In the runup to World War II, President Franklin Delano Roosevelt enlisted the entire US economy in an effort to scale up production of war material…By the time the war was won, the economy was up and humming with a massively expanded workforce (drawing in women and African Americans) and turbocharged productive capacity. Investments made during the war mobilization yielded a robust middle class and decades of sustained, broadly shared prosperity. A similar mobilization will be necessary for the US to decarbonize its economy fast enough to avert the worst of climate change. To do its part in limiting global temperature rise to between 1.5° and 2° Celsius, the US must reach net-zero carbon emissions by 2050 at the latest. To achieve this, the full resources of the US economy must be bent toward manufacturing the needed clean-energy technology and infrastructure. FDR began with two questions. First, he asked not what was politically feasible but what was necessary to win the war. He also asked not how much funding was available in the federal budget but how much productive capacity was available in the economy — what was possible. Saul Griffith is trying to answer those same questions on climate change: what is necessary, given the trajectory of global warming, and what is possible, given the resources in the US economy.