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“The fossil fuel industry is the biggest industry in the world,” billionaire SpaceX and Tesla CEO Elon Musk said in an interview for the National Geographic documentary “Before the Flood.”

The film features interviews with scientists, policy makers, and others working to combat the emissions that are dangerously destabilizing our climate.

Musk discussed his vision for a global shift toward more localized, clean energy system of solar panels and batteries.

But he said the power of the fossil fuel sector represents a significant concern.

“They have more money and more influence than any other sector. So I think the more that there can be a sort of popular uprising against that the better.”

Musk argued though that because the fossil fuel industry represents such a titanic obstacle in the fight against carbon emissions, there’s limits on what individual people can do to work against their influence.

“What’s really fundamental is that unless there’s a price put on carbon—”

The interviewer, Leonardo DiCaprio (who served as host and science journalist for the purposes of the film), cut in, saying, “We’re never going to be able to make the transition that we need to in time.”

“Correct,” Musk said. “And the only was to do that is basically with a carbon tax.”

A carbon tax is basically a tax on fuels and other activities that leech carbon dioxide, a major greenhouse gas, into the atmosphere. The idea is that it shifts a portion of the cost of climate damage from society writ large to the emitter, and disincentivizes behaviors that harm the environment.

DiCaprio also interviewed a prominent economist and former Bush and Romney advisor who supports the idea, and compared it to efforts to combat cigarette smoking.

You can watch the documentary “Before the Flood” in full below.