For the last two decades, climate talks, and their top-down multinational approaches, have largely failed to curb rising temperatures. Since then, a number of subnational actors (provinces, cities, businesses, and civil society organizations, among others) have sought to tackle climate change from the bottom up. For example, at a summit in New York last year, various subnational associations pledged to take action to reduce greenhouse gas emissions. Around 75 mayors from around the world, recognizing that cities account for some 70 percent of all greenhouse gas emissions, signed a Mayors Compact to accelerate ongoing efforts to shrink their carbon footprint. And major civil society organizations and businesses also signed various pledges on a range of initiatives, from expanding energy efficiency to halting deforestation.

These initiatives are promising, but they will not do enough. According to at least one study, the subnational initiatives agreed to at last year’s summit have the potential to reduce emissions by only a fifth of the required reduction needed to keep global warming under two degrees Celsius—a threshold that if exceeded, may trigger fiercer storms and increased droughts. Subnational progress is limited because ground-up climate diplomacy has largely operated on an independent track from international diplomacy. The risk with these parallel approaches is that ground-up goals will not be incorporated into top-down ones, which risks marginalizing their efficacy.

Unlocking the potential of subnational climate action will require integration of subnational and international initiatives. And the two entities that can bridge that gap are California and Germany—two of the world’s pioneers when it comes to climate policies.