Green building blocks reveal the complex anatomy of climate change mitigation technologies

Achieving net-zero emissions requires rapid innovation, yet the necessary technological knowhow is scattered across industries and countries. Comparing functionally similar green and nongreen patents, we identify "Green Building Blocks" (GBBs): modular components that can be added to reduce existing technologies' carbon footprints. These GBBs depict the anatomy of the green transition as a network that connects problems -- nongreen technologies -- to GBBs that mitigate their climate-change impact. Node degrees in this network are highly unequal, showing that the scope for climate-change mitigating innovation varies substantially across domains. The network also helps predict which green technologies firms develop themselves, and which alliances they form to do so. This reveals a critical dependence on international collaboration: optimal innovation partners for 84% of US, 87% of German, and 92% of Chinese firms are foreign, providing quantitative evidence that rising economic nationalism threatens the pace of innovation required to meet global climate goals.