What caused the hottest day on record?

The world is warming at an alarming rate, with climate experts suggesting that the 4th of July was the hottest day on Earth in more than 100,000 years, and the El Niño weather phenomenon is almost certainly making things worse. The heatwave sweeping southern Europe at the moment has been so intense that the Italian Meteorological Society has dubbed it Cerberus, after the three-headed monster that features in Dante's inferno.  Roshan Salgado D'Arcy is a science communicator who’s doing a PhD looking at climate communication.

Roshan - We've got to be really careful about pinpointing climate change as a specific cause of any particular weather event. And this is no different. There's two ways we can answer what's causing this heatwave. The first is the very technical answer, which goes into things about atmospheric physics, air pressure. In a very literal sense, it's caused by a high pressure area of air sitting on top of Europe. But if you take a more big picture, a holistic earth system perspective, you can think of it in terms of energy. And that's where the climate change element comes in. Because our weather system and our climate is driven by the amount of energy available to the atmosphere and the oceans. And what we are effectively doing is trapping more and more energy in the atmosphere in particular because of our emission of carbon dioxide predominantly. We are giving more energy to natural systems. So we can't say specifically that this heat wave is caused directly by climate change, but we can absolutely say that we have given it more energy to exacerbate the heat further.

Chris - And the role of El Nino, what is that and how might it contribute not just here, but beyond?

Roshan - So, El Nino is a natural phenomenon which would occur with or without climate change. If you think of it in terms of energy, a basic description is that it is the movement of energy, specifically heat, from the oceans to the atmosphere. And specifically that's the Pacific Ocean. So as far as El Nino's role in the current European heat wave, it's very hard to draw a direct link because El Nino's direct effects are almost always concentrated around the Pacific. But of course the Pacific is a huge, huge ocean. It takes up a ridiculously large chunk of Earth's surface. So inevitably it has effects all over the world. So on a local level, for example, El Nino tends to cause a lot more heavy rainfall along the west coast of America, but it also dries out on the other side of the Pacific, say around Indonesia. But as far as linking it to the heatwave is concerned, it's much harder to make that connection. But of course, coming back to the point about energy, by releasing this energy from the ocean into the atmosphere, it can almost certainly play some kind of role. But it is also worth mentioning that the full effect of El Nino won't be really felt until later this year. So it's still only just getting going.

Chris - And in human terms, what are the consequences, both short and long term, of these extreme weather situations that we are experiencing?

Roshan - Well, on a very tangible level, it literally has killed people. So a study came out this week, in fact, which looked at heatwaves from last year, 2022, specifically in Europe. And it found that approximately 60-61,000 people died as a direct result of heatwaves in Europe. That's not an insignificant number.

Chris - What did they die of?

Roshan - It's all kinds of heat related effects. Heat stress for example, dehydration are probably the two main factors. Heat has physiological effects on the body and the human body can only survive up to so much heat. And we are seeing temperatures in the 45 degrees plus in Europe, which is insane. And that is pushing the limits of what human beings can survive. You don't want to be exposed to that for too long.

Chris - So what should be on the priority list for policymakers?

Roshan - Well, here's the thing, it's not going to get better, and that sounds really pessimistic, but all the heat we've seen so far is locked into the system. So it's going to keep getting worse until we get to a point where we stop putting CO2 into the atmosphere. So that is the biggest take home message: we have to get to net zero as fast as possible because that's the only way we'll stop this getting worse.