Instant Genius - What's going on with the weather? - Dann Mitchell

Episode Date: August 16, 2018

This summer has been one of the hottest on record, so we asked climate change researcher Dann Mitchell what has caused the summer heatwave, can we expect more, and is there anything we can do about it? Hosted on Acast. See acast.com/privacy for more information. Learn more about your ad choices. Visit podcastchoices.com/adchoices

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so you can experience exceptional sound at home. Music just as the artist intended. Visit name audio.com to learn more. So we've seen this year, actually the jet stream is in a state where it's allowing flow from North Africa to get up to Europe. And that's bringing the heat associated with the heat wave there towards our continent, which is one of the contributing factors for the heat wave in the UK. You're listening to the Science Focus podcast from the BBC Focus magazine team. We're the UK's best-selling science and technology monthly, available in print and in several digital formats throughout the world.

Find out more at ScienceFocus.com or look out for us in your app store. Hello and welcome to the Science Focus podcast. I'm Alice Lipscomb-Southwell, the production editor of BBC Focus magazine. This summer has been one of the hottest on record, with temperatures reaching 35.1 degree centigrade in Surrey. The scientific consensus is that extreme weather such as this, is being driven by changes in the climate due to human activity. But how exactly is this happening? Can we expect more of the same? And is there anything we can do about it?

Our commissioning editor, Jason Goodyear, talked to Dr Dan Mitchell, a climate change researcher based at the University of Bristol to find out more. But before we start, we'd like to apologise for poor quality of audio in this podcast at certain points. So I don't think I'm alone in saying this,

but this summer definitely seems to be one of the hottest that I can remember. I mean, is that really the case? Well, the summers just for the UK have been persistently hot. They're certainly not the hottest on record. But in terms of number of days of moderate to high heat in a row, and they have been really, really quite high, for Northern Ireland and for parts of Scotland,

then there's certainly been some records broken. in County Tyrone, for instance, there were some records broken. So we're nearly there, but we're not quite at the record for maximum daily heat in a certain day. So one of the major contributing factors to this seems to be something known as the jet stream. So often when talking about weather and the climate, we mention the jet stream. But what exactly is it? So the jet stream is a consequence of our planet. spinning and being a sphere. So every, well, a lot of planets have jet streams and you can see them

very clearly, for instance, on Jupiter. But the jet stream is just a region of very high winds. On our planet, they're located at the tropopause, so that's around 10 kilometers in height. And they're located at the region of maximum temperature gradient, which is mid-Latose. So about 30 to 60 degrees in the northern hemisphere and in the southern hemisphere. So we have different jets. But the interesting thing about the jets is they can carry heat from one place to another place. They can block weather systems from going anywhere.

And they generally do a lot of things for connecting extreme events. So the jet streams in our hemisphere have been moving around quite a bit. So they've been looking a bit like waves. And those waves can travel all the way up to the north pole and then really far down to near the equator as well, not quite the equator. That means they can bring cold air from the pole down towards the equator or warm air from the equator up towards the mid-latitudes. And so we've seen this year, actually the jet stream is in a state where it's allowing flow

from North Africa to get up to Europe. And that's bringing the heat associated with the heat wave there towards our continent, which is one of the contributing factors for the heat wave in the UK. So not only has it been unusually hot this year, it's also been, it seems to me anyway, to have been unusually dry. So seeing the satellite pictures of the UK, looks very brown and the land looks very parched. Do the two things go hand in hand, the hot temperatures and the dry weather? They don't always. This season they certainly have, and that's because, again, of the jet stream.

So I said the jet stream is like a wave. That wave can also break, much like waves break on a beach, for instance. And when it breaks, it causes a region of high pressure which blocks weather systems coming through. And that's exactly what we've seen here. We've seen a region of high pressure blocking storms and wind and rain coming from the Atlantic. So in that case, it not only heaps up the, surrounding area, but it does also stop rain coming in. So we do get these drier regions. In some sense, that can be a good thing because if we had high relative humidity, for instance, where it's a lot of moisture in the atmosphere, actually the heat can feel a lot more intense because our bodies naturally to dissipate heat, we sweat. And if there's a lot of humidity in the air, we can't sweat. So actually you feel a lot hotter. So although the dryness has contributed to the heat wave,

there are some benefits of it not being so moist as well. So I said it's been very dry, but we have had the odd heavy thunderstorm. And I've heard talk of something called a Spanish plume. Sounds very exotic. I mean, first of all, what is this? And is this causing the heavy, heavy rain bursts? Well, so a Spanish plume is very similar to what I was talking about before. So it's, when the flow of wind is from the equator upward, then the wind goes over Spain and it brings a lot of the heat associated with Spain into the UK. So that's what's meant by the Spanish plume. And actually, we've seen that Spanish plume almost extend down to Africa.

So, you know, in some sense, you could call it an African plume instead of a Spanish plume. And this is one of the main mechanisms by which we get a heated summer in Europe. So it's more to do with the heat. But, of course, it's bringing some drier air with it. does make it less moist as well. But it's not actually stopping the rain. That's a different mechanism. So we've seen a lot of extreme heat waves in the Middle East, the US, Greece, etc. this year. But it's not the case for all countries, isn't it? So I've heard Iceland, for example, is having a particularly wet summer this year. Yeah, so Iceland, I talked a little bit about how

the jet stream is very wavy. And depending on what side of the wave you are on, If you're on the equator-wood side, then you can get a lot of heat. If you're on the poleward side, you might get a lot of rain and a lot of cold air as well. So this blocking that we've had over the UK that blocks the weather systems from getting to us, but it stools them over Iceland because that's where they're coming from. So you'll often see that when we get good weather in the UK, Iceland gets bad weather and vice versa, the systems are really strongly linked. So another weather pattern that's often talked about is the El Nino. It's often involved or plays a role in these extreme weather events.

But I believe that's not the case this year. Yeah, exactly. So El Nino is a pattern of ocean tech. temperatures in Central Pacific, which can reach all over the globe. So in 2016, we had a strong El Nino and that caused that year to be the warmest year on record. Last year, I believe we had a Laninia, and we still had very high temperatures. And the Laninia counteracts high temperatures. So that was sort of a clear sign that human-induced warming has played a role in last year because even with this large negative El Nino event, we still saw warm temperatures.

This year, El Nino is very much in a neutral phase at the moment. It's set to go into a moderate positive phase in a couple of months. But yes, that means El Nino played no role in the current heat wave, which makes it even more extraordinary as to why we got so many heat waves and so prolonged heat waves as well. So climate change, again, you know, 95 probably more percent of scientists, I think it's extremely likely that climate change has played a significant role in our recent climate. Those other 5% of scientists really sort of argue about the degree to which climate change plays a role

rather than whether it does or not. So we're very sure that climate change has played a role within these events. In fact, a team has done an attribution study on this UK heat wave recently, and they showed that it was made two times more likely due to human-induced climate change. And that's simply because of the fact that the entire land has been warming by about 1.6 degrees, since pre-industrial times. So any heat wave we have, it's going to be 1.6 degrees hotter

than it would have been without human-induced climate change, at least. And then there are local factors which sort of might moderate that temperature increase. So you could imagine, you know, where we were having temperatures of, say, 28 degrees in the UK before, those temperatures are getting closer to 30 degrees. And when you're during,

a heat wave every degree really count. So we're sort of very sure that climate change has played a part in that. There also seems to be, over the last few years, an increase in other extreme weather events such as hurricanes, tsunamis, etc. I mean, is this linked in with this situation? Well, I would say actually there hasn't been an increase in hurricanes. Hurricanes are a really complex one. The general consensus is that globally, the number of hurricanes will decrease with climate change, but those that are category four or five, the strongest hurricanes will increase. So we'll get more strong hurricanes, but fewer overall.

So that's why it seems to a person like me, they're more in the news, but it's just because there are more of the stronger ones. It's an interesting one because if you go to Jamaica or the Caribbean, for instance, they're obviously very interested in the strong hurricanes, but actually being continuously hit by category three hurricanes, it's still a very bad thing for them. So they're interested in the whole spectrum. Just in the UK, it's really the devastating ones we see on the news.

So sort of long-term, what do you think is going to happen in the future? Is it inevitable? temperatures are going to continue rising? They're definitely going to increase in the future. I guess the Paris Agreement on climate change, which was a sort of groundbreaking achievement that came about in December 2015, should help us to reduce some of the increase we're expecting, depending on if we can get countries like the US on board. So we would definitely expect some increase in temperatures. I guess the really worrying one in terms of that is sea level rise because there's a lot of momentum in sea level rise. So even if we stopped emitting greenhouse gases now, the sea level

would still rise for a very long time because of the memory in it. So the sooner we stop emitting green out gases, the sooner we can stop those sort of long-term climate change impacts. So for the people that are listening that perhaps want to do something about turning this trend around, what would you say the most important couple of things that they can do to help with climate change? Well, I think writing to your MPs really creating a political willpower to do this. There have been a number of studies out now showing that we can stabilise our greenhouse gas emissions if all of our governments start working together and start thinking about the long-term picture in terms of way beyond the usual timescales of political office, so way beyond four or five years.

And that's the problem. So I think the strongest thing we can do is really lobby our governments to take action. Of course, saving energy in your house is always. going to be a great thing. More vegetarian diets are always going to be a great thing. And the more everyone can do that great. But it's our politicians that we really need to get on board. Sure. Then just by way of closing then, what's the forecast looking like for the rest of the summer? For the UK, we, yeah, we're expected to have some more heat coming in. It's quite hard to tell forecasts beyond actually a week

and not particularly accurate. We do have seasonal forecasts which generally show that this summer will be warmer than usual. So we'd expect it to be warmer, but it's quite hard to tell the details. That was Dr Dan Mitchell, a climate change researcher,

talking about extreme weather and the summer heat wave. Thanks for listening to the Science Focus podcast. In this month's issue of BBC Focus magazine, we're hunting for life's cosmic origins on the back of ancient asteroids, celebrating NASA's 60th birthday, and asking why we haven't developed a male contraceptive pill yet. And there is, of course, much more inside. If you liked what you heard, then why not subscribe and leave a review?

You can find us on iTunes, ACAST, Stitcher, and many of your favourite podcast apps. Find out more at sciencefocus.com. Thank you for listening to the Science Focus podcast from the BBC Focus magazine team. We're the UK's best-selling science and technology monthly, available in print and in several digital formats throughout the world. Find out more at ScienceFocus.com. We'll look out for us in your app store. This podcast is sponsored by Name, Audio and Focal.

The texture and emotional depth of music can be lost through digital sources or poor signal. Name Audio believes you can have digital precision with analogue warmth. Alongside French acoustic specialist focal, Name creates high-end audio systems combining innovation with craftsmanship, so you can listen to music, just as the artist intended. Discover more at name audio.com. Ambition comes in all shapes and sizes. At First Citizens Bank, we roll with your goals,

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