Tree Rings And Corals Place El Nino Among Millennium Extremes

Climate records compiled from tree rings and corals indicate the El Niño event developing in the tropical Pacific could become one of the strongest in the past millennium, according to The Climate Brink on October 12, 2026. Researchers compared modern measurements with historical climate reconstructions to estimate its potential ranking.

The event has already reached record levels in the instrumental record, with Niño 3.4 sea surface temperature anomalies passing the previous record set in November 2015 on September 20, according to The Climate Brink.

The Climate Brink reported that daily Niño 3.4 anomalies reached 3.4 degrees Celsius during the week described in the analysis, while September recorded the highest monthly Niño 3.4 temperature anomalies on record.

Forecasts from 14 seasonal models analyzed by The Climate Brink showed the event could peak near 4 degrees Celsius. About 80% of model runs placed the peak between 3.3 degrees Celsius and 4.6 degrees Celsius.

The analysis also noted uncertainty remains because forecast models underestimated the event's size earlier in the year and overestimated it during the previous two months. The first week of October remained above 3 degrees Celsius, making the October forecast of 3.6 degrees Celsius possible.

Historical comparisons rely on multiple records because direct thermometer measurements only extend back to 1877. The Climate Brink used tree ring studies, coral records, and historical documents to evaluate El Niño intensity before modern observations.

Tree ring research by Cook and Cane (2024) reconstructed winter sea surface temperatures across the equatorial Pacific using 544 tree ring chronologies, with 81 extending back to the 1100s. The reconstruction found the largest pre-1871 winters reached about 2.1 degrees Celsius.

Modern major El Niño winters, including those in 1877-78, 1982-83, 1997-98 and 2015-16, measured between 2.3 degrees Celsius and 2.5 degrees Celsius on the same index, according to the analysis.

Cook and Cane wrote that recent decades show unusually large El Niño activity compared with earlier centuries.

"The positive excursions (i.e., El Niño events) in recent decades are generally higher than at any time since 1100," said Cook and Cane.

The Climate Brink also cited coral research published by Julia Cole and colleagues in Science using 28 coral records from five Galápagos islands. The coral samples provide climate information dating back to around 1130.

The coral records measure long-term changes in sea surface temperature variability rather than the peak strength of individual El Niño events. The study found year-to-year temperature swings increased after the late 19th century and coral records after 1984 were mostly above the pre-industrial range.

Historical event chronologies compiled from records including ship logs, mission records, and climate proxies also show that several of the most extreme classifications occurred during the 20th century.

The Climate Brink noted that some earlier classifications may not fully capture event intensity, including the 1997-98 El Niño being rated as "weak" in one chronology despite its known significance.