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, putting fizzy water into the ocean, and sending chalk into the atmosphere so that it can reflect sunlight and theoretically cool down the earth.

"We'd have to put chalk up at a rate of 10 teragrams a year to undo the effects of CO2 we've already released," he said. Here's how he visualized that on stage:

"It would be like one hose for the entire Earth," he said.