Heatwave in Europe: What is the 'Omega Block' and why isn’t It climate change’s fault?

Temperatures reached record highs this Saturday in several countries in Central and Eastern Europe. Switzerland reached 101.8 degrees Fahrenheit in Basel, while Denmark reached 98.6 F and the Czech Republic exceeded 105.4 F. In Germany, the extreme heat damaged the A2 highway near Berlin, where the asphalt cracked. In addition, Deutsche Bahn, the country’s main state-owned railway company, recommended avoiding non-essential travel due to problems with the railway infrastructure and advised travelers with health issues to avoid traveling if possible.

Health authorities in France reported approximately 1,000 additional deaths since June 24 compared to expected levels. Public Health France noted that these figures are not yet finalized, but they reflect the impact of extreme heat, especially on vulnerable people.

The high temperatures have made for alarming headlines, but the scientific explanation points primarily to a natural atmospheric pattern known as an "omega block."

What is an omega block?

The name comes from the uppercase Greek letter omega (Ω), whose shape mimics the pattern formed by the jet stream in the upper atmosphere. According to meteorologist Chris Martz, in an omega block, a powerful high-pressure ridge forms at an altitude of between 18,000 and 19,000 feet above sea level—that is, halfway up the troposphere—flanked by two low-pressure systems on either side.

This configuration "traps" the atmospheric flow. In the current case, a large anticyclonic ridge has allowed the horizontal transport of very warm air from the Sahara toward western Europe. As it moves northward under the influence of the anticyclonic flow, in a clockwise direction, this air mass is compressed without exchanging heat with its surroundings, which further increases its temperature.

This process is entirely natural and is part of the planet’s normal meteorological variability.

The scientific debate: Does climate change play a role?

Martz emphasizes that this process is entirely natural and has no connection whatsoever to climate change or greenhouse gas emissions.

Contrary to what is often claimed, various scientific studies indicate that the faster warming of the Arctic (known as Arctic amplification) is reducing the temperature difference between the pole and mid-latitudes.

This smaller difference could, paradoxically, lead to weaker upper-level winds and reduce the frequency of atmospheric blockages at mid- and high latitudes, according to research such as that by Hassanzadeh et al. (2014) and Woollings et al. (2018).

Europe has experienced a notable number of extreme heat waves since 2019, a phenomenon somewhat less common in other regions of the world. The notable exception was the heat wave in the northwestern United States in June–July 2021, although subsequent studies indicate that it was not all that extraordinary from a historical perspective.

Other plausible explanations

Beyond average global warming, Chris Martz points to two main factors for the increase in heat events in Europe:

Even in a pre-industrial climate, record-breaking heat waves would still occur due to natural variability. In fact, in the midst of a heatwave in Europe, the global average temperature recorded a slight decrease on some days, illustrating that this is primarily a matter of the redistribution of air masses.

Meteorology vs. Sensationalism

The atmosphere and the oceans form a chaotic system of two turbulent fluids in constant interaction. In this context, extreme phenomena are to be expected. The current omega block is a classic example of how weather systems can generate persistent heat conditions without the need to invoke long-term climate causes.

As meteorologist Chris Martz recommends, it is essential to obtain meteorological information from reliable technical sources and to avoid sensationalist headlines that simplify or distort the complexity of the climate.