The frequency and intensity of cold spells is decreasing in the Northern Hemisphere due to rising temperatures, according to a new study by Weronika Osmólska at the National Centre for Atmospheric Science and University of Leeds.

As part of her PhD, Weronika researched the changes in cold spells between 1980-2025, using a new method that tracks cold spells in space and time. She analysed four cold spell characteristics – frequency, intensity, area, and persistence. 

Though there can be other contributing factors to changes in cold spells – such as loss of sea ice and shifting weather patterns which can change how much temperature fluctuates about the background warming – Weronika’s research shows that the dominant driver to decreasing cold spells is the rise in Earth’s average temperatures. Global warming is making cold spells less frequent, less intense, and smaller across most of the Northern Hemisphere.

Weronika explains her method: “Local cold events in this study were identified when the temperature dropped below the 5th percent of all temperature values for three consecutive days. Events that meet this requirement are then tracked. We use the winds over the event area to estimate where the cold extreme might be present on the next day. If there is an extreme in this region on the next day, we label this as part of the same cold spell event. This way we build a catalogue of all cold spells, with the knowledge of their location and pathway.”

“This is the first study that considers and compares how cold spells have changed as a result of mean background temperature rise and also from changes in the temperature variability about this background temperature rise,” she emphasises.

When asked about the most unexpected discovery during her research, Weronika shares: “Only in Northern North America, the reduction in temperature variability about the background mean warming was found to also significantly decrease the frequency and the severity of cold spells. More specifically, we find that the changes in these temperature variabilities in northern North America are found to contribute to one third of the total change in intensity from mean background warming effects. Based on other studies this reduction of temperature variance might be caused by sea ice loss, leading to cold extremes warming faster than hotter extremes.”
Weronika’s work contributes to a growing body of evidence. Research published by the Intergovernmental Panel on Climate Change (IPCC) confirms that winter cold spells have been decreasing since 1950 and that anthropogenic greenhouse gases are very likely the main cause for this.

Weronika shares: “In Europe, studies show there has been a decline in cold spell frequency, with a severity comparable to the European cold winter of 2009/10 being half as likely to occur as a consequence of anthropogenic climate change. IPCC reports also state that, on land, the magnitude of temperature extremes increases more strongly than global mean temperature, and the highest increase of temperature is projected in Arctic regions, at about three times the rate of global warming.”

Where did Weronika’s interest in cold spells come from? She shares:

“Cold spells and snowfall were always a rare occurrence in the winter in the UK, so I found myself wondering when I was younger how they form and why. I think this made me want to research extreme cold weather events to further understand them.”

Though cold spells can be harmful to human health and infrastructure, warmer winters have negative impacts too – including the increase of pests or illnesses, disrupted water supplies and drought risks, and agriculture failures.

Read the research paper published in AGU Geophysical Research Letters to learn more about Weronika’s work on cold spells.