13.03.2024 | SLF News
SLF climatologist Christoph Marty joins us for an interview to explain why it can snow even in mild winters as well as the difference between the winters of 2022/23 and 2023/24, and to take a look into the future.
Mr Marty, in late November and early December there was snow chaos in large parts of the Alps and the Prealps, and in Ticino we had three metres of fresh snow just a few days ago. All the same, the winter of 2023/24 is the mildest since measurements began 60 years ago. How does this all fit together?
Even in a mild winter there may be snow that reaches the lowlands for a few days, covering this whole area rather than just some locations. All that is needed is a particular interplay of cold air and precipitation, and we had that at the end of November and start of December and in January. If we just look at the number of snow days on the Swiss Plateau, this winter hasn't been that bad. The first masses of snow even took the ski resorts by surprise. They weren't even ready to open yet at that time. But that changed pretty quickly.
When exactly?
Just in time for the start of the Christmas holidays. Then the general weather conditions changed: it got warmer and the snow melted away. As a result, the landscape became green again at lower elevations. The high-altitude ski resorts are still reaping the rewards of the strong start to the winter. But across the winter as a whole (i.e. the months from December to February), the temperature was 3.6 degrees Celsius above normal, according to the Federal Office for Meteorology and Climatology (MeteoSwiss), making it the mildest winter since measurements began in 1864 and the sixth consecutive winter when the temperature was more than one degree Celsius above normal.
However, last year there wasn't as much snow even though it was slightly cooler!
This slight drop in temperatures doesn't do much good when there is little precipitation like last winter. In the winter of 2022/23, the air was mainly very dry and warm, resulting in a lack of snow at all altitudes. This winter has been rather damp and mild so far, with most precipitation falling as rain below 1,000 metres, leading to below-average snow depths. Only above 1,500 metres was there above-average snowfall, but some of this snow melted away again due to the much milder temperatures, and so there are above-average snow depths only above 2,000 metres. This winter so far has therefore been characterised by a lack of snow below 1,500 metres and a lot of snow above 2,000 metres. And yet the two years also have something in common.
What's that?
The impact at low altitudes is the same. Climate change dramatically increases the likelihood that air masses will be warmer than before. Today, if a warmer air mass comes from the southwest, it will be two degrees Celsius warmer than pre-industrial times. This makes a huge difference to the snow because it reacts extremely sensitively to temperatures above zero degrees Celsius. In the lowlands, Swiss winter temperatures used to be just below zero degrees. Now they're often above this, meaning that it rains more often and the snow that has fallen melts more quickly. Therefore, the lower the altitude, the more obvious the lack of snow was during both winters.
Are we seeing a trend here?
It's surprising enough when one year is milder than the one before – especially when it happens for the fourth time in a row as it has now, because the fact that climate change will make it warmer in the long run doesn't mean that every winter in the future will be warmer than the previous one. It's likely that one of the next few winters will be a little cooler than the previous ones. It could definitely get a little colder in the Alpine region in the short term, with short bursts of relatively heavy snow. But one thing is clear: it won't be as cold as it used to be.
What's your forecast for the decades ahead?
Things are definitely not looking good at altitudes up to 1,500 metres. I'm not saying that every year in the future there will be less snow than the previous year, but the further we look into the future, the less snow there will be.
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