Make a big volcanic eruption
the world warmer or colder?

Dr. Arnd Bernaerts
4 min readApr 11, 2021


A volcanic eruption in Iceland hit the headlines a few weeks ago. After a break of 800 years, another volcano erupted on Reykjanes peninsula, just 20 miles south of Reykjavik. The event was spectacular but had no major impact.

Yesterday, April 10 2021, an explosive eruption has rocked La Soufriere volcano on the eastern Caribbean island of St. Vincent. The first explosion shot an ash column 10 kilometers into the sky and that the majority of the ash was headed northeast into the Atlantic Ocean. That occurred four days short of the 42nd anniversary of the last sizable eruption, in 1979, and a previous eruption in 1902 killed some 1,600 people. Meanwhile on April 11, about 16,000 people have had to flee their ash-covered communities. Experts warn that the explosions could continue for days or even weeks, and that the worst could be yet to come.

Recently we run a MEDIUM story: “An eruption on Iceland looms. Is a Plan B prepared?” Today the question is, what will happen after a big volcano eruption? It seems that science is not yet prepared to provide a reliable answer. Will it get warmer or colder? The general saying goes: Volcanic eruptions cause COOLING!

Here is at first an opposite view from Zambri et al. 2017, (Excerpts from Abstract):
Observations show that all recent large tropical volcanic eruptions (1850 to Present) were followed by surface winter warming in the first Northern Hemisphere (NH) winter after the eruption. Recent studies show that climate models produce a surface winter warming response in the first winter after the largest eruptions but require a large ensemble of simulations to see significant changes. It is also generally required that the eruption be very large, and only two such eruptions occurred in the historical period: Krakatau in 1883 and Pinatubo in 1991. …..Though the results depend on both the individual models and the forcing data set used, we have found that models produce a surface winter warming signal in the first winter after large volcanic eruptions, with higher temperatures over NH continents and a stronger polar vortex in the lower stratosphere. (cont.)

Dr. Brian Zambri et al., seem not o have cared a lot about observed details. The forceful eruption of Krakatoa, August 26–27th, 1883, was also the first scientifically well recorded and studied eruption of a volcano, from the very beginning to its disastrous ending. The magazine NATURE covered the event extensively. The eruption of Krakatoa, darkened the sky worldwide for years afterwards. The final explosive eruption was heard 4,830 km (3,000 miles) away, 20 million tons of sulfur released into the atmosphere; produced a volcanic winter, reducing worldwide temperatures by an average of 1.2 °C (2.2 °F) for five years. Weather patterns were chaotic for years, and temperatures did not return to normal until 1888 (Wikipedia).

Although it was quickly determined that the amount of solar energy received was clearly reduced for a period of several years, little attention was paid to the development of the atmospheric temperature. The blockage must have fluctuated strongly and have varied greatly, depending on the observation point. In total, the blockage effect has been calculated at an average of approximately 10% over a span of four years, whereby the reduction of solar energy in the northern hemisphere (Paris) was at its greatest in fall of 1885, reaching a value of 25%. (MORE HERE)

Now what about the question: warming or cooling? The answer is simple. There is at first a warming for some months, a few years, depending on the location in question. Close to the oceans the temperatures rise or drop will be moderate. Distant areas will get colder condition, and the average is going to drop pounced the longer the ashes block out sun ray. After few years also coastal region will feel the change. The severity of this process depends on the ocean and their heat capacity. The fairly short duration of Krakatoa’s ashes in the air reduced the impact on the just emerging industrialization. A comparable event today would push civilization toward an unimaginable global catastrophe.

A unique climatic event was offered to science for their better understanding of big volcano eruption. Hopefully the more recent eruption remain modest, and the next serious one is far away.

Extended Version

MEDIUM Story, March 18, 202, on Iceland Volcano Looming:

B. Zambri, full text: