Post erroneously pins record-breaking July heat on old Tonga eruption

"How can anyone claim to be a 'Guardian' of the environment and not know about the world's recent unprecedented event which is causing today's global warming spike? Tonga," says the July 24, 2024 post, in response to recent coverage of record-breaking heat by The Guardian newspaper (archived here).

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A screenshot of a post on X taken on July 31, 2024

As well as X, the claim gained traction on other platforms in late July after two consecutive days of heat that broke records, according to the European environmental agency Copernicus (archived here).

On social media, posts sought to downplay the impact of extreme temperatures, with several directly tying the recent "spike" to the volcanic activity from two years prior.

Scientists are researching several recent natural phenomena -- including the Tonga eruption and a strong El Niño weather cycle --  to better understand the heat anomalies observed in 2023 and 2024 (archived here).

They consider these factors on top of the impacts of human-caused warming, noting that global carbon emissions from fossil fuels have significantly increased since 1900 (archived here and here).

Massive eruption

In January 2022, the Hunga Tonga-Hunga Ha'apai volcano erupted underwater with a force equivalent to hundreds of atomic bombs, the most powerful eruption ever recorded with modern equipment.

It also unleashed the fastest underwater currents ever recorded, triggering a 15-meter (50-foot) tsunami which demolished homes and killed at least three people on the Pacific island kingdom.

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Factfile on Jan 15 Tonga volcano eruption and tsunami (AFP / John SAEKI, Laurence CHU)

Volcanic eruptions can temporarily affect climate (archived here) and the Tonga eruption triggered natural reactions that are still being investigated.

But it "was not responsible for the recent record warming," said Alan Robock, distinguished professor at Rutgers University (archived here) said on July 26, 2024.

Ongoing scientific research by Texas A&M University and NASA scientists, found that "the Hunga eruption cooled the climate" by a very small amount (archived here).

Robock explained that despite the eruption putting "a lot of water vapor into the stratosphere, which would cause warming" it also "emitted a small amount of sulfur dioxide, which form sulfate particles that reflected sunlight and caused cooling."

He said recent research "shows that these effects almost canceled, but that the sulfate effect was slightly larger and caused cooling."

Slight 'net cooling'

Early analyses of the eruption's impact by NASA scientists pointed to a potential for warming due to the excess water vapor (archived here).

By September 2023, however, a joint study between Texas A&M University and NASA scientists identified that the added stratospheric water vapor was offset by a larger stratospheric aerosol attenuation of solar radiation -- blocking sunlight and cooling the atmosphere -- and that there may actually be "a net slight cooling" affecting the globe's Southern Hemisphere.

A follow-up July 2024 paper confirms such a trend, with authors saying: "Our results show that during most of the Hunga period there is global net cooling, except for the Jan-Feb. 2022 period right after the eruption, when the water vapor forcing peaked, and before most of the aerosol shroud has formed." (archived here).

"By dismissing the volcanic eruption as a major factor in the recent warming, the team's study reinforces his point that human-induced greenhouse gas emissions are the primary driver of climate change," Grant Hawkins, a spokesman for Texas A&M University (archived here), said in a statement sent to AFP on July 31.

"This focus is particularly relevant, given the ongoing debate and misinformation about the causes of global warming."

Emission rates

The warming effects tied to an eruption do have ongoing impacts, scientists say. 

Christoph Kern, a research physicist for the USGS Volcano Science Center (archived here), told AFP on July 26 that the CO2 emitted during an eruption remains in the atmosphere for decades.

"But while the rate of CO2 release occurring during very large volcanic eruptions can briefly match anthropogenic emission rates, such eruptions only last for hours while anthropogenic emissions are continuous. On average, volcanoes thus only contribute about 1 percent to the total atmospheric CO2 flux each year" (archived here).

Volcanic emissions and other "magmatically active regions" release an estimated 280 million to 360 million tons of carbon per year, according to research (archived here) -- by a team of scientists for the Deep Carbon Observatory.

In contrast, human-led activities produced a new record high of 37.4 billion tons carbon dioxide (archived here) in 2023 alone, according to the International Energy Agency.

AFP's fact-checks on false and misleading claims about climate change are available here.