The Broken Thermostat

Scientists expected relief from a cooling La Niña cycle, but 2025 revealed that the planet’s thermostat is officially broken.

[Speaker 1]: If you just looked at the headlines this morning, you might have felt a strange sense of relief. The data is finally in, and 2025 wasn't the hottest year on record. It came in third. [Speaker 2]: That’s right. According to the final numbers from Copernicus and NOAA, 2025 finished with a global temperature anomaly of 1.44 degrees Celsius above the pre-industrial average. That puts it just behind 2023 and 2024. [Speaker 1]: And in a world where we’ve grown used to smashing records every single year, coming in third feels like maybe the fever is breaking. Like we caught a break. [Speaker 2]: But we didn't. In fact, when you look at the mechanics of why 2025 was the third hottest year, it’s arguably a more dangerous signal than setting a new record. [Speaker 1]: Because of the context. [Speaker 2]: Exactly. Because of the background conditions. 2023 and 2024 were driven by El Niño-a natural climate cycle that releases massive amounts of heat from the ocean into the atmosphere. It’s the planet’s heating cycle. But 2025 was different. [Speaker 1]: 2025 was a La Niña year. That’s the cooling cycle. That is supposed to be the planet’s thermostat kicking in to bring the temperature down. [Speaker 2]: And that’s the chilling milestone we’re looking at today. The thermostat kicked in, but the house didn't cool down. We just lived through a cooling phase that was hotter than almost every warming phase in human history. [Speaker 1]: Which means the mechanism we rely on to regulate the climate-the natural swing between hot and cold years-has been overwhelmed. The thermostat isn't just set too high. It’s broken. [Speaker 2]: It’s Tuesday, January 20, 2026, and you’re listening to The Angle. [Speaker 1]: I want to stay on this idea of the broken thermostat, because I think it explains why the mood among climate scientists today is so grim, despite the lack of a new record. Usually, we think of global warming as a staircase. Step up, flat for a bit, step up again. [Speaker 2]: Right. And we assumed La Niña would be the flat part. Historically, trade winds pick up, they push warm surface water west, and cold water rises from the deep ocean to cool the atmosphere. It’s a very efficient air conditioning system for the planet. [Speaker 1]: But this year, the AC was running at full blast, and the temperature barely budged. So the question is, where is all this heat coming from that it can overpower a planetary cooling cycle? [Speaker 2]: There are two main drivers here. One is a battery, and one is a shield. Let’s start with the battery. The ocean. [Speaker 1]: We talk about air temperature because that’s what we feel, but the ocean is where the story actually happens. [Speaker 2]: The ocean absorbs about 90 percent of the excess heat we trap with greenhouse gases. It’s a massive thermal buffer. And in 2025, that buffer was full. We saw record Ocean Heat Content. In just the last year, the oceans absorbed roughly 23 zettajoules of heat. [Speaker 1]: Zettajoules is one of those numbers that’s too big to visualize. But to put that in human terms, 23 zettajoules is roughly equivalent to twelve Hiroshima-sized atomic bombs detonating every single second, for the entire year. [Speaker 2]: That is the energy equivalent we added to the ocean in 2025. So when La Niña tried to bring up cold water to cool us down, it couldn't find enough cold water. It was just churning warm water. [Speaker 1]:…