Many of the world’s leading models are now projecting warming rates that most scientists, including the modelmakers themselves, believe are implausibly fast. In advance of the U.N. report, scientists have scrambled to understand what went wrong and how to turn the models, which in other respects are more powerful and trustworthy than their predecessors, into useful guidance for policymakers. ... Climate models used by next month’s Intergovernmental Panel on Climate Change report project more warming over an 1850–1900 baseline than those in a 2013 report. Scientists are using recent observed warming to rein them in.