Drafted in December 2015, the Paris climate agreement’s main goal is to limit the average global temperature increase to below 2C (3.6F). If that threshold is exceeded, climate scientists believe subsequent severe weather events will be irreversible.
“We will see more extreme heat, damaging storms, coastal flooding and risks to food security,” Michael Oppenheimer, a professor of geosciences and international affairs at Princeton, told the New York Times.
Signed by 195 nations and enacted last year, the accord works to avoid this disaster scenario by lowering planet-warming emissions.
Technically, the agreement is legally binding, in that it requires participating governments to accept and work toward the 2C threshold. But in reality, its powers of enforcement are weak: Emission targets themselves aren’t binding. For example, President Obama pledged to curb U.S. carbon dioxide emissions by 26% to 28% by 2025. If that goal is not met, there won’t be any legal repercussions.
Obama has called the climate change accord the the "best chance we have to save the one planet we have.” In contrast, President Trump’s stance has fluctuated from hostility to ambivalence. During the campaign, he promised to pull out of the agreement — and despite a few signs he was wavering, it appears he will follow through on this. (Always the showman, Trump amped up the will-he-or-won’t-he reveal on Twitter.)
In theory, Trump can’t pull out of the accord for four years without breaking international law. But as Scientific American notes, there are a couple loopholes. Trump could exit the UNFCCC entirely, or send representatives to observe climate negotiations but not participate in them.
The U.S. produces the second-largest amount of greenhouse emissions in the world, behind only China.