August 23, 2023

Climate Shift Index alert

Climate Central analysis shows that human-caused climate change made the record-breaking heat forecast for much of Europe five times more likely.

Note: This is an ongoing event that may continue beyond 25 August. Use the Global Climate Shift Index map to stay updated on the latest climate-related heat in your region. 

Forecasts for the five-day period starting Friday (22-25 August) show the potential for much of Europe to experience unusually warm conditions. Analysis using the Climate Shift Index (CSI) shows that human-caused climate change made this heat much more likely.

Forecasted Temperatures

  • Maximum daily temperatures are expected to be above the long-term average across mainland Europe.

  • The highest temperature anomalies over this period are expected in France and northern Spain. In these regions, temperatures are expected to be more than 10°C hotter than normal across the three days. Meanwhile, central Europe will be more than 5° warmer than normal.

  • This pattern continues the very warm conditions experienced in southern Europe, including Spain, France, and Italy this summer

Over the three day period starting August 22, 369 major European cities are forecast to be more than 10°C above normal. Notable cities include:

  • Toulouse, France (+18.7°C, CSI=5.0, 3 days)

  • Lyon, France (+17.5°C, CSI=5.0, 3 days)

  • Geneva, Switzerland (+16.0°C, CSI=5.0, 3 days)

  • Zaragoza, Spain (+13.7°C, CSI=5.0, 3 days)

  • Genoa, Italy (+13.4°C, CSI=5.0, 3 days)

  • Viseu, Portugal (+13.2°C, CSI=4.3, 3 days)

  • Vienna, Austria (+12.1°C, CSI=3.7, 3 days)

  • Munich, Germany (+10.9°C, CSI=4.0, 3 days)

  • Bucharest, Romania (+10.8°C, CSI=5.0, 3 days)

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 majority of Spain, southern France, Switzerland, Italy, Slovenia, Austria, Bulgaria, Romania, Moldova, Kosovo, and Turkey reach an average CSI value of 5 across these 5 days, meaning that climate change is expected to make this event at least 5 times more likely. This indicates that this is an exceptional climate change event in these regions.

  • Meanwhile, almost the entirety of the rest of mainland Europe is expected to experience some level of attributable temperatures, with CSI values ranging between 2 and 4 over the course of the event. These values indicate that climate change is expected to make temperatures at least 2-4 times more likely in those locations

  • The United Kingdom is expected to mostly reach CSI values of 1 or 2, indicating a detectable-to-dominating climate influence, or temperatures made at least 1.5-2 times more likely.

Over that period 24 European capitals will have 2 or more days with a significant climate fingerprint. Notable cities include:

  • Bern, Switzerland (+13.3°C, CSI=5.0, 3 days)

  • Vienna, Austria (+12.1°C, CSI=3.7, 3 days)

  • Budapest, Hungary (+11.8°C, CSI=4.3, 3 days)

  • Vaduz, Liechtenstein (+11.7°C, CSI=5.0, 3 days)

  • Madrid, Spain (+11.5°C, CSI=5.0, 3 days)

  • Bucharest, Romania (+10.8°C, CSI=5.0, 3 days)

  • Zagreb, Croatia (+ 9.7°C, CSI=5.0, 3 days)

  • Rome and Vatican City (+ 9.4°C, CSI=5.0, 3 days)

  • Athens, Greece (+ 4.6°C, CSI=3.3, 3 days)

  • Paris, France (+ 7.9°C, CSI=2.7, 2 days)

Full dataset available here

CSI Heat Alert Europe Update August 2023 (EN)

Potential impacts from this event:

  • The event coincides with the peak of August travel season in Europe. Tourists at outdoor sites and beaches will be exposed to unusually warm conditions. People visiting from cooler places are likely to be more vulnerable.

  • Exposure to risky heat can trigger heat-related illnesses, including heat exhaustion and heat stroke, a life-threatening condition. Agricultural workers and others working outside will have higher exposure.

  • The unusually hot conditions in southern France coincide with the typical start of the wine harvest.

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: 

“Europe is about to experience a continent-wide heatwave that will stress people in most countries. Pollution from burning coal, oil, and natural gas, made these unusually hot and potentially dangerous conditions much more likely. ”

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:

"Europe’s current heatwave 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 Europe 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