If global warming is real, then why is it so cold?
We are hearing this question quite often today and it will be asked many times by many people over the next few days as record low temperatures are set in many parts of the United States. Here in Minnesota, for example, we have a good chance of setting a record low daily high beating the previous record of 14 degrees below zero F. We may or may not beat the record daily low but we are going to get close. (Donald trump is probably the most famous person to have gotten this wrong over the last few days.)
Global warming is real. The apparent contrast between extreme cold and global warming is actually an illusion. If we look at the local weather in many parts of the US we see a giant blob of cold “Arctic air” moving south to engulf our humble hamlets and cities, as though the Arctic Coldness that we know is sitting on the top of our planet, like a giant frosty hat, is growing in size. How can such a thing happen with global warming?
Actually, if you think about it, how can such a thing happen at all? Imagine a somewhat different scenario. Imagine the giant global hulu-hoop of warmth we know of as the tropics suddenly expanding in size to engulf the United States, Europe, Asia, and in the south, southern South America, southern Africa, Australia, etc. for a week or so, then contract back to where it came from. How could that happen? Where would all the heat necessary for that to happen come from? That seems to be a violation of some basic laws of physics. Now, cold is not a thing — it is the absence of heat — but the same problem emerges when we imagine the giant frosty hat of arctic air simply getting many hundreds of percent larger, enough to engulf the temperate regions of the planet. As easy as it might be to imagine such a thing given the images we see on regional weather maps, it is in fact not possible. The physics simply does not work that way.
What is happening instead is the cold air mass that usually sits up on the Arctic during the northern Winter has moved, drooped, shifted, gone off center, to engulf part of the temperate region. Here in the Twin Cities, it is about 8 below zero F as I write this. If I go north towards the famous locality of International Falls (famous for its cold temperature readings often mentioned on the national news) it will in fact be colder. If I go even farther north, at some point it will start to get warm again, as we leave the giant blob of cold air that has engulfed us. In fact, it is relatively warm up on the North Pole right now. Alaska and Europe are relatively warm as well.
The graphic above from the European Centre for Medium-Range Weather Forecasts shows what is happening. The Polar Vortex, a huge system of swirling air that normally contains the polar cold air has shifted so it is not sitting right on the pole as it usually does. We are not seeing an expansion of cold, an ice age, or an anti-global warming phenomenon. We are seeing the usual cold polar air taking an excursion.
So, this cold weather we are having does not disprove global warming.
In fact, the cold snap we are experiencing in the middle of the US and adjoining Canada may be because of global warming. The Polar Vortex can go off center any given winter, but we have been having some strange large scale weather activity over the last few years that is thought to be related to global warming and that may have contributed to this particular weather event (explained here). This may be an effect of this strangeness, though the jury is still probably out on this particular weather event.
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