I m karishma vaswani reporting from singapore. nations around the world have been reacting to yesterday s landmark climate report, warning that urgent action is needed to avoid catastrophe. experts agree that without big reductions in global carbon dioxide emissions, the world cannot win the fight against climate change. china is the world s largest emitter of carbon dioxide, followed by the united states and india. in a moment, we ll get an assessment from our correspondents barbara plett usher in the us and danjohnson in delhi, but first here s robin brant in shanghai. china is the world s most populous nation. and for some years now, it s also been the world s most polluting nation. rapid economic growth here over the last 20 years, fuelled by plentiful coal, means that china is now the world s biggest emitter of carbon dioxide. it s responsible for more than one quarter of all the greenhouse gas emissions on the planet. half the coal burned in the world is burned here, and it s goi