On any given day, some region of the globe is likely to be affected by significant negative temperature anomalies. Depending on the severity, extreme cold periods may be deemed cold air outbreaks (CAOs). These CAOs can be detrimental to the agricultural industry and human health, especially in less prepared regions. A systematic CAO classification was developed using a set of criteria concerning magnitude, duration, and spatial extent from two gridded reanalysis datasets from 1979 – 2018. Trends in CAOs were calculated for different regions across the globe and the results from each reanalysis dataset compared with one another to identify discrepancies. CAOs were found to have decreased in spatial extent, frequency, duration, and magnitude across much of the globe, particularly across Alaska, Canada, and the North Atlantic, while an increase in CAOs was observed in Eastern Europe, Central Eurasia, and the Southern Ocean.