The climate accord orders Europe to cut greenhouse gas emissions by 20% by 2020 compared with 1990 levels.

环境协议要求欧洲各国温室气体的排量到2020年与1990年相比同比减少20%。

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According to the EPA, ethanol produced from corn at a modern refinery powered by biogas can represent a 20 percent greenhouse gas reduction compared with regular gasoline.

据美国环保署说，与普通汽油相比，在一个靠沼气发电的现代炼油厂使用玉米提取的乙醇能使温室气体排放降低20%。

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Coal is relatively cheap compared with oil and natural gas, although coal prices have tripled in the past few years.

其次，与石油和天然气相比，煤炭价格也比较便宜，尽管煤价在过去的几年里增长了两倍。

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The switch to Sunoco Green E15, the official fuel of NASCAR and a renewable, low-carbon power source, reduced greenhouse gas emissions by 20% compared with unleaded gas.

FORBES: NASCAR Green Is Really Purple

Microturbines provide high electrical efficiency compared with traditional gas turbines in the same size class.

FORBES: America's Other Energy Revolution And Why It Matters

But there are at least two major obstacles hindering wider adoption of plug-in electric vehicles: the premium that drivers will have to pay for an electric car compared with a gas-powered vehicle and the limited number of electric car charging stations nationwide.

FORBES: More Electric Cars Are Making Their Way Across the Country