Decline in Quarterly Mortality Ratings - Spike Observed During Heat Waves - Decrease in Mortality Rates in Q2 Followed by Uptick During Heatwave
In the 27th calendar week of 2025, a severe heat wave swept across Europe and North America, resulting in a concerning surge in hospitalizations and deaths related to cardiovascular diseases. The statistic office reported an 8% increase in overall mortality rates compared to the average of the previous four years for that week, with a 12% higher mortality rate specifically for cardiovascular diseases.
The heat wave, which occurred from June 30 to July 6, was particularly severe, with record-breaking temperatures above 32°C, reaching over 40°C in parts of Europe. This extreme heat placed excessive stress on the human body, leading to heat-related illnesses and deaths.
Older adults, especially those aged 65 and above, were disproportionately affected, as their bodies have reduced ability to regulate temperature and many have pre-existing health conditions. The statistic office estimated that during the heat wave, an estimated 570 excess deaths were expected within just a few days, with the majority among older adults with underlying conditions.
Heat exacerbates chronic illnesses such as cardiovascular diseases, diabetes, and respiratory issues. High temperatures increase strain on the heart and lungs, worsening outcomes for those with compromised immune systems. Socioeconomic and racial factors also played a significant role, with heat-related deaths tending to be higher among low-income populations and marginalized groups who often lack access to air conditioning, live in dense urban environments, or face barriers to cooling resources like cooling centers.
The impact of climate change also contributed to the intensification of the heat wave. Human-induced climate change has raised baseline temperatures by about 1.3°C above pre-industrial levels, making the 2025 heat wave 1°C to 4°C hotter and increasing mortality risks.
In some areas, insufficient public health preparedness, lack of warning systems, and limited access to emergency cooling measures further contributed to higher heat-related mortality. The statistic office issued a warning about the potential health risks associated with the heat wave and advised the public to take precautions to protect themselves, including staying hydrated and seeking air-conditioned environments.
The 27th calendar week of 2025 marked the second consecutive week of increased mortality rates due to a heat wave. The number of heat-related hospital admissions increased by 25%, underscoring the global scale of this health threat exacerbated by ongoing climate change. Similar trends were observed in New York City, where over 500 heat-related deaths were reported each summer.
As the frequency and severity of heat waves continue to increase due to climate change, it is crucial for public health officials to improve preparedness, infrastructure, and access to cooling resources to protect vulnerable populations and reduce heat-related mortality.
Science has shown that extreme heat, like the one experienced in the 27th calendar week of 2025, can worsen health-and-wellness issues, particularly for older adults and those with underlying health conditions. In the second quarter, the number of deaths decreased, but increased drastically during the heatwave, raising concerns about the impact of climate change on health.
