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Hello and welcome to Just Have a Think. The original plan for this
week's program was to continue our focus on climate mitigation technologies with a
look at some of the astonishing developments taking place with graphene around the world,
but it would be a bit remiss of a climate and sustainable energy channel if we completely
ignored the record temperatures at both ends of the scale that have been afflicting places like
Australia in the southern hemisphere and the U.S. and Canada in the northern hemisphere this month,
so we'll be looking at graphene in a later program and instead this week we're going to
take a look specifically at the cold snap that's walloped the Midwest in recent days. We'll also
give a whole video to looking at the changes in the Australian climate a bit later in the year
so it'd be great to get some first-hand experience and anecdotes from those of you watching from that
part of the world. Coming back to the States though, I know everyone's throwing the phrase
'polar vortex' around as if it's some kind of once-in-a-lifetime freak phenomenon - which it
isn't. Now I'm quite sure that you well-informed folks out there will already be well up to speed
with this and what caused such dramatic drops in temperatures across the Midwest this week,
but nevertheless I thought it was worth taking a look at information from some of the experts
in the field to get their perspective on why this particular cold snap has been so extreme,
and why they appear to be happening more often because, apparently, it's a perfect example of
how global warming is having an effect on climate change. And that's a concept that can sometimes
be a bit confusing for some people. So what's it all about? How can global warming cause minus 40
degrees in Chicago? To be fair to Mr. Trump it is, on the face of it, completely counterintuitive.
Here in the UK we have a great science communicator called Simon Clark. Simon has a
PhD in atmospheric physics from the University of Exeter and he's been talking to us about climate
matters on his YouTube channel for several years. Last winter, when we experienced very similar
circumstances to the ones we're seeing this week, Simon released a very informative video explaining
the complicated meteorological interactions that drive these events, and you can watch
that presentation by clicking here. An equally inspirational and educational commentator over
there in the states is Ethan Siegel. Ethan is a theoretical astrophysicist and science writer who
runs a blog called 'Starts with a Bang'. In his article for forbes.com this week, Ethan tells us
that these extreme cold snaps have gotten more severe in recent years due to a combination of
global warming and a phenomenon you've likely heard of - the polar vortex. We all know that
our planet is warmer in the mid latitudes near the equator than it is at the poles. The warm
air from the equator tends to move towards the cold air in the Arctic, but because the earth
also spins these air currents get dragged around with it, giving us prevailing winds like the jet
stream. The temperature difference also causes a low-pressure zone that rotates at each pole,
and it's this that the scientists call a polar vortex. The jet stream circulates at a height
of about six to seven miles above the surface of the earth, which is about 30,000 feet, which
is the height that commercial airliners fly at, hence why the flight from the U.S. to Europe is
usually quite a bit quicker than the flight going the other way. The polar vortex is much higher,
at about 30 miles above the Earth's surface. The bigger the difference in temperature between the
equatorial air and the arctic air, the faster and straighter the jet stream moves around the
planet and the more circular and well-defined the polar vortex is. As Ethan Siegel tells us,
when the vortices are at their strongest you get a single cell, and the air is extremely well
confined. But the Arctic is warming much faster than the rest of the planet, and this is something
I discussed with Professor Peter Wadhams during our conversation back in November last year...
so in even in the IPCC report they've said that the Arctic is warming by 1.9 degrees Celsius in
that... just in the last 30 years. And that's... that's reducing the differential between the the
mid latitude warmer regions and the arctic cold region, which as I understand it is...is having an
effect on the jet stream. It is an effect where it implicates sea ice and Arctic warming very
strongly. The person who originated the theory is Jennifer Francis from Rutgers University, and most
people agree with her analysis now, that... that what's happening is the Arctic's warming about
four times as fast as the rest of the planet, so the difference in temperature between the Arctic
air mass and tropical air masses is... is getting less. Because the temperature difference has gone
down, the driving force for the jet stream is less, so the jet stream slows down and as it
slows down instead of being a straight line it goes into lobes - north-south lobes, like a it's
like a river flowing over a flat estuary. It tends to meander. So you've got a meandering jet stream,
and with a... with a meandering it means that... that arctic air is carried down to much lower
latitudes than it should get to. And then in between, there's regions where tropical air is
carried to much higher latitudes. So the second effect of this warming is that the polar vortex
also weakens and starts to lose its neat circular shape. Ethan continues "the phenomenon that causes
the polar vortex to break down is known as sudden stratospheric warming, where the upper layers of
the atmosphere increase in temperature by about 30 to 50 degrees Celsius, which is 54 to 90 degrees
Fahrenheit, over the span of only a few days." A warmer earth, he says, makes sudden stratospheric
warming events more likely and more frequent and those events destabilize the polar vortex,
bring cold air down into the mid latitudes, and cause the extreme weather we're experiencing
right now in the States. You can actually watch these developing weather systems for yourself at
Google's Earth Null School. This is an animation from the last winter showing how we'd normally
expect to see the polar vortex. Even though this one's a little bit further south than we'd
normally expect it to be you can see that it's a continent sized doughnut of winds rotating in a
neat circle at speeds of up to about 200 miles an hour. And this is a compilation animation showing
this winter's actual polar vortex on the left and the consequent jet stream on the right during
January 2019. By the 3rd of January the polar vortex had split into three vortices with the two
main circulations happening over Scandinavia and North America. By the time we get to the 9th and
10th the vortex has strengthened towards the top end of Canada before collapsing again to reform a
secondary rotation further south towards the Great Lakes. At the same time if you take a look at the
jet stream on the right hand side you can see a really dramatic trough pulling all that sub-zero
arctic air right down through Canada and into the United States. If we stop the clock at the 25th of
January and take a closer look, you can really clearly see how those temperatures of minus 40
are being carried directly down from the North Pole straight into the northern states, and you
can also see just how chaotic the Jetstream is all around the globe. Approaching today's date, which
is Sunday the 3rd of February, the polar vortex looks to be heading back north and the Jetstream
trough is finally moving on as the earth begins to warm. Scientists tell us that extreme weather
events like this will become more commonplace, with many climatologists predicting an unstable
polar vortex bringing us storms like this multiple times a decade. Here's Professor Peter Wadhams
again..."and the problem of with all that is these extreme events will keep happening now,
because that's the way the jet stream has become. We're not going to escape from either extreme heat
or extreme cold events during... during the winter. So we... it's not weather... extreme
weather we're getting, it's extreme climate. The... the climate has changed." Welcome to the
new normal, says Ethan Siegel, courtesy of global warming, where the Arctic can't even remain cold
in the dead of winter. That's it for this week. I hope you enjoyed this little interlude in our
planned schedule. If you found it useful and informative then please do share the video and
hit the like button. You can also subscribe, and if you hit the bell icon when you do that you'll
be notified of when all the new programs come out. And you can do that by clicking here. As always,
thank you very much for watching, stay warm if you're in the north, and stay cool if you're in
the south! Have a great week and remember to just have a think. See you next week.