All six major eruptions studied since 1850 were followed by stronger ocean cold spells

Six large volcanic eruptions between 1883 and 1991 were each followed by stronger marine cold spells worldwide, according to a study in Ocean-Land-Atmosphere Research. Jan Kempert of South Westphalia University of Applied Sciences and Raven Quilestino-Olario of the University of Cologne analyzed daily sea surface temperatures from 1850 to 2024. The paper was published on Nov. 6.

Help yourself and the planet: The Cool Down makes it easy to help yourself while helping the planet, with smart, simple changes to save more and waste less in your everyday life.

Get The Cool Down →

We may earn a commission if you sign up.

Volcanic winters, the cooling that follows sulfate aerosols thrown into the stratosphere, had rarely been tested against ocean cold extremes.

Six eruptions from Krakatau to Pinatubo

The team examined Krakatau (1883), Santa Maria (1902), Novarupta (1912), Agung (1963), El Chichón (1982) and Pinatubo (1991), all described in the EurekAlert summary of the paper. The authors compared cumulative marine cold spell intensity after each eruption with conditions at other times, adjusting for selected natural climate variations and long-term trends. Their conclusion was that all six eruptions were followed by signs of stronger marine cold spells globally.

The six eruptions are spread across the tropics and high latitudes: Krakatau in Indonesia, Santa Maria in Guatemala, Novarupta in Alaska, Agung in Bali, El Chichón in Mexico and Pinatubo in the Philippines. Pinatubo in June 1991 was the best instrumented of the group, which is why it is the most commonly cited volcanic cooling case.

The physical idea is straightforward. Large eruptions inject sulfur gases that become sulfate aerosols in the stratosphere, reflecting sunlight and cooling the surface for a year or more. The new paper asks whether the oceans show that chill not as a lower average but as an increase in the cumulative intensity of cold extremes, summing how far and how long temperatures stay below normal during each cold spell. Pinatubo is the textbook case, and the USGS Pinatubo materials describe the 1991 eruption in detail.

The 1816 Year Without a Summer, which followed the Tambora eruption, lies outside the window because the dataset starts in 1850. Background on that episode is in a general reference entry, while the Pinatubo case is documented by the U.S. Geological Survey’s Pinatubo resources. Tambora is therefore a missing seventh test for the reconstruction, and the authors do not claim results for it.

Defining a marine cold spell in COBE-SST3

A marine cold spell, in the paper’s definition, is a stretch of at least five consecutive days when sea surface temperature runs unusually cold against the local seasonal norm. The researchers used COBE-SST3, a reconstruction of daily upper-ocean temperatures stretching from 1850 to 2024. Reconstructing daily values for the 19th century necessarily involves sparse observations, and the authors say they want to look more closely at uncertainties in historical records. The paper is formally called Uneven Imprints of Major Volcanic Winters on Weakening Global Marine Cold Spells since 1850. The five-day minimum separates persistent cold events from day-to-day noise in the daily record.

Because the definition is local and relative, a cold spell in the North Atlantic and one in the tropical Pacific are judged against their own seasonal baselines. That lets a single global count capture very different ocean regimes, but it also means the results depend on how well the reconstruction captures each region.

Six eruptions is a small sample, and the authors treat the result as consistent across all six rather than as a precise size estimate for any one. The paper reports no conflicts of interest, and its analysis adjusts only for selected natural climate variations, so other influences on a given decade could still blur individual cases. The result describes the direction of the response, not a forecast: it says nothing about how strongly a future eruption would chill particular basins, and the regional unevenness suggests any new event would again produce winners and losers.

Uneven regional responses and a weakening long-term trend

The paper’s wording anticipates the findings, and the findings match: some regions saw strong cold extremes after the eruptions while others saw weaker or even opposite responses. Marine cold extremes have also become less frequent and less intense across the past 175 years, the authors report, so a volcanic cooling signal appears against a background that is shifting toward warmer water.

Kempert and Quilestino-Olario describe the work as a first look at volcanic winters in the ocean cold-extremes record. The research was funded by the German Academic Exchange Service (DAAD, program 57698564), the University of Cologne Graduate School of Geosciences, and the German Research Foundation’s Priority Program 1158. The Cologne Quaternary Geology group hosts the doctoral research. The team notes no competing interests, and the work is a modest, desk-based reanalysis of an existing temperature reconstruction rather than a new observing campaign.

Marine heatwaves as the next test

The same dataset is slated for a follow-up on marine heatwaves, again with attention to observational uncertainty. The full paper is at DOI 10.34133/olar.0177. The open question the authors leave is why regional responses differed so much after eruptions of similar global reach. Heatwaves are the obvious counterpart, since the long-term drift the authors describe, fewer and weaker cold extremes, is the other face of ocean warming, and the follow-up would use the identical daily reconstruction so the two analyses can be compared directly.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.

Help yourself and the planet: Get The Cool Down →

We may earn a commission if you sign up.