Coral record: El Niño swings 36% wider than in 1,000 years

The fact

A thousand years of Pacific sea surface temperature, season by season, drilled out of living and fossil corals in the Galápagos: that is what the journal Science published on 27 August. The record puts El Niño variability 36.5% above the preindustrial millennium, with the break concentrated in the past forty years.

Why it matters

Climate arguments usually turn on a rising average. This one turns on something else: the size of the swings around that average. The El Niño-Southern Oscillation (ENSO) is the single largest driver of year-to-year climate extremes: droughts, floods, wildfires, coral bleaching and failed harvests, from Southeast Asia to the Horn of Africa to the Pacific coasts of the Americas. A wider swing means the same regions hit harder, and more often.

The second lesson is about method. Thermometers reach back only about 175 years, too short to separate a trend from noise in a system whose natural swings are already large. Coral skeletons, by contrast, log every season in their chemistry. By stretching the baseline to a millennium and then testing it against twelve last-millennium simulations driven by volcanic eruptions and solar variability, the authors show the recent signal falls outside what natural variability can produce.

The stake is concrete for anyone who prices risk off the historical record: insurers, dam and grid operators, agricultural commodity buyers, port planners. Their models assume a stable distribution. If the spread itself moves, the “once in fifty years” figure behind premiums, reservoir rules and design standards describes a climate that no longer exists.