In some climate circles, solar geoengineering is akin to a swear word. Also known as solar radiation modification (SRM), it means deliberately modifying the earth’s atmosphere to reflect solar radiation. It provokes forceful pushback, because it’s unclear how it would affect the earth’s agriculture, ozone layer and ecosystems.

But it’s been attracting interest because it’s clear it would do one thing well: cool the planet.

If we’re not moving fast enough on emissions reductions and carbon removal to avoid 1.5 degrees Celsius of warming, could solar geoengineering, despite its risks, be less dangerous than a hotter world?

In this episode, Shayle talks to Dan Visioni, a climate modeler who studies solar geoengineering at Cornell University’s Sibley School of Mechanical and Aerospace Engineering.

They discuss what solar geoengineering might look like in the real world. 

Stratospheric sulfate injections would mimic the effects of volcanic eruptions like Mount Pinatubo in 1991, which cooled the planet by 0.5 degrees Celsius in the following year. 

Marine cloud brightening would use salt aerosols to brighten a type of cloud that reflects solar radiation, a phenomenon already created by ocean-going ships.

They also cover cirrus cloud thinning and—straight out of a sci-fi movie—space mirrors.

They explore key questions, such as:

  • What do we know about the potential effects on ozone, precipitation and ecosystems? What do we need to research and what could we learn by testing?
  • Which could scale faster—Carbon dioxide removal or solar geoengineering? 
  • Solar geoengineering could cost a tiny fraction of the amount required to scale up CDR. Does that mean it could buy us time to draw down emissions more cheaply? Or does the relative affordability enable a rogue actor to deploy it without international collaboration?
  • And who gets to decide whether the world deploys solar geoengineering? Whose hand is on the thermostat, so to speak?


  • Nobel prize winner Paul Crutzen’s influential 2006 paper on stratospheric sulfur injection
  • A provocative New York Times Op-Ed promoting geoengineering from David Keith, professor of applied physics and public policy at Harvard who studies geoengineering

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