Cities are not just where 3.5 billion of us live—they are where more than  half of humanity uses electricity, drives cars, and throws out garbage, among myriad other activities that emit greenhouse gases. Now, a global coalition has released the first standardized method for measuring and reporting a given city’s greenhouse gas emissions. 

As home to 3.5 billion of the world’s population, cities and urban areas play a crucial role in combating global climate change. And today, many of their leaders are announcing steps to do just that.

China just announced a mitigation goal to peak its emissions by 2030 or earlier, while the United States committed to reduce its national emissions by 26-28 percent below 2005 levels by 2025. And countless other cities and countries have set similar emissions-reduction targets.