A team led by Lara Wallberg from the Max Planck Institute for Meteorology has developed a promising approach to the Long-term prediction of hot summers developed in Europe. The researchers were able to prove that heat accumulation in the North Atlantic can serve as a reliable indicator of extreme heat periods on the continent. This correlation should enable forecasts to be made up to three years in advance. The study, which was published in the journal Geophysical Research Letters, could improve the protection of vulnerable groups, be relevant for agriculture and also for sailors. According to the research findings, Europe is facing another hot summer in 2025.
Cause in the ocean
The improved forecasts are based on a now recognised connection between the natural oscillation of the North Atlantic and hot summers in Europe. Lara Wallberg explains: "Three years before extremely warm European summers, the heat content of the ocean begins to rise, trapping the heat along the North Atlantic Current by 40 degrees north." In the following two years, this heat absorption increases further and the North Atlantic current shifts northwards. This leads to warm subtropical water reaching higher latitudes and influencing the temperature gradients between the ocean and atmosphere. During extremely warm European summers, this accumulated heat would then be released into the atmosphere mainly through the heat transport of the subpolar gyre and reach Europe via the jet stream.
Improved model simulations
To test the reliability of their forecasting method, the researchers carried out so-called post-prediction experiments. They compared model simulations that took into account the connection between heat build-up in the North Atlantic and heat extremes with those that did not include this mechanism. The result: the simulations using the new approach modelled past hot summers much more reliably. Of 18 warmer-than-average summers between 1964 and 2021, ten could be accurately predicted - including the number of hot summer days and the extent of the heat.
According to Lara Wallberg, these new model calculations also predict a hot summer in Europe in 2025. This prediction is in line with forecasts from the European Centre for Medium-Range Weather Forecasts.
Significance for the sport of sailing
For owners and charterers, these forecasts could mean better long-term planning of cruises. Past summers were sometimes extremely hot, especially in the Mediterranean region. During the day, it was almost impossible to stay on deck without sun protection, and fittings such as winches could hardly be touched without gloves. Heated boat hulls barely cooled down to a tolerable level at night, and the possible sleeping areas in the cockpit and on deck were literally coveted.
However, if you already know in your annual planning that an extreme summer is very likely, you can switch to the early or low season or plan for a more northerly sailing area. When choosing a boat, charterers can also look out for additional installations such as air conditioning, which is no longer a rarity, especially on catamarans. Owners can consider installing a Retrofit air conditioning yourself. Even small ones, Mobile air conditioning systems can already provide relief. The purchase of suitable sun and heat protection devices may also seem more sensible when you know that extreme heat is imminent.
Tips against heat on board
- Ensure sufficient air circulation on board, for example by using USB-powered fans or windscoops.
- Optimise the use of insulated containers for ice and cold drinks. Wide-necked insulated containers for food are particularly suitable for storing ice cubes.
- Install flexible shade providers such as awnings or parasols to reduce direct sunlight.
- Utilise on-board fridges efficiently and consider alternative cooling methods such as using frozen juice cartons as replacement cooling elements.
- When planning your route, take into account the hottest times of day and, if necessary, use the early morning or late evening hours for journeys.
You can find more tips against heat on board in this article.
