Decripting present and future synoptic circulation patterns associated with cold and snowy spells over Italy

Decripting present and future synoptic circulation patterns associated with cold and snowy spells over Italy

It’s widely believed that episodes of significant cold or snow should become less likely as a result of global warming. The Intergovernmental Panel on Climate Change fifth assessment report describes a “very likely” decrease in the number of ice days and low-temperature days with higher temperatures. There is also a strong consensus that average snowfall and snow cover are already decreasing in the Northern Hemisphere, and empirical evidence supports this view. An observed decrease in average snowfall in northern Italy over the last few decades has been linked to the rise in temperature due to climate change. Similar findings hold for the Alpine region, and for central and southern Italy.

A closely related issue is the dynamics of compound extreme cold and snowy events. As recent research has underlined, counterintuitive effects could make the trends for such compound events work differently. In the right conditions, for example, warmer surface and sea surface temperatures can enhance convective snowfall precipitation. In the case of Japan, one study has shown that the interaction between the Sea of Japan polar air mass convergence and topography may enhance extreme snowfalls in future climates, despite rising temperatures. Other research has shown in an ensemble of global climate simulations that while average daily snowfall will decline significantly with global warming, only small fractional changes will likely affect daily snowfall extremes.

In a recent study, Miriam, D’Errico, Flavio Pons and colleagues explore a number of questions surrounding this issue in greater detail. They focus on Italy, where recent cold and snowy spells have strongly affected ground and air transport. These researchers analyse simulations produced in a global circulation model under different emission scenarios, finding that both cold spells and snow should decrease overall. However, after averaging over many events, they also find that temperatures in the most plausible scenarios will still often be low enough to generate significant snowfall in single events. In conclusion, they suggest that the disruptive effects of these compound events may be substantially amplified by a broad and mistaken expectation that such events will become extremely unlikely on a warming planet.

D’Errico, M., Pons, F., Yiou, P., Tao, S., Nardini, C., Lunkeit, F., and Faranda, D.: Present and future synoptic circulation patterns associated with cold and snowy spells over Italy, Earth Syst. Dynam., 13, 961–992,, 2022.

Cold spells from documentary sources. Data recorded in (a) Campobasso (686 m altitude); (b) Bologna (54 m altitude). Each ball represents one cold-spell event. The diameter is proportional to the number of snowfall days. The y axis shows the snowfall measured during each event. The colour shows the minimum near-surface temperature recorded during the event (see “Sources and dataset” section).