Participants attend the opening session of high-level segment of 2013 UN Climate Change Conference in Warsaw, Poland, on Nov. 19, 2013. [Xinhua/Zhang Fan]

(L-R) UN Framework Convention on Climate Change (UNFCCC) Executive Secretary Christiana Figueres, United Nations Secretary General Ban Ki-moon, Polish Prime Minister Donald Tusk and Marcin Korolec, President of COP19/CMP9, Polish Minister of Environment attend the opening session of high-level segment of 2013 UN Climate Change Conference in Warsaw, Poland, on Nov. 19, 2013.(Xinhua/Zhang Fan)

Polish Prime Minister Donald Tusk speaks during the opening session of high-level segment of 2013 UN Climate Change Conference in Warsaw, Poland, on Nov. 19, 2013.(Xinhua/Zhang Fan)

Xie Zhenhua (C), head of Chinese delegation, attends the opening session of high-level segment of 2013 UN Climate Change Conference in Warsaw, Poland, on Nov. 19, 2013.(Xinhua/Zhang Fan)

United Nations Secretary General Ban Ki-moon speaks during the opening session of high-level segment of 2013 UN Climate Change Conference in Warsaw, Poland, on Nov. 19, 2013.(Xinhua/Zhang Fan)

UN Framework Convention on Climate Change (UNFCCC) Executive Secretary Christiana Figueres, United Nations Secretary General Ban Ki-moon, Polish Prime Minister Donald Tusk and Marcin Korolec, President of COP19/CMP9, Polish Minister of Environment (1st L to 4th L) attend, along with other participants, the opening session of high-level segment of 2013 UN Climate Change Conference in Warsaw, Poland, on Nov. 19, 2013.(Xinhua/Zhang Fan)

UN Framework Convention on Climate Change (UNFCCC) Executive Secretary Christiana Figueres (L) and United Nations Secretary General Ban Ki-moon attend the opening session of high-level segment of 2013 UN Climate Change Conference in Warsaw, Poland, on Nov. 19, 2013.(Xinhua/Zhang Fan)

United Nations Secretary General Ban Ki-moon speaks during the opening session of high-level segment of 2013 UN Climate Change Conference in Warsaw, Poland, on Nov. 19, 2013.(Xinhua/Zhang Fan)