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SEEN FROMYour browser does not support the element. afar—as it first was, by human eyes, on Christmas Eve 1968—Earth is a wonder. When the astronauts of Apollo 8 saw their bright, cloud-girdled home rise over the barren lunar horizon they recognised at once that it was dynamic, beautiful and exceptional: something to be cared for.But the view from space does not only inspire: it also informs. Satellites reveal how Earth is changing, and thus what sort of care it needs. And the latest such diagnostic information is that, although Earth remains as beautiful as ever, it has been getting a little less bright.Satellite data show that, since the turn of the century, Earth’s albedo—the amount of incoming sunlight it reflects—has been dropping. Because light not reflected is absorbed, that adds heat to the system and exacerbates global warming. It is part of the reason why , until the 2010s around 0.18°C a decade, now appears to be well over 0.2°C a decade. In the decade to 2023 (admittedly a particularly hot year) it was 0.26°C. For ecosystems under stress the rate of warming can matter a lot; for humans faster warming brings forward extremes that might not have been seen for decades.One reason for this dimming is air pollution—or, rather, its absence. Fossil fuels contain traces of sulphur along with the carbon and hydrogen that give them their name; the sulphur dioxide that is created when hydrocarbons burn forms tiny airborne particles that make the air smoggy. This is deadly. Every year global deaths from air pollution number in the millions.Preventing sulphur emissions from getting into lungs improves people’s health, productivity and spirits. This is why the Chinese Communist Party has been keen on such reductions. And China’s efforts have been impressive; over the past two decades scrubbing sulphur from smoke stacks has reduced its gargantuan emissions by about 90%. Likewise, restrictions on the sulphur content of fuel used by shipping has seen emissions on the high seas plummet since 2020.Reducing sulphur emissions also lowers albedo. Sulphate particles scatter light. As a result, some of it bounces back into space. Sulphate particles can also serve as seeds for the water droplets that make up clouds. Fewer such seeds can make clouds less bright; sometimes clouds do not form at all.Quite how much of Earth’s accelerated warming can be put down to the reduction in sulphur emissions is uncertain. The workings of clouds are complex and sulphur is not the only factor at play. But atmospheric scientists have long expected more warming when this offset is removed. As one of the greatest of them, Paul Crutzen, wrote in 2006: “Air-pollution regulations, in combination with continued growing emissions of CO, may bring the world closer than is realised to the danger [of catastrophic global warming].”In his seminal paper Crutzen also noted that there was an alternative. Particles high in the stratosphere stay aloft far longer than those close to the surface, and so provide much more cooling per tonne. A thin layer of sulphates deliberately added to the stratosphere could provide the same amount of cooling as all the thick, polluting smogs clogging the lower atmosphere while doing much less damage to human health. Crutzen did not advocate this. But he did say it should be researched more vigorously, and that there might be deteriorations which warrant action. One such, he suggested, would be seeing the rate of warming rise above 0.2°C a decade.Since then, the amount of research into solar geoengineering with stratospheric aerosols has increased substantially. But it remains pitifully small, in part because the experts whom governments listen to on climate and research policy are leery of it. A report to the European Commission at the end of 2024 added to calls for a moratorium on practical steps towards it, and argued for various restrictions on research. And it is indeed a daunting prospect, not least because it requires a high level of trust in science, a resource declining even faster than the world is warming.Crutzen wanted swift cuts in greenhouse-gas emissions to render debates about geoengineering moot; he also feared that this was just “a pious wish”. The world’s capacity to do without fossil fuels has increased a lot since then. But emissions have yet to decline, and warming is speeding up. As well as cutting emissions, governments should urgently heed Crutzen’s call for research and discuss how such powers might be used. The message of Apollo 8 still applies; the bright, beautiful world needs to be cared for.
