Skiers prepare to ski despite the lack of snow at the ski resort of Peyragudes, southwestern France on January 5, 2023. Credit: Charly Triballeau/AFP via Getty Images.
The lack of snow during this ski season in Europe has been particularly pronounced, but the snow coverage has been declining constantly on the Alps for a few decades. Snow requires sufficiently moist air exposed to temperatures below 2 °C to allow ice crystals to form, agglomerate, and fall under their own weight. It is a key component of the global climate that regulates temperatures and hydrological systems and it is heavily affected by man-made global warming1. The extension and duration of the snowpack has been systematically monitored only for a few decades, but to better understand climate change it’s important to be able to look further back in time.
A team from the University of Padova and the Institute of Atmospheric Sciences and Climate (CNR-ISAC) in Bologna has reconstructed the evolution of the snowpack on the Alps over more than 600 years. Their method saw them date the growth rings of shrubs to a specific year, and to extract data on the climate and atmospheric conditions under which they formed.
“We applied this methodology not to trees but to shrubs, in particular juniper” explains Marco Carrer, forest ecologist at the University of Padua and first author of the study published in Nature Climate Change2. “At high altitudes juniper grows horizontally very close to the ground and records the duration of the snow cover in its rings. It is a long-lived plant and typically lasts from 350 to 700 years, sometimes even a millennium”. The growing phase of juniper is strongly dependent on how early it manages to re-emerge from the snow that covers it.
By combining the measurements of the growth rings with a computer model that simulates the evolution of the snowpack, the researchers reconstructed the snow conditions over the last six centuries. They showed that over the last 50 years, the Alps experienced a 5.6% reduction per decade in the annual duration of the snow cover. Such a quick decline had never occurred before, and the current duration of the snowpack cover is 36 days shorter than the long-term mean over the whole 600-years period.
By studying a larger sample of shrubs, the researchers hope to be able to further extend the chronology. It would be extremely useful to go back 2,000 years, they say, to investigate the warm period during the Middle Age and understand whether there is any correspondence with the current events. Also, the data used in this study comes from a specific point in the Italian central Alps, and the team would like to broaden the image to the entire Alpine arch, and possibly beyond. The juniper is also widespread in northern Europe and Greenland, including where trees no longer grow. “Researchers in this field used to be stopped by the absence of trees,” says Carrer. “Our study expands the possibilities for this kind of research”.
