Such meddling could cause unforeseen ecological consequences, they say. And then there are political risks: Researchers fret that even proposing a techno-fix for global warming could lessen the urgency to reduce global emissions of carbon dioxide, the primary driver of global warming, and other greenhouse gases.
Yet the dangers of climate change are becoming more apparent with each passing year. A new study in the journal Nature Climate Change warns that by the 2100, the planet has only a 5 percent chance of limiting temperature rise to 2 degrees Celsius (3.6 degrees Fahrenheit) above pre-Industrial Age levels — a threshold above which many climatologists warn truly scary things will happen to Earth’s atmosphere and oceans.
Forecasts like that make large-scale climate engineering proposals worth studying, says Ken Caldeira, climate researcher at the Carnegie Institution for Science in California.
“Transforming our energy system will take the better part of a century and temperatures are likely to go up substantially while that’s happening,” he said. “If you think there’s a substantial chance of catastrophic outcomes, then solar geoengineering approaches are the only things that could cause the Earth to cool down within a politically relevant timescale.”
Geoengineering, he said, is best understood as a temporary ecological painkiller that could be administered while the world undergoes the difficult surgery of transitioning to a low-carbon economy.
“The consequences of global warming may be so bad that it’s worth doing something as dramatic and risky as deploying these solar geoengineering ideas at large scale,” Caldeira said. “But geoengineering is not a substitute for emissions reduction. It’s a compliment to emissions reduction.”
Yet if such a program were to proceed — which approach should be used?
Caldeira and an international team of researchers from China and India recently proposed a novel idea of combining multiple approaches to create “cocktail geoengineering,” in an attempt to calibrate both temperature changes and fluctuations in precipitation.
Their first ingredient is one of the most prominent ideas in geoengineering — spraying aerosols into the stratosphere to reflect some of the sun’s incoming rays back into space.
Climate models suggest this approach would reduce global rainfall, however, because when beams of sunlight hit the Earth, they warm the oceans and cause evaporation, which in turn falls back down as rain.
Caldeira and his colleagues looked at combining the stratospheric aerosol technique with another approach — thinning high cirrus clouds, which are involved in regulating the amount of heat that escapes from the planet to outer space.
The team found that blending the two techniques would likely reduce global temperatures and maintain global precipitation amounts at their pre-industrial levels.
Yet the climate model examined by Caldeira and his team has an unresolved drawback, he said. The overall level of precipitation would stabilize, but rainfall would likely be redistributed around the globe, potentially overrunning some areas and drying out others.
“For every different locality, you wouldn’t do much better using the cocktail than you would just using stratospheric aerosols alone,” Caldeira said.
Nevertheless, Caldeira said climate models suggest geoengineering would be effective at mitigating the worst impacts of climate change for most people — buying time for nations to reduce their greenhouse gas emissions.
“If you actually trusted the models, and you were really concerned about climate damage, then you’d take this very seriously,” he said.
But others who agree on the need to drastically reduce carbon dioxide emissions say that taking geoengineering seriously creates more problems than it solves. Among them is Pat Mooney, executive director of ETC Group, an organization that monitors the introduction of new technologies, especially in underdeveloped countries.
Mooney worries that as geoengineering gains a higher profile, politicians will use it as an excuse not to make the painful economic changes necessary to reduce emissions.
Geoengineering “gives our politicians another excuse not to do anything,” Mooney said by phone from Nova Scotia, Canada. “It doesn’t solve the problem. It just puts another weapon in the hands of incompetent politicians.”
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