Trends in Northern Hemisphere cold spells across the winter periods 1980/81-2024/25

Midlatitude cold spells (CSs) are often associated with disruptions to transportation and energy infrastructures and increased risk to life and livelihoods. While the Sixth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC AR6 2021) assessed that CSs have become less frequent across most land areas due to human caused climate change, some studies suggest that their frequency may not be declining everywhere.In this work, we investigate Northern Hemisphere trends of CS characteristics in reanalysis data since the winter 1980-81, using a novel spatio-temporal CS tracking algorithm based on daily 2m temperature anomalies (Osmolska et al., 2025). We analyse the changes in frequency, severity, duration and area of CSs identified using raw and detrended temperature data to disentangle the effects of mean background warming (thermodynamics) versus circulation changes (dynamics).We show that in the Northern Hemisphere, the average winter frequency of CSs decreases due to background warming at a rate of 19 days decade-1, with similar trends in North America, Europe and East Asia. These regions are also experiencing less severe CSs, with the average 5th percentile temperature threshold in the Northern Hemisphere increasing by 0.3 K decade-1. We find that the decline in the cumulative annual area occupied by CSs is mainly due to the decrease in frequency, with the area decrease being equal to 1x108 km2 per decade. Finally, we also show that the average duration of CSs has significantly decreased in northern North America (-1.3 days decade-1) and southern Europe (-1.0 days decade-1).When dynamical effects are considered alongside the thermodynamical effects, we show that dynamical variability contributes to CS becoming less frequent in the Northern Hemisphere (-2.9 days decade-1), and contributes to a decreasing persistence and cumulative CS area over northern North America. In all other regions, we found minimal change in CS characteristics from circulation changes.In this work, we demonstrate that the rise in mean temperature is the primary driver of recent Northern Hemisphere CS trends; however, changes in dynamical variability have contributed to regional reductions in CSs in northern North America in contrast to some studies which have suggested circulation changes have enhanced CSs there.