Bill Nye the “Science Guy” slammed President Trump’s decision to pull the U.S. out of the Paris climate agreement, saying clean energy is “the future.”

In an appearance on MSNBC on Thursday, Nye warned that climate change would affect all people, especially those in future generations.

“Bill, is that the best use of our resources today?” MSNBC host Stephanie Ruhle asked. “To think about generations 20, 30, 100 years in the future when there’s people who need jobs and education and safety today?”

“Are you kidding? Climate change affects us tomorrow. Climate change affects everyone in the world because we all share the air," Nye responded.

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“You can’t build a border wall against carbon dioxide emissions. The time to get to work on this is right now.”

Nye, a frequent critic of Trump’s environmental policies, joined a protest at the White House on Thursday in favor of the Paris deal.

“The demonstration began after today’s announcement,” he tweeted. “People are concerned about the lack of US leadership jeopardizing the whole planet.”

The demonstration began after today's announcement. People are concerned about the lack of US leadership jeopardizing the whole planet. pic.twitter.com/FScGD1qGzq — Bill Nye (@BillNye) June 1, 2017