The warming of Earth’s climate doesn’t mean that the whole planet’s temperature is higher all year long. Temperate latitudes still experience cold, snowy winters. And there’s even some evidence that climate warming could increase the severity of winter weather in the Northern Hemisphere, as polar vortices are destabilized and frigid Arctic air sweeps southward across North America, Europe, and Asia.
The extent of that effect, however, is somewhat controversial. (See the article by James Overland, Physics Today, March 2016, page 38.) Weather varies from year to year, and extreme winter events are nothing new. It’s challenging to attribute any one of them to the effects of climate change.
But now Hannah Bailey of the University of Oulu in Finland and her colleagues have done just that. They looked at an extended snowfall event, in February and March of 2018, that blanketed much of Europe and reached as far south as Rome. And they found a direct link between that snowfall and the warming of the Arctic Ocean.
They established the link through isotope geochemistry. The processes of the water cycle—evaporation, diffusion, condensation, and precipitation—are sensitive to molecular mass, and they treat isotopes slightly differently. From the levels of the minor isotopes deuterium and oxygen-18 in a particular volume of water, one can glean some information about the water’s provenance, including where it evaporated into the atmosphere before falling to Earth as rain or snow. By analyzing the isotopic makeup of the 2018 snowfall, Bailey and colleagues traced the moisture’s source to the Barents Sea, part of the Arctic Ocean northeast of the Scandinavian peninsula.
The Barents Sea used to reliably freeze over in the winter. But in 2018, 60% of its surface was free of ice. Because a frozen body of water can’t supply nearly as much moisture to the atmosphere as open water can, the researchers concluded that without Arctic warming, the 2018 snowfall wouldn’t have happened—at least not in the same way.
Analysis of just one event is limited in what it can predict for the future. But climate models project that the Barents Sea could be entirely ice-free by the end of the century. In years to come, the sea could be a significant source of European snow and rain. (H. Bailey et al., Nat. Geosci., 2021, doi:10.1038/s41561-021-00719-y.)