President Joe Biden is set to miss a United Nations roundtable on climate action this afternoon in New York, stoking concern that other G-7 leaders will also forgo the session meant to help pave the way for international global warming negotiations later this year.

The expected absence of Biden served to underscore a warning that came Tuesday in the speech that opened the meeting of the United Nations General Assembly. “The climate crisis is the defining issue of our time. It must be the first priority of every government and multilateral organization,” said U.N. Secretary-General Antonio Guterres. “And yet climate action is being put on the back burner — despite overwhelming public support around the world.”

The closed-door meeting slated for today, to be hosted by Guterres and the president of Egypt, is meant as an informal exchange on climate matters ahead of the U.N.’s November climate summit in the Egyptian resort of Sharm el-Sheikh. Biden is expected to host a Global Fund to Fight AIDS, Tuberculosis and Malaria event at the same time, according to people familiar with the matter. The two events are set to take place across Manhattan, already snarled by traffic from visiting diplomats’ motorcades, and the president’s schedule has been compressed by his attendance at Queen Elizabeth’s funeral.

Biden won’t be the only high-profile leader to skip the climate roundtable. French President Emmanuel Macron will also miss the session because “he has other meetings,” an aide said on Tuesday.

“This is a global crisis that requires a global response, and discussion at the leader level is always essential,” said David Waskow, director of the World Resources Institute’s international climate initiative.

An administration official said Special Presidential Envoy for Climate John Kerry will attend today’s climate talks and pushed back on the idea that Biden’s absence showed a lack of commitment to addressing global warming.

The warning from Guterres on Tuesday comes as more than 1 million people in Puerto Rico lack power after Hurricane Fiona this week dropped upwards of 30 inches of rain in parts of the island. Meanwhile, Pakistan continues to recover from historic floods worsened by climate change that impacted 33 million people.