World: 'The Kyoto accord, which aims to curb the air pollution blamed for global warming, has come into force seven years after it was agreed. The accord requires countries to cut emissions of carbon dioxide and other greenhouse gases. Some 141 countries, accounting for 55% of greenhouse gas emissions, have ratified the treaty, which pledges to cut these emissions by 5.2% by 2012. But the world's top polluter - the US - has not signed up to the treaty.' (BBC)