The past couple of years have set worryingly high temperature records, but was the extraordinary global heat of 2023 and 2024 just a freak event down to natural variability, rather than a sign of something more worrying? Some climate scientists think so.
鈥淔rom a model perspective, yes, it鈥檚 variability that we expect,鈥� at Leipzig University in Germany told a meeting of the European Geosciences Union in Vienna last week.
But there is still much debate about the issue, and some think the rise in temperature could be a sign that global warming is accelerating.
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Surface temperatures worldwide were expected to exceed the long-term warming trend in 2023 and 2024 because of an El Ni帽o event, which releases heat from the oceans into the atmosphere. In reality, the rise was much higher than can be explained by an El Ni帽o, with records repeatedly being smashed.
This has led to many efforts to understand the 鈥渃razy jump鈥�, as Haustein put it. The big question is whether it is a one-off or a sign of some change that is going to result in accelerated warming from now on. 鈥淒o we need to freak out?鈥� Haustein asked.
He thinks the answer is no. In simulations performed by his team, there were jumps similar to what was observed as a result of natural variability alone.
Haustein compares to the situation to what happened in the 2010s, when a run of cold years led to claims that global warming had stopped. Just as those cold years were a one-off, the recent big increases could be too.
But there may be other explanations. In a separate talk at the meeting, at the Helmholtz Centre for Polar and Marine Research in Germany described findings by his team that suggest the record heat was due to a decline in low-lying clouds, meaning less heat was reflected back into space. This could be natural variability, but it could also be the start of an ongoing change, meaning faster warming in the future.
Goessling acknowledged that several studies have shown that natural variability alone can produce such big jumps. But he compared the situation to finding a body: the cause of death could be natural causes, but if you find a knife in its back, that is the more obvious explanation.
鈥淚 think this knife could be something like what is going on with the absorbed solar radiation, that this is increasing quite a bit more than we expect [due to fewer low clouds],鈥� Goessling told the meeting.
In other words, just because natural variability could explain the heat jump, that doesn鈥檛 necessary mean it is the most likely explanation, he said. Over the coming years, it will gradually become clear which hypothesis is correct.
EGU General Assembly 2025
