Global initiatives aimed at combating climate change would face significant setbacks if U.S. President-elect Donald Trump decides to withdraw the nation from the Paris Agreement once again, according to the European Union‘s climate policy chief.

Sources from Trump’s transition team indicate that plans for executive orders to exit the United States—currently the second-largest emitter of greenhouse gases after China—from this pivotal global climate treaty are in place.

EU climate commissioner Wopke Hoekstra expressed to Reuters that such a move would severely undermine international climate diplomacy. He emphasized that if the U.S. were to exit the Paris Agreement again, it would necessitate a stronger commitment from other nations to enhance their climate diplomacy efforts.

Hoekstra remarked, “There is no alternative to ensure that everyone contributes, as climate change affects all indiscriminately.” He highlighted the necessity for global collaboration in addressing this pressing issue during U.N. climate discussions.

The Paris Agreement serves as the cornerstone of U.N. climate negotiations, where nearly 200 countries convene to strategize on emission reductions and financial support for these initiatives. The United States has historically played a crucial role in these discussions, notably collaborating with China—both the largest polluter and the second-largest economy—to establish the foundation for recent international climate agreements.

A shift in U.S. policy is anticipated with Trump’s return to the presidency on January 20. He has previously dismissed climate change as a hoax and withdrew from the Paris Accord during his first term from 2017 to 2021. Recently, he cautioned the EU to increase its purchases of U.S. oil and gas or risk facing tariffs.

Hoekstra stated that the EU intends to “constructively engage” with the new U.S. administration on various issues, including climate change. He mentioned that the Commission is reaching out to U.S. representatives across the political spectrum, including those at the non-federal level. “It is essential that our American partners remain involved and collaborate with us as much as possible, and that is something I will actively pursue,” he remarked.

However, as Brussels faces increasing pressure to enhance its climate leadership in light of a potential U.S. retreat, the EU is poised to miss a February deadline for all nations to submit updated national climate plans to the U.N. The outgoing Biden administration has already released the U.S. contribution. Hoekstra acknowledged that the timing of the EU’s political cycle does not align with the U.N. deadline, but assured that Europe would have its 2035 climate plan prepared by this year’s U.N. climate summit in November in Belem, Brazil. “The key is to ensure we present an ambitious target before arriving in Belem,” he emphasized. “I can assure you that we will achieve this.”