In the final days of Barack Obama's presidency, a scientific initiative overseen by the White House urged new research into controversial geoengineering techniques that could help avoid the most dire consequences of global warming.
Few paid much attention at the time. Unveiled in mid-January, the recommendation was tucked into a few paragraphs of a 119-page report — while the world stared preoccupied as Donald J. Trump became President of the United States.
But the report marked a sea change: It was the first time that the group, which unites 13 federal agencies to study climate change and set research objectives, recommended exploring the sensitive subject of climate engineering — the idea of deliberately modifying the planet's climate system in order to limit or reverse the negative effects of global warming.