GOP Presidential candidate Donald Trump said in May that he would back out of the recent Paris climate agreement. Commentators argued that that would be legally difficult after the deal is ratified this year. But experts speaking with Climate Central now say that there are at least three ways that President Trump could abandon it.

Those options range from aggressive to passive. The aggressive option, according to Arizona State University law professor Dan Bodansky, would be to withdraw from an older agreement, the 1992 UN Framework Convention on Climate Change. President Trump would have to give one year notice of this withdrawal, after which the U.S. would also be considered as having withdrawn from the Paris agreement.

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The passive option would be for President Trump to remain in the agreement, but roll back environmental regulations, simply undermining America’s commitments to reduce greenhouse gas emissions. Under the Paris agreement, failing to meet emissions goals would incur few concrete penalties.

The third option (which commentators initially argued was the only one) is by far the slowest. Three years after the Paris agreement goes into effect, which is very likely to be before January of 2017, signatory nations can withdraw with one year’s notice. That would get the U.S. out of the agreement by the end of the first Trump term.

Not-yet-actually-President Trump has described global warming as a “hoax,” and said in 2012 that it was “created by and for the Chinese in order to make U.S. manufacturing non-competitive.”

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But leaving climate science to one side, withdrawal from the Paris accord is also starting to look like bad business. Jobs in renewable energy are growing as much as 5% a year, while employment in oil and gas drops by double digits and oil and gas providers struggle financially.

Amazingly, China has more than four times as many renewable energy jobs as the U.S. Withdrawal from the Paris agreement would tighten domestic markets for renewable energy installation and technology, making it harder for U.S. startups to build a foothold for reaching the global marketplace. So, ironically, it could actually give a big boost to China in an expanding global industry.

But it seems that, if Trump wins in November, he could actually stand by his claim.