Climate Shift Index Alert•April 29, 2025
Near record, early season heat signals climate change’s impact on U.K. spring
The United Kingdom is experiencing unusually high spring temperatures, with heat expected to intensify following the fourth-warmest London Marathon on April 27. Forecasts show that upcoming temperatures through April 30 could be as much as 8.1°C above normal, potentially breaking national and local records. Climate Central analysis shows that human-caused climate change has made these high temperatures five times more likely.
Note: This event may continue past April 30. Use the Global Climate Shift Index map to stay updated on heat in your region.
How has climate change influenced this warmth?
Between April 29-30, daily average temperatures are expected to reach Climate Shift Index (CSI) levels of 5 in a portion of North and Central U.K., including Newcastle, Middlesborough, Plymouth, Blackpool, and Aberdeen. A CSI level 5 indicates that human-caused climate change made this heat at least 5 times more likely, signifying an exceptional climate change event.
Between April 27-30, 6.4 million people in the U.K. were exposed or are forecasted to be exposed to at least one day with a CSI level 5.
During this period, 42 million people in the U.K. — 61% of the population — experienced or are forecasted to experience at least one day of unusually warm late-April temperatures made at least three times more likely due to climate change (CSI level 3).
City | Date | Temperature departure from normal (°C above normal) | CSI level that day |
|---|---|---|---|
Middlesborough | April 30 | 8.4° | 5 |
Newcastle | April 30 | 7.6° | 5 |
Blackpool | April 30 | 6.8° | 5 |
Aberdeen | April 30 | 4.1° | 5 |
Plymouth | April 30 | 3.4° | 5 |
Leeds | April 30 | 8.4° | 4 |
Belfast | April 30 | 6.2° | 4 |
Manchester | April 30 | 7.1° | 3 |
Birmingham | April 29 | 6.7° | 3 |
Cardiff | April 30 | 5.7° | 3 |
London | April 30 | 5.1° | 2 |
Table 1. Select cities with significant Climate Shift Index (CSI) levels and temperature anomalies (departure from normal temperatures) on certain dates during April 27-30, 2025. The CSI level is based on the average daily temperature for that city.
Impacts
More than 56,000 runners participated in the fourth-warmest London Marathon on April 27, where temperatures reached around 22°C and carried a CSI level 1 — indicating a detectable influence of climate change on the unusual warmth.
Forecasters predict this “warmest spell of the year” could be the hottest April weather since 2018, with near-record highs of 28-29°C (82-84°F) expected to close out the month.
Spring is the fastest warming season in the U.K. due to climate change. This unusual heat is also driving a high pollen forecast for London and southern England.
Heat-related mortality in the U.K. rises significantly around 29°C, making the rapid onset of this early-season heat a particular concern.
What do experts say?
Dr. Kristina Dahl, VP of Science at Climate Central, said:
"We are seeing exceptional heat this week in the U.K. that could break records, just weeks after an unprecedented number of wildfires — and it is only April. This is not early summer; it is a stark warning of how climate change is driving extreme conditions earlier in the year. As long as we continue burning fossil fuels, dangerous heat like this will increasingly pose health risks well beyond the summer months."
To request an interview with a Climate Central scientist, please contact Shel Winkley at swinkley@climatecentral.org.
How do we know climate change is influencing this heat?
The Climate Shift Index uses peer-reviewed methodology and real-time data to estimate how climate change has increased the likelihood of a particular daily temperature.