The two-week United Nations conference on climate change is halfway over, and no matter what else happens, it has already been a clear-cut success in two critical areas.

As important as a global accord is, the most influential actors on climate change have been cities and businesses, and leaders in both groups made it clear that they will not wait for an agreement that, if it comes together, won’t even take full effect until 2020.

Mayors and officials representing more than 500 cities organized and attended their own summit in Paris (which Paris Mayor Anne Hidalgo and I co-hosted). It was the first time local leaders had ever gathered in such numbers during a UN climate-change conference. They came not only to ensure that their voices were heard by heads of state, but also to express their determination to act on their own, and to learn from one another and share best practices.

Cities account for about 70 percent of global greenhouse-gas emissions, and while some heads of state have been arguing over which countries should do more, cities recognize that reducing their emissions is in their own best interest. After all, when cities cut their emissions, they help their residents live longer, healthier lives. When they improve the energy efficiency of their buildings, they save their taxpayers money. When they invest in modern low-carbon infrastructure, they raise their residents’ standard of living. Taken together, these actions make cities more attractive to businesses and investors. Even if climate change were not a concern, reducing emissions would be smart policy.

David Fuller's view

We cannot afford to ignore the risk that climate change is actually occurring. 

I commend the rest of this editorial and also the accompanying video to readers.