Observational and modeling studies indicate that decade-to-century-scale climate change is most pronounced in the high latitudes. Moreover, the greenhouse-component of climate change is indicated by models to be greatest during the winter months, in which case the greenhouse signature should appear in extreme cold arctic airmasses. To explore this possibility, the NCEP reanalysis-derived temperatures spanning the most recent 60-year time period have been analyzed over the source regions of continental polar airmasses in North America. Decadal composites confirm that the most extreme cold airmasses have shown signs of warming, at least in terms of surface temperature, since the late 1940s. In addition to the reduction in intensity of the coldest airmasses, our results strongly support the notion that extreme cold air arctic outbreaks have decreased in frequency and duration over time. These trends in winter extremes could have implications for middle as well as high latitudes, because any change in the strength of a cold airmass in its source region will likely affect the minimum temperatures reached during its southward propagation.