Chinese President Xi Jinping, accompanied by his wife Peng Liyuan, arrives in Paris, capital of France, to attend the opening ceremony of an international conference on climate change on November 29, 2015. HUANG JINGWEN / XINHUA

The 2009 climate conference in Copenhagen was at the time deemed humanity's "chance" to address global warming.

We missed it.

This time, with US President Barack Obama "hamstrung" by a Congress at home that is yet to even agree that human activities are the cause of global warming;

With countries divided on how to assign "common but differentiated responsibilities";

With countries' combined commitments to reducing greenhouse gas emissions falling dramatically short of what is needed to limit the rise in temperature within 2 degrees Celsius by 2030;

And with developed countries failing to honor their promise of $100 billion to support climate-change mitigation actions by developing countries;

It will take strenuous endeavors by all parties to make sure the Paris gathering will not be remembered as another lost chance.

Whatever happens, whatever it takes, China will, and must, be a staunch forerunner in humanity's fight against global warming. That message grew louder and clearer not only with President Xi Jinping's presence at the Paris event, the first time a Chinese head of state has attended the global climate talks, but also his pledges of China's action.

Expectations run high that China and the United States, the world's two largest greenhouse gas emitters, can lead by example, especially because the two issued a joint announcement on climate change late last year.

Although progress on the US side has been less than desirable, it is time for both nations to demonstrate what being a "responsible major country" means.

And China's contributions and leadership are more credible than ever because they are more deeply and firmly rooted in the country's own needs to deliver "green development" and upgrade its industrial structure.

The confidence, optimism, and sense of urgency Xi is delivering to Paris have the support of a widening domestic consensus driven home by practical needs for clear air, clean water and safe soil. There is growing confidence in China that a difference will be made, even at the cost of an economic slowdown.

An important goal of the Paris summit is to reach a legally binding agreement that applies to all signatories. This should be more likely with China committing more.

For a long time, developed countries have dragged their feet on the pretext that developing countries like China had not committed enough.

Now it is their turn to catch up.