Snow Storm, Night, Brooklyn by Steven Pisano

It’s winter again for us in the Northern Hemisphere, which means the occasional cold spell and maybe even some snow. Though the weather you get depends on where you live in the Northern Hemisphere. But there’s one thing you can count on when it gets cold or snowy anywhere on our planet: climate science deniers will not be far behind to misrepresent what it means.

Which is understandable, after all most of the public doesn’t know how to make sense of extreme cold and heavy snow fall in a warming world. They look out of the window and wonder why this is happening. Climate science deniers then jump on this to cause further confusion and distort what experts say on this. But climate science deniers haven’t been jumping on cold weather events where I live (The Netherlands).

This is because winter hasn’t started here, we are still stuck in a very warm autumn. It’s almost 10°C above the average temperature you would expect for this time of year, with very few nights where we had temperatures dip below freezing (and then barely). So far this is the sixth warmest winter for my country. This warm weather is confusing plants so much that some are sprouting months before they should.

The surprising thing is that the cold weather in the United States and the very warm weather here in Western Europe are linked. And both are linked to changes in our climate thanks to our warming world. But let me start with why the United States is so cold and Western Europe is so warm.

What’s causing this is the jet stream making some odd and long loops across the Northern Hemisphere. One of these loops is over the United States, allowing the cold Arctic air to displace itself towards the United States. It’s this Arctic air that’s making it so cold, and you can see the loop in the jet stream above the areas where it’s so cold:

Jet stream position map from weather.com

In Western Europe we’re also dealing with a loop in the jet stream. But the direction/placement of this loop brings warm air to our region, you can see it moving this warm air towards Western Europe in this picture:

Jet stream position map from netweather.tv

Normally the jet stream doesn’t make these kind of twists and turns when it travels around the Northern Hemisphere. They do happen, but the past few years they are more common and tend to be stronger and longer lasting. The reason for this is in how the jet stream works.

The jet stream is caused by the temperature difference between the equator and the North Pole. The cold air in the arctic is denser and because of that the atmosphere isn’t as hight as the warm atmosphere at the equator. This then causes the warm air to flow towards this dip in our planets atmosphere. But it doesn’t move in a straight line because our planet spins (Coriolis effect), this then deflects this moving air to the right causing the jet stream. The colder the arctic is compared to the equator the stronger this jet stream is. When you have a strong jet stream you don’t get these large loops. Just like a fast flowing river will tend to move in a straight line and a slow moving river tends to make all kinds of strange twists and turns.

And this is the point where our warming climate plays a role. When our planet warms it doesn’t do this at the same rate everywhere on the globe. There’s a phenomenon known as polar amplification, where the poles warm a lot faster and more than the equator does. This is happening in the Arctic and this is causing the temperature difference between the North Pole and the Equator to decrease; which weakens the jet stream. This is what is causing a lot of the weird weather we’ve seen the past couple of years:

This is exactly what climate researchers were expecting to happen in a warmer climate. It’s also expected that these weird loops in the jet stream will last longer — they will stay in one place longer — and that the loops will become taller and move more towards the Arctic. Meaning they can move more cold air south and more warm air to the north. Creating all kinds of bizarre weather where it can be a lot colder in Europe than in Siberia.

How all this works and will play out is quite complex, but it was expected and is caused by global warming. One of the main reasons for these big changes is the ice loss in the Arctic:

Not that strange as melting sea ice means that the Arctic is warming. This warming then replaces cold ice with warmer open ocean, which then can warm the atmosphere above the Arctic. By now you would have an idea what this means for how strong the jet stream would be.

Of course this cold weather can be confusing, which is exactly why climate science deniers jump on this. They can use this to reaffirm their own world view and sow doubt among the public. Ignoring one very important detail, it’s called global warming for a reason. We have very different things happening in Australia, where it’s unusually warm:

Same for other regions in the world, for example Argentine just came out of it’s worst heat wave since records began in 1906. Or November in 2013 being the warmest on record, with a particularly noticeable warm spot above Russia:

Of course all examples of cold and warm weather I just gave is just that, weather. What matters is if what we see matches with the predictions made for global warming, and what the global trend is.

Despite what a lot of the climate science deniers claim or say on weather events and about our warming planet, it doesn’t change that our planet is still warming. And strange as it might seem at first glance, the cold weather in the United States is linked to it; just like the warm weather in Western Europe, Argentina, and Australia.

There will always be cold spells and heavy snow fall somewhere on our planet, especially when it’s winter. It’s something I’ve said to climate science deniers since 2011. But to them context doesn’t matter nor does it matter what the experts say on this:

For climate science deniers only one thing matters: use everything possible to discredit valid science. No matter how silly or unfounded the claims are or the reasoning behind it is.