A night in the heat

1. Whose night
2. What is in place
3. Through the night

The evidence behind the night

• Older people in a Kolkata informal settlement were 4.3 times more likely than older people in a nearby village to face dangerous heat, with a heat index of 45 °C or more, because their homes stayed hotter than the outdoors, especially at night.Source: Weitz, Mukhopadhyay and Das, International Journal of Biometeorology, 2022 (opens in a new tab)
• Each 1 °C rise raises the odds of preterm birth by about 5%, and a heatwave by about 16%.Source: Chersich et al., BMJ, 2020 (opens in a new tab)
• In 2014–2023, each infant in India faced an average of 7.7 heatwave days a year, 47% more than in the 1990s.Source: Lancet Countdown, India data sheet, 2024 (opens in a new tab)
• Tin roofs, poor ventilation and crowded rooms can make homes hotter inside than out, leaving nowhere safe to rest. Thin roofs cool slowly, so the worst comes at night: in low-income homes measured across South Asia, tin-roofed houses stayed warmer indoors than the outdoor air.Source: Frontiers in Built Environment, 2022: Ahmedabad informal settlements up to 7.6 °C hotter (opens in a new tab)
• Older people living alone are among the most likely to die in a heatwave. Many victims of Chicago’s 1995 heatwave died alone at home.Source: Semenza et al., New England Journal of Medicine, 1996: heat-related deaths in the July 1995 Chicago heatwave (opens in a new tab)
• When nights stay hot, the body has less chance to recover from the day, so the next day can start already depleted.Source: Minor et al., One Earth, 2022: rising temperatures erode human sleep (opens in a new tab)

Watch: care and the body in the heat

The other two simulations · Older people · Pregnant women and babies · Practical actions at home · In clinics