The landmark Paris Agreement on climate change, adopted by the 196 parties to the United Nations Framework Convention on Climate Change (UNFCCC) in December 2015, later joined by the State of Palestine, was opened for signature on 22 April 2016. It was immediately signed by 175 states, and ratified by 15. The accord, the key instrument in the international effort to mitigate the social and economic impact of global warming, will replace the 1997 Kyoto Protocol at the end of the latter's second commitment period in 2020. Although many details remain to be ironed out before the agreement can be implemented, rapid ratification by the three largest emitters – China, the United States and the European Union – was expected to catalyse strong and decisive action. The narrow approval by United Kingdom voters on 23 June 2016 of the UK's exit from the EU (known as 'Brexit'), however, has complicated matters, with implications for the ratification and implementation of the agreement and for its capacity to prevent dangerous climate change.
To enter into force, the Paris Agreement requires ratification by at least 55 countries collectively accounting for 55% of global greenhouse-gas emissions. This must happen before 2020 if the accord is to succeed. As of August 2016, it had been signed by 180 parties, including the EU and all 28 current EU member states. However, only 23 of these countries have formally ratified the agreement, representing just over 1% of global emissions. Both France and Hungary have approved ratification, but have not yet submitted their formal documentation.