A Comparison of Impacts to Northern Hemisphere Winter Storm Tracks between the IPCC AR4 and AR5 Climate Change Scenarios

In recent years, the role of synoptic scale storms in the current and future climate has been an area of interest for the climate community. This study focuses on northern hemisphere extra-tropical winter (JFM) cyclones to determine if their frequency, intensity, and precipitation patterns are impacted by global warming. To accomplish this, we utilize a software package that generates storm tracks by determining sea-level pressure minimum, applied to data from the Intergovernmental Panel on Climate Change (IPCC) 4th Assessment Report (AR4) and 5th Assessment Report (AR5). From the AR4 and AR5, an ensemble of 5 different models is created to evaluate the storm tracks and minimize single model bias. There is general agreement between the current climate in the AR4 and AR5 runs when compared to the NCEP Reanalysis I data set. For the future climate scenarios, the AR4 A1B scenario (~760 ppm CO₂), the AR5 RCP4.5 (~650 ppm CO₂) and AR5 RCP8.5 (>1370 ppm CO₂) are compared. The A1B ensemble shows no significant change in the location of the Atlantic or Pacific track. However, there is a slight decrease in mid-latitude storm frequency with more intense storms near the Hudson Bay region. An increase in precipitation is also found along the west and east coasts of North America in A1B. The two AR5 scenarios differ somewhat from the A1B scenario as well as from each other. Both AR5 scenarios depict an overall increase in the intensity and a decrease in mid-latitude storm frequency. The RCP8.5 scenario depicts a greater decrease in frequency when compared to the RCP4.5. Taking a closer look at the active storm track region, the RCP8.5 exhibits an increase in the North Atlantic and a decrease in the North Pacific. Poleward of these active storm regions, intensity decreases in the North Atlantic and increases in the North Pacific, indicating a weakening of the Icelandic low and a strengthening of the Aleutian low in response to global warming. Future work will focus on precipitation patterns for the AR5 ensembles to determine if their storms are more efficient rainfall producers similar to our results comparing A1B with the current climate.