Cold winters in Europe – a solar link?

Frozen Britain, 2010 (source:NASA)

Recent cold winters in Europe are often cited by those ignorant of climate science as proof that global warming either doesn’t exist, or, if it does, it is an insignificant issue linked to natural changes in solar activity. This is wrong on a whole number of levels.

Statistically speaking, the significance of a few icy winters in a row is questionable, but possible solar drivers of regional and global climate change are most definitely worth pursuing. Not only has my old colleague Mike Lockwood posed the question, he has with fellow space scientists Richard Harrison, Tim Woollings and Sami Solanki presented temperature and other data which show how such climate anomalies are more common when solar activity is low, and put forward a plausible hypothesis to explain the link.

Using the most comprehensive but regionally specific temperature data available, and comparing these with long-term observations of the Sun’s magnetic field, Mike and his colleagues were able to study trends across the entire northern hemisphere. What they found in the data could have something to do with a phenomenon known as ‘blocking’, in which the jet stream that brings high altitude winds from west to east across the Atlantic loses its way for weeks at a time before it reaches Europe. What happens is that an anticyclone (or s-shaped folding) is formed from the interaction of cross-Atlantic westerly winds with strong north-easterlies from the Arctic, and this blocks the normally warming effect on Europe of the jet stream.

Note that this is very much a regional and seasonal climate phenomenon, and has nothing to do with the observed global temperature trend. And of course with real-world geophysics there are anomalies within anomalies, and it can all get a bit messy, as Mike explains…

“If we look at the last period of very low solar activity at the end of the seventeenth century, we find the coldest winter on record in 1684. But, for example, the very next year, when solar activity was still low, saw the third warmest winter in the entire 350-year record.

“The results do show however that there are a greater number of cold UK winters when solar activity is low.”

Such caveats aside, what we have here is further compelling evidence of strong coupling between the Earth’s stratosphere and that part of our atmosphere within which weather and climate occurs. The meteorological effect of blocking is put forward as a way of explaining historical and more recent temperature anomalies in Europe, but for now the findings are only suggestive of a link between cold winters and low solar activity. What it certainly does prove is the need for a more rigorous treatment of stratospheric effects in climate forecasting models.

Further reading: Lockwood et al., “Are cold winters in Europe associated with low solar activity?“, Environ. Res. Lett. 5, 024001 (2010)