Below are temperature statistics from two modern global climate models (GCMs). Included on each page are winter (DJF) mean temperatures and standard deviations as simulated by the models. These panels illustrate how the mean temperatures are coldest over the snow and ice covered regions of the Northern Hemisphere. In addition, the variability (as measured by the standard deviations) are also highest over those same snow and ice covered regions. These summaries are output from GCMs simulating conditions as close to possible to the past 20-years (1981-2000). They use observed greenhouse gass concentrations for the 1981-2000 period.

The second set of panels show the frequency of cold air outbreaks over the 1981-2000 as simulate by the climate models. The frequency is expressed as CAO days/year. In these plots, CAOs are defined as the number of winter days whose temperature is below the mean by at least two standard deviations for an extended period. The right panels show the number of cold air outbreaks projected to occur by the GCM for the years 2081-2100 in a moderate greenhouse gas increased climate scenario (the IPCC SRESA1B scenario).

Finally, in the bottom panels, we present the change in CAO frequency projected by the models for this greenhouse gas increased climate scenarios in both absolute differences (# days per year) in the left panel, and as a percentage change in frequency in the right panels. In both difference panels, blues and greens denote decreases in cold air outbreak frequencies and yellows and reds indicate increases in CAO frequencies for the 2081-2100 period.