Southern Europe is experiencing a heat wave with temperatures expected to be reaching 45oC over parts of Spain, southern Italy and Greece. There is a possibility of the European temperature record of 48.8oC in Sicily in August 2021 being exceeded. At the same time, the UK and Scandinavia are experiencing unsettled weather with repeated weather systems passing through.
Why is there this extreme heat over southern Europe?
There are three separate drivers affecting the continental heat wave, each operating on different timescales. Firstly, there is an extensive region of high pressure over much of Europe leading to a stable region. This pattern of high pressure is a regular occurrence and can last for several weeks and is associated with hot weather in the summer. Secondly, an El Nino event has been developing in the Pacific, with expansive regions of warm water at the surface in the tropics and central Pacific. These El Nino events occur typically every two to seven years and are associated with higher surface temperatures over much of the globe. Thirdly, warming is occurring decade by decade over the globe due to the increase in greenhouse gases in the atmosphere. These three factors have combined together to lead to the extreme heat over southern Europe.
Why is there a different response over the UK?
Our experience of the weather and climate change is dictated by the pressure patterns over the globe and the associated meandering path of the Jet Stream, a fast moving ribbon of air in the upper atmosphere. The UK experiences warmer, drier weather when the Jet Stream is to the north of the UK and instead experiences colder, wetter weather when the Jet Stream is to the south. We are currently in a regime where the Jet Stream is to the south of the UK leading to the colder, wetter weather. This path of the Jet Stream is connected to the extensive high pressure system over Europe.
For the last mini heat wave the UK experienced in July 2021, exceptionally warm air was brought over the UK from southern France and Spain. The different UK responses in the UK to this July and that in 2021 is due to the detailed pressure pattern over the Atlantic and Europe, affecting where extreme heat is redistributed.
What is the connection with climate change?
It is always difficult to connect a weather event to climate change. We have often had these patterns of air flow and these patterns by themselves are not unusual. What is unusual is the extent of the warming. Weather model assessments of the last UK record warming revealed that the extent of this warming was 10 x more likely due to climate change. This analysis is likely to carry over to the present heat wave over southern Europe saying that the high temperatures being reached are much more likely due to climate change.
We have known for several decades that increasing the amount of carbon dioxide in the atmosphere leads to an increase in global-mean surface temperature. However, the last Intergovernmental Panel on Climate Change report released in 2021 concluded that human-caused emissions of greenhouse gases “have led to an increased frequency and/or intensity of some weather and climate extremes”, including droughts, extreme heat and record floods threatening the livelihoods for millions of people. So what we are seeing over much of continental Europe is part of a bigger picture of climate extremes occurring across the globe.
What needs to be done?
We can mitigate against the personal effects of a heat wave if travelling in southern Europe by seeking the shade, carrying water and choosing our travel plans carefully. However, the bigger picture is what can we do about climate change? The only long-term solution is dealing with carbon emissions and reducing the amount of carbon we utilise. Some of the solution here is personal in terms of our lifestyle choices in terms of what we eat, how we travel and how we heat or cool our homes and workplaces. However, real progress is only made when those individual choices are repeated on scale via co-ordinated action involving regional or national government, to provide investment in how to produce energy cleanly and sustained funding to move to a low carbon future.
Professor Ric Williams spoke to BBC Radio Merseyside about the current heat wave affecting Europe, you can listen to the interview here > BBC Radio Merseyside (from 2 hours 7 mins).
Find out more about the University’s engagement in this Youtube video: