of millions of years." This has now been rectified. Please accept our apologies.