U.S. President Barack Obama spoke by phone Friday with French President Francois Hollande to discuss the upcoming Paris climate conference — with both leaders emphasizing their personal commitment to reach an “ambitious and durable” treaty to avert the worst effects of global warming, the White House said.

The call came a day after Hollande and France’s foreign minister responded to comments by U.S. Secretary of State John Kerry, who said Wednesday that the December agreement in Paris was “definitely not going to be a treaty.”

Kerry also said the text would not set “legally binding reduction targets.”

Leaders from nearly 200 countries are set to meet on Nov. 30 to Dec. 11 in the French capital to formalize national pledges to cut carbon emissions and plans to transition to renewable energy. The meeting is meant to culminate in the signing of a global climate treaty that would phase out carbon emissions.

Hollande responded to Kerry’s remarks Thursday from Malta, where he was attending a European Union-African summit on migrants.

“If the agreement is not legally binding, there won’t be an agreement, because that would mean it would be impossible to verify or control the undertakings that are made,” Hollande said.

Kerry’s French counterpart, Laurent Fabius, said Thursday that the Paris climate talks are not just “hot air.”

“The fact that a certain number of dispositions should have a practical effect and be legally binding is obvious, so let’s not confuse things, which is perhaps what Mr. Kerry has done,” Fabius said.

The legal status of the Paris treaty is one of the issues expected to be resolved in December. The U.S. wants only national enforcement, while the European Union and developing nations are urging an internationally binding text to slow climate change.

Congress questioned the State Department last month about the legal nature of the Paris agreement, and Fabius has acknowledged that Kerry faces domestic political sensitivities.

A State Department attorney responded to the Congressional query by saying that the U.S. national pledge “is not intended to constitute an obligation the United States must fulfill under international law.”

But in 2011, world leaders agreed that any global climate treaty would “develop a protocol, another legal instrument or an agreed outcome with legal force” by the end of 2015.

The treaty is meant to establish actions each country will carry out in coming decades — including reducing carbon emissions from industry, energy and transportation sectors, and replacing fossil fuels with green energy including solar or wind.

The U.N. hopes those actions will keep the global temperature rise under 2 degrees Celsius (3.6 degrees Fahrenheit) above pre-industrial levels by 2100.

Most scientists believe that if the warming increase is kept below 2 degrees, the worst effects of climate change could be avoided. But others, including leaders of the Marshall Islands — a low-lying atoll nation in the South Pacific — has called for a 1.5-degree warming maximum, arguing that anything more would swamp their nation, which stands an average of just three feet above sea level and is already experiencing increased flooding because of climate change.

“Out here in the middle of the Pacific Ocean, climate change has arrived,” Marshall Islands President Christopher Loeak said in a video address to his fellow heads of state ahead of last year's United Nations meeting in New York.

“Our atoll nation stands at the front line in the battle against climate change,” Loeak said. In order to avoid the worst effects of climate change, he said the world must embrace a carbon-free vision by the middle of the century.

“Without it, no sea wall will be high enough to save my country,” Loeak said.

Scientists said last week that global temperatures in 2015 were set to reach 1 degree Celsius pre-industrial temperatures for the first time. The U.N. Intergovernmental Panel on Climate Change has warned the world would see a 3-degree rise by the end of the century if things don’t change.

Many researchers say a world 3 degrees warmer would see a significant drop in food production, an increase in urban heat waves, more droughts and wildfires, and rising seas that could threaten low-lying coastal areas or cause mass migrations from atoll nations like the Marshall Islands.

Experts have also warned that the effects would likely lead to a refugee crisis that would dwarf the one unfolding in Europe, as many areas of the world would become uninhabitable — including the Arab Gulf region, which scientists said could become unlivable for humans by 2070.

With wire services