Humans may need to re-engineer the climate

For decades, “geoengineering” was a forbidden subject in climate circles. Talking about adjusting the Earth’s energy balance by, for example, using mirrors, white roofs or aerosols to reflect solar radiation away from the planet and back into space could legitimize a strategy that should be a last resort. Fiddling with the Earth’s thermostat could have unintended effects on natural systems. Moreover, geoengineering might not address all the problems associated with rising carbon dioxide levels, such as ocean acidification. Better simply to stop emitting heat-trapping gases.

But humans have not cut greenhouse emissions quickly enough. As temperatures rise and extreme weather becomes more common, researchers have estimated that current greenhouse gas levels will result in economic losses from climate change of 11 to 29 percent of the world’s income by 2050 — and global emissions rates are still rising. Though permanent cooling requires pulling carbon out of the atmosphere, temporarily cooling the planet might be worth trying at some point in the future, given the likelihood of future warming past any acceptable benchmark.

If, that is, world leaders answer some pressing questions: Who gets to decide when to re-engineer the weather, with what technology and at what scale? That will take a lot more research on geoengineering’s impacts and some international framework to guide its deployment. Unfortunately, the global climate establishment is not doing this work, putting the world at risk that public or private organizations might eventually take matters into their own hands, with potentially disastrous consequences.

Climate geoengineering is so cheap and potentially game-changing that even private entrepreneurs have tried it out, albeit at small scales. Climate engineering scholars David Keith at the University of Chicago and Wake Smith at Yale think it would take no more than 15 souped-up Gulfstream jets to send up, say, 100,000 tons of sulfur per year into the lower stratosphere to block solar rays, at an annual cost of some $500 million. This could happen in as little as five years.

Such a small deployment — about 0.3 percent of the sulfur pollution emitted globally each year — would be unlikely to have a very large impact on the climate and weather systems. Mr. Keith and Mr. Smith estimate the cooling would delay the global rise in temperatures by about one-third of a year — about half the impact as from eliminating all emissions from the European Union. And, yet, they note, “it could trigger political instability and invite retribution from other countries and international bodies that would not respond well to entities fiddling with the planet’s thermostat without global coordination and oversight.”

Cooling the Earth by 1 degree Celsius for a decade would require sending up several million tons annually, in part because sun-reflecting aerosols endure only about a year in the stratosphere. Aircraft have not yet been developed to deliver that much stuff that high. Setting up a proper fleet could take more than a decade. But hard-hit countries will increasingly be tempted to try to use such a shortcut to stave off further warming. And, if they act on their own, all hell would probably break loose.

One might think this prospect would inspire concerted diplomacy. It would seem urgent to establish agreed-upon guardrails around a technology that remains little-understood but whose deployment would have widespread yet unequal effects for different countries around the world. It might make sense to fund experiments on a limited scale before somebody decides to go big to cool Saudi Arabia and, oops, inadvertently messes with the monsoon in India.

Yet most of the world’s governments refuse to engage. This year, the U.N. Environment

Assembly in Nairobi rejected a proposition by the Swiss to appoint an expert group to collect and offer advice on the state of knowledge about the science of Solar Radiation Management, its development, deployment and potential impacts, including risks, benefits and uncertainties. The assembly couldn’t even agree on a watered-down proposal to establish a repository for existing scientific information on the technology. This was the second time world negotiators made this mistake; a similar proposition by Switzerland was rebuffed at the Environment Assembly in 2019.

But the world needs to know exactly what its options are. It looks by now inevitable that the Earth’s temperature will rise 1.5 degrees Celsius above the preindustrial average, beyond which catastrophic impacts on the climate are expected. The U.N. Environment Program says the warming is on track to hit 2.9 degrees by the end of the century.

Assessing the risks of messing up the weather by blocking the sun against the risks of letting the world broil requires a better understanding of the technology and its effects. Along with that, figuring out how to decide if, when and how to deploy such technology will be extremely difficult, given its heterogeneous impacts. But this effort is indispensable — and, increasingly, urgent.