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What is the "Omega Block" causing Europe's intense summer heatwave?

A weather pattern called an 'omega block' is sustaining the intense heatwave that has engulfed Western Europe and caused more than 50 deaths in France.

What you need to understand about Omega blocks and whether climate change could make them more frequent in future years.

What is an 'Omega?Block'?

The Greek letter O is the shape of an omega block. It has a bulge between two low pressure systems that are cooler and warmer.

The "blocking element" refers to the way in which warm, high-pressure air becomes stuck. In normal conditions, the Jet Stream carries weather systems from west to east.

This flow can be disrupted during an Omega Block and can buckle north and south dramatically, isolating pressure systems. These patterns are slowed down by weaker steering winds, and by temperature contrasts in the atmosphere.

This causes a hot, still air to be trapped in the same place. Omega blocks can last for up to 10 days.

WHAT HAPPENS WHEN AN OMEGA BLOCKS?

Conditions become 'hot and dry' in the area of high pressure. High pressure suppresses the formation of clouds, which results in clear skies and sunny skies.

Conditions like this are baking France, and Spain where temperatures have exceeded 40° Celsius (104° Fahrenheit).

Low-pressure zones flanking the hotspot are likely to experience cooler and rainier conditions.

According to the UK Met Office, Britain is on the boundary of the high-pressure systems and cooler air in the northwest, causing intense heat in south and east and cooler and wetter conditions to be found in north and west.

Is climate change responsible?

Scientists are not yet in agreement on how climate change affects the frequency of blockage events, although some research suggests that global warming increased their frequency this century in northern and western Europe.

The global scientific consensus, however, is that climate change increases the 'frequency and intensity' of heatwaves.

Since pre-industrial times, greenhouse gas emissions, mostly from burning coal and oil, have warmed the earth by approximately 1.4 C.

Heatwaves are more intense when temperatures are higher.

Scientists stated on June 26 that the European heatwave was "virtually unavoidable" without?climate changes caused by humans. This has made this week’s oppressively hot temperatures at night 100 times more probable than it would have even been two decades ago.

World Weather Attribution, a group of climate scientists, said that a similar heatwave in the same month fifty years ago would have been around 3.5° Celsius cooler than this one.

The heat that results from patterns such as omega blocks can be much more intense because of the way climate change has increased global temperatures. (Reporting and editing by Richard Lough, Ros Russell, and Kate Abnett)

(source: Reuters)