Introduction
Few countries shape the fate of global climate governance as much as the United States (U.S). As the world’s second-largest emitter and a geopolitical heavyweight, U.S participation—or absence—casts a long shadow over the Paris Agreement. Over the past decade, the Paris regime has weathered three major U.S. policy shifts: Trump’s withdrawal, Biden’s return, and now the specter of a “Trump 2.0” exit. What do these swings mean for the future of international climate law?
Trump’s Withdrawal, Biden’s Return
In 2017, then-President Donald Trump announced the U.S. withdrawal from the Paris Agreement, calling it a “bad deal” for America. The formal exit took effect on November 4, 2020, making the U.S. the only country in the world outside the Paris framework. This move shook international confidence, emboldened reluctant countries, and weakened momentum in negotiations on finance and emissions reductions.
Within hours of taking office in January 2021, President Joe Biden signed an executive order to rejoin the Paris Agreement. The U.S. returned officially in February 2021, restoring diplomatic ties and pledging to cut emissions 50–52% below 2005 levels by 2030. Biden’s administration aimed to reinvigorate climate diplomacy, co-lead the Global Methane Pledge and push for stronger ambition at COP26 and COP28.
Trump Return 2.0 and Effect on Global Compliance
On 20 January 2025, President Trump signed Executive Order 14162 titled “Putting America First in International Environmental Agreements”, directing the United States to withdraw from the Paris Agreement once again. The formal notification was deposited with the UN Secretary-General, and in accordance with Article 28 of the Agreement, the withdrawal will become effective one year after notification, unless a different effective date is specified.
The U.S. withdrawal could weaken morale and ambition among other Parties, who may feel disadvantaged. Furthermore, it could create financing shortfalls and affect trust, especially in developing countries. It could also undermine the perceived legitimacy of global climate law when major states can exit at will. Most importantly, the U.S.’s shifting stance — from withdrawal to return, and now withdrawal again — reveals both vulnerabilities and strengths of the Paris regime. The strength in the flexible design allowed broad participation and sustained functioning even when the U.S. stepped out. Whilst the weakness lies in its enforcement mechanism, where major parties can treat participation as subject to domestic politics. For international law, the question thus becomes: When a global commons treaty lacks enforceability and a major party withdraws, how can it maintain integrity and effectiveness?
Legally, this also highlights some critical points, the Paris Agreement has no sanctions or enforcement mechanism if a major emitter opts out. Thus, withdrawal undermines the bottom-up architecture of the treaty, which relies on major emitters staying engaged to incentivise others. Especially as the strength of the Paris Agreement lies in collective action, transparency, and ambition. For which U.S’ participation historically had placed diplomatic pressure on other major players (e.g., China, India) to enhance their own pledges, bolstered the amounts pledged in climate finance via pledges to avenues such as the Green Climate Fund and the forthcoming New Collective Quantified Goal (NCQG). This finance could shape global norms, technology transfer, and multilateral climate initiatives.
Conclusion
The Paris Agreement has survived one U.S. withdrawal, but a second could erode the fragile trust at its core. For climate-vulnerable nations, these swings are not abstract—they determine access to finance, resilience, and survival. Whether the Paris regime emerges stronger or fractured will depend not only on Washington’s choices but also on how the rest of the world responds.
Image by Gerd Altmann from Pixabay
