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Heatwaves: how hot can it get?
- Hospital admissions and mortality rates are rising as a deadly trajectory continues with the ongoing heatwave.
- A heatwave is defined by local authorities as a persistent period of temperatures slightly above normal, with specific regional thresholds: in the UK, three consecutive days between 25°C and 28°C; in New York, at least three days at or above 32°C; and on the Indian plains, temperatures exceeding 40°C while remaining 4.5°C above typical for two days.
- Persistent weather blocks lasting weeks or months form when high-pressure anticyclones develop in the ridges of the meandering polar front jet stream, trapping heat like a lid and creating self-perpetuating "heat domes."
- Depleted soil moisture shifts heat from evaporation into the ground, further heating the air, while high humidity reduces the efficiency of sweat evaporation, increasing perceived heat.
- A wet bulb temperature above 35°C indicates a lethal danger where the human body cannot cool down, likely causing death within approximately six hours even for young, healthy individuals.
- Wet bulb temperatures are rising globally, with many countries reaching 31°C and select stations in South Asia, the Persian Gulf, and the southwest coast of North America recording readings near or above 35°C for short periods.
- Excessive heat stresses circulatory systems and breathing, increasing mortality particularly among the elderly and those with underlying conditions, while the frequency of tropical nights (temperatures not dropping below 20°C) is rising.
- Countries unaccustomed to extreme heat are identified as particularly susceptible without immediate adaptation, with Afghanistan, Central Asia, and parts of Central America predicted to face devastating heatwaves.
- Continued atmospheric warming is expected to cause heatwaves worse than historically seen over larger areas, and under extreme scenarios, wet bulb temperatures could render specific regions effectively unlivable.
- Scientific understanding of climate change's impact on atmospheric circulation remains incomplete, with models contradicting each other on whether blocking systems will become more or less frequent.
- Even if greenhouse gas levels stabilize, the planet's higher average temperature will ensure a continued increase in heatwaves.
- Governments at national, city, and local levels are required to implement further protective measures, while the public must understand risks to protect themselves and one another.