title: The Likelihood of Recent Record Warmth.
abstract: 2014 was nominally the warmest year on record for both the globe and northern hemisphere based on historical records spanning the past one and a half centuries. It was the latest in a recent run of record temperatures spanning the past decade and a half. Press accounts reported odds as low as one-in-650 million that the observed run of global temperature records would be expected to occur in the absence of human-caused global warming. Press reports notwithstanding, the question of how likely observed temperature records may have have been both with and without human influence is interesting in its own right. Here we attempt to address that question using a semi-empirical approach that combines the latest (CMIP5) climate model simulations with observations of global and hemispheric mean temperature. We find that individual record years and the observed runs of record-setting temperatures were extremely unlikely to have occurred in the absence of human-caused climate change, though not nearly as unlikely as press reports have suggested. These same record temperatures were, by contrast, quite likely to have occurred in the presence of anthropogenic climate forcing.
authors.affiliation: Department of Meteorology, The Pennsylvania State University, 503 Walker Building, University Park, PA 16802.
authors.forename: Michael E
authors.initials: ME
authors.lastname: Mann
authors.affiliation: Earth System Analysis, Potsdam Institute for Climate Impact Research P.O. Box 60 12 03, 14412 Potsdam, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Rahmstorf
authors.affiliation: Large Lakes Observatory, Department of Earth and Environmental Sciences University of Minnesota Duluth, 2205 E. 5th Street RLB 205, Duluth, MN 55812-2496.
authors.forename: Byron A
authors.initials: BA
authors.lastname: Steinman
authors.affiliation: Departments of Meteorology and Statistics, The Pennsylvania State University, 503 Walker Building, University Park, PA 16802.
authors.forename: Martin
authors.initials: M
authors.lastname: Tingley
authors.affiliation: Department of Meteorology, The Pennsylvania State University, 503 Walker Building, University Park, PA 16802.
authors.forename: Sonya K
authors.initials: SK
authors.lastname: Miller