The nature of these two countries’ bilateral engagement will dictate how the low-carbon economic “pie” will get carved up, and thus how fast the global economy as a whole can be transformed. Responsibility for this transformation lies irrevocably with China and the US, not only because they are the world’s biggest emitters, but also because only they have the capacity to invest enough in clean-tech Rampamp;D, provide a large enough labor force, and support a large enough change in global policy.