President Trump has fulfilled his campaign promise to pull the United States out of the Paris Agreement, the United Nations accord that commits almost every country in the world to reduce its emissions of greenhouse gases. But today's announcement only anticipates legal actions to follow several years from now; under the terms of the Paris Agreement, the United States cannot notify the United Nations of its intention to withdraw until November 4, 2019.
By opting to withdraw from the Paris Agreement and not the umbrella UN Framework Convention on Climate Change (UNFCCC), Trump effectively delayed action for several years. Invoking the withdrawal clause of the UNFCCC would have allowed US departure in one year. So there is time to renegotiate the deal, if other countries are willing to do so, and there is time for US voters to voice their displeasure or support of Trump's decision at the ballot box in forthcoming elections.
Here's how a country can withdraw from the Paris Agreement. Article 28 of the Paris Agreement specifies that a party to the agreement can notify its intent to withdraw starting three years after the entry into force of the agreement for that party. The withdrawal would then take effect one year after such notification. The Paris Agreement entered into force on November 4, 2016—30 days after ratification by parties accounting for at least 55 percent of total greenhouse gas emissions.
The United States signed the Paris Agreement on April 22, 2016 and notified the United Nations of its ratification on September 3, 2016. Thus, the United States has been a party to the agreement since its initial entry into force on November 4, 2016. The earliest that the United States can notify its intention to withdraw is November 4, 2019. Doing so, the United States could then withdraw from the pact any time after November 4, 2020—the day after the next US presidential election!