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

The expected absence of Mr Biden served to underscore a warning that came on 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 organisation," said UN 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 Wednesday, to be hosted by Mr Guterres and the president of Egypt, is meant as an informal exchange on climate matters ahead of the UN's November climate summit in the Egyptian resort of Sharm el-Sheikh.

Mr Biden is expected to host an event by the Global Fund to Fight Aids, Tuberculosis and Malaria 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.

Mr Biden would not 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 Mr David Waskow, director of the World Resources Institute's international climate initiative.

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

The official said Mr Biden has rallied global support around climate, including at a forum this past June attended by representatives of 21 countries, the European Commission and the UN.

The warning from Mr 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 (76cm) of rain in parts of the island. Meanwhile, on the other side of the world, Pakistan continues to recover from historic floods worsened by climate change that impacted 33 million people.

Earlier this year, scientists warned that the goal in the Paris Agreement to limit warming to 1.5 deg C was officially on life support.

As more and more climate disasters hit, countries are also struggling with threats to democracy, inflation, the ongoing pandemic, Russia's war on Ukraine that has upended energy markets, tensions between China and Taiwan, and more. These issues preoccupied world leader speeches that followed Mr Guterres' own on Tuesday.

"The multiple and often interconnected crises of recent years have exposed significant gaps in global governance," said Mr Kassym-Jomart Tokayev, the president of Kazakhstan.

Before reiterating his country's goal to reach net zero carbon emissions by 2060, he emphasised how the UN sustainable development goals were hindered by the pandemic, geopolitical conflict and the triple threat of climate change, biodiversity loss and pollution.

When climate change was briefly mentioned at the UN's opening day, leaders spoke about the need to cooperate on the crisis and funnel more money into adapting to a warmer world and supporting people suffering from climate impacts already here.

The tempo of increasingly intense climate-related disasters has intensified calls for rich, developed countries to help pay for losses tied to warming.

Senegalese President Macky Sall specifically called for funding to help the African continent adapt to the warming impacts of climate change locked in, and Colombian President Gustavo Petro warned about efforts to cut down the Amazon and other local forests, critical sinks of carbon dioxide.

Others pointed to disparities in who produces planet-warming pollution.

"As many of you are experiencing, the climate crisis is particularly affecting our continent, the Americas and especially the Caribbean," said Chilean President Gabriel Boric. "But our country, as many of yours, many of the global South, produces and is responsible for a minimum greenhouse gas emissions. In our case, it's only 0.24 per cent."

He noted that the large economies in the Group of 20 produce 80 per cent of greenhouse gases.

"It is clear nowadays that no country, large or small, humble or powerful, can save itself on its own," Mr Boric added.

Echoing this point, King of Jordan Abdullah II bin Al-Hussein said: "Consider the climate crisis. No country can help our injured Earth alone. We need partnerships that can create real change."

With the next major UN climate talks only two months away, Mr Guterres called on world leaders to finally "put fossil fuel producers, investors and enablers on notice".

He said: "Polluters must pay. Today, I am calling on all developed economies to tax the windfall profits of fossil fuel companies.

"Those funds should be redirected in two ways: to countries suffering loss and damage caused by the climate crisis, and to people struggling with rising food and energy prices." BLOOMBERG