The United States is officially out of the Paris Agreement under the administration of President Donald Trump.
It was making it the only country to quit the historic climate pact twice.
It makes the U.S. the only country to abandon the global pact, having previously rejoined in 2021 under President Biden after an initial 2017 withdrawal.
The United States is the world's second biggest greenhouse gas emitter after China.
The only other UN member states outside the Paris agreement are Iran, Libya and Yemen.
The Paris Agreement is a legally binding international treaty adopted in 2015 (COP21) by 195 parties to limit global warming to well below 2∘C —ideally 1.5∘C —above pre-industrial levels.
It requires countries to submit increasingly ambitious, voluntary climate plans known as Nationally Determined Contributions (NDCs) every five years.
The 1.5 °C target is generally accepted to refer to a 20-year average, rather than a single year.