A generation ago climate change planning did not exist in most places, and although scientists had known about the possibility of global warming for many years few policymakers were taking it seriously. Even today efforts to combat global warming are still in the early stages. But the threat is so great that this crisis more than any other is now driving much sustainability planning. Over the coming decades every jurisdiction on Earth-from entire countries down to the smallest towns and rural districts-will need to figure out how to nearly eliminate its greenhouse gas (GHG) emissions and how to adapt to a changing climate.