Countries look at ways to tinker with Earth’s thermostat

THE IDEAUNUNEA of cooling the climate with stratospheric sunshades that would shield the planet from the sun’s warming rays moved up the international agenda this week, with mixed results. On the one hand, new research suggested that it is theoretically possible to fine-tune such a shield without some of its potentially damaging consequences. Publication of this work coincided with a proposal at the biennial Environment Assembly (), held in Nairobi, Kenya, for an expert review of such geoengineering methods. This was the highest-level discussion of the topic so far. On the other hand, the more than 170 nations involved could not arrive at a consensus. In a fitting illustration of the heat surrounding geoengineering, the proposal was withdrawn at the eleventh hour.Under the Paris Agreement, governments have pledged to keep average global warming to “well below” 2°C above pre-industrial levels and to try to limit maximum warming to 1.5°C. Many see these targets as wishful thinking: the planet is already roughly 1°C warmer than it was in pre-industrial times, global greenhouse gas emissions are still on the rise and national pledges to cut them fall short of what is needed to hit the 2°C target, let alone 1.5°C.