This July, during Britain's record-breaking hot summer, a curious row broke out on X over climate science. Reform's deputy leader Richard Tice shared a Telegraph article headlined: "Heatwaves caused by fall in pollution." He said cleaner air, rather than carbon dioxide, was behind higher temperatures and claimed the public had been "gaslit". He was wrong to suggest that carbon dioxide is not the primary driver of global warming.
But the science he was distorting is real - and much more interesting than his original claim. The fossil fuels that we've been burning for more than a century produce two very different kinds of pollution. As is well known, carbon dioxide warms the Earth.
But less well-known is sulphur pollution, which forms vast numbers of tiny particles in the air and reflects sunlight back into space, partly counteracting the warming effect of carbon. Thanks to clean-air policies around the world - like the US's Acid Rain Program in the early 1990s, that reduced gas pollution from power plants - sulphur emissions are falling sharply while carbon dioxide emissions remain near record highs. Scientists increasingly believe the loss of that cooling effect is slightly speeding up global warming.
The past three years were the three warmest ever recorded, and the Met Office says 2027 is "very likely" to replace 2024 as the warmest year on record. And away from social media, the argument over Tice's tweet raised an even more interesting - and worrying - question. Is it possible that our planet is actually more sensitive to greenhouse gases than we imagined?
And if so, might the climate be changing more rapidly than we feared? Global temperatures jump around naturally from year to year. El Niño, for example, a natural warming of the Pacific Ocean, can temporarily push them higher.
So a run of record hot years does not necessarily mean the underlying rate of global warming has increased. Reto Knutti and his team at ETH Zurich have tried to strip out the effects of El Niño and other natural fluctuations to reveal the underlying trend. "It's pretty clear that the rate of warming has accelerated," says Knutti, a professor of climate physics at the Swiss university and a former co-ordinating lead author for the IPCC - the UN-backed body that produces the world's most authoritative assessments of climate science.
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