A thousand years of coral skeletons from the Galapagos Islands now back up what climate scientists have long suspected but struggled to prove: El Nino events are getting stronger because the planet is getting hotter. A reconstruction of eastern Pacific sea surface temperatures published Thursday in the journal Science found that strong El Nino events have occurred more frequently over the past century than at any point in the thousand years before the Industrial Revolution began pumping greenhouse gases into the atmosphere. [1]

The finding, led by University of Michigan palaeoclimatologist Julia Cole, lands as a record-breaking El Nino gathers strength in the Pacific this year — the third strong event in just 11 years, something forecasters say has never been observed before. [1] Wire photography has already moved on to the visible consequences: Indonesian wildfires burning near a housing complex in Kubu Raya this year, images distributed by AFP under captions noting the blazes "might have been intensified by the strong El Nino." [1] That is the consequence story. Cole's coral record is the mechanism story, and it is the one service journalism keeps skipping.

"It doesn't look like a fluke," Cole told Nature of the pattern her team found. [1] The distinction matters because the debate over whether human-caused warming is intensifying El Nino has been notoriously hard to settle. Computer models struggle to fully capture the intricate feedback between winds and water that drives the El Nino-Southern Oscillation, the natural swing between warm and cool phases in the tropical Pacific. Reliable instrumental temperature records in the remote eastern Pacific barely exist before the twentieth century, leaving scientists with a blank stretch of ocean history against which to judge whether today's El Ninos are unusual. [1]

Corals fill that gap because their skeletons grow in bands that capture month-to-month temperature swings — fine enough resolution to pick out something as fleeting as an El Nino event centuries after it happened. Earlier coral records from the central Pacific already pointed to a recent trend toward more frequent strong El Ninos. But those records missed the eastern Pacific, where El Nino's warming signal is strongest, leaving what Cole's team considered an incomplete picture. University of Southern California palaeoclimatologist Julien Emile-Geay compared relying on the central Pacific alone to a doctor trying to measure a patient's heartbeat with a stethoscope placed on the ankle. [1] The Galapagos sit at the actual heart of El Nino — but corals there are scarce, because the islands' upwelling currents create conditions too extreme for most reef-building species to survive, which is part of why this record took so long to assemble. [1]

Cole's reconstruction changes that. By sampling Galapagos coral skeletons and cross-referencing centuries of growth bands against known El Nino years, her team produced a continuous record stretching back a thousand years — long enough to establish a genuine pre-industrial baseline rather than guessing at one. Set against that baseline, the frequency of strong El Ninos in the past hundred years stands out as anomalous. Many of the climate models scientists use to project this century's weather agree the trend should continue: more frequent strong El Ninos as warming persists. [1]

The stakes are not abstract. El Nino events produce a temporary surge in global average temperatures and reshape weather patterns across entire continents, with consequences for both ecosystems and economies that ripple well past the Pacific basin itself. "We need to think about how to prepare better so that these aren't as catastrophic for us," Cole said. [1] That is a policy statement built on paleoclimate evidence, not a wildfire photo caption — and it is precisely the register that wire coverage of this year's El Nino has largely left out, favoring the visible disaster over the buried mechanism that makes the disaster more likely.

Cole is careful about the limits of her own method. Corals, she noted, function as "a time machine to look into the past" — not the future. [1] The uncertainty that remains is real: even as the frequency trend looks solid, the underlying ocean-atmosphere physics that determine exactly how a warming climate reshapes El Nino's cycle are still not fully understood, and translating a thousand-year backward-looking record into a forward-looking forecast is a different scientific problem than the one Cole's team just solved.

What the coral record does settle, at least provisionally, is the question of whether this year's headline-grabbing El Nino is a coincidence or a pattern. The wildfire photographs will keep running as long as the fires burn. The coral cores are the reason those fires are becoming more predictable, even if they are not yet less severe.

-- DARA OSEI, London