Virtually all climate policy discussions assume that climate science compels us to make large and rapid reductions in greenhouse gas emissions. But any realistic policy must balance the hazards, risks, and benefits of a changing climate against the world’s growing demand for reliable, affordable, and clean energy. To strike that balance, climate policymakers will consider society’s values and priorities, its tolerance for risk, equities among generations and geographies, and the efficacy, costs, and collateral impacts of any policy. This paper reviews some of the scientific, techno-economic, and societal facts and circumstances that should inform those policy decisions and draws some straightforward conclusions from them.