At TED, a conference about big ideas that's largely attended by tech luminaries, it was inevitable that geoengineering — the idea of changing the earth's atmosphere to halt or reverse climate change — would come up. During the 2017 TED talks in Vancouver, Canada, multiple speakers brought up geoengineering ideas — but one climate scientist pushed back.

On Wednesday morning, computer theorist Danny Hillis got onstage and proposed a series of ideas for what he called a "thermostat to turn down the temperature of the earth."

Hillis, the founding partner of tech innovation company Applied Invention, rattled off a number of geoengineering concepts that have popped up in recent years, including building giant parasols in space,