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Solar geoengineering could offset global warming without causing harm

A hand with a spray bottle spraying a solution that is making a harsh sky blue.
Illustration: Lazaro Gamio/Axios

Researchers studying the potential consequences of dispersing tiny particles into the upper atmosphere, where they would reflect incoming solar radiation and offset global warming, have come up with a way to avoid producing ill effects in some regions, such as drought.

Why it matters: Solar geoengineering, which would involve dispersing sulfate aerosols into the stratosphere, is viewed as a possible way to offset some of the global warming that would result from doubling the amount of carbon dioxide in the atmosphere compared to preindustrial levels. However, concerns have been raised about its potential to unintentionally harm particular countries or regions.

The new study, published Monday in Nature Climate Change, finds that this futuristic fix is neither the panacea that some advocates portray it to be nor is it an option that would automatically cause significant harm to some parts of the globe.

What they did: For the new study, researchers at Harvard, MIT, Princeton and Georgia Tech used computer models to project how climate change would play out if solar geoengineering were used to cut in half the global warming from a simulated doubling of CO2. They looked at differences in regional precipitation and shifts in extreme weather events, including tropical cyclones, between a world with and without solar geoengineering.

What they found: Contrary to earlier studies that focused on solar geoengineering schemes that would aim to cancel out all human-caused global warming, the new study found that halving the amount of warming would not have widespread, significant negative impacts on temperature, water availability, the intensity of hurricanes or extreme precipitation.

  • Trying to offset all the warming, on the other hand, could cause significant harm to some regions, previous studies have shown.

But, but, but: There are many "ifs" in this study, from the possible flaws in climate models to assumptions about how solar geoengineering would be conducted. Therefore, the results should be taken with some caution.

  • This study does move the geoengineering conversation forward, however, by showing the benefits from solar geoengineering used as a complement to emissions cuts rather than a substitute for them.

What they're saying: "This suggests solar geoengineering could have large and equally distributed benefits, but it doesn't prove it. It's an idealized model," study co-author David Keith tells Axios. "There are still huge uncertainties. And also it's clear that if misused, solar geoengineering could have huge damages."

Keith cautioned against seeing geoengineering as a way to avoid human-caused global warming.

"If people are thinking this is a get out of jail free card, a technological fix it means we don’t need to cut emissions, then they are mistaken. Or to be harsher: delusional."

Gernot Wagner, a research associate in environmental science and engineering who works with Keith but did not co-author this study, tells Axios that the work shows that geoengineering could be done in such a way that the positive effects significantly outweigh the negative side effects.

"Many who look at solar geoengineering for the first time consider it too good to be true. This study shows that there really is a broad consensus among climate models that its effects, when done sensibly, are net positive. The emphasis, of course, needs to be on 'when done sensibly.' None of this means that solar geoengineering is a good idea. The governance challenges are vast."

The big picture: Geoengineering is viewed by many as controversial, since it would involve deliberate human intervention with the climate, with potentially unforeseen consequences, in order to combat human-caused global warming. At a UN Environment Assembly meeting in Nairobi this week, officials are trying to grapple with some of the governmental implications of researching and deploying geoengineering technologies.

Why you'll hear about this again: With the world on track for more than 2°C, or 3.6°F, of global warming this century relative to preindustrial levels, policy makers may turn to geoengineering as a way of damping warming, and therefore reducing the severity of its impacts.