As the climate conference continues in Copenhagen, an official US agency declares greenhouse gases a threat to human health

That development in the US is expected to give a boost to the United Nation's climate change conference in Copenhagen, as it enters its second day. At the start of the two-week summit, Danish Prime Minister Lars Rasmussen said a comprehensive deal to curb carbon emissions was within reach. Delegates are working on a new climate treaty to replace the UN's Kyoto Protocol, which runs out in 20-12.