Why is the UK feeling the heat more than ever? | This Is Why

0:00 – 4:37

When 40 degrees stops feeling exceptional

It opens with a sharp bit of irony: parts of London Climate Week, the largest independent climate event in Europe, had to be cancelled because the city was too hot. At the same time, trains were disrupted, the national grid was under pressure, schools were closing, and emergency departments were filling up. That is the first big point of the episode. Heat in the UK is no longer just a matter of discomfort. It is a systems test. Tom Clark says this heat wave is expected to be "really hot" and, crucially, "sweaty." That contrast matters. He compares it to July 2022, when the UK broke its all-time heat record and "just passed 40°" in central England. That earlier event was drier and came with wildfire risk. This one follows thunderstorms and a cooler, wetter spell, which means more moisture is sitting in the air. Forecasting the exact peak is difficult, but he says "39 degrees potentially potentially higher" is on the table, and this is happening a full month earlier than the 2022 event. It also comes after a record May heat wave. The unexpected angle is that the headline temperature does not tell the whole story. Clark had assumed humidity was simple, then went to a University of Roehampton heat chamber to test it. In a 40 degree room with humidity turned up, he found his sweat "literally running off my fingertips" into puddles on the floor. The body cools by evaporating sweat, but if the air is already packed with moisture, that evaporation stalls. You keep sweating, but the cooling system fails. That becomes especially dangerous over several days. Night temperatures around 20 degrees might sound survivable, but if the air stays humid, the body cannot properly reset. For frail people, people with heart conditions, and people with diabetes, that prolonged strain can push core body temperature up and create a serious health risk. Outdoor workers face similar stress. Clark reaches back to the 1976 heat wave, when there was "28 30% excess mortality" during the period. He is careful not to claim this event will match that, but the point lands hard: heat kills, and humid heat is a quieter, more exhausting kind of danger than the dramatic wildfire images people may remember from 2022.