China is the world's heaviest polluter, and contributes that largest chunk (25%) of global CO2 emissions. (The value is closer to 30% by now). China's environmental pollution is mainly driving by a rising population and heavy industrialization over the past few decades. Also, because many countries have accepted limits legislation about cleaner industrial practices (ex. Kyoto Protocol), they have moved manufacturing to countries with less strict environmental practices and cheaper labor, such as China (which is not covered by Kyoto Protocol limits).