A new study reveals a 25% rise in extremely hot days across the world’s major capitals since the 1990s, heightening risks for millions amid accelerating global warming. Experts warn urgent adaptive action is needed to protect vulnerable populations and urban infrastructure.
The world’s major capital cities are enduring a sharp rise in extremely hot days, with recent analysis indicating a 25% increase since the 1990s. This surge translates to thousands more days above dangerous temperature thresholds each year, placing millions of urban residents at heightened risk from the intensifying climate crisis. The study by the International Institute for Environment and Development (IIED) reveals that across 43 of the globe’s most populous capitals, the total number of days exceeding 35°C jumped from an average of 1,062 annually between 1994 and 2003 to 1,335 days from 2015 to 2024.
Cities as diverse as Washington DC, Madrid, Tokyo, Beijing, and London are experiencing this rise, with some regions seeing particularly dramatic changes. For instance, Rome and Beijing have doubled their days above 35°C, while Manila’s count has tripled. Madrid now faces 47 extremely hot days yearly compared to 25 in earlier decades, and London, despite its temperate climate, has seen the number of days over 30°C double. The analysis highlights not only the global scale of warming but the direct human toll it exacts, especially among elderly and impoverished populations in rapidly expanding urban areas, where exposure to the urban heat island effect is exacerbated by inadequate housing.
The escalating frequency and intensity of heatwaves are linked to continued fossil fuel emissions, which, despite international climate targets, have not yet begun the urgent decline necessary to limit warming to 1.5°C above preindustrial levels. Record temperatures recorded in 2024 across continents—from North America to Asia and Africa—underscore this trend. Japan, for example, endured its all-time highest temperature of 41.2°C in July, which led to over 10,000 hospitalisations. Europe recorded at least 16,500 heat-related deaths during the summer months, demonstrating the lethal consequences of unchecked climate change. Beyond the heat itself, many cities are grappling with “climate whiplash,” extreme shifts between heavy rainfall and severe drought, which compound the vulnerabilities of urban infrastructures and populations.
International efforts to address this crisis are gaining momentum. The Global Center on Adaptation (GCA) launched “The Heat is On” campaign to promote life-saving interventions such as cooling centres, shaded rest areas, early-warning systems, and climate-smart work schedules. Macky Sall, GCA chair and former president of Senegal, emphasised that extreme heat is an immediate threat with broad economic and social ramifications, advocating for investment in proven adaptive solutions to safeguard communities. However, critics of some national responses, including the UK government, have labelled their preparations as insufficient and fragmented, pointing to the need for more comprehensive and coordinated action.
Experts warn that reliance on air conditioning alone will not solve the mounting challenges. Anna Walnycki of IIED stressed the urgency for funding to improve building insulation, ventilation, and urban shade, along with developing effective heat action plans. This is especially pressing given that roughly a third of the world’s urban population lives in slums or informal settlements, where poor-quality housing leaves residents disproportionately vulnerable to heat stress.
Supplementing these findings, other research corroborates the alarming increase in extreme heat events. For instance, a related IIED study identified a 52% rise in days above 35°C in 20 of the largest global capitals over the past three decades. Cities such as Jakarta and Buenos Aires have witnessed especially sharp increases in such hot days, presenting severe public health challenges. Further analyses suggest that by 2050, under a 3°C warming scenario, cities like New York, London, Los Angeles, Seoul, and Shanghai will experience at least 20% more extreme heat days annually compared to 2022, raising serious concerns for urban planning and infrastructure resilience.
In the United States, data show that 80% of 247 cities have faced more frequent stretches of extreme heat—defined as three or more consecutive days exceeding the 90th percentile temperature since 1970. Cities like Nashville and Raleigh now experience several additional heat streaks each year, exacerbating health risks for their populations. This trend resonates globally: climate studies indicate that most locations worldwide have seen increases in extremely hot days annually, with many now enduring over two weeks more of dangerously high temperatures than in the 1970s.
Collectively, these findings paint a stark picture of a warming world where urban residents, especially the most vulnerable, face growing hazards unless urgent adaptation and mitigation measures are implemented. The escalating toll of heat underscores that climate change cannot remain a distant policy concern but must be addressed as an immediate public health and social justice imperative.
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Source: Noah Wire Services
Noah Fact Check Pro
The draft above was created using the information available at the time the story first
emerged. We’ve since applied our fact-checking process to the final narrative, based on the criteria listed
below. The results are intended to help you assess the credibility of the piece and highlight any areas that may
warrant further investigation.
Freshness check
Score:
8
Notes:
The narrative presents recent data from 2015-2024, indicating a 25% increase in extremely hot days compared to 1994-2003. Similar findings were reported in June 2024 by the International Institute for Environment and Development (IIED), noting a 52% increase in days over 35°C in 20 major capitals over the past three decades. ([iied.org](https://www.iied.org/52-jump-days-over-35degc-worlds-biggest-capital-cities?utm_source=openai)) The earlier report focuses on a subset of cities and a different time frame, suggesting the current narrative offers updated and more comprehensive data.
Quotes check
Score:
9
Notes:
The narrative includes direct quotes from experts such as Macky Sall, GCA chair and former president of Senegal, and Anna Walnycki of IIED. These quotes are not found in earlier reports, indicating they are original to this narrative.
Source reliability
Score:
10
Notes:
The narrative originates from The Guardian, a reputable UK-based news organisation known for its rigorous journalism standards. The IIED, cited within the narrative, is a well-established research organisation specialising in environmental and development issues.
Plausability check
Score:
9
Notes:
The claims align with established scientific understanding of climate change impacts on urban heat. The narrative provides specific data points and expert opinions, enhancing its credibility. The inclusion of recent temperature records, such as Japan’s all-time high of 41.2°C in July 2024, supports the plausibility of the reported trends.
Overall assessment
Verdict (FAIL, OPEN, PASS): PASS
Confidence (LOW, MEDIUM, HIGH): HIGH
Summary:
The narrative presents recent, original data on the increase in extremely hot days in major cities, supported by credible sources and expert opinions. While similar findings were reported in June 2024, the current narrative offers updated and more comprehensive information, enhancing its freshness and originality.
