The heatwave in Europe has pushed the zero-degree limit - the altitude at which the temperature dips into the minus - to a record height of 5,298 metres in Switzerland.
This new record was recorded on the sweltering night of August 20-21, the Federal Office for Meteorology and Climatology (MeteoSwiss) said on Monday on the platform X, previously known as Twitter.
The previous record was 5,184 metres, set on July 25, 2022.
MeteoSwiss experts measure the zero-degree limit twice a day using weather balloons launched from their regional centre in Payerne, canton Vaud. In summer, the zero degree is typically between 3,000 metres (in June) and almost 4,000 metres (in July).
MeteoSwiss says that the zero-degree isotherm near the ground, calculated in this case by measuring stations, has risen by 200-700 metres, depending on the season, since the beginning of surveys in 1864. Since the 1970s, this rise has accelerated, especially in spring and summer, says MeteoSwiss.
The zero-degree isotherm separates the layers of air which have a temperature above 0°C at low altitudes from those with a temperature below the freezing point at higher altitudes, says MeteoSwiss.
Owing to its very important influence on the development of vegetation, the limit of snowfall and the water cycle, the zero-degree isotherm is an integral part of weather forecasts.