of Harvard University’s Solar Geoengineering Research Program: In 15 years’ time, as the impacts of warming worsen, planes loaded with sulphate particles start taking off from airfields around the world. They fly to 65,000 feet, well above existing air lanes, and spray their loads into the stratosphere: 4,000 flights in the first year, 8,000 in the second, 12,000 in the third, and so on until, after another 15 years, fleets of purpose-built, high-altitude tankers are making 60,000 flights annually. The thickening shroud of particles would fight climate change by mimicking the output of volcanic eruptions that deflect solar radiation streaming into the atmosphere. Famously, the eruption of sulphate particles from Mount Pinatubo in the Philippines in 1991 caused a global cooling of up to 0.6 degrees C formost promising answer lies in going back to nature — in restoring natural forests.

Maybe there is a simpler solution. Maybe the most promising answer lies in going back to nature — in restoring natural forests. A broad coalition of environmentalists – from those who embrace corporate environmentalism, such as The Nature Conservancy (TNC), to the British anti-capitalist columnist George Monbiot – have recently endorsed this “natural” climate solution. Their touchstone is a 2017 paper by Bronson Griscom of TNC and 24 others, which concluded that a third of the measures required between now and 2030 to keep the world on track to stabilize climate could be achieved cost-effectively by boosting natural ecosystems. They could take an extra 11 billion tons more CO2 out of the air each year.