Detectable impacts of Climate Change in the UK; a new review for the next Climate Change Risk Assessment

2022 was another year of “unprecedented” weather. Provisional figures indicate that it was the warmest so far recorded, with almost every month hotter than average. Much of the country had a notably mild New Year, despite the cold snap in mid-December. This was preceded by the third warmest autumn on record, and that by a scorching summer, with the hottest day ever recorded in July. But summer’s heat waves were also accompanied by a rise in the number of daily deaths across the country. People around the world are becoming increasingly more aware of events like these, and their impact in the UK is particularly concerning amidst the ongoing cost-of-living, energy, and NHS crises.

Aerial view of the Wennington wildfire, London, 19 July 2022. Source: Harrison Healey, Wikimedia Commons (CC BY 3.0).

Ahead of the Fourth UK Climate Change Risk Assessment (CCRA4), the Climate Change Committee (CCC) are asking what we know about the impact of past and present climate change on natural and human systems here in the UK specifically. At the global level, the 2021 IPCC sixth assessment working group I (AR6 WGI) report concluded: “It is unequivocal that human influence has warmed the atmosphere, ocean and land.” This single sentence has been informed by decades of research by people at the cutting edge of climate science, and the evidence to support it has grown stronger in every IPCC report since they began. The report goes on to say: “Human-induced climate change is already affecting many weather and climate extremes in every region across the globe.” In last year’s follow-up AR6 WGII report on impacts, adaptation, and vulnerability, an extensive assessment of the science led to the conclusion that the magnitude and proliferation of extremes caused by human-induced climate change were having widespread, adverse impacts on both nature and people. Last summer’s heatwaves, and the concurrent dangers to health, homes, and the environment, were a graphic illustration of the nature of such human-induced impacts.

The study of impacts that informed this conclusion is the remit of climate scientists who specialise in “detection and attribution”. This is about looking at what is changing around us and being able to pinpoint the cause(s) – and particularly, whether human-induced climate change is at the root. To inform CCRA4, the CCC have commissioned a joint Bristol and Exeter University team to conduct a comprehensive review of the detection and attribution of climate change in the UK. The first part will cover the detection and attribution of weather and climate changes in the UK, relevant to specific “Climate Impact Drivers”. The second will cover attribution of impacts on societal, infrastructural, economic, and biodiversity sectors. We aim to find out what studies have been done so far, where the gaps are, and whether they can be filled, or if they would require substantial new methodological or data advances. We aim to identify variables which are key drivers of multiple impacts, and, importantly, where further attribution analysis is needed – especially when the impacts are critical for UK risk.

Detection and attribution is a rapidly evolving field, with focus only relatively recently moving from meteorological attribution (e.g., weather extremes) to impact attribution (e.g., consequences for humans and ecosystems). Our systematic review of the literature and final report will be key to tying it all together, especially with the UK focus required by the CCC. But to be able to present the most up-to-date findings, and thus make informed recommendations, we need to ensure that we have considered all relevant studies. So, if you, or someone you know, has published on this topic – whether UK specific or not – we’d like to know about it! Help shape and inform the next UK Climate Change Risk Assessment.


This blog was written by Regan Mudhar, Professor Dann Mitchell (University of Bristol), Professor Richard Betts and Professor Peter Stott (University of Exeter/UK Met Office).

Will July’s heat become the new normal?

Saddleworth Moor fire near Stalybridge, England, 2018.  Image credit: NASA

For the past month, Europe has experienced a significant heatwave, with both high temperatures and low levels of rainfall, especially in the North. Over this period, we’ve seen a rise in heat-related deaths in major cities, wildfires in Greece, Spain and Portugal, and a distinct ‘browning’ of the European landscape visible from space.

As we sit sweltering in our offices, the question on everyone’s lips seems to be “are we going to keep experiencing heatwaves like this as the climate changes?” or, to put it another way, “Is this heat the new norm?”

Leo Hickman, Ed Hawkins, and others, have spurred a great deal of social media interest with posts highlighting how climate events that are currently considered ‘extreme’, will at some point be called ‘typical’ as the climate evolves.

As part of a two-year project on how future climate impacts different sectors (, my colleagues and I have been developing complex computer simulations to explore our current climate as well as possible future climates. Specifically, we’re comparing what the world will look like if we meet the targets set out in the Paris agreement: to limit the global average temperature rise to a maximum of 2.0 degrees warming above pre-industrial levels but with the ambition of limiting warming to 1.5 degrees.

The world is already around 1 degree warmer on average than pre-industrial levels, and the evidence to date shows that every 0.5 degree of additional warming will make a significant difference to the weather we experience in the future.

So, we’ve been able to take those simulations and ask the question: What’s the probability of us experiencing European temperatures like July 2018 again if:

  1. We don’t emit any further greenhouse gases and things stay as they are (1 degree above pre-industrial levels).
  2. Greenhouse gas emissions are aggressively reduced, restricting global average temperature rise to 1.5 degrees above pre-industrial levels.
  3. Greenhouse gas emissions are reduced to a lesser extent, restricting global average temperature rise by 2 degrees above pre-industrial levels.

What we’ve found is that European heat of at least the temperatures we have experienced this July are likely to re-occur about once every 5-6 years, on average, in our current climate. While this seems often, remember we have already experienced 1C of global increase in temperature. We’ve also considered the temperature over the whole of Europe, not just focusing on the more extreme parts of the heatwave. If we considered only the hottest regions, this would push our current temperature re-occurrence times closer to 10-20 years. However, using this Europe-wide definition of the current heat event, we find that in the 1.5C future world, temperatures at least this high would occur every other year, and in a 2C world, four out of five summers would likely have heat events that are at least as hot as our current one. Worryingly, our current greenhouse gas emission trajectory is leading us closer to 3C, so urgent and coordinated action is still needed from our politicians around the world.

Our climate models are not perfect, and they cannot capture all aspects of the current heatwave, especially concerning the large-scale weather pattern that ‘blocked’ the cooler air from ending our current heatwave. These deficiencies increase the uncertainty in our future projections, but we still trust the ball-park figures.

Whilst these results are not peer-reviewed, and should be considered as preliminary findings, it is clear that the current increased heat experienced over Europe has a significant impact on society, and that there will be even more significant impacts if we were to begin experiencing these conditions as much as our analysis suggests.

Cutting our emissions now will save us a hell of a headache later.

This blog is written by Dr Dann Mitchell (@ClimateDann) and Peter Uhe from the University of Bristol Geographical Sciences department and the Cabot Institute for the Environment.

Dann Mitchell