US exit from key UN climate treaty exposes cracks in US constitutional norms

The withdrawal of the United States from the United Nations Framework Convention on Climate Change (UNFCCC) under the Trump administration has precipitated hot legal controversies and constitutional issues both domestically and internationally, as the withdrawal could result in constitutional and illegal implications that might cause severe damage to the global climate regulatory system.

This came through a major announcement in a presidential memo on Wednesday, and it is historic in the sense that it is the first country in the world ever trying to pull out of the UNFCCC, which is the underlying treaty framework of any international climate talks since 1992. Even though Trump pulled out of the Paris Accord, the UNFCCC commitment is a whole lot more profound, and in 1992, it was approved unanimously by the US Senate over three decades ago, and some experts say that Trump might be doing something illegal here.

Does the president have the authority to exit a Senate-ratified treaty?

At the heart of the controversy lies a constitutional gray area: can a US president unilaterally withdraw from a treaty that was ratified by the Senate?

“In my legal opinion, he does not have the authority,” said Harold Hongju Koh, former legal adviser to the US State Department and now a professor at Yale Law School. Koh argues that a “mirror principle” should apply—meaning the same level of congressional consent required to enter a treaty should be required to exit it.

The UNFCCC entered into force in 1992 as a result of a unanimous Senate vote and was signed by then President George H.W. Bush. This is in contrast to the Paris Agreement, which was never formally submitted to the Senate, with President Barack Obama treating it as merely an executive agreement.

“This is not Paris,” said Michael Gerrard, director of Columbia University’s Sabin Center for Climate Change Law. “The UNFCCC is a treaty in the constitutional sense.”

The Constitution says nothing about how to withdraw from a treaty, and the Supreme Court has never issued a definitive ruling on the subject. In 1979, the court sidestepped an opportunity to set a clear standard after President Jimmy Carter withdrew from a treaty with Taiwan, leaving presidents with lots of leeway—but leaving the legal question unsettled as well.

Executive power versus congressional authority

Those who support the Trump administration’s use of the president’s power claim that the history of the past supports presidential discretion. According to Curtis Bradley, a law professor at the University of Chicago and former State Department attorney,

“Presidents have consistently withdrawn from treaties without the approval of Congress” and have done so “without much contestation.”

But critics argue that “precedent cannot replace the rule of law” in this case. Senator Sheldon Whitehouse, a very vocal climate supporter in Congress, said that

“the announcement is not just corrupt but illegal”

and that the administration is “acting as an agent of the fossil fuel industry” rather than the public good.

“Once the Senate ratifies a treaty, only the Senate can withdraw from it,”

Whitehouse said, adding that Trump’s move threatens democratic checks and balances. Several legal experts expect lawsuits challenging the withdrawal, particularly if the administration submits a formal notice of termination to the UN—something Trump’s memo notably failed to confirm.

A signal of retreat as climate impacts accelerate

Beyond legality, the withdrawal sends a powerful geopolitical signal at a moment of escalating climate crisis.

The decision comes as 2025 has already seen record-breaking global temperatures, intensifying wildfires in California, catastrophic flooding in South Asia, and prolonged droughts across Africa and Latin America. According to the World Meteorological Organization, global emissions must fall by nearly 45% by 2030 to avoid breaching the 1.5°C warming threshold—a target that now appears increasingly out of reach.

By abandoning the UNFCCC, the US risks sidelining itself from climate negotiations that shape global carbon markets, climate finance, and adaptation funding—areas where American firms and researchers have historically wielded significant influence.

Jean Galbraith, an international law expert at the University of Pennsylvania, warned that the move reinforces perceptions of the US as “an unreliable partner for long-term commitments.”

Fossil fuels, geopolitics, and selective multilateralism

Trump’s withdrawal also aligns with a broader shift in US foreign policy toward resource nationalism and fossil fuel expansion.

The decision followed days after Trump celebrated the capture of Venezuelan president Nicolás Maduro and outlined plans to ramp up oil extraction in Venezuela under US influence. The administration has repeatedly framed climate institutions as obstacles to “energy dominance,” echoing language used by fossil fuel lobby groups.

Secretary of State Marco Rubio defended the exit by accusing international institutions of being “captured by actors advancing their own agendas,” a phrase critics say masks a broader rejection of multilateral accountability.

Melinda St Louis of Public Citizen described the move as “a profoundly irresponsible retreat from international leadership,” warning that climate harms disproportionately affect vulnerable populations with little contribution to global emissions.

Can the US rejoin—or has the damage been done?

Experts remain divided on whether a future administration could easily rejoin the UNFCCC.

Some argue that Trump’s withdrawal nullifies the 1992 Senate approval, meaning re-entry would require a new two-thirds Senate vote—a near-impossible task in today’s polarized political climate. Others, including Galbraith and former climate envoy Sue Biniaz, believe the original ratification remains valid and could allow a future president to rejoin without new Senate consent.

Regardless of the legal mechanics, many experts say the reputational damage may be lasting.

“Climate action won’t stop globally,” Biniaz said,

“but US leadership has taken another serious blow.”

Trump’s withdrawal from the UNFCCC represents more than a legal dispute—it is a symbolic and strategic retreat at a time when coordinated global action is increasingly urgent.

As climate disasters intensify and international cooperation becomes more essential, the US decision risks isolating Washington, emboldening climate denial elsewhere, and undermining decades of fragile progress.

Whether courts intervene or future administrations reverse course, the episode underscores a growing reality: climate policy in the United States remains hostage to political volatility, with consequences that extend far beyond its borders.