Countries must put a price on planet-warming carbon dioxide emissions, European Commission President Ursula von der Leyen told the United Nations COP26 summit on Monday. “We need to agree to a robust framework of rules, for example, to make global carbon markets a reality. Put a price on carbon, nature cannot pay that price anymore,” von der Leyen said in Glasgow.

Negotiators at the COP26 conference will attempt to agree on rules to form a carbon market under the Paris climate accord, a divisive issue that derailed the last U.N. climate summit in 2019.

In turn, US president Joe Biden on Monday sought to assure world leaders the United States would fulfil its promise to slash greenhouse gas emissions in half by the end of the decade. Biden joined leaders from over 100 countries in Glasgow for the start of the COP26 climate conference.

Biden, who succeeded former president Donald Trump in January, pledged earlier this year that the United States would cut its greenhouse gas emissions 50-52% by 2030 compared with 2005 levels. The White House has expressed confidence it can achieve that, even as a bill that would help further those goals languishes in Congress. “We’ll demonstrate to the world the United States is not only back at the table but hopefully leading by the power of our example,” he said. “I know it hasn’t been the case, and that’s why my administration is working overtime to show that our climate commitment is action, not words”, he said.

Nearly 90 countries have joined the U.S.- and EU-led effort to slash emissions of the potent greenhouse gas methane 30% by 2030 from 2020 levels, a pact aimed at tackling one of the main causes of climate change, a senior Biden administration official said. The partnership will be formally launched later on Tuesday.

Also, more than 100 global leaders late on Monday pledged to halt and reverse deforestation and land degradation by the end of the decade, underpinned by $19 billion in public and private funds to invest in protecting and restoring forests.