Last year, US president Obama and China’s president Xi Jinping set ambitious targets to reduce greenhouse gases over the next decade. Now, also mayors from both nations started collaborating in the fight against climate change, starting with an agreement between two of the world’s most polluted cities, Los Angeles and Beijing. Their deals commit to low-carbon urban planning and transportation, as well as environmental technology and economic development. Today, leaders of 11 Chinese cities and provinces, including Beijing, are also announcing that their carbon emissions will peak as early as 2020, a decade ahead of the national target of an emissions peak by 2030. It’s inspiring to see large cities in China and the US collaborate on these goals. Let’s hope they keep each other on track.