Speaking as the talks enter their second week, he said not enough has been done to combat climate change and called for united action.
Mr Obama, who arrived in Glasgow on Sunday night, said larger nations should shoulder more of the burden of fixing the climate crisis – as a theme of the talks on Monday is support for poorer countries to cope with the problem.
A veteran of the failed UN climate summit in Copenhagen and the successful meeting in Paris which secured the world’s first comprehensive climate treaty, Mr Obama was speaking at an event by COP26 organisers the UNFCCC on island resilience.