Extreme Winters Caused by natural Solar Cycle?

Living not far outside of London growing up, the idea of a thick blanket of snow to play in on a winter's day was only ever a distant fantasy. You see it in the American movies all the time, and you soon learn that a 'white Christmas' doesn't really exist. When the snow fell in 2009, my inner child only had one thing in mind!

What's the significance of this? Well, it was the coldest winter on record in over 25 years, and the UK received record levels of snow. It would be easy to throw climate change to an extreme anomalous event such as this, but recent findings suggest an alternative...

Climate scientists at the UK Met Office have recently carried out a new study on the fluctuations of the sun's UV radiation. They attempted to create a link between solar activity and seasonal weather.

Satellite measurements were used and fluctuations in solar radiation were discovered to be five times as large as previously thought. They put their data into the Hadley Centre model and were able to show how these fluctuations affected regional weather.

The paper emphasises that there findings do not suggest a link to long-term global warming, rather that there is a real correlation between ultraviolet levels and meteorological variables. They show that there is actually little direct change in globally averaged temperatures as the solar activity drives cold winters in northern Europe and the United States, but mild winters are subsequently found over southern Europe and Canada.

How does it work?

UV is absorbed in the stratosphere (the upper atmosphere) by ozone. When there is less UV to absorb, the stratosphere is relatively cooler. The Hadley centre model shows that the effects of this percolate down through the atmosphere. It is described in the paper as a 'top-down stratosphere to troposphere pathway'. As it does this, it changes wind speeds, including the jet stream that circles the globe above Europe, Russia and North America. The resultant change is a reduced air flow from the west to the east, moving colder air into the UK and northern Europe. The image below shows these changes in wind speed and pressure between Ocotber and March 2010. There is then a re-distribution of temperatures across the region, leading to the milder winters in southern Europe and Canada.

Source

Is it quite as clear cut?

The scientists suggest that other factors may have been at play for the colder winter temperatures, including the decline of sea ice levels and El Nino. In all honesty, it could be any combination of these factors, but they suggest that the solar cycle was acting in a way to facilitate these conditions.

What's the advantages of this (other than building giant snowmen)? 

The UV measurements could be used for better forecasting. UV levels won't be able to tell us what the day-to-day weather will do, but it would enable improved forecasts for winter conditions months ahead. They would play an important role in long-term contingency planning.

In summary, the winter weather seen across the UK and Atlantic between 2009-2011 appears to back up the scientists findings. The next stage of investigation would be to look at UV measurements across a longer time-scale, to see if the patterns hold true.