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.
The document, released by the US Global Change Research Program (USGCRP), aims to provide a roadmap for government research into climate change. The USGCRP was established in 1990, and submitted the document to Congress in January.
The report cites a need "to understand potential pathways for climate intervention or geoengineering and the possible consequences of any such measures, both intended and unintended."
The group called for studying both of the two main avenues for geoengineering: removing carbon dioxide from the atmosphere, and spraying chemicals into the sky in order to reduce the amount of incoming solar radiation that would become trapped within Earth's atmosphere.
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Climate engineering is controversial, however - not least because it might go horribly wrong.
Former US Vice President Al Gore, one of the world's most high-profile advocates for fighting climate change, has called the idea "utterly insane."
"We are already engaged in a planet-wide experiment with consequences we can already tell are unpleasant for the future of humanity," Gore told journalists in 2014. "So the hubris involved in thinking we can come up with a second, planet-wide experiment that would exactly counteract the first experiment is delusional in the extreme."
Yet the group called only for research into the subject - not action - and made clear that geoengineering should take a back seat to efforts to reduce emissions of carbon dioxide.
Another reason to better understand the subject would be to help the United States detect, and possibly react to, efforts by other countries, or even private-sector actors, to launch a geoengineering initiative on their own, the report said.
"The need to understand the possibilities, limitations, and potential side effects of climate intervention becomes all the more apparent with the recognition that other countries or the private sector may decide to conduct intervention experiments independently from the US government," the document said.
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The USGCRP said its thinking had been influenced by a 2015 government-sponsored study carried out by a committee under the National Academies of Sciences, which recommended research into climate intervention techniques, including limited outdoor experiments using controlled emissions.
That study suggested that removing carbon dioxide from the atmosphere, while expensive and difficult, carried well-understood benefits and risks.
However, attempting to spray chemicals into the air to deflect sunlight, the study said, would only temporarily delay the warming effect of carbon dioxide, and bring unknown side-effects and dangers.
The recommendation by the USGCRP in January followed a slew of measures by the Obama administration aimed at extending climate-friendly policies beyond the end of his presidency - including a moratorium on new coal mine leases on federal land and an attempt to permanently block oil production in Arctic seas north of Alaska.
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