The decision, which also covered five other gases, ruled that climate change poses an "enormous problem" in both "magnitude and probability", and that the " greenhouse gases that are responsible for it endanger public health and welfare within the meaning of the Clean Air Act".
"This finding confirms that greenhouse gas pollution is a serious problem now and for future generations," said EPA Administrator Lisa P. Jackson in a statement.
The ruling, known as an "endangerment finding", now enters a 60-day public review period, following which the EPA will be able to use the existing Clean Air Act to impose limits on heavy polluters of carbon dioxide, methane, nitrous oxide, hydrofluorocarbons, perfluorocarbons and sulphur hexafluoride.
The Obama administration has repeatedly signalled that it would prefer to regulate greenhouse gas emissions through a new climate bill based on a nationwide carbon cap-and-trade scheme – a position the EPA supports.
The Kyoto Protocol establishes legally binding commitments for the reduction of four greenhouse gases (carbon dioxide, methane, nitrous oxide, sulphur hexafluoride), and two groups of gases (hydrofluorocarbons and perfluorocarbons) produced by "Annex I" (industrialized) nations. ... Kyoto includes defined "flexible mechanisms" such as Emissions Trading, the Clean Development Mechanism and Joint Implementation to allow Annex I economies to meet their greenhouse gas (GHG) emission limitations by purchasing GHG emission reductions credits from elsewhere, through financial exchanges, projects that reduce emissions in non-Annex I economies, from other Annex I countries, or from Annex I countries with excess allowances.