Any global conference that includes so many countries can’t be expected to agree on much more than the lowest common denominator. But the fact that the lowest common denominator is now so high — a willingness by 188 countries to offer plans to steadily and verifiably reduce their carbon emissions — means we still have a chance to meet what scientists say is our key challenge: to avoid the worst impacts of global warming that we cannot possibly manage and to manage those impacts that we can no longer avoid. That is a big, big deal.