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I’ve said it before. If you are not confused about the Sun’s role in global and regional climate variations, you haven’t been paying attention.

The latest manifestation of the Sun-climate debate takes place in the pages of Nature Geoscience (paywall), here and here. The UK Met Office also issued a press release on the subject a few days ago.

The conclusion is that the Sun’s low activity, in particular its low ultraviolet (UV) output, is influencing the stratosphere in such a way as to produce unusually cold winters in parts of Europe, including the UK.

“Our research confirms the observed link between solar variability and regional winter climate,” lead author Sarah Ineson of the UK Met Office told Reuters.

The press has reported that Ineson’s team focused on data from the recent solar minimum which was during 2008-10, a period of unusual calm for the sun and intense, record-breaking winters in the UK.

Using computer models they found that when they introduced a reduction in UV radiation from the sun it can affect high-altitude wind patterns in the Northern Hemisphere, triggering cold winters. When solar UV radiation is stronger, the opposite occurs, the researchers say.

More study is clearly needed. It’s preliminary work and, of course, based on computer modeling and all the limitations implied in that. The data only spanned a few years. “So questions remain concerning both accuracy and also applicability to other solar cycles,” Ineson said.

But then, in my view, these caveats are ignored and the usefulness of this work taken too far. “While UV levels won’t tell us what the day-to-day weather will do, they provide the exciting prospect of improved forecasts for winter conditions for months and even years ahead. These forecasts play an important role in long-term contingency planning,” Ineson said.

El Nino As Well

Low solar UV radiation is not the only factor that the Met Office believes can cause severe UK winters. In 2008 its climate scientists “confirmed” links between the El Nino Southern Oscillation and the weather over Europe in late-winter.

A letter, also in Nature Geoscience, explained how they had used computer models. Then Sarah Ineson said, “we have shown evidence of an active stratospheric role in the transition to cold conditions in northern Europe and mild conditions in southern Europe in late-winter during El Nino years.”

The problem with this “confirmation” was demonstrated rather dramatically the very next year.

In October 2009 the Met Office predicted a mild winter because of El Nino. Temperatures in December would be above average, they said. In reality December temperatures were a whopping 1.1 degrees below the recent average.

The Sun’s Influence This Coming Winter

There are other problems with the Met Office’s latest research.

Firstly, it refers to 2008-2010 when the Sun’s activity was low, and the UK experienced three severe winters in succession. The problem is that the activity of the Sun as we enter the UK 2011 winter is not the same as it was in the past few years.


Fig 1. Click on image to enlarge.

Solar activity is back to what it was in 2004-5, and we didn’t experience severe winters in those years, see here, and here, and here.

So, if anything, the logic behind this particular piece of research points towards the Winter of 2011 being a mild one!

I don’t believe that this latest research increases the probability of a severe UK winter this year. It will be interesting to see what happens.

UV Or Not UV

The other problem concerns recent, highly publicised, research by Joanna Haigh of Imperial College London, a co-author on the current Nature Geoscience paper.

Her work rests on the fairly recent observations that show that solar UV and optical radiation vary in anti-phase – although the figures are not totally rock solid, it seems that when solar optical radiation is low the UV is high and that UV varies to a greater degree than previously suspected. This led to headlines all over the world that when the sun goes through a decrease of activity, such as the slide towards solar minimum, it might actually be warming the earth.

So, on the one hand we have research that suggests that during the last solar minimum, 2008 – 10, low solar UV resulted in cold European winters. On the other hand we have research that suggests that during the same solar minimum enhanced UV may have actually provided a warming effect!

But what does this tell us about the forthcoming winter? Will it be mild or severe?

Place You Bets

We in the UK have had three very severe winters, 2008, 2009 and 2010. The big question is, is it a coincidence?

The Met Office is in a quandary. It has to advise the UK government on winter preparations. Politically it can’t afford to get it wrong again this year. Despite what it said in retrospect last year’s predictions were a disaster.

In 2010, contributing to the Quarmby Report the Met Office said,

2.10. We have explored these issues in some depth with the climate research team at the Met Office Hadley Centre. The starting point is the slow but steady rise in average global temperatures. The consensus on the UK is that on average summers will become warmer, and winters will become warmer and wetter, though the next 10–15 years may be dominated by natural variability. When severe weather events happen they may be more extreme in terms of heat and rainfall.

12.11. Although the probability of severely cold winters in the UK is gradually declining, there is currently no evidence to suggest similar changes in extremes of snow, winds and storms in the UK.

12.12. We have also explored whether or not the occurrence of two successive severe winters influences the probability of a third in succession – in other words, is there any evidence of clustering? There is some small influence from year to year but these matters are still very uncertain and it would be safer to assume that there is statistical independence between one winter and the next.

12.13. In other words, we are advised to assume that the chance of a severe winter in 2010–11 is no greater (or less) than the current general probability of 1 in 20.

Boy, were they wrong!

Mean temperatures over the UK were 5.0 °C below average during December and 0.3 °C below average in January.

In April this year the Met Office told me, when pressed, that, after a third severe winter, they still believed that they were not connected. They said there was currently a 1 in 8 chance of a fourth severe winter in 2011. They were unimpressed with my view that the chances of three consecutive 1 in 8 chances was a 1 in 512 if the events were truly independent.

Four independent 1 in 8 severe winters has a probability of 1 in 4096 which is way outside the bounds of chance. (In the Quarmby report they say that the probability of a severe winter was 1 in 20. Four years at 1 in 20 gives a 1 in 160,000 chance.)

Predictions, they say, are difficult, especially about the future. Just over ten years ago we were warned that snow in the UK would become a thing of the past. Within a few years Dr David Viner of the Climatic Research Unit at the University of East Anglia said winter snowfall will become “a rare and exciting event.”

A decade later snow is now more of a problem than ever, despite global warming. The fact is that nobody knows if the forthcoming winter will be severe or mild. The only wise advice that can be given is to plan as if 2011 is going to be like the previous three winters, and one doesn’t need multi-million pound computers to make it.