A review of past changes in extratropical cyclones in the northern hemisphere and what can be learned for the future

Extratropical cyclones, a major phenomenon of the mid-latitude atmospheric dynamics, show strong variability over a range of time scales. Future projections hint at an increase of cyclonic intensity and the associated precipitation, an important fact to be considered when developing future risk assessments. This review presents a first overview of studies which (a) puts the current variability and projected future climate changes of extratropical cyclone characteristics in a long-term perspective, (b) shows connections to natural external forcings, and (c) deepens our understanding of cyclone intensification processes for past climate periods. We summarize the current state of knowledge for two periods in the past-the last millennium and the Last Glacial Maximum (LGM, 21,000 years ago). For these two periods, the sparse information from paleo proxy archives are compared to climate modeling results on global and regional scales. For example, strong changes of the climate mean state, induced by orbital forcing and associated feedbacks, show strong effects on different cyclone characteristics, for example, a southward shift of the storm tracks over the North Atlantic during the LGM. Other findings indicate that dynamic processes could play at least an equally important role as thermodynamic processes for the variations of cyclone-induced precipitation. This is in contrast to the projected future changes in cyclone-related precipitation, which are driven primarily by thermodynamic processes. The review demonstrates how a paleoclimatic view can foster an extended process understanding and be instrumental to better understand future changes in extratropical cyclones and associated characteristics. This article is categorized under: Paleoclimates and Current Trends > Modern Climate Change

Automated summary

This review presents an overview of the variability and projected future changes of extratropical cyclone characteristics in the context of past climate periods, emphasizing the impacts of climate mean state changes on cyclone characteristics. Dynamic processes are found to play an important role in cyclone-induced precipitation variations in the past, while future changes in cyclone-related precipitation are primarily driven by thermodynamic processes. A paleoclimatic perspective can enhance process understanding and help in better understanding future changes in extratropical cyclones and associated characteristics.