People who own all-electric cars where coal generates the power may think they are helping the environment.
电动汽车的用电来自燃煤发电厂，使用电动汽车的人可能认为他们保护了环境。
But a new study finds their vehicles actually make the air dirtier, worsening global warming.
但是一项新的研究表明，电动汽车实际上对空气污染更不利，且会加剧全球变暖。
The controversial study raises major questions over the future of 'green' cars.
这项颇受争议的研究提出了有关“环保”车未来的一些问题。
'Unfortunately, when a wire is connected to an electric vehicle at one end and a coal-fired power plant at the other end, the environmental consequences are worse than driving a normal gasoline-powered car,' said Ken Caldeira of the Carnegie Institution for Science, who wasn't part of the study but praised it.
卡耐基科学研究所（Carnegie Institution for Science）研究员肯·卡代拉（Ken Caldeira）说：“不幸的是，当一根线把电动车和一个燃煤发电厂连在一起时，造成的环境污染比普通的汽油车更严重。” 肯·卡代拉并未参与这项研究，但是对该研究表示赞赏。
Driving vehicles that use electricity from renewable energy instead of gasoline could reduce the resulting deaths due to air pollution by 70 percent, it concluded.
该研究指出，驾驶可再生能源发电的电动车来取代汽油车，可以使因空气污染造成的死亡率下降70%。
Ethanol isn't so green, either, the researchers claimed.
研究员表示，乙醇也不是那么环保。
'It's kind of hard to beat gasoline' for public and environmental health, said study co-author Julian Marshall, an engineering professor at the University of Minnesota.
研究报告撰写者之一朱利安·马歇尔（Julian Marshall）表示，出于民众健康和环保的考虑，“想要取代汽油很有难度”。朱利安是明尼苏达大学（University of Minnesota）的工程学教授。
'A lot of the technologies that we think of as being clean ... are not better than gasoline.'
“很多我们认为清洁的技术……其实都比汽油好不到哪里。”
The key is the source of the electricity all-electric cars need.
关键取决于电动汽车用电的来源。
If it comes from coal, the electric cars produce 3.6 times more soot and smog deaths than gas, because of the pollution made in generating the electricity, according to the study that is published Monday by the Proceedings of the National Academy of Sciences.
周一发表在《美国国家科学院院刊》的这项研究指出，如果电来自煤，那么使用电动车产生的煤烟和烟雾造成的死亡是汽油车的3.6倍，因为燃煤发电过程产生了污染。
They also are significantly worse at heat-trapping carbon dioxide that worsens global warming, it found.
同时该研究发现，由煤产电排放的温室气体二氧化碳更加剧了全球变暖。
The study examines environmental costs for cars' entire life cycle, including where power comes from and the environmental effects of building batteries.
调查研究了一辆车使用周期过程中付出的环境代价，包括能源从哪里来，制造电池又造成了多少环境影响。
But if the power supply comes from natural gas, the all-electric car produces half as many air pollution health problems as gas-powered cars do.
但是如果电力来自天然气，电动车产生的空气污染造成的健康问题将会汽油车的一半。
And if the power comes from wind, water or wave energy, it produces about one-quarter of the air pollution deaths.
如果能源来自风、水或者潮汐能，空气污染造成的健康问题将是原来的四分之一。
Hybrids and diesel engines are cleaner than gas, causing fewer air pollution deaths and spewing less heat-trapping gas.
混合动力和柴油发电机要比汽油清洁，造成的死亡人数更少，温室气体的排放也更少。
But ethanol isn't, with 80 percent more air pollution mortality, according to the study.
但根据研究，乙醇不属于此类，造成的空气污染的致死人数要高出80%。