The United States withdrew from the 2015 Paris Agreement in November 2020, following an announcement in June 2017 that the United States would withdraw by President Trump and giving formal notice of its intention to leave the agreement in November 2019. After the election of Joe Biden as President in 2020, the United States rejoined the Paris Agreement in 2021. In April 2021, Nicholas Chan wrote for The Interpreter:

For how long will this moment last? Or will the world once again face a US climate “Groundhog Day” come the next presidential electoral cycle in three years? This prospect depends on whether the Trumpist foreign policy approach to multilateralism persists in the Republican party [...]

The Paris Agreement is a legally-binding international treaty on Climate Change, agreed upon at the 2015 United Nations Climate Change Conference (COP 21). The Paris Agreement’s long term temperature goal is to keep global warming below 2 degrees celsius above pre-industrial levels, and preferably below 1.5 degrees celsius. Global emissions would need to be cut by around 50% in order to reach the 1.5 degrees celsius goal, and in 2019 the United States had the second highest level of CO2 Emissions behind China.