A climate crisis is upon us.  Human-caused global warming is already changing our planet’s climate in dramatic ways, and the effects are forecast to become far worse by the end of the century without rapid and radical changes to the global energy economy and the other forms of human activity that generate CO₂ and other greenhouse gases, such as methane.  The ten hottest years on record have all occurred since 1998, with the past five years topping the list.¹  We already see the disappearance of the arctic ice pack, massive glacial melting in Greenland, sea-level rise, massive wildfires in northern Canada, the Amazonian rainforest, the western United States, Spain, France, and Siberia, ever more violent storms, and rapidly warming ocean temperatures.  If we are to avoid potentially catastrophic climate change by 2100 by limiting the rise of global mean surface air temperature to 2.0°C, compared to the twentieth-century average, then we must aim for the complete decarbonization of the energy economy, which will then also include a more or less totally electrified, global transportation system, by no later than 2065.²  The question is, “How do we do that?”