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China pledged at the United Nations climate change summit to make deep carbon-emission cuts by 2020, reportedly by up to 45 percent. Some are calling it the first time the country has vowed to take firm action against global warning. China, one of the worst polluters in the world, ranks first in emissions, with the United States in second place. Chinese Vice Premier Zhang Gaoli said, "China will make even greater effort to address climate change and take on international responsibilities." Zhang said China would aim to cap emissions or have them peak "as early as possible." President Obama said at the summit that climate change is moving faster than efforts to address it, and that the U.S. and China have a responsibilty to lead other nations. At the summit,a number of countries, as well as business and financial leaders, promised bold new action, and U.N. Secretary-General Ban Ki-moon said, "The summit delivered" and called it "a historic day."