The terrifying climate metric measuring humidity-heat combinations that make human survival impossible, even in shade with water.
Deadly Threshold
Wet-bulb temperature combines heat and humidity. At 35°C (95°F) wet-bulb, humans cannot cool down through sweating—death occurs within hours, even for healthy people in shade with unlimited water. A 2010 study warned large regions could become uninhabitable by 2070. In July 2019, wet-bulb conditions briefly hit 35°C in Pakistan and Iran.
2021 Heat Dome
The Pacific Northwest heat dome (June 2021) approached wet-bulb limits, killing 1,400+ in U.S./Canada. Portland hit 116°F with high humidity. The event made wet-bulb temperature mainstream climate concern—not just extreme heat but unsurvivable conditions. Climate scientists warned this would become common in South Asia, Middle East, and U.S. by mid-century.
Societal Implications
Wet-bulb limits force questions about climate adaptation limits. Air conditioning helps but requires electricity during peak demand and fails during blackouts. Outdoor work becomes impossible. The concept shifted climate discourse from economic costs to human survival—billions could face deadly conditions absent massive emissions cuts.
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