The US has officially left the Paris Agreement under President Donald Trump, becoming the only country to withdraw from the climate pact twice; it first exited in 2017 and rejoined in 2021 under President Biden. The US is the world's second-largest greenhouse gas emitter after China. Besides the US, only Iran, Libya and Yemen among UN members are outside the deal. Adopted at COP21 in 2015 by 195 parties, the agreement seeks to hold warming well below 2°C, preferably 1.5°C, with NDCs updated every five years.