More than 70 world leaders were due to address the one-day virtual gathering aimed at building momentum for much steeper cuts in planet-warming emissions on the fifth anniversary of the 2015 Paris climate accord.

British Prime Minister Boris Johnson told the summit what he called "the green revolution" could provide millions of jobs worldwide, while French President Emmanuel Macron praised U.S. President-elect Joe Biden for his plan to rejoin the Paris climate accord, saying "Welcome back, welcome home.” President Donald Trump had pulled the U.S. out of the agreement in 2019.

Indian Prime Minister Narendra Modi said the country was doubling down on clean energy sources and was on track to achieve the emissions norms set under the 2015 Paris climate change accord.

Pope Francis also spoke Saturday and encouraged nations to work out a strategy to reduce net carbon emissions to zero and committed Vatican City, the world's smallest state, to doing so by 2050.