If geoengineering goes rogue

Reaching for the sunshade: July 2030

Efforts to cut emissions may fall short. What if some countries try to fix things a different way? An imagined scenario from 2030

THE PARIS climate deal commits its signatories to cuts in climate-changing greenhouse-gas emissions over the coming decades. But even if countries stick to their promises (and some may not), that may not be enough to avert catastrophe. Imagine that by 2030 global temperatures are still creeping up, and sea levels are tens of centimetres higher—significantly worsening the impact of storm surges that push seawater over low-lying areas and corrode coastal infrastructures. In Europe and America, summer heatwaves and winter flooding have become more severe. In America’s southern states, the Caribbean and South-East Asia, coastlines are battered by stronger tropical cyclones. The global South suffers worse droughts and more irregular monsoons, undermining fragile agricultural systems and causing famines and civil unrest. The reality of global climate change becomes apparent to rich and poor countries alike.

Under these conditions, it seems likely that some countries will propose the use of a technique called “solar geoengineering” to cool the planet or slow its warming. One way to do this involves injecting tiny reflective particles into the stratosphere, where they would act as a sunshade by bouncing part of the sun’s energy back out into space. Something similar also happens naturally: big volcanic eruptions have, in the past, thrown large amounts of material into the atmosphere, cooling the planet for months or years. The eruption of Mount Pinatubo in the Philippines in 1991, for example, reduced temperatures in the northern hemisphere by as much as 0.5ºC for four years. Solar geoengineering would, its advocates say, do the same thing in a more controlled manner.

Imagine that the idea starts to gain political support. The first detailed international discussions of the options, starting in the mid-2020s, are fraught. Developing countries,…