The Paris Agreement was adopted in December 2015 and entered into force in November 2016, with the United States among the original signatories under President Barack Obama.
The United States formally withdrew from the agreement in November 2020 under President Donald Trump, rejoined in February 2021 under President Joe Biden, and initiated withdrawal again in January 2025 under President Trump's second administration.
Under its 2021 nationally determined contribution, the United States pledged to reduce greenhouse gas emissions 50–52% below 2005 levels by 2030.
Supporters argue stronger U.S. commitments are needed to limit warming to 1.5°C above pre-industrial levels, citing IPCC findings that current global pledges fall short of that target.
Critics argue the agreement imposes economic costs on the United States while allowing China, the world's largest emitter, to continue increasing emissions through 2030 under its own pledge.