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New research from Climate Central indicates that climate change accounted for 27% of the rate of heat-related emergency room visits in the U.S. during the warm seasons from 2018 to 2025. The study found that all U.S. regions experienced increased visit rates due to climate change, with the highest rates occurring in southern and western states. A notable peak occurred during the June 2021 northwestern U.S. heat wave, where daily visit rates were approximately 50 times higher than the regional average, with 27% of that rate attributed to climate change.

The report finds that August 2026 saw widespread above-average temperatures across the U.S., with an average anomaly of 1.6°F across 192 cities. The Southwest was the hottest region, and 39 cities recorded one of their top-five hottest Augusts on record. Long-term trends show August warming since 1970 in 187 of the 192 analyzed locations, with Reno, Nevada, seeing the largest increase.

Analysis of 243 to 247 major U.S. cities reveals that 95% have seen an increase in unusually warm summer nights since 1970, with an average increase of 24 nights per summer. Using the Climate Shift Index (CSI), the report finds that human-caused climate change now strongly influences an average of 27 warm summer nights per year, compared to just one in the 1970s. The most severe impacts are concentrated in Florida and Puerto Rico, where some cities experience over two months of climate-driven warm nights annually. These trends exacerbate heat stress, disrupt sleep, and increase energy demand for air conditioning, disproportionately affecting vulnerable populations and those in urban heat islands.

Analysis of cooling degree days (CDD) shows that 97% of 241 major U.S. cities experienced increased cooling demand since 1970, with an average increase of 37%. This trend, combined with a 31% rise in residential electricity prices between 2020 and 2025, increases the financial burden on households, particularly low-income families. In 2020, the ten states with the highest cooling costs saw average household expenditures between $378 in Hawaii and $712 in Arizona. Future projections suggest U.S. household cooling demand will rise 43% by 2050. The report also highlights systemic risks, including electricity grid strain, increased carbon emissions from fossil-fuel-reliant cooling, and the urban heat island effect caused by waste heat from air conditioners.

In July 2026, the United States experienced widespread above-average temperatures, with an average anomaly of 1.5°F across 192 cities. The Northern Rockies and Plains were the warmest region, exceeding normals by more than 4.0°F. Long-term data indicates that 185 of the 192 analyzed cities have warmed since 1970, with Reno, Nevada, showing the most significant increase. Climate attribution analysis using the Climate Shift Index (CSI) showed that San Juan, Puerto Rico, had 31 days where temperatures were at least two times more likely due to climate change.

Climate change accounted for 27% of the rate of heat-related emergency room visits in the U.S. during 2018-2025. August 2026 was the warmest August on record globally, with record warmth affecting 13.2% of global land and ocean areas. In the U.S., Summer 2026 was the warmest on record for the contiguous region, and August 2026 was the warmest August for average, maximum, and minimum temperatures since 1895. Drought affected at least 81% of the contiguous U.S. as of September 8, 2026, and nearly 8.3 million acres burned year-to-date, driven by increased 'fire weather' days. Attribution analysis using the Climate Shift Index (CSI) indicates human-caused climate change drove summertime warming trends in 91% of analyzed U.S. cities. Additionally, a strong El Niño event is projected to peak around February 2027, with global temperature anomalies potentially reaching 1.7C above pre-industrial levels.

July 2026 was tied for the warmest July on record globally and was the all-time warmest July for the contiguous U.S. This extreme heat, driven by human-caused climate change and a strengthening El Niño, has led to a significant increase in cooling degree days—a proxy for energy demand—across most major U.S. cities. The report also details widespread drought affecting at least 70% of the contiguous U.S. and record-low sea-ice extents in both the Arctic and Antarctic.

The 2026 World Cup saw nearly half of its matches played on days with a climate change signal for temperature or dangerous humid heat. Over 55% of matches occurred in cities where daily highs exceeded the 82.4°F (28°C) athletic performance threshold, with 35 of those in non-climate-controlled stadiums. Miami Stadium was the hottest non-climate-controlled venue, with an average daily high of 93.4°F (34.1°C) and dangerous humid heat on almost every match day. The hottest single game was Paraguay vs. France in Philadelphia on July 4, 2026, reaching 101°F (38.3°C). France was the most heat-exposed team, playing seven of eight matches in non-climate-controlled stadiums, while the champion, Spain, faced lower heat exposure due to more games in climate-controlled venues.

Climate Central's analysis of 239 major U.S. cities from 1970 to 2025 found that 95% of these cities experienced an increase in 'mosquito disease days'—days with temperatures suitable for West Nile virus transmission. On average, these cities saw an increase of 18 days per year. The largest increases occurred in the Southeast, Northeast, and Northwest regions, with San Francisco, CA, seeing the highest increase of 52 days. The report also notes that while West Nile virus is the most common mosquito-borne disease in the U.S., warming is expanding the risk and range of other viruses like dengue and Zika, particularly along the Gulf Coast and into the Ohio Valley and Upper Midwest by 2050.

The U.S. experienced 12 billion-dollar weather and climate disasters from January to June 2026, causing at least $31.9 billion in damages and 183 fatalities. This period ranks fifth for the most events in the first half of any year since 1980. Severe storms were the dominant disaster type, accounting for eight of the 12 events. Historically, the average number of such disasters per year has risen from three in the 1980s to 20 events annually between 2016 and 2025, with the average time between events shrinking from 82 days to 16 days in the same comparison.

Climate Central's analysis reveals that the average person globally lost nearly 56 hours of sleep annually due to nighttime heat from 2020 to 2025, with approximately six hours attributed to climate change. The most significant climate-linked sleep losses occurred in Middle Eastern cities, where residents in Saudi Arabia, Oman, and the UAE lost between 12 and 16 hours of sleep per year due to climate change. Globally, the amount of temperature-related sleep loss linked to climate change has at least doubled since the early 1970s, increasing from about two hours to five hours per year. Vulnerable populations, including adults over 65 and those in lower-middle-income countries, face higher risks, and while air conditioning provides some protection, access remains unequal and tied to income.

Climate Central analysis reveals that residents in 65 of the largest U.S. cities experience an average of 8°F of additional heat due to the built environment. The document details mitigation strategies including green space, shade structures, water features, and cool pavements/roofs, while highlighting that heat exposure is disproportionately higher in historically redlined areas and low-income neighborhoods.

In June 2026, the United States experienced slightly above-average temperatures, with an average anomaly of 0.7°F across 192 analyzed cities. The Southwest was the warmest region, with temperatures more than 2.9°F above normal, and Flagstaff, Arizona, recorded the most unusual warmth at 4.0°F above normal. Long-term trends show that 189 of the 192 cities have warmed since 1970, with Reno, Nevada, seeing the greatest increase of 10.6°F. Climate attribution analysis using the Climate Shift Index (CSI) indicates that San Juan, Puerto Rico, had 30 days where temperatures were at least two times more likely due to climate change.

Since the 1970s, the global average number of dangerous humid heat days—defined as those with a maximum wet-bulb temperature of 25°C or higher—has more than doubled, rising from 10 to 23 days per year. Climate Central's analysis indicates that human-caused climate change is now the primary driver of this trend, accounting for 64% of all such days since 1970 and 83% of the 23 dangerous days recorded in 2025. The most significant increases are observed in tropical humid regions, including Southeast Asia, coastal West Africa, and tropical South America, though increases are also noted in drier areas like the Arabian Peninsula and the southwestern United States.

Climate Central's analysis of weather data from 1970 to 2025 shows that all four Grand Slam tennis tournaments have experienced an increase in hot days (defined as $\ge$28°C). The French Open has warmed the fastest, with average temperatures rising by 3.5°C. Climate change is attributed with adding 160 extra hot days across the four events, with the U.S. Open seeing the highest absolute increase. Additionally, the frequency of heavy rain days ($\ge$10mm) has increased for the French Open, Australian Open, and Wimbledon.

Climate Central analysis indicates that climate change increases the probability of performance-impairing heat (above 28°C) for 97 out of 104 scheduled 2026 World Cup matches. Nearly half of the matches face at least a 50% chance of such heat, with the highest impact seen in the June 26 match in Guadalajara. To mitigate health and performance risks, organizers have implemented mandatory hydration breaks and increased evening matches, though only three stadiums (Atlanta, Dallas, and Houston) are fully climate-controlled.

June 2026 was the second-warmest June on record globally, with the Arctic experiencing its warmest June ever. In the U.S., 66% of the contiguous region faced abnormally dry or drought conditions by July 7, 2026, and the West and Southwest regions saw their warmest January-June period on record. A very strong El Niño is forecast to develop between October and December 2026, with an 81% probability, likely pushing global temperatures to or above 1.5C by October. Climate Central's analysis indicates human-caused climate change is a key driver of summertime warming in 91% of analyzed U.S. cities.

Climate Central analysis shows that 14 of the 16 host stadiums for the 2026 World Cup are experiencing more extremely hot days during the June-July tournament period than in 1970. Human-caused climate change is responsible for an average of 49% of these extreme heat days across all stadiums, with the highest impact seen in Miami and Mexico City. In 10 repeat host cities, the frequency of extremely hot days has tripled on average since they last hosted the tournament.

Climate Central analyzed data from 476 weather stations to track fire weather trends in the contiguous U.S. between 1973 and 2025. The analysis reveals a significant increase in fire weather days, particularly in the western U.S., where conditions are intensifying in spring and summer. While the eastern U.S. has seen smaller increases, some areas in the Southeast and Northeast are experiencing more frequent fire weather. The report highlights that climate change is driving these trends through warming temperatures and decreasing relative humidity, which prime landscapes for wildfires to ignite and spread.

In April 2026, the United States experienced an average temperature anomaly of 3.4°F across 192 cities, with the Ohio Valley being the warmest region. The report highlights that 183 of the analyzed cities have shown long-term warming trends since 1970, with Reno, Nevada, seeing the greatest increase. Climate attribution analysis indicates that in San Juan, Puerto Rico, temperatures on 19 days in April were at least two times more likely due to climate change.