During a recent speech at a French university, Tesla CEO Elon Musk made his case for why governments need to impose a revenue-neutral carbon tax.

Removing hidden subsidies and imposing a fee on carbon, Musk told audience members at public research school Pantheon-Sorbonne University in Paris, France, will hasten the switch from fossil fuels to greener energy sources.

“The important thing to appreciate is we are going to exit the fossil fuels era,” said Musk. “It is inevitable that we will exit the fossil fuels era because at a certain point we will simply run out of carbon to mine or burn. The question is really when do we exit the era, not if.”

Musk said the goal should be to move away from fossil fuels “as quickly as possible,” with society instead using sustainable energy sources that “will be good for a billion years.” He named water, solar, wind and geothermal sources as examples.

“So how do we accelerate this transition away from fossil fuels to the sustainable era?” Musk asked the audience. “We need to have a carbon tax. To make it sort of something which is neither a left or a right issue, we should make it a revenue-neutral carbon tax. This would be a case of increasing taxes on carbon but then we’re reducing taxes in other places.”

“In order to give industry time to react this could be a phased-in approach that maybe takes five years before the carbon taxes are very high. That means only companies that don’t take action today will suffer in five years.

“But there needs to be a clear message from the government in this regard. Because the fundamental problem is the rules today incent people to create carbon. This is madness. Whatever you incent will happen. That’s why we’re seeing very little effect thus far.”

Though carbon is a part of the natural world, complete with its own natural cycle, Musk said people have added far more carbon to the cycle than can be process.

“We’re taking billions of tons of carbon that’s been buried for hundreds of millions of years and is not part of the carbon cycle, we’re taking it from deep underground and adding it to the carbon cycle,” Musk told the audience.

“This is what I’d call the turd in the punch bowl. We added all this extra carbon to the carbon cycle, and the net result is that the carbon in the ocean’s atmosphere is growing over time. It’s much more than can be absorbed by the ecosystem.”

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Musk illustrated the amount of increased carbon in the carbon cycle with a graph spanning hundreds of millions of years.

“The result is a steady increase in the carbon in the atmosphere and in the ocean,” noted Musk, showing a graph that spanned hundreds of millions of years. “In the last few hundred years, [carbon parts per million] went into a vertical climb. This is the essence of the problem.”

During his speech, Musk also emphasized that the switch from fossil fuels to sustainable energy sources should be done as soon as possible.

“If we delay the change, the best case is simply delaying that transition to sustainable energy,” he said. “At the risk of being repetitive, there’s going to be no choice in the long term to move to sustainable energy. It’s total logical. We have to have sustainable energy or we’ll simply run out of the other one.”

A video of Musk’s speech, complete with the question and answer session that followed, can be seen below.