Climate · risk
Extreme weather event
Definition
An extreme weather event is, in the IPCC Sixth Assessment Report definition, an event that is rare at a particular place and time of year, where "rare" normally means as rare as or rarer than the 10th or 90th percentile of a probability density function estimated from observations. The class includes heatwaves, cold waves, heavy precipitation and storms (including tropical cyclones), and meteorological drought; severity or impact can also qualify an event as extreme even where its statistical rarity is moderate. The World Meteorological Organization distinguishes "severe weather" — weather posing risks to life or property — as a related but distinct category.
References
IPCC 10th/90th-percentile definition, severe-weather distinction, attribution context
hydrometeorological hazard classification, hazard characterisation by location, intensity, frequency and probability
Overview
What it means
Extremes are defined relative to local climate, so the same temperature can be normal in one region and extreme in another. Single events are rarely attributable to one cause, but extreme-event attribution science quantifies how climate change alters their frequency and intensity — for example, making heat extremes more likely and more severe.
How it is used
Used in climate-risk assessment, disaster-risk reduction, insurance pricing, adaptation planning and attribution studies linking events to anthropogenic warming.
Why it matters
Human and economic losses from climate change arrive mainly through extremes rather than averages; defining them consistently underpins warning systems, resilience investment and loss accounting.