Summer heatwaves made twice as likely by climate change

Meteorological autumn has begun across the northern hemisphere. The cooler days are welcome for some after what has been a hot and challenging summer season. From the Arctic right down to the tropics we have witnessed high temperatures, droughts, wildfires, floods and landslides.

This has had a widespread impact on human health, agriculture, ecosystems and infrastructure which tragically resulted in many deaths.

Here at home our summer has been a good deal less extreme, but nonetheless unusually dry and warm with some new records set at Met Éireann’s stations. Settled weather developed in the middle of May and continued through June and for much of July as an exceptionally dry, Scandinavian air mass dominated most of Europe.

The widespread record temperatures which occurred over western and northern Europe this summer were caused by a stationary “blocking” area of high pressure which developed when the jet stream, a band of high level winds which steers weather systems around the globe, was situated much farther to the west and north than usual.

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The current weather extremes are in line with previous global and regional climate projections for Ireland which we have been producing for over 15 years

While such weather patterns are not infrequent, the underlying cause for the increased intensity of this type of event is thought to be related to the more rapid warming in Arctic regions compared to the rest of the world, known as Arctic amplification.

This has resulted in a decrease in the temperature difference between the mid-latitudes and the Artic and a weakening of the circulation between these two regions.

The result is an occasional “stalling” of weather systems where weather patterns linger for longer in the same place and is an example of how weather patterns might be modified in a warmer climate.

Extreme weather

The extreme weather events being experienced around the globe are occurring in a warming world, and while human influence on the climate system is well established, attributing or linking specific extreme weather events with man-made climate change is complex as no one weather event has a single cause.

Attribution science is a rapidly developing field of study which aims to determine the mechanisms responsible for extreme weather and climate change. Many attribution studies have found that the probability of extreme events has increased because of higher temperatures caused by human related greenhouse gas emissions.

Scientific attribution studies involve complex data analytics and can take months to complete, but it is now becoming possible using advanced computing systems to provide rapid attribution information for certain events, albeit not peer reviewed, within a few days of an event.

Phoenix Park weather station

One such preliminary study by the World Weather Attribution (WWA) network, based in part on data from Met Éireann’s Phoenix Park weather station, has estimated that the recent heatwave over Ireland has been made twice as likely because of climate change.

Met Éireann’s immediate role in extreme weather events is to provide accurate observations, climatological analysis, forecasts and warnings to protect human life and property allied with the National Emergency Coordination Group.

In order to provide information on future events we are part of the huge global effort under way to provide robust projections of the future climate. Met Éireann together with other Irish scientists are actively involved in a wide range of projects undertaking climate modelling and attribution research, including the award winning MÉRA (Met Éireann ReAnalysis) a high resolution study of Ireland’s past climate.

The current weather extremes are in line with previous global and regional climate projections for Ireland which we have been producing for over 15 years.

This ongoing climate change research ensures that Irish society and decision makers have access to the best available, scientifically verifiable, information related to both past and future climate and weather related extremes.

To prepare for the increased societal risks due to a changed climate, Ireland’s first National Adaptation Framework was published earlier this year.

Under this plan Government departments are required to prepare sectoral adaptation plans in relation to priority areas for which they are responsible.

Evelyn Cusack is head of forecasting at Met Éireann and Séamus Walsh, is head of climatology and observations at Met Éireann