This video was made possible by Brilliant.org If you live in the Northern Hemisphere right now, you might have noticed that it’s really rather hot in the UK. We’re experiencing a weeks long heat wave so severe that when it rained recently it was greeted with jubilation. In England! In Sweden, a surge of wildfires has occurred, including more than a dozen inside the Arctic Circle, where temperatures have topped 30 degrees and in Japan, an unprecedented heatwave has killed more than 65 people in a single week. It’s all but impossible to sleep, horrible to work outside and the land itself is shrivelling up. So, why is this happening? Well as always seems to be the case, there are 3 main causes WAIT! NO NO NO NO NO NOT YET! Cause Number 1: The Atlantic. More specifically, the oceans surface temperature. The surface temperature in the North Atlantic varies in a complex fashion every day. But underneath that variability there’s a see-saw pattern. If you look at the average monthly temperature of the Atlantic over several decades, you see this oscillation between warmer than average and colder than average temperatures. This is called the It’s caused by the huge ocean circulation known as the AMOC – as well as, surprisingly, clouds. I’ll leave a link below to a paper if you’re interested. In fact, every time you see a number on the screen, that’s a reference in the description. Whether the Atlantic is in a warm or a cool phase has a huge impact on parts of the climate like hurricane formation, Arctic sea-ice cover, and global temperatures. And right now, the AMO is in the very positive phase, meaning that the Atlantic is really warm compared to normal. That has a direct effect on the continents surrounding the Atlantic, with lots more thermal energy in the Northern Hemisphere, warming Europe and North America, and making Africa and Europe wetter, while making North America drier. Wait what? The UK resembles Tatooine right now? (Incidentally, you might like the video I did about the planets in Star Wars) While the relationships presented in these papers show what happens on average – so, on average, in the past, when the Atlantic has been warmer than normal, Europe has been wetter than normal. What that average response doesn’t account for is the effect of other climate phenomena and variability on the weather, such as Cause Number 2: The jet stream being particularly weak. The jet stream is a narrow band of fast-moving air that circles the North Pole about ten kilometres up – typically, between about 50 – 60 degrees North. It’s caused by the temperature difference between the pole and the equator, combined with the rotation of the Earth. And, it’s a major factor in what weather we get in the mid-latitudes. At the moment, the jet stream is particularly weak, meaning that the air in the jet is moving slower than normal, but also, that the meanders we see in the jet stream aren’t moving from West to East as fast as normal. Because the jet stream marks a boundary between colder polar air and warmer, temperer air, if meanders in the jet stream stay put for a while, that means that regions south of the jet stream experience warmer than average temperatures for a long time. And conversely, regions north of the jet experience colder than average temperatures for a long time. The UK and Scandinavia, as well as lots of other places I didn’t mention, are all south of the jet stream, and have been for a while. High pressure systems have been sat on top of these places and refused to budge. That means that colder and moisture struggles to get in and alleviate the hot, dry conditions. On the flipside, Iceland for example, has had it’s greyest, wettest summer since 1914. And that’s because Iceland’s been on the other side of the jet stream, sitting further north amongst the persistently cold temperatures. So, Iceland has been cold and wet. The lucky bastards. So what caused the jet stream to be so weak and stationary? Well, that’s quite possible reason number 3: Global Warming. The world is warmer now than it was before the Industrial Revolution, warming faster than any natural cycle allows for, and that warming is directly attributable to human activities – notably, the release of gases like Carbon Dioxide into the atmosphere. There is no debate – the science is unequivocal. If you dispute any of those facts, then, you are wrong. Well, the comments on this video are going to be fun. The globe isn’t warming evenly however. Due to a phenomenon known as the poles are warming faster than the rest of the planet, which reduces the equator to pole temperature gradient. And because the jet stream is fed by that temperature gradient, this results in a weaker jet stream, with bigger meanders. And the bigger the meanders in the jet stream, theory tells us, the more slowly they’re going to move around the Earth. So we get persistent weather patterns, like Japan, and the UK, and Iceland are experiencing. As with all weather events, it is nigh-on impossible to directly attribute a particular event to global warming. These conditions could well have occurred in an atmosphere without a single molecule of anthropogenic origin. But, what we’re observing at the moment certainly matches what we would expect to see in a planet that has undergone global warming. And apart from the weaker jet stream, and persistant associated high pressure systems, the warming caused by these local, short term weather systems gets added on top of the decades-long pattern of global warming we’ve seen, to give record temperatures. In fact, the weak jet stream and warm Atlantic also occurred together in 1976, when the UK had a record-breaking heatwave, which is now regarded as a “yardstick” event This current weather is the most severe heatwave the UK has seen since then, and monthly average temperatures are higher in some parts of the country now than they were in 1976. So thanks to global warming, extreme events are getting that bit more extreme – and research indicates that they’ll be more frequent too. This summer in the Northern Hemisphere is a good example of what climate change is probably going to look like this century. When factors come together such as a warm Atlantic and a weak jet stream, the additional heat trapped in the Earth’s system by anthropogenic emissions will take what would have been a big weather event, and make it an extreme one. Highs will get higher, and as we saw this winter with “The Beast from the East”, (You might want to watch my video about that) the lows will get lower in some places too. But the net effect will be trending towards a warmer on average climate. So when will this current heatwave end in the UK? Well, weather is notoriously difficult to predict! Long range forecasts from the UK Met office indicate that the summer isn’t going to cool off significantly by mid to late August. The high pressure system just isn’t budging. Most likely, it’s going to be uncomfortably warm, with a few cooler days, until September. And then of course, the weather will have to change. Because, you know – Seasons, But weather prediction is incredibly difficult, especially when looking more than about a week ahead. So, this may well turn out to be wrong! For the time being, keep hydrated, avoid the central line, check on elderly neighbours, and if you can, enjoy the sun! Responsibly. This video was sponsored by Brilliant.org. If you’re interested in how the world works, you should check out their expertly curated courses on Science and Maths – including the physics of the everyday. In this course, you’ll get hands on with problems about Nuclear Power, the Coriolis Effect in hurricanes, and, high pressure systems like we’ve been talking about in this video. Brilliant is so well put together, and I’ve recently had some subscribers get back to me saying they’ve really enjoyed doing their courses – as have I. So, if you’d like to join them and the Brilliant community worldwide, then hit the link in the description! That’s Brilliant.org/SimonClark And if you’re one of the first 200 people to do so, then you’ll get 20% off your premium annual subscription. Thanks to Brilliant for sponsoring this video, and thank you for watching it. I hope I was able to provide a little bit more detail than just “It was the jet stream that did it LOL” If you did enjoy it, please do leave a comment down there in the comments section. I would love to do more videos on atmospheric topics, and I basically just don’t know if people would watch them. It’s my forte, it’s what I know the most about, I’d like to make more videos about it, but I could do with a bit of feedback on this. So, if you enjoyed the video, do drop it a like, leave a comment, check out the references in the description, and I’ll see you in the next one. Thank you again for watching.