【Secret Confessions (2025) No Label Episode 45】

Solar geoengineering is Secret Confessions (2025) No Label Episode 45widely viewed as risky business.

The somewhat sci-fi concept -- to use blimps, planes, or other means to load Earth's atmosphere with particles or droplets that reflect sunlight and cool the planet -- has crept into the mainstream conversation as a means of reversing relentless climate change, should our efforts to slash carbon emissions fail or sputter. But geoengineering schemes come with a slew of hazards. A number of studies have cited the ill consequences of messing with Earth's sun intake, including big falls in crop production, the likelihood of unforeseen adverse side effects, and critically, a weakened water cycle that could trigger drops in precipitation and widespread drought.

Yet new research, published Monday in the journal Nature Climate Change, acknowledges these problems but finds a potential fix: only deploying enough reflective specks in the atmosphere to reduce about half of Earth's warming, rather than relying on geoengineering to completely return Earth to the cooler, milder climate of the 19th century. In other words, giving Earth a geoengineering dose that would reverse a significant portion of the warming, but not enough to stoke the problematic side effects.

"We wanted to clear up if some of the issues that we’ve seen were the result of doing too much geoengineering," said Peter Irvine, a postdoctoral researcher at Harvard University's John A. Paulson School of Engineering and Applied Sciences and lead author of the study.

In the early 2000s, the notion of geoengineering sounded like a "really outlandish idea," Irvine admitted. But this new research, building on other studies, illustrates that such a planetary-wide undertaking -- if applied cautiously, incrementally, and with careful dosing -- might not be so far-fetched, after all.

"It looks like, surprisingly, it works quite well," said Irvine.

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That's not to say Irvine and his research team are promoting the idea of deploying geoengineering on the planet anytime soon. They aren't. Rather, this research is a piece of the puzzle that may ultimately reveal if geoengineering could work without unleashing widescale harm to the planet, particularly plunges in rainfall (in part due to reduced sunlight resulting in less energy driving rainfall and precipitation).

"I don’t think it makes any sense to do it now," David Keith, a solar engineering researcher at Harvard University and study coauthor, said. "And if it doesn’t make sense, we shouldn’t do it," he added, noting that any geoengineering deployment would likely still be some two decades away.

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"This is the type of work that researchers should be doing to understand the potential climate impacts of solar geoengineering," said Jon Proctor, who researches the impacts of geoengineering on agriculture and had no role in the study. "However, we are still far from understanding the full costs and benefits of solar geoengineering to economic and ecological wellbeing," added Proctor, who is a Ph.D. candidate in agriculture and resource economics at UC Berkeley.

To see how providing a "half dose" of geoengineering would affect the planet, the study's researchers visited the National Oceanic and Atmospheric Administration's (NOAA) super-advanced climate model at the Geophysical Fluid Dynamics Laboratory to simulate Earth's future climate. Specifically, they doubled the carbon dioxide levels in the atmosphere (from 1990 levels) and then "turned down the sun," so to speak, to mimic the effects of solar geoengineering under such conditions.

The results cut Earth's warming by about half. And critically, the cooling effect did not wreak havoc on Earth's water system by decreasing rainfall in vast regions around the world. In such a carbon-saturated atmosphere, the simulated geoengineering also tempered extreme, crippling deluges (which are becoming more common as the climate warms) and reduced the intensity of hurricanes. "By choosing to half warming, we’re going to get close to restoring the water cycle," said Irvine.

A smaller portion of the world -- about half a percent -- saw an uptick in the extreme weather stoked by climate change.

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Such a geoengineering endeavor certainly wouldn't solve all the planet's environmental woes in a warmer world. "No -- it's not perfect," said Irvine. But halving warming might cut into the weather extremes wrought by the highest atmospheric carbon dioxide levels Earth has experienced in millions of years. Already, Earth's CO2 levels are likely the highest they've been in some 15 million years.

"I hope that the paper can be a springboard to rethink some common assumptions."

The possibility that geoengineering could alter the globe's water cycle and produce widescale drought is a big red flag, said Keith, but he hopes this study illustrates that such damaging changes might be avoided, though there's still ample research to be done. "I hope that the paper can be a springboard to rethink some common assumptions [about geoengineering]," he said.

What's more, Keith emphasized that this study isn't just coauthored by known geoengineering researchers like Keith and Irvine, but diverse, well-respected atmospheric scientists like MIT's Kerry Emanuel, an accomplished climate researcher. "Having these different names on the paper should make this be considered more seriously," said Keith.

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If the time ever comes for geoengineering -- in a political climate where climate deniers in powerful government positions still make unfounded claims that plants are in dire need of more carbon -- Keith underscores that it can't be an emergency, last ditch effort, like deploying a parachute. Whether achieved by big weather balloons, blimps, or other methods, solar geoengineering would have to be done carefully, methodically, and incrementally.

In short, it's a fantasy that a massive fleet of blimps will one day suddenly take to air and release bounties of reflective particles in the skies when crops fail and Antarctica unleashes an unstoppable flow of ice into the seas.

"Solar engineering might not be a good choice in an emergency," said Keith. "If it makes any sense at all, it makes sense to gradually ramp it up."

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