The US government is to regulate carbon dioxide emissions, having decided that it and five other greenhouse gases may endanger human health and well-being.
美国政府拟规范二氧化碳的排放标准，同时包括另外五种危及到人类健康和幸福的温室气体。
The EPA's first action could cut emissions from cars
The Environmental Protection Agency (EPA) announced the move following a review of the scientific evidence.
The decision marks a major change from the Bush presidency, when the EPA argued it could not regulate CO2 because the gas was not a pollutant（污染物质）.
Developing countries have asked for the US to show leadership on climate.
Many are not prepared to curtail（缩减，剥夺） their own emissions（散发，传播） without firm indications（适应症，显示） that the US is willing to make significant reductions（减少，缩小）.
Carbon-cutting legislation is being proposed in Congress, but the EPA decision - known as an "endangerment finding" - will allow the agency to mandate（命令，指令） some cuts without waiting for the draft bills to become law.
"This finding confirms that greenhouse gas pollution is a serious problem now and for future generations," said EPA administrator Lisa Jackson.
"Fortunately, it follows President Obama's call for a low-carbon economy and strong leadership in Congress on clean energy and climate legislation; and... the solution is one that will create millions of green jobs and end our country's dependence on foreign oil."
'Disproportionate（不成比例的） impacts'
In 2007, the Supreme Court instructed the agency to review the evidence on climate change with a view to reconsidering its stance（踏脚处，位置） on the possible threats of climate change.
In the endangerment finding, the EPA now cites a number of impacts that it believes may impact significantly on US citizens, including:
an increased risk of droughts and floods sea level rise more intense storms and heatwaves（热浪，酷暑期） harm to water supplies, agriculture and wildlifeMs Jackson concluded that these impacts would fall disproportionately on people who were poor or in ill health, and on indigenous（本土的，本地的） groups.
The EPA quoted a 2007 report by a group of retired（隐退的，退休的） generals and admirals（舰队司令，海军上将） who said that climate change presented "national security challenges" for the US.
Environmental groups said this was the latest sign that the Obama administration is taking a very different line on climate change from its predecessor.
"This reclaims the US role on the international stage as a leader," said Phyllis Cuttino, director of the US global warming programme at the Pew Environment Group in Washington DC.
"The EPA's next step will probably be to grant the 'California waiver（放弃，弃权）', which would allow states to restrict（限制） tailpipe（尾喷管） emissions, and that we expect to happen very soon," she told BBC News.
Under the Bush administration, the agency denied California the right to set targets for vehicle efficiency, for which it needed a waiver from federal law.
At least 15 states plan to follow California's lead.
The EPA's decision now goes out to public consultation（请教，咨询）. The agency says it will "conduct an appropriate process and consider stakeholder（利益相关者） input" before imposing restrictions on any part of the economy.
The endangerment finding also empowers（授予权力，允许） the EPA to regulate the other five greenhouse gases included in the Kyoto Protocol（京都议定书） - methane（甲烷）, nitrous oxide（一氧化二氮）, hydrofluorocarbons（氟烷）, perfluorocarbons（全氟化碳） and sulphur hexafluoride（六氧化硫）.