It was an astonishing turnaround from the days of Donald Trump, who thumbed his nose at climate change science and pulled out of the Paris Accord.
President Biden announced the US would halve its carbon emissions – on 2005 levels – by 2030.
Xi Jinping said China, the world’s largest polluter, would be carbon neutral by 2060.
Even Vladimir Putin and Brazil’s Jair Bolsonaro made positive noises. But how much difference will it really make?