The Paris Agreement is the long-delayed outcome of three decades of hard climate diplomacy. The UN Framework Convention on Climate Change (UNFCCC), signed at the 1992 Rio Earth Summit, set a goal but left the method vague. The 1997 Kyoto Protocol imposed binding targets only on developed countries; the United States never ratified, China and India were excluded by design, and Canada withdrew in 2011. The 2009 Copenhagen summit (COP15) collapsed over a north-south rift. Over the next six years bilateral US-China diplomacy (most decisively the November 2014 Obama-Xi joint announcement), voluntary national pledges and rotating chairs (France prepared COP21 with an obsessive focus on logistics) laid the ground.

The architecture of the agreement is a radical break from Kyoto. Instead of top-down country targets, Paris adopts a bottom-up structure: every party submits a Nationally Determined Contribution (NDC) it sets itself, and updates it every five years with a more ambitious version (the no-backsliding principle). What is binding is not the number that gets you to the goal, but the transparency of the process: common reporting, review and a five-yearly Global Stocktake. The temperature goal — well below 2°C with pursuit of 1.5°C — was inserted in the final weeks at the insistence of small island states (AOSIS), and it became the political basis of the 2018 IPCC Special Report on 1.5°C. Developed countries pledged $100 billion a year in climate finance from 2020; the figure was only approached in 2022.

Implementation has been bumpy. The agreement entered into force on 4 November 2016 — clearing the 55 countries + 55% of global emissions threshold in less than a year, the fastest entry into force in the history of multilateral climate treaties. In June 2017 US President Donald Trump announced withdrawal; in February 2021 Joe Biden rejoined on one of his first days in office. The European Union legislated its 2050 net-zero target in 2019; China announced its 2060 net-zero pledge in 2020. COP26 in Glasgow (2021) put the 'phase-down' of coal into the text; COP27 in Sharm el-Sheikh (2022) for the first time established a 'loss and damage' fund; COP28 in Dubai (2023) completed the first Global Stocktake and produced the first cover decision in history to mention 'transitioning away from fossil fuels.'

The science does not support easy optimism. The IPCC's AR6 synthesis (2022) showed that even full implementation of current NDCs would put warming at 2.5–2.8°C; the 1.5°C threshold is likely to be crossed in the 2030s. In 2023 the annual global average temperature exceeded 1.45°C above pre-industrial levels for the first time (WMO). Yet Paris succeeds as an infrastructure even where it falls short as a target: the entire institutional ecosystem that now measures where emissions go, counts fossil-fuel subsidies and ties climate risk into financial reporting was built under this frame. Trump's second withdrawal (January 2025) is testing the non-US backbone of the deal; the EU's Carbon Border Adjustment Mechanism (CBAM) and China's 2024 export dominance show that climate has moved out of climate policy proper into the heart of industrial policy.