Paris Agreement

Following an executive order issued on 20 January 2025, the United Nations Secretary-General circulated a depositary notification on 27 January 2025 recording that the United States had again initiated withdrawal from the Paris Agreement. Under the treaty’s rules, the withdrawal does not take effect immediately, but the move nonetheless created renewed uncertainty around global climate diplomacy and the pace of collective ambition. The episode highlighted a recurring tension at the heart of the Paris system: the agreement’s broad inclusiveness makes it durable, yet its dependence on nationally chosen commitments leaves it vulnerable to abrupt policy reversals in politically influential countries.

At COP28 in Dubai, parties adopted the outcome of the first Global Stocktake, often referred to as the UAE Consensus. UNFCCC described it as the central outcome of the summit and a major step in translating the Paris Agreement’s review-and-ratchet design into practical direction. The decision recognized that current efforts were insufficient, called for stronger 2025 national plans, backed tripling renewable energy capacity and doubling energy efficiency improvements by 2030, and included language on transitioning away from fossil fuels in energy systems. This was a milestone because it connected scientific assessment directly to the next round of national commitments under Paris.

The technical dialogue of the first Global Stocktake under the Paris Agreement culminated in a synthesis report that assessed collective progress toward the treaty’s long-term goals. Its central message was stark: despite measurable advances, global action remained insufficient and the world was not on track to meet the Agreement’s temperature objectives. This mattered because the stocktake is one of the core accountability devices built into Paris. By aggregating evidence across mitigation, adaptation, and support, it provided the factual basis for the next cycle of national climate plans and made it harder for governments to claim that current efforts were adequate.

At COP27 in Sharm el-Sheikh, governments agreed to create a loss-and-damage fund for vulnerable countries suffering climate impacts. Although loss and damage extends beyond the Paris Agreement alone, the decision marked a major evolution in the political life of the Paris era by acknowledging that mitigation and adaptation were not the only pillars needed for climate justice. The breakthrough addressed a longstanding demand from developing countries and broadened the treaty system’s legitimacy. It showed that implementation of the Paris framework was increasingly tied to questions of fairness, finance, and support for communities already facing severe climate harms.

The Glasgow Climate Pact, agreed at COP26, became one of the most consequential political follow-ups to the Paris Agreement. It urged governments to revisit and strengthen their 2030 emissions targets, reflecting alarm that existing national plans were insufficient to keep the 1.5 degree goal alive. The pact also brought unusually explicit language on coal and fossil-fuel subsidies into the UN climate process. While it did not amend the Paris treaty itself, Glasgow was important because it used the Paris ratchet mechanism in practice, turning the agreement’s abstract promise of progressively stronger action into a direct demand for near-term policy tightening.

After President Joe Biden moved on his first day in office to reverse the earlier decision, the United States officially rejoined the Paris Agreement on 19 February 2021. Reentry restored universal participation among the world’s major economies and strengthened the run-up to the next major climate summit. The return was important not simply because of U.S. emissions, but because it reestablished American involvement in climate finance, diplomacy, and the pressure for stronger national pledges. It also illustrated how the Paris framework was designed to survive leadership changes while allowing countries to reengage without renegotiating the treaty.

The first U.S. withdrawal from the Paris Agreement took legal effect on 4 November 2020, exactly four years after the treaty had entered into force. This was symbolically potent because it briefly removed one of the world’s largest historical emitters from the agreement’s legal obligations and diplomatic processes. In practical terms, the episode tested the resilience of the Paris system: other major parties stayed in, and international negotiations continued without reopening the treaty itself. The moment demonstrated both the vulnerability of climate diplomacy to domestic political change and the agreement’s broader institutional durability.

President Donald Trump announced that the United States intended to withdraw from the Paris Agreement, arguing that the accord disadvantaged the American economy. The announcement was a severe political shock because the United States had been central to the deal’s design and to the diplomacy that secured its adoption. Although the withdrawal process could not take effect immediately under the treaty’s rules, the decision raised doubts about long-term durability, weakened confidence in collective ambition, and prompted other governments, cities, states, and companies to publicly reaffirm their support for the Paris framework.

On 4 November 2016, the Paris Agreement formally entered into force, less than a year after its adoption. This was a major turning point because the accord’s mechanisms for implementation, reporting, and future strengthening now rested on an active treaty rather than a pending commitment. Entry into force also confirmed that governments had chosen speed over delay despite domestic political debates in many countries. The event marked the beginning of the Paris era in climate governance, replacing the older divide between developed and developing countries with a universal system of nationally determined climate action and periodic revision.

By 5 October 2016, enough parties representing enough global greenhouse gas emissions had ratified the Paris Agreement to satisfy its dual threshold for activation. UN climate officials described the speed as unprecedented in recent treaty practice. This milestone mattered because it converted the accord from a celebrated diplomatic text into an imminent legal reality. Once the threshold was reached, the Agreement was set to enter into force 30 days later, ensuring that countries would move quickly from negotiation to implementation and that the first governing meetings under the new regime could proceed without years of delay.

When the United States and China, the world’s two largest emitters at the time, formally joined the Paris Agreement on the same day, the treaty’s prospects changed dramatically. Their participation signaled that the accord had support from the most consequential economies and pushed the ratification totals much closer to the threshold required for entry into force. This moment was important not only for arithmetic but for political legitimacy: it reassured many governments that the agreement would not remain a symbolic declaration, but would soon become an operative legal framework with broad participation from major emitters.

At United Nations Headquarters in New York, the Paris Agreement opened for signature and attracted an unprecedented number of signatories on its first day. The ceremony demonstrated that the political momentum generated in Paris had not dissipated after adoption. Signing did not by itself make states legally bound, but it publicly committed governments to move toward ratification or accession and underscored the expectation of rapid implementation. The size of the first-day turnout helped build confidence that the Agreement could pass its entry-into-force threshold far faster than most multilateral environmental treaties.

On 12 December 2015, 195 parties at COP21 adopted the Paris Agreement by consensus, creating the first nearly universal climate treaty built around nationally determined contributions and a shared long-term temperature objective. The agreement committed countries to hold warming well below 2 degrees Celsius above pre-industrial levels and to pursue efforts to limit it to 1.5 degrees Celsius. It also established recurring cycles for stronger pledges, reporting, and review. The adoption was widely treated as a diplomatic breakthrough because it brought developed and developing states into one common legal framework after decades of fragmented climate governance.

The Paris climate conference began with unusually high political expectations after years of difficult negotiations under the UN climate regime. Heads of state and government gathered early in the summit to signal support for a durable deal that would apply to developed and developing countries alike. The opening of COP21 mattered because it concentrated global attention on converting the broad framework sketched in Lima into specific legal text on mitigation, adaptation, finance, transparency, and long-term temperature goals. The two-week meeting became the decisive diplomatic setting for the Agreement’s final form.

At COP20 in Lima, governments adopted the Lima Call for Climate Action, a compromise decision that created the basic negotiating architecture for what would become the Paris Agreement a year later. It asked countries to prepare nationally determined contributions, preserving national flexibility while still moving all parties into a common framework. The Lima outcome did not settle the hardest political questions, but it narrowed the field of dispute and made it possible for negotiators to arrive in Paris with a draft structure for a universal climate deal rather than starting from scratch.