Paris Agreement

The Paris Agreement was reached at the UN Climate Change Conference, COP21, in Paris on 12 December 2015, and entered into force on 4 November 2016.^1,3 Article 2 sets its aim: hold the rise in global average temperature to well below 2 °C above pre-industrial levels, and pursue efforts to limit it to 1.5 °C.² It also aims to strengthen the ability to adapt, and to make finance flows consistent with low emissions and climate-resilient development.² The UN Treaty Collection listed 194 Parties on 24 October 2026.³ The United States withdrew in 2020, rejoined in 2021, and withdrew again with effect from 27 January 2026.³

Each Party shall keep up a series of nationally determined contributions, or NDCs, which set out the actions it will take to cut its emissions and to adapt.^1,2 A new one is due every five years, and each is to go beyond the one before.² Developed countries are to lead with economy-wide absolute emission reduction targets. Developing countries are encouraged to move toward such targets over time.² The targets are set by each country, not imposed; what is binding in international law is the process of reporting and review.⁴ The secretariat keeps the NDCs in a public registry.²

Article 13 sets up an enhanced transparency framework. Developing countries that need it get flexibility in applying the framework.² Each Party shall regularly provide a national inventory report of greenhouse gas emissions by sources and removals by sinks, prepared with good practice methods accepted by the Intergovernmental Panel on Climate Change. It also reports what is needed to track progress on its NDC.² Both undergo a technical expert review.² Parties send these as Biennial Transparency Reports. The first were due by 2024, with one every two years after that.⁴ The Agreement does not define how the temperature rise is measured. The IPCC's 2018 special report on 1.5 °C took 1850 to 1900 as pre-industrial and measured warming as a 30-year global average of air temperature over land and sea surface temperature.⁴

Article 14 asks the Parties to take stock of their collective progress on mitigation and adaptation and on the support given, in the light of equity and the best available science.² The first global stocktake was due in 2023, and then every five years.² It concluded at COP28 with a decision on speeding up action by 2030, including a call to move away from fossil fuels in the next round of commitments.¹ Its outcome is to inform the Parties' next NDCs.²

The Agreement follows the Kyoto Protocol, adopted in Kyoto on 11 December 1997 and in force from 16 February 2005.⁵ Kyoto placed the duty to cut emissions on the developed countries listed in its Annex I, as historically responsible for the greenhouse gases already in the atmosphere, and gave their targets legal force.^4,5 Its first commitment period ran from 2008 to 2012, and the Doha Amendment extended it to 2020.⁵ The United States did not ratify it, and Canada withdrew from it in 2012.⁵ Under Paris all Parties submit emissions plans and set their own targets.⁴

The modelling work runs at two scales. A country writing an NDC needs an inventory of its emissions and removals. It also needs projections of its emissions under the policies it has or proposes. Integrated assessment models such as GCAM, and simulators such as En-ROADS, link choices in energy and land to emissions and temperature. Global temperature against its 1850 to 1900 level is one of the series on Vitals, beside the warming at which tipping elements are estimated to tip. A place planning to adapt starts at weather and climate.