On this Monday’s morning weather forecast (11/12/2017) it was stated: “It was very cold yesterday, in fact, the coldest we’ve seen since December 2010 with a maximum of minus 6.2 degrees C recorded in Braemar …”
Now we all know that the weather, especially here in Great Britain, is somewhat random. Even with giant super-computers at their disposal, our forecasters can only predict what’s going to happen about 5 days in advance, although lately, they’ve been struggling even with that.
So, if 5 days is a struggle for forecasters could there have been anything going on 7 years ago (in 2010) that might have any relevance now?
I know it sounds most unlikely, but the answer is yes.
Older folk may well look back and remember some winters that were cold and some that were warm but connecting the dots on decadal timescales, even for those blessed with a good memory, is difficult to do.
So, here’s a graph to make this task easier.
The Solar Cycle
This graph shows how the numbers of spots on our Sun waxes and wanes over time. (Scientists have been diligently counting sunspots and writing it all down for hundreds of years even though, to begin with, nobody knew why the Sun had spots or whether they did anything!)
Notice the regular pattern which repeats roughly every 11 years. The length of each cycle changes a bit however the maximum number of sunspots from cycle to cycle has in the past varied a lot.
When the Sun has lots of spots, it is said to be active, and when there are few or none it is said to be quiet.
Looking at the graph one can see that the extreme cold snap in December 2010 mentioned above and the one we’re in now both occurred near a minimum on the graph when there were few sunspots.
However, there was also significant snow across the UK in the winter of 2013 just before the peak on the graph around 2014 however, as one can see, that peak was more than half-way down from the peak of 1980. This suggests that it is not the minimum on the graph per se but rather a low number of sunspots that in the past have coincided with unusually cold winter temperatures.
The reason for this is that the type of solar radiation (aka sunlight) we receive from the Sun varies with the number of spots on the Sun which, as we have seen waxes and wanes with the solar cycle. When the Sun is active (lots of spots), it emits more extreme ultraviolet which is blocked and absorbed by nitrogen and oxygen high in the atmosphere. This heats the upper atmosphere, especially at the poles, and the polar vortices form a nice circular ring about each pole trapping the cold polar air so here in Blighty we enjoy winters that are warm and toasty. (Relatively speaking!)
Now when there are fewer sunspots (as we are seeing at present), the Sun produces less extreme ultraviolet. So, there is less heating of the upper atmosphere, especially at the pole where it’s winter and the jet stream there starts to wander away in a wavy pattern. As a result, weather becomes more chaotic with cold arctic air plunging much further south than usual giving us severe cold snaps. At the same time, the warm moist tropical air in some places streams towards the North pole. (This explains why we’re now seeing record cold temperatures in places far South but, confusingly, also record highs far North.) Where these warm and cold air streams meet and interact severe weather such as atmospheric rivers ensue. This not only increases precipitation in some regions but reduces it in others, causing droughts.
Added to this, when the Sun is quiet it is less efficient at blocking incoming cosmic rays, and since these rays trigger cloud formation, a quiet Sun will also give us skies that are cloudier than usual.
Also, since the total solar irradiance does not fall much when the Sun is quiet, in spite of a significant reduction in extreme ultraviolet light, it means that more of the Sun’s heat gets through the upper atmosphere and into the lower atmosphere where it then adds to the energy available to drive weather systems.
Finally, increases in cloudiness and areas with settled snow both reduce the Earth’s albedo, reflecting more sunlight and leading to cooling.
If the Sun’s behaviour follows the path predicted by many, with sunspot numbers staying low for a protracted period, I don’t think the cold will be the greatest concern but rather crop losses resulting in food shortages and increasing prices caused by the effects of bad weather on agriculture on a global scale.
Much was written during the period when this happened before known as the Maunder Minimum when the Thames froze in winter. It was a time of famine and social unrest and political upheaval in many parts of the world.
This, combined with the unnecessarily expensive and unreliable energy we now have, may lead to many finding themselves having to make a heat or eat decision in the coming years.
It seems that old Chinese curse: “May you live in interesting times” may have been put upon us.
And as for PM May’s announcement that all petrol and diesel cars and vans will be banned by 2040?
Good luck with that!
Note: Although I’ve highlighted what I regard as the main factors affecting our weather on decadal timescales linked to solar activity the reality, especially over longer timescales, is more complicated. For a deeper look at this topic, I suggest this link.