Earth is warming faster. Scientists are closing in on Why

Paradoxically, cleaner emissions from ships and power plants are playing a role.

Dr Gavin Schmidt, a leading climate modeller and the boss of the National Aeronautics and Space Administration's Goddard Institute for Space Science (GISS) in New York City, is not noted for his humility. Nevertheless, writing in Nature, a journal, in March 2024, he confessed to being humbled by his inability, and that of his colleagues, to understand the extraordinary 12 months through which they had just lived. The year 2023 had been around 0.2 deg C hotter than had been expected.

Not just humbled: worried, too. If climate modellers' accumulated knowledge and spiffy models could not explain what had just happened, it might mean that climate change had pushed the workings of the earth into "uncharted territory...fundamentally altering how the climate system operates". Both the speed of climate change and the workings of the climate might be changing. The future might look even worse than it used to.

Nine months later, in Washington, Dr Schmidt and his colleagues returned to the subject at the annual meeting of the American Geophysical Union (AGU), the world's largest gathering of earth scientists. The sessions that took place on the topic felt at times like a murder inquiry, with the evidence for one suspect or another gone through meticulously. The probable verdict is now clearer than it was in March; some suspects have been ruled out, new clues have emerged which point to others. The conclusion looks likely to be that the world can expect somewhat higher rates of warming. But the case is still not closed.