Risky Heat Added by Climate Change: June to August 2026
⚠️ UNDER EMBARGO UNTIL: Wednesday, September 16, 2026 at 12:01 am ET ⚠️
KEY FACTS
Climate Central’s latest global analysis shows where people felt the strongest influence of human-caused climate change on daily average temperatures between June and August 2026.
Every day during the last three months, more than one-quarter of the global population felt a strong climate change influence.
In the U.S., the average person experienced about 26 days with a strong influence of climate change (CSI level 2 or higher) during meteorological summer (June, July, August).
More than 69 million people in the U.S. experienced at least 30 days of risky heat added by climate change this summer. Risky heat days are hotter than 90% of those recorded in a local area from 1991-2020.
In 141 U.S. cities (out of 247), climate change accounted for at least half of the risky heat days people experienced this summer.
Seven of the top 10 most unusually hot countries in the world were in Europe — led by France and the Holy See, which were virtually tied as the most unusually hot countries in the world.
Asia had the largest total population exposed to risky heat: 2.8 billion people (58% of Asia’s population) were exposed to at least 30 days of risky heat.
VISUALS
LEARN MORE
DATA EXPLORER
FULL REPORT
Exceptional summer heat fueled by carbon pollution
Heat-trapping pollution (mainly from burning coal, oil, and gas) brought unusual heat to nearly all regions of the world during the past three months.
This was especially true for places in the Northern Hemisphere during their meteorological summer (June, July, August). Some 54 countries experienced their hottest June to August of the 1970-2026 period, including France, Italy, and the United Kingdom.
According to NOAA, the contiguous U.S. experienced its hottest summer and hottest month (July 2026) on record. The U.S. faced extreme heat while hosting more than a million international visitors for the World Cup and celebrating the nation’s 250th anniversary.
In some parts of the world, these exceptionally hot temperatures were influenced by an additional factor: a strengthening El Niño that added an extra layer of warmth on top of an already hot season.
Measuring heat and the influence of climate change
This Climate Central analysis used the Climate Shift Index (CSI) to quantify the influence of human-caused climate change on daily average temperatures experienced in 252 countries, territories, and dependencies and 949 cities (including 247 U.S. cities) from June 1, 2026, to August 31, 2026. See Methodology for details.
Climate Central analyzed three measures of heat exposure:
Climate Shift Index (CSI) values: Developed by Climate Central’s scientists, this metric quantifies the local influence of climate change on daily temperatures. Positive CSI levels (1 to 5) indicate temperatures that are increasingly likely because of climate change. This analysis focuses on the average person’s experience of unusually warm conditions strongly influenced by climate change (CSI level 2 or higher).
Risky heat days: Risky heat days are days with temperatures hotter than 90% of those observed in a local area over the 1991-2020 period. Heat-related health risks rise when temperatures climb above this locally defined threshold.
Temperature anomalies: Temperature anomalies show how much warmer or cooler conditions were than the 1991-2020 average. Temperature anomalies highlight conditions that people would recognize as unusual.
Explore interactive maps with data for 252 countries and 949 cities (including 247 U.S. cities).
Billions of people experienced more heat due to climate change
Every day from June to August 2026, more than one-quarter of the global population felt a strong climate change influence.
More than 1.5 billion people on the planet experienced 30 or more days of risky heat added by climate change in June to August 2026.
The impact of this heat was deadly, with record heat spiking hospitalizations and heat-related deaths around the world.
Explore interactive maps with data for 252 countries and 949 cities.
Climate change influenced record-setting heat in the U.S.
The U.S. experienced exceptional summer heat. According to NOAA, 2026 saw the hottest summer and hottest month (July) on record for the contiguous U.S. On average, the U.S. was about 1.4°F warmer than normal during June to August (compared to the 1991-2020 average).
In the U.S., the average person experienced about 26 days with temperatures strongly influenced by climate change (CSI level 2 or higher) this summer.
During these three months, around 293 million people in the U.S. — 86% of the total population — were exposed to at least 30 days of risky heat. People in California, Texas, Florida, and New York account for about one-third of those people.
The western U.S. felt exceptional summer heat.
On average, summer temperatures were highest above normal in western states, led by Colorado (4.4°F), Utah (3.8°F), and Nevada (3.8°F).
Western states also comprise four of the top five states with the most risky heat days: New Mexico (66 days), Nevada (63), Colorado (61), and Utah (58).
Cities across the U.S. experienced more risky heat due to climate change
More than 69 million people in the U.S. experienced at least 30 days of risky heat added by climate change.
In 141 U.S. cities, climate change accounted for at least half of the risky heat days people experienced this summer.
San Juan, Puerto Rico, saw more risky heat days added by climate change than any other U.S. city (71 days).
People in Florida experienced the most risky heat fueled by climate change
Approximately 22 million people in Florida (96% of the state’s population) experienced at least 30 risky heat days added by climate change.
Among U.S. states, Florida experienced the most risky heat days added by climate change (44 days).
Explore interactive maps for more data on U.S. states and cities.
Risky and unusual heat felt throughout North America
Canada experienced more than a month’s worth of risky heat days (33 days) — more than half of which (17) were added by climate change. This was amid a season of wildfires made worse by climate change.
In Mexico, people experienced around three weeks’ worth of risky heat days (24 days) — nearly all of which (20) were added by climate change.
Every Central American and Caribbean nation analyzed saw more than two months’ worth of days with temperatures strongly influenced by climate change (CSI 2 or higher), including Jamaica, Puerto Rico, Turks and Caicos, and Guatemala (90 days for each).
The climate change burden around the world
Beyond North America, countries in Europe, Asia, and Africa felt some of the strongest effects of climate change-driven heat during June, July, and August.
Countries in Europe saw temperatures that were much hotter than usual — more so than other countries around the world
Seven of the top 10 most unusually hot countries in the world were in Europe, including France, Switzerland, and Italy.
France and the Holy See were virtually tied as the most unusually hot countries in the world, with average summer temperatures 3.5°C (6.3°F and 6.4°F, respectively) above normal.
More people in Asia felt the influence of climate change than on any other continent
Asia had the largest total population exposed to risky heat: 2.8 billion people (58% of Asia’s population) were exposed to at least 30 days of risky heat.
Asia had the largest population exposed to at least 30 days of risky heat added by climate change — led by India (117 million people), China (94 million), and Indonesia (83 million).
People across Africa frequently experienced temperatures strongly influenced by climate change.
Six countries in Africa experienced temperatures strongly influenced by climate change during the majority of days (at least 95%) in this three-month period: Réunion (92 days), Rwanda (91 days), Ilemi Triangle (90 days), Uganda (89 days), Ethiopia (88 days), and Comoros (88 days).
In 37 African nations, climate change accounted for at least half of the risky heat days people experienced during these three months. Some countries only experienced risky heat days because of climate change — including Uganda, where all 27 risky heat days were added by climate change.
Explore interactive maps with data for 252 countries and 949 global cities.
RELATED RESOURCES
LOCAL STORY ANGLES
Is climate change influencing daily heat extremes in your local area?
Climate Central’s Climate Shift Index (CSI) system provides tools, data, custom maps, and local alerts to answer this question in real-time. Here are three ways to use the CSI:
Use the tools. Climate Central’s Climate Shift Index map tool shows which parts of the world are experiencing high CSI levels, every day. Explore the global CSI map for today, tomorrow, and any day in the recent past.
Access KML to create custom CSI maps. Get access using the panel links in the map tool.
Sign up for alerts. Sign up here to receive custom email alerts when significant CSI levels are detected in your local area.
CONTACT EXPERTS
To request an interview with a Climate Central expert about this analysis, please contact Tom Di Liberto at tdiliberto@climatecentral.org.
FIND EXPERTS
Submit a request to SciLine from the American Association for the Advancement of Science or to the Climate Data Concierge from Columbia University. These free services rapidly connect journalists to relevant scientific experts.
Browse maps of climate experts and services at regional NOAA, USDA, and Department of the Interior offices.
Explore databases such as 500 Women Scientists, BIPOC Climate and Energy Justice PhDs, and Diverse Sources to find and amplify diverse expert voices.
Reach out to your State Climate Office or the nearest Land-Grant University to connect with scientists, educators, and extension staff in your local area.
METHODOLOGY
Calculating the Climate Shift Index (CSI)
The CSI is grounded in peer-reviewed attribution science and was launched by Climate Central in 2022. The data is accessible via our free map tool. Positive CSI levels 1 to 5 indicate conditions that are increasingly likely in today’s climate. A CSI level of 1 means that climate change is detectable (technically, the temperature is at least 1.5 times more likely). CSI levels 2 and higher correspond with the multipliers (2 = at least 2 times more likely, 3 = at least 3 times more likely, etc.). CSI level 5 events would be very difficult to encounter in a world without climate change — not impossible, but extremely unlikely.
All CSI levels reported in this brief are based on daily average temperatures and ECMWF ERA5 data from Jun 1, 2026, to Aug 31, 2026. See the frequently asked questions for details on computing the CSI, including a summary of the multi-model approach described in Gilford et al. (2022).
Daily Global Population Exposure
For each day, we identified the grid cells with CSI values of 2 or higher. Using 2020 Gridded Population of the World v4 estimates, we calculated the proportion of the population living in each of these cells. Where CSI values were 2 or higher, we summed the proportions globally and multiplied by the estimated global population of 8.3 billion to produce an up-to-date estimate of the global population exposed to CSI level 2 or higher.
Country Analysis
The country-level analysis includes 252 countries, territories, and dependencies. It excludes entities that are smaller than 0.25°, the size of a grid cell. We calculated the average temperature anomaly, number of days at or above CSI 2, and population exposure to CSI 2 (based on average temperature) over the Jun 1, 2026, to Aug 31, 2026, period. For each country, we then selected the data within its geographical boundary and found the population-weighted temperature anomaly and the population-weighted number of days at CSI level 2. Reported temperature anomalies are relative to each country’s 1991-2020 normal daily June, July, and August temperatures.
Map layer data comes from the Global Administrative Unit Layers (2024) from the Food and Agriculture Organization of the United Nations (FAO). The boundaries used in this analysis reflect this record of disputed boundaries and the naming conventions for such territories. The layers are aligned with guidance from the United Nations Cartographic Section.
Where possible, population estimates were drawn from the U.S. Census Bureau's International Database and rounded to the nearest thousand. Other estimates were drawn from the Gridded Population of the World v4.
U.S. State Analysis
The state-level analysis includes 50 states and the District of Columbia in the United States. It excludes entities that are smaller than 0.25°, the size of a grid cell in our underlying data. We calculated the temperature anomaly, number of days at or above CSI 2, and population exposure to CSI 2 (based on average temperature) over the June 1, 2026, to Aug 31, 2026 period. For each state, we then selected the data within its geographical boundary and found the population-weighted temperature anomaly and the population-weighted number of days at CSI 2. Reported temperature anomalies are relative to each state’s 1991-2020 normal daily June, July, and August temperatures.
Population estimates were drawn from the Gridded Population of the World v4.
City Analysis
We analyzed 960 cities from around the world, drawn from GeoNames. We include cities that meet one or more of the following criteria: it has a population of more than 1 million; it is the capital of a country, territory, or province; it has the largest population in a country or territory; or it is one of the 100 most-populated cities in China (which excludes some cities that have a population of 1 million or more). We also include a selected list of additional U.S. cities.
For each city, we found the CSI and temperature anomaly time series from the nearest 0.25° grid cell. We then computed the mean temperature anomalies over June 2026, July 2026, and August 2026, and the number of days at CSI level 2 (based on average temperature). Reported temperature anomalies are relative to each city's 1991-2020 normal daily June, July, and August temperatures.
Risky Heat Days
The analysis of risky heat days considered days with temperatures hotter than 90% of temperatures observed in a local area over the 1991-2020 period. This 90th temperature percentile is a conservative approximation of the local minimum mortality temperature (MMT) — the daily average temperature with the lowest risk of heat-related death — based on Tobías et al. (2021) and Gasparrini et al. (2015). Above the MMT, relative risks of heat-related illness and death increase steeply, because people are not used to or cannot cope with these temperatures. MMTs vary across climatic zones, tending to be higher in temperate and continental regions and lower in arid and tropical ones, because health-related heat thresholds depend on the local climate and related long-term adaptation among local populations.
To find the risky days added by climate change, we calculated counterfactual temperatures — estimates of what temperatures would have been in a world without climate change. Using our CSI model, we determined the probability of meeting or exceeding an observed temperature in today’s climate, then found the equivalent temperature in a world without climate change. For each day and location, if the counterfactual temperature was below the threshold but the observed temperature was above it, we counted that day as added by climate change.
Graphics for 244 U.S. Cities
The set of local graphics included in this release show daily CSI levels and daily average temperature anomalies (relative to 1991-2020 normals) from June 1, 2026 to August 31, 2026. Daily temperature data were obtained for 247 U.S. cities from the Applied Climate Information System, which is developed, maintained, and operated by NOAA’s Regional Climate Centers. Local graphics were not produced for three cities that were missing more than 50% of daily data over this three-month period: Clarksburg, WV; Jackson, ID; and Laredo, TX.
Climate Matters © 2026 by Climate Central is licensed under CC BY 4.0
This license grants permission to use, distribute, and reproduce all text, graphics, and multimedia content published on this page in any medium, provided that Climate Central is credited per the CC BY 4.0 license.
Permission to use data and other materials published on this page is granted for non-commercial uses, commercial news purposes, and educational purposes as governed by Climate Central's Terms of Use.