Scientists have learnt to predict where to expect hot summers in Europe

This is not about the usual weather forecast. Scientists are talking about something else: it is possible to assess in advance where and when the probability of a severe summer heat wave becomes higher. Such a forecast doesn't guarantee a heat wave, but it helps you see the risk earlier.

The study is published in the journal Geophysical Research Letters.

The authors tested whether North Atlantic surface temperatures could be used for long-term climate forecasts of European summers. The abstract of the paper states that they analysed MPI-ESM 1.2-LR model projections for 1-5 years and used 64 variants of model calculations.

Details

The ocean heats and cools much more slowly than air. Therefore, it can store a "trace" of future heat longer than the atmosphere. If extra heat builds up in the North Atlantic, it could change the exchange of heat between the ocean and the atmosphere and then affect summer weather in Europe.

The scientists compared forecasts that took into account the North Atlantic surface temperature with conventional approaches. They were not interested in days and weeks, but a horizon of several years. This type of forecast is called a decadal forecast: it assesses climate risks for the coming years, not the weather for tomorrow.

The main result: warmer parts of the North Atlantic are associated with a higher probability of hot summers in Europe. The study's abstract says that the probability of hot years was positively correlated with the surface temperature of the North Atlantic.

Put simply: if the ocean is warmer than normal in the right areas, Europe is more likely to get conditions favourable to a severe summer heatwave in a few years. That doesn't mean the heat wave will necessarily happen. But the odds are getting higher.

Drought has proven more difficult to deal with. While heat waves and dry weather often go together, precipitation depends on more factors. The paper points out that the North Atlantic's link to hot summers looks promising, but the prediction of hot-dry years remains less reliable.

The reason is that rain is much harder to predict years in advance. It is influenced by winds, cloud cover, soil conditions, air mass movement and random weather fluctuations. So the ocean can give a signal of future heat risk, but does not give a simple answer to the question of exactly where there will be drought.

Another important part of the mechanism is atmospheric circulation. A warm North Atlantic can influence the jet stream, a powerful "ribbon" of winds high in the atmosphere. If it changes, areas of high pressure may be more likely to linger over Europe. And that usually means fewer clouds, more sunshine and hotter weather.

Researchers at the Max Planck Institute for Meteorology have previously reached similar conclusions: they reported that unusually hot European summers are often preceded by a build-up of heat in the North Atlantic, sometimes several years before the event itself.

Why it matters

For Europe, heatwaves are already one of the most dangerous summer risks. It affects human health, hospitals, the energy system, crops, water resources and tourism. If the risk of a very hot summer can be assessed in advance, cities and services have more time to prepare.

For example, authorities can plan ahead for cooled public spaces, check hospital readiness, prepare warning systems, revise heat schedules and assess risks to agriculture.

But it's important not to overestimate the outcome. It's not a tool that will say, "it's going to be 40 degrees in so-and-so city in July." It's a way to understand in advance that the probability of a hot summer has become higher. For climate adaptation, even this probabilistic signal can be useful.

Background

People usually think of a summer heat wave as a short-term phenomenon: the anticyclone arrived, the skies cleared, and temperatures rose. But extreme heat can have deeper ocean-related causes.

The North Atlantic is one of the key regions for Europe's climate. It influences heat transport, humidity, winds and the position of the jet stream. Therefore, changes in the ocean may not show up immediately, but months or years later.

A new study continues this line of enquiry: scientists are trying to understand which ocean signals can be used for early warning. So far, they're doing best with heat waves. With drought and a combination of heat and drought, the forecast remains much less certain.

Source

Research: Leocardia Zheng, Jana Sillmann, Leonard Borchert, Decadal Predictions of the Link Between European Hot-Dry Compound Summers and North Atlantic Sea Surface Temperature, Journal of Geophysical Research Letters, 2026.