Cities commit to combating emissions.

• Position: Global Warming

More than 200 cities have set greenhouse gas reduction goals or targets. Action in these cities, which represent a combined population of 439,000,000 people, could propel countries to meet their Intended Nationally Determined Contributions--the national greenhouse gas reduction pledges embodied in the Paris Agreement.

"The challenge over the next several decades is an enormous one," write Michael Renner and Tom Prugh, contributing authors and codirectors of a report issued by WorldWatch Institute, Washington, DC. 'This requires not change around the edges, but a fundamental restructuring of how cities operate, how much they consume in resources, and how much waste they produce, what they look like, and how they are structured."

The C40 Cities Climate Leadership Group has expanded to more than 80 cities. The Compact of Mayors, launched at the 2014 United Nations Climate Summit, is the largest coalition of city leaders addressing climate change.

Cities today host more than half of the planet's human beings and represent about 70% of global energy consumption and greenhouse gas emissions. If trends continue, urban populations are expected to increase to 6,000,000,000 by 2045, at which point two-thirds of all people will live in urban environments. "If current trends in urbanization continue unabated, urban energy use will more than...