The clues that hint our planet might be heating faster than we realised

Burning coal and oil releases sulphur dioxide, which forms tiny particles known as sulphate aerosols. These particles are bright and reflect some sunlight before it can reach and warm the planet’s surface.

NASA

You’ve probably heard the greenhouse analogy used to explain global warming. Gases like carbon dioxide make it harder for heat to escape from the Earth, rather like the glass windows of a greenhouse.

Well, sulphur pollution acts a bit like dust on the greenhouse windows. The more dust that gathers on those windows, the less sunlight gets inside, and the slower the greenhouse heats up in the first place.

Dr Øivind Hodnebrog, a principal researcher at Cicero, the Norwegian climate research institute, has studied how falling aerosol pollution affects the climate. “Sulphate aerosols, they are really small particles, but they are bright particles,” he says.

As well as reflecting sunlight, aerosols also cool the planet by changing the formation of clouds. Aerosols act like tiny seeds around which water vapour can condense, making some clouds brighter or longer-lived. Pollution from ships can even create bright trails through marine clouds visible from space. So more aerosols mean brighter clouds and more reflection, and so less warming.

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But sulphur pollution also damages human health (it can get into our lungs and make it harder to breathe), and causes acid rain, which can destroy forests and kill fish — and so countries have spent decades cutting it. Emissions have fallen sharply in Europe, North America and China, while new rules have also reduced sulphur pollution from shipping.