Boris Johnson told a press conference at the COP26 climate summit that developed nations “must do more”.
He answered questions on the string of environmental announcements made in Glasgow and said he was “cautiously optimistic” of a deal on reducing global warming.
Earlier President Joe Biden announced a “game-changing” pledge to cut global methane emissions by 30 per cent by 2030.
It is one of the most potent gases and is responsible for a third of current warming from humans.
Meanwhile, more than 100 world leaders backed a "landmark agreement" to end deforestation by 2030 in the first major deal of the COP26 conference.
Jair Bolsonaro and Xi Jinping are among global leaders who will commit to the declaration on Tuesday to help protect vast areas from land-clearing, which significantly contributes to emissions.
