实现20%目标成本最低、效率最高的方法莫过于建立统一的欧盟碳市场，欧盟到2020年年均需耗费约960亿美元来实现这一目标。
The most cost-efficient way to achieve the 20% target would be to operate a single, EU-wide carbon-market, which would cost the EU about $96 billion annually by 2020.