Could dimming the sun be the key to cooling things down before the climate crisis worsens? Some scientists say yes, that we can cool the Earth by launching tons of sulfur dioxide into the stratosphere. It’s a type of solar geoengineering that was once seen as preposterous, meant to exist only in the pages of a sci-fi novel. But now, it’s a reality.

To find out for ourselves, we travel to Northern California, where two entrepreneurs are launching sulfur-filled balloons from the top of stacked shipping containers. Later, we talk with scientists on both sides of this issue to find out if solar geoengineering could help prevent catastrophic tipping points or introduce a whole new slew of cascading consequences.

Clarification (June 18, 2026): This episode has been updated to more accurately reflect David Keith's relationship to the carbon removal company he founded.