Extreme heatwave sets records across Europe: The continent continues to experience extreme summer heat as temperatures have surged well above normal seasonal levels across several countries. Thermometers in parts of France and Spain have climbed above 40°C, with prolonged heat and little relief even during the night. Authorities have reported heat-related deaths in France amid the worsening conditions, as hospitals come under pressure and emergency services respond to rising cases of heat stress. The situation has also disrupted transport networks and strained energy systems across affected regions. At the heart of this persistent weather pattern lies a large-scale atmospheric setup known as the ‘omega block’, a formation capable of locking weather systems in place for days or even weeks.While such phenomena are not new, the intensity of heat linked to them is now unfolding in a much warmer climate than in previous decades.
Heatwave alert: Why it’s called an omega block and how it forms
The omega block is named after the Greek alphabet omega (Ω), since the formation of pressure systems within the atmosphere takes the shape of an omega symbol.In the middle of the formation lies a broad region of high atmospheric pressure, which is bordered by two regions of low atmospheric pressure. The omega block causes an arch formation in such a way that the high pressure system is blocked and cannot move forward across the continent as it would do under normal circumstances.In normal circumstances, weather systems are pushed from west to east along the jet stream, which is an air current that moves above the earth. However, in case of an omega block formation, the jet stream changes its course. It does not run straight anymore but turns north and south.
The role of high pressure in building extreme heat
High-pressure systems encourage sinking air. As the air descends, it warms and suppresses cloud formation, leaving long periods of sunshine and very little rainfall.Without clouds reflecting sunlight, the ground absorbs increasing amounts of solar energy throughout the day. Dry soils can make the situation even worse because less energy is used for evaporation, allowing surface temperatures to rise even further.The absence of strong winds also means the hot air remains largely in place. Instead of being replaced by cooler air masses, heat continues to accumulate over the same region. During lengthy blocking events, temperatures often build day after day rather than peaking briefly before easing.
How omega blocks divide heat, cloud and rainfall across countries
An omega block does not create the same conditions everywhere. Areas directly beneath the central high-pressure system usually experience hot, settled weather with little rain. That has been the case across much of France and Spain during the recent heatwave.Meanwhile, the neighbouring low-pressure systems can produce almost the opposite conditions. Regions positioned beneath those areas are more likely to see cloud, rain and lower temperatures. Countries located close to the boundary between the contrasting air masses may experience mixed conditions depending on their exact location.In the United Kingdom, for example, southern and eastern areas have experienced intense heat, while northern and western regions have remained comparatively cooler and wetter because they lie closer to the edge of the blocking pattern.
How long these weather patterns can last
Unlike passing weather fronts that move through within a day or two, omega blocks are often slow to break down. Many remain in place for several days, though some continue for more than a week. In certain situations, they can persist even longer if the surrounding atmospheric circulation changes very little.This persistence is one reason they attract attention from meteorologists. A heatwave becomes much more dangerous when high temperatures continue for an extended period, particularly if nights stay unusually warm and prevent buildings and the human body from cooling down.
Is climate change creating more omega blocks
Scientists are still examining whether climate change has altered how often blocking patterns develop.Some research suggests that parts of northern and western Europe may have experienced an increase in these events during recent decades, but there is not yet a broad scientific agreement that global warming has directly increased their frequency everywhere.The atmosphere is highly complex, and several interacting processes influence the formation of blocking patterns. That makes it difficult to separate long-term climate influences from natural weather variability.
How a warming climate is intensifying modern heatwaves
While debate continues over the number of omega blocks, there is much stronger evidence for another trend: heatwaves themselves are becoming hotter and more frequent because of climate change.Human activities, particularly the burning of coal, oil and natural gas, have increased concentrations of greenhouse gases in the atmosphere. As a result, the average global temperature has risen by roughly 1.4°C since the pre-industrial era.That rise acts as a higher starting point whenever a heatwave develops. A blocking pattern that might once have produced very warm conditions is now capable of generating far more extreme temperatures simply because the background climate is warmer.