From Sidewalks to Saunas: Heatwaves and Their Growing Impact on Major Cities

When summer rolls in, cities don't just warm up—they sizzle. Towering buildings and a lack of green space turn urban areas into massive heat traps, intensifying already rising global temperatures. Across the world, major cities are experiencing longer, hotter, and more dangerous heat waves than ever before. But this isn’t just about discomfort—it’s a public health crisis.

Source: UCLA Newsroom

Heat Island Effect:

Step into any major city during a summer heatwave, and you'll feel it instantly—the stifling, suffocating warmth that seems to rise from every surface. This isn’t just your imagination; it’s the urban heat island effect at work. Urban areas, packed with concrete, asphalt, and tall buildings, can be 10°F (about 5.5°C) hotter on average than surrounding rural regions. In some cases, surface temperatures in cities can soar 50 to 90°F (10 to 32°C) above the actual air temperature.

Why it Matters - Effects of Heatwaves on Cities:

The Paris Climate Agreement was a treaty brought up in late 2015, which aimed to limit global temperature increases below 2 degrees celsius ( 35.6 fahrenheit). In your eyes, it may not seem like such a hard thing to accomplish, and may not have the biggest impact on the climate. It just so happens that most of the countries who signed did not follow through with the plan. The consequences? A dangerous combination of environmental stress and economic strain.

Data collected by the IPCC (Intergovernmental Panel on Climate Change) shows that when temperatures climb above 95°F (35°C), the risk of heat-related illnesses spikes. Conditions like heat stroke, heat exhaustion, and heat rash become common, especially among the elderly, young children, and people with preexisting health conditions. Long-term exposure to excessive heat can also worsen respiratory and cardiovascular problems. However, the tolls do not stop there. Extreme heat can also affect cognitive and academic abilities, making it harder to concentrate and affecting performance.

On an economic level, the effects are significant. With more people relying on air conditioning to cope, energy demands soar, putting stress on power grids and causing electricity costs to shoot up. According to recent data, extreme heat already costs the U.S. economy about $100 billion annually, and that figure is projected to rise to $500 billion by 2050 if global temperatures continue to climb.

Heatwaves Worsen Urban Inequality

As the planet warms, not all cities will suffer equally. The harsh reality is that cities with the fewest resources will bear the greatest burden. With limited infrastructure, weaker institutions, and rapid, often unplanned growth, low-income urban areas are less equipped to cope with extreme heat.

If the world warms by 3°C instead of 1.5°C, cities will experience an average of 29 more extremely hot days each year. Here are some examples:

• South Asia: +40 extremely hot days

• Sub-Saharan Africa: +38 days

• Latin America & the Caribbean: +34 days

• Lower-middle-income cities: +38 extra days

• Low-income cities: +34 extra days

These are regions already grappling with limited financial and institutional capacity, making adaptation even harder. As global temperatures climb, climate impacts will intensify existing inequalities, leaving the most vulnerable cities—and the people in them—at highest risk.

According to the IPCC, marginalized urban populations are the most exposed to the dangers of climate change. Roughly 1 billion people live in slums or informal settlements, often located in the hottest and most polluted parts of a city. These homes—typically made of poorly insulated materials like corrugated metal—offer little protection from the heat. Take Mumbai, for example: one study found that one urban slum averaged 6°C (11°F) hotter than surrounding neighborhoods. 

As slums continue to grow throughout the developing world, the dangers of excessive heat will only become more deadly. Protecting vulnerable urban populations must be a top priority in the global response to climate change.

References:

“Heat Island Effect.” EBSCO Research Starters: Earth and Atmospheric Sciences, EBSCO Information Services, https://www.ebsco.com/research-starters/earth-and-atmospheric-sciences/heat-island-effect. “Data: The Future of Extreme Heat in Cities.” World Resources Institute, 7 June 2023, https://www.wri.org/insights/future-extreme-heat-cities-data. IPCC Interactive Atlas: Regional Information. Intergovernmental Panel on Climate Change, https://interactive-atlas.ipcc.ch/regional-information. Intergovernmental Panel on Climate Change. Climate Change 2022: Impacts, Adaptation, and Vulnerability. Working Group II Contribution to the Sixth Assessment Report of the IPCC. Chapter 6, 2022, https://www.ipcc.ch/report/ar6/wg2/downloads/report/IPCC_AR6_WGII_Chapter06.pdf.

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