A bleeding polar bear is pictured in this 2006 file photo in an island in Norwegian. [Photo/Xinhua]

It was a bottom-up approach with loosely-structured commitments and little monitoring, reporting and verification.

Nevertheless, significant progress has been achieved under the agreement. China, for example, is on track to deliver its Copenhagen commitment according to a United Nations Environmental Program progress report.

Indeed, it could be argued that the Copenhagen Accord achieved no less than the Kyoto Protocol.

Moreover, it was the Copenhagen Accord that helped conceive the Durban Platform, which has now led the world to Paris, with its highly anticipated new agreement based on the Intended Nationally Determined Contributions (INDCs). This is a typical bottom-up approach, and one with significant potential.

The top-down approach central to the Kyoto Protocol and the (unfulfilled) dream of Copenhagen is gone, as well as the strict definition of a legally binding agreement.

There is also now recognition of political realities in countries like the United States, and the need for flexibility in implementation. Interestingly, the apparent relaxation of standards has not affected the encouraging outcome– unexpected even a year ago - of the US-China Joint Announcement on Climate Change and Clean Energy.

In the lead-up to the Paris conference, all major greenhouse gas emitters and the vast majority of the UNFCCC Parties have submitted INDCs that are more ambitious than ever.

An approach that is bottom-up and nationally-driven, instead of top-down and legally-binding, seems to be producing promising results, and has certainly been more embraced by world leaders. A new climate governance system is on the horizon with an anticipated new climate regime in the form of the Paris Agreement.

Many have complained about the slow progress of international climate negotiations.

Recognizing the limitations of negotiations at the technical level, many have called for the greater involvement and stronger leadership from political leaders. Two decades of climate talks have taught us an important lesson: that for climate change, the principal challenge for humanity (in the words of Pope Francis in 2015), technical negotiations alone cannot succeed.

Therefore, the strongest commitment from world leaders is critical to the success of efforts to meet the challenge. The unprecedented number of heads of states attending the Paris Conference is a symbol of unprecedented commitment from a united leadership on climate change.

We should not underestimate the many challenges ahead: How can the commitments under the INDCs be reviewed and verified? How can climate finance for developing countries be delivered adequately and fairly? How can nations work together to develop the technology needed for a decarbonized economy?

United leadership has been the key, long-awaited element. Only when political commitments are made will breakthroughs result in technical negotiations. Let us seize the historical opportunity to make a global climate governance work.

Qi Ye is Director of Brookings-Tsinghua Center for Public Policy, and Wu Tong is a Visiting Scholar to Tsinghua University in Beijing, China. The authors wish to thank Kenneth Lieberthal and Ryan McElveen for their comments and edits.