Professor Ric Williams is Chair in Ocean and Climate Science and co-lead of the University of Liverpool’s Climate Futures Research theme:
This summer, Southern Europe experienced a heat wave with temperatures reaching 45oC over parts of Spain, southern Italy and Greece. At the same time, the UK and Scandinavia are experiencing unsettled weather with repeated weather systems passing through.
What caused the extreme heat over southern Europe?
Three separate drivers affected the continental heat wave, each operated on different timescales. Firstly, there was an extensive region of high pressure over much of Europe which led 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 developed 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 has occured decade by decade over the globe due to the increase in greenhouse gases in the atmosphere. These three factors combined together which cuased the extreme heat over southern Europe in 2023 which was the hottest summer ever recorded.
Source: Global-mean surface air temperatures for the 30 warmest boreal summers (June-July-August) in the ERA5 data record, ranked from lower to higher temperature - Data: ERA5. Credit: C3S/ECMWF. (https://climate.copernicus.eu/summer-2023-hottest-record)
Why was 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. During summer 2023, we had 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 was 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 recent heat wave over southern Europe saying that the high temperatures reached were 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 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).
Postcard from the Straits of Florida
As part of the research project he is leading, Professor Ric Williams has undertaken a research cruise to the Florida Straits.
Professor Williams is the Principal Investigator on a £4 million collaborative research project to explore how the Gulf Stream affects the climate system through the transport of nutrients and carbon.
The purpose of the five-day long research cruise was to deploy scientific instruments including moorings and floats with sensors and autonomous vehicles into the fast-flowing waters of the Florida Straits to assess nutrient and carbon levels and the amount of turbulence in the Gulf Stream.
Find out more: Postcard from the Straits of Florida