The world is not reducing emissions fast enough to mitigate the most deadly effects of climate change, so it’s time to study temporary methods to cool the Earth by blocking some of the sun’s rays, according to an internationally recognized group of scientists.

Every four years, scientists backed by the United Nations put out a report assessing the progress of the Montreal Protocol, a landmark 1989 environmental treaty that regulated chemicals that harmed the ozone layer. For the first time ever, the report has an entire chapter addressing stratospheric aerosol injection, more colloquially called solar geoengineering.

It’s a way to cool the atmosphere temporarily by injecting sunlight-reflecting particles of sulfur dioxide, or perhaps another substance, into the upper atmosphere, similar to what happens naturally with volcanic eruptions.

The idea has been mentioned in earlier reports, but “what’s different this time is the prominence,” explained David Fahey, one of the co-chairs of the scientific assessment panel.

The pressing question regarding stratospheric aerosol injection is whether this kind of solar geoengineering is more damaging to the Earth than the climate change it would temporarily mitigate. There’s no simple answer, which is why more study is required.

“It depends on: What are you injecting? What altitude you’re injecting it. How much you’re injecting. What latitude are you injecting? What time of year are you injecting? And are you doing more than one injection?” Fahey told CNBC. Generally speaking, conversations about releasing particles into the stratosphere are referring to sulfur dioxide, but there are no clear answers to the other questions.

“We’re actually advancing the ball a bit here by having the first full chapter in this framework where every nation in the world is at the table,” Fahey said. ”‘It depends,’ is a really, really important message on this topic at this stage.”

A chart in the report summarizes how the scientists believe geoengineering should be considered — not as a solution to climate change, but as a way to lower temperatures temporarily. Reducing greenhouse gas emissions will eventually work to slow global warming, but that’s a very slow process. Releasing sulfur dioxide into the stratosphere is fast and cheap compared to more long-term solutions.


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