The heatwave gripping much of western Europe is not only the result of high temperatures. It is also being prolonged by a stubborn weather pattern that has slowed the normal movement of air across the continent.
The pattern is known as an Omega block, a type of atmospheric blockage that can keep the same weather conditions locked over one region for several days, and sometimes longer. In the current case, it has helped trap hot, dry air over parts of Europe, pushing temperatures above 40C in countries including France and Spain and contributing to serious public health risks.
More than 40 deaths have been reported in France alone, many of them linked to attempts to escape the heat in water. The event has again underlined how dangerous prolonged heat can become when weather systems stop moving.
How the block works
Under normal conditions, the jet stream helps carry weather systems from west to east. This movement usually prevents one pattern from dominating for too long. During an Omega block, that flow is disrupted.
A large area of high pressure becomes lodged between two areas of low pressure. The result is a stalled system in which the central high-pressure zone acts like a dome, holding warm air in place and preventing cooler, wetter conditions from moving in.
This is why the heat does not break quickly. With little cloud cover and limited rainfall, the ground continues to heat up day after day. The high-pressure system also suppresses the formation of clouds, allowing more sunlight to reach the surface and intensify the rise in temperatures.
Why some areas are hotter than others
The effects of an Omega block are not uniform across Europe. Areas sitting beneath the central high-pressure zone experience the most intense heat, dry conditions and clear skies. These are the conditions affecting France and Spain, where temperatures have climbed beyond 40C.
By contrast, regions positioned closer to the low-pressure systems on either side can see very different weather. These areas may experience cooler air, rain or unsettled conditions. The UK has been near the boundary between the heat over continental Europe and cooler air to the northwest, leaving southern and eastern areas much warmer while the north and west have seen more changeable weather.
This sharp contrast is part of what makes blocking patterns so significant. While one region remains locked in dangerous heat, nearby areas can experience a completely different summer pattern.
The climate change question
Scientists have not reached a firm conclusion on whether climate change is making Omega blocks more frequent. The connection between climate change and heatwaves, however, is much clearer.
Human activity, mainly the burning of coal, oil and gas, has already warmed the planet by about 1.3C compared with pre-industrial levels. That means today’s heatwaves begin from a warmer baseline. When a blocking pattern develops, the heat trapped beneath it is more intense than it would have been in the past.
Researchers say heatwaves in Europe are now around 2C to 4C hotter than they would have been without human-caused global warming. This does not mean climate change creates every individual weather pattern. It means that when those patterns occur, they can produce more severe and more dangerous extremes.
A weather trap with higher stakes
Omega blocks are not new, but their impact is becoming more concerning in a warming climate. A pattern that holds heat in place for several days can now push temperatures into ranges that place lives at risk, especially for older people, children, outdoor workers and those with existing health conditions.
The current heatwave shows how a stalled atmosphere can turn hot summer weather into a prolonged emergency. The Omega block explains why the heat is staying in place. Climate change helps explain why the heat is hitting harder.
Source: AMNA
