The ideas the field is built on

Learn

• What is a climate normal?A climate normal is a 30-year average a place is measured against. Why 1991–2020 is the current standard period, why 1961–1990 and 1951–1980 still matter, and how the choice changes every verdict.→
• What a sigma anomaly meansSigma (σ) counts how many standard deviations a reading sits from a place's normal. What ±1σ, ±2σ and ±4σ mean in plain language, and why it beats a raw temperature difference.→
• Return periods, explainedA 1-in-100-year event has a 1% chance in any year — and about a 26% chance in thirty years. How return periods work, and why they describe the old climate, not the calendar.→
• Normal depends on when you were bornThe thirty years you grew up in set your sense of normal. How a birth-year baseline changes what looks extreme, with the arithmetic shown.→

Teaching this? See Not Normal in the classroom.