While the Paris Agreement became international law this week—making it technically impossible for a president to withdraw before 2019 or 2020—Trump could simply refuse to recognize the agreement’s obligations, the vast majority of which are non-binding. Trump also said, late in the campaign, that he would cut off American support for UN climate science.

Second, Trump will almost certainly terminate President Obama’s Clean Power Plan, a set of EPA regulations meant to reduce emissions from the power sector. Lux Research, a global energy consulting group, estimated before the election that Trump’s policies would lead to the emission of an additional 3.4 billion tons of carbon dioxide into the atmosphere, as compared to Clinton’s.

These two factors alone could push the world over the edge. The Intergovernmental Panel on Climate Change estimated that the planet could only stand another five years of emissions at current rates before it would become impossible to keep the global mean temperature from rising 1.5 degrees Celsius. If emissions increased under a Trump administration, as Lux projects, then the world could overshoot that carbon budget well before 2021.

Trump appears to doubt the existence of climate change itself. Though he later denied saying it, Trump tweeted before the campaign began that climate change was a hoax invented by the Chinese government to depress American industry.

“The Paris Agreement was signed and ratified not by a President, but by the United States itself. As a matter of international law, and as a matter of human survival, the nations of the world can, must, and will hold the United States to its climate commitments,” said Carroll Muffett, the president and CEO of the Center for International Climate Law.

“Donald Trump now has the unflattering distinction of being the only head of state in the entire world to reject the scientific consensus that mankind is driving climate change,” said Michael Brune, the executive director of the Sierra Club, in a statement. “No matter what happens, Donald Trump can’t change the fact that wind and solar energy are rapidly becoming more affordable and accessible than dirty fossil fuels. With both the market and grassroots environmental advocacy moving us toward clean energy, there is still a strong path forward for reducing climate pollution even under a Trump presidency.”

Indeed, Brune’s statement hints at the next steps for climate activists. The Sierra Club has successfully retired more than 190 coal plants since 2003, leading a campaign that has relied more on local activism than federal support. Even if Trump seeks to expand the construction of coal-burning plants, those campaigns will likely continue.

Activists are also likely to seek the creation of emissions-restriction plans in individual states. While Washington defeated a carbon-tax referendum last night, that measure was opposed by the state’s left. Other state efforts at mitigating climate change have found more success. Earlier this year, California passed a series of state laws that will dramatically alter that state’s energy profile, granting its state agency the freedom to cut emissions by 40 percent by 2030. It seems likely that environmental leaders will seek similar measures in other states.