Back in 2009, China was a reluctant partner during major climate negotiations in Copenhagen that eventually collapsed amid recriminations between rich and poor nations. This time around the world's biggest polluter is regarded as a driving force behind what could be a comprehensive deal at a world climate summit in Paris.

The change in stance has a lot to do with the record levels of foul air that often hang over China's major industrialized urban centers, undermining public health. The resulting backlash over the smog has made President Xi Jinping's government far more serious about combating climate change and investing in cleaner forms of energy.

China's resolve will be tested along with other countries as world leaders, including U.S. President Barack Obama and China's Xi, gather in the French capital Monday. The talks organized by the United Nations are scheduled to run for two weeks and include the biggest-ever gathering of leaders on a single day.