Monday, March 25, 2013

How does Cold UK Weather fit in with Global Warming?

Coldest March for 30 - or is it 50 - years.
Snow hits the North East.
More flooding, another house hit by a landslide.

Extreme weather. Why?

Any fule kno that our current run of bad weather, not just the present abnormality, but also the last two dark summers, is due to the northern polar jet stream being too far south. Normally it is around Scotland. Recently it was as far south as Spain.

So why is the jet stream doing this? Several factors come into play to produce any one event in the atmosphere, because it is a system.

The central cause is a "blocking high"  - a large region of settled high pressure that may stay put for weeks - in the region of Scandinavia. This diverts the jet stream south.

So why is the blocking high there? Several factors.

Melting of Arctic ice due to global warming encourages the development of regions of high pressure.
Arctic warming also weakens the contrast between northern cold and southern warmth, which normally keeps the jet stream in a tight band.

Also, the stratosphere in the region of the north pole has undergone a sudden warming event in January.
Generally, stratospheric cooling is produced by enhanced greenhouse gases, but sudden warming events overturn this pattern. The warming contributes to the development of the blocking high.

We are also in a period of solar minimum, and that also encourages blocking highs.

Therefore, when the solar activity begins to pick up again, which may happen any year now, there may be a slight lessening of the blocking high problem, but don't hope for too much of an improvement, because the Arctic warming part of the problem is not going to get better any time soon.

So that, as far as I can see, is the general situation. Now let's look at a couple of political points.

First, the argument made by contrarians "It is cold today, therefore global warming is not happening" is one of their weakest talking points. Boris Johnson used it, thereby demonstrating the paucity of his cognitive abilities. It grieves me to have to make these kind of remarks, but I have no choice. It is like getting into a fridge to prove that global warming does not exist. The fact is that we may be colder than usual here, but Greenland is warmer than usual.

Second, note that solar and greenhouse gases are both implicated, even if the solar component is relatively minor. This really needs stressing, because contrarians are continually making the mistake of saying "It's all solar", or "Why is the surface temperature flat while CO2 is rising?" They are thinking in simple mechanistic terms, not in systems terms, where several factors collude in producing a certain result.  Part of the reason for the contrarians' misconcption is because the sun is so powerful - indeed, it contributes 100% of the heat earth receives. However, although the sun does vary measurably, the variation is very small compared to its total input.


Rangjan said...

Do you know of anywhere this is writen in a non-insulting way? I get a lot of queries about this from people who are ignorant or curious, but who I wouldn't want to be called "pathetic" or "dumb" or "useless", and I would like to be able to refer them to a website that explains this topic.

DocRichard said...

You're right Rangjan. I usually try to be emotionally neutral, but sometimes frustration gets the better of me. I'll edit the post as soon as I can.

Thanks for the admonishment.