September 5, 2023

Climate Shift Index alert: United Kingdom, September 2023

Climate Central analysis shows that human-caused climate change made the record-breaking heat forecast for Ireland and the U.K. 2-5 times more likely.

Note: This is an ongoing event that may continue beyond 8 September. Use the Global Climate Shift Index map to stay updated on the latest climate-related heat in your region.

Forecasts for the three-day period starting Wednesday (6-8 September) show the potential for the U.K. and Ireland to experience unusually warm conditions. Analysis using the Climate Shift Index (CSI) shows that human-caused climate change made this heat much more likely.

UK-Ireland September 2023 CSI

Forecasted Temperatures

Daily high temperatures are expected to be well above the long-term average.

The highest temperature anomalies over this period are expected over southern England and Wales.

Unusually warm conditions will occur across mainland Europe, especially France, during this period.

Over the three-day period starting 6 September, six major cities (population 300,000 or more) are forecast to have average high temperatures more than 10°C above the 1991-2020 average for this week:

  • London +11.0° C

  • Leicester +10.7° C

  • Coventry +10.6° C

  • Leeds +10.6° C

  • Sheffield +10.4° C

  • Birmingham +10.3° C

Attribution Analysis

The Climate Shift Index uses peer-reviewed methodology to estimate how climate change has increased the likelihood of a particular temperature. It can be run using historical or forecasted temperatures. It allows for an early estimate of the influence of climate change on weather that complements detailed analyses by World Weather Attribution.

The average Climate Shift Index (CSI) for the period 6-8 September will reach level 5 for most of Great Britain. CSI level 5 means that human-caused climate change made the temperatures more than 5 times more likely.

Most of Ireland will be at or above CSI level 2 meaning the temperatures there are more than twice as likely in a climate forced by extra carbon dioxide.

For 16 cities including London, Edinburgh, Cardiff, Belfast, and Dublin, each day during this period will be at or above CSI level 3 (3 times more likely due to climate change).

Six cities — Birmingham, Bristol, Cardiff, Coventry, Leicester, and London — are expected to be at CSI level 5 throughout this period.

Reporting resources as this heat event unfolds:

To request an interview with a Climate Central scientist, please contact Peter Girard at


Dr. Andrew Pershing, VP of Science at Climate Central, said: 

“This week, Britain and Ireland will experience unseasonably warm conditions. Burning coal, oil, and natural gas made these conditions much more likely.”

Dr. Friederike Otto, Senior Lecturer in Climate Science at the Grantham Institute for Climate Change and the Environment, and co-lead of World Weather Attribution said:

"This week's heat in the U.K. has been made hotter by climate change that is the result of human activities like burning coal and other fossil fuels. This is now the case for every heatwave, everywhere in the world. Until net greenhouse gas emissions end, heatwaves in the U.K. and elsewhere will continue to become hotter and more dangerous.

“Heatwaves are one of the biggest threats posed by climate change. High temperatures are responsible for thousands of deaths across the world every year, many of which go under-reported. Despite this overwhelming evidence, there is still little public awareness of the dangers that extreme temperatures present to human health."

About the Climate Shift Index

Climate Central’s Climate Shift Index®, grounded in the latest peer-reviewed science, maps the influence of climate change on temperatures across the globe, every day. 

Climate Shift Index levels indicate how much human-caused climate change has altered the frequency of daily temperatures at a particular location. Level 1 indicates that climate change is detectable in that day’s temperature. Level 2 means that climate change made exceptionally warm temperatures in a given location at least twice as likely. Level 5 is the maximum and indicates temperatures at least 5 times more likely because of climate change.

For this analysis, temperatures come from NOAA’s Global Forecast System model.

Previous Climate Shift Index alerts