A similar mechanism could create even nastier water-cycle problems. Stratospheric aerosols may cool the continents more than they cool the oceans, equalizing the normal pressure difference between land and sea—and, in turn, killing the seasonal monsoons of Asia and Africa. Food prices worldwide would skyrocket.
Some researchers are investigating whether these secondary problems could be addressed by adjusting where or how aerosols are sprayed, but Robock said this was “like putting a Band-Aid on a Band-Aid.”
“We still have to see if that’s better than not doing it at all,” he told me.
Other sessions at the conference focused on other unknowns about solar geoengineering beyond weather. Little research has been conducted into how ecosystems would respond to prolonged global dimming. Some researchers also worry that spraying sulfur dioxide into the high stratosphere could damage the ozone layer, though recent research has suggested this risk is smaller than once thought.
And, of course, there are outstanding questions about who will get to make the call—morally, politically, and technologically—that it’s time to deploy solar geoengineering.
The existence of a large, organized field to study geoengineering is itself a recent development. Eleven years ago, the Dutch climate scientist and Nobel laureate Paul Crutzen called for researchers to seriously investigate solar geoengineering “as an escape route against strongly increasing temperatures” in an article in the journal Climatic Change. Today, the paper is considered the founding article in the field, allowing researchers to seriously study solar geoengineering.
“It was a big deal—not in anything that [the paper] said, but in that it said anything about solar geoengineering at all,” said Gernot Wagner, a co-director at the Harvard solar-geoengineering program, and an attendee at last month’s meeting. “There was a decades-long taboo to work on this topic.”
“Now, there are hundreds of peer-reviewed papers on this topic. It’s developing as a research field that people take seriously, where people are interested in formulating testable hypotheses, and where people work on advancing the state of knowledge across the field,” he said.
The new Chinese program is a testament to the scientific seriousness of the field, he said. “That it’s funded through the regular Chinese scientific apparatus, that in itself is important. These things don’t happen overnight.”
It’s still unclear whether solar geoengineering will ever be deployed. Some researchers, like Wagner, consider it a virtual certainty. “It’s not a question of if, it’s a question of when someone will pull the trigger,” he told me.
In his book Climate Shock, written with the economist Martin Weitzman, he argues that it will be a principle in the 21st century:
Geoengineering is so cheap to do crudely, and it has such high leverage, that it almost has the exact opposite properties of carbon pollution ... It’s so cheap that someone will surely do it based on their own self-interest, broader consequences be damned.
Ken Caldeira wasn’t so sure—though he said that last month’s meeting helped solar geoengineering seem real to him. “The meeting made me take it a little more seriously as something practical, and not just theoretical,” he said.