On August 4, 2017, the Trump administration officially announced to the United Nations that the United States intends to withdraw from the Paris Agreement as soon as it is legally entitled to it.  The formal declaration of resignation could not be submitted until after the agreement for the United States came into force on November 4, 2019 for a three-year date.   On November 4, 2019, the U.S. government filed the withdrawal notice with the Secretary-General of the United Nations, custodian of the agreement, and formally withdrew from the Paris Agreement a year later, when the withdrawal came into effect.  After the November 2020 elections, President-elect Joe Biden promised to reinstate the United States in the Paris Agreement for his first day in office and renew the U.S. commitment to climate change mitigation.  The agreement stipulated that it would only enter into force (and thus become fully effective) if 55 countries that produce at least 55% of global greenhouse gas emissions (according to a list drawn up in 2015) accept, approve or adhere to the agreement.   On April 1, 2016, the United States and China, which together account for nearly 40% of global emissions, issued a joint statement confirming that the two countries would sign the Paris climate agreement.  175 contracting parties (174 states and the European Union) signed the agreement on the first day of its signing.   On the same day, more than 20 countries announced plans to join the accession as soon as possible in 2016. The ratification by the European Union has achieved a sufficient number of contracting parties to enter into force on 4 November 2016.
The objective of the agreement is to reduce the global warming described in Article 2 by improving the “implementation” of the UNFCCC The Paris Agreement has a bottom-up structure, unlike most international environmental treaties that are “top down”, characterized by internationally defined standards and objectives and which must be implemented by states.  Unlike its predecessor, the Kyoto Protocol, which sets legal commitment targets, the Paris Agreement, which focuses on consensual training, allows for voluntary and national objectives.  Specific climate targets are therefore politically promoted and not legally binding. Only the processes governing reporting and revision of these objectives are imposed by international law. This structure is particularly noteworthy for the United States – in the absence of legal mitigation or funding objectives, the agreement is seen as an “executive agreement, not a treaty.” Since the 1992 UNFCCC treaty was approved by the Senate, this new agreement does not require further legislation from Congress for it to enter into force.  The negotiators of the agreement stated that the INDCs presented at the time of the Paris conference were insufficient and found that “the estimates of aggregate greenhouse gas emissions in 2025 and 2030, resulting from planned contributions at the national level, do not fall into scenarios at 2oC at the lowest cost, but lead to a projected level of 55 gigatonnes in 2030.” and recognizes that “much greater efforts to reduce emissions will be required to keep the increase in the global average temperature below 2 degrees Celsius, by reducing emissions to 40 gigatonnes or 1.5 degrees Celsius.”  [Clarification needed] Although mitigation and adjustment require increased climate funding, adjustment has generally received less support and mobilized less private sector action.  A 2014 OECD report showed that in 2014, only 16% of the world`s financial resources were devoted to adaptation to climate change.  The Paris Agreement called for a balance between climate finance between adaptation and mitigation, highlighting in particular the need to strengthen support for adaptation from the parties most affected by climate change, including least developed countries and small island developing states.