Scientists have reported that approximately 4 billion people, which constitutes about half of the global population, experienced at least one extra month of extreme heat attributed to human-caused climate change between May 2024 and May 2025. This alarming situation, highlighted in a recent analysis conducted by World Weather Attribution, Climate Central, and the Red Cross, has led to increased instances of illness, death, crop failures, and significant strain on energy and healthcare systems.
The report emphasizes that while disasters such as floods and cyclones often dominate media coverage, extreme heat is arguably the most lethal of all extreme weather events. Many heat-related fatalities go unreported or are misattributed to other medical issues, such as heart disease or kidney failure. Through peer-reviewed methodologies, scientists examined the extent to which climate change escalated temperatures during extreme heat events and assessed how much more likely these occurrences have become due to climate change. Findings indicated that in nearly all countries worldwide, the frequency of extreme heat days has at least doubled in comparison to a scenario devoid of climate change.
The Caribbean islands were particularly affected, with Puerto Rico experiencing a staggering 161 days of extreme heat during this period. In a hypothetical scenario without climate change, only 48 such days would have been recorded. Charlotte Gossett Navarro, the chief director for Puerto Rico at the Hispanic Federation, a nonprofit organization focused on social and environmental issues within Latino communities, shared her firsthand experience of the oppressive heat, stating, “It makes it feel impossible to be outside.” She recounted difficulties in enjoying outdoor family activities due to the extreme temperatures, which left her feeling dizzy and unwell throughout the summer.
Frequent power outages, a recurring issue in Puerto Rico due to years of neglected grid maintenance compounded by the damage from Hurricane Maria in 2017, further exacerbate the challenges posed by extreme heat. Navarro highlighted the discomfort caused by power loss, noting that while it may be merely uncomfortable for healthy individuals, it poses a significant life-threatening risk to those with pre-existing health conditions. “If you are someone relatively healthy, that is uncomfortable, it’s hard to sleep…but if you are someone who has a health condition, now your life is at risk,” she remarked.
According to Friederike Otto, an associate professor of climate science at Imperial College London and one of the report's authors, heat waves act as silent killers. Unlike other natural disasters, deaths during heat waves often occur in hospitals or poorly insulated homes, rendering them invisible in statistical data. Low-income communities and vulnerable populations, including older adults and individuals with health issues, bear the brunt of extreme heat conditions.
The report also specified that the extreme temperatures experienced in Central Asia in March, South Sudan in February, and the Mediterranean region in July were only possible due to climate change. Notably, at least 21 individuals died in Morocco in July after temperatures soared to 118 degrees Fahrenheit (48 degrees Celsius). Many people have recognized that temperatures are on the rise but remain unaware of the underlying climate change driving this trend, as noted by Roop Singh, head of urban and attribution at the Red Cross Red Crescent Climate Centre.
Singh urged for rapid expansion of responses to heat challenges through improved early warning systems, heat action plans, and comprehensive long-term urban planning to address the escalating threat posed by extreme heat. Initiatives led by cities to combat extreme heat are increasingly emerging across South Asia, North America, Europe, and Australia, showcasing cooperative efforts among governments and agencies. One such initiative includes a tree-planting project in Marseille, France, aimed at increasing shaded areas to help mitigate heat impacts.
The report outlines various strategies for preparing for heat waves, including the establishment of monitoring and reporting systems for extreme temperatures, provision of emergency health services, establishment of cooling shelters, updating building codes, enforcement of heat safety regulations in workplaces, and innovative urban design to enhance heat resilience. However, the scientists warn that without a transition away from fossil fuels, the severity and frequency of heat waves will continue to escalate, rendering protective measures increasingly ineffective.
