Global warming is from human activity, not sea volcanos or El Niño | Fact check

The claim: Trees absorb all CO2 in US and modern climate change is caused by El Niño and undersea volcanoes

An Oct. 13 Facebook video (direct link, archive link) shows conservative media personality Stu Burguiere talking about climate change with Joe Bastardi, a meteorologist and skeptic of CO2-driven climate change.

"First of all, let's play devil's advocate," Bastardi says. "Let's say CO2 is the culprit that it's supposed to be. Well, the United States has enough foliage to get rid of all the emissions we have. We have 229 billion trees in the United States.''

He then claims it's impossible for CO2 to be responsible for modern global warming. Instead, "it was a combination of cumulative build-up of water vapor over the years since these underwater volcanoes have been going off." He also says El Niño events are also responsible.

The video was viewed more than 260,000 times in six weeks.

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Our rating: False

U.S. forests absorb CO2 and store carbon in trees and soils, but they don't absorb anywhere near 100% of U.S. CO2 emissions, according to government estimates. While El Niño causes temporary global warming and the 2022 Hunga Tonga-Hunga Ha’apai volcanic eruption has likely done the same, the sustained global warming documented since the late 1800s is caused by human greenhouse gas emissions, experts said.

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A 2015 study published in Nature estimated that the U.S. has around 228 billion trees, similar to the figure given in the video. But they don't take up all U.S. carbon.

The U.S. Geological Survey reports that U.S. forests, grasslands and shrublands absorb about 12% of the country's carbon dioxide emissions. The U.S. Forest Service reports a different mix of U.S. resources, including forest land, woodlands and urban trees, absorbed about 15% of U.S. CO2 emissions in 2019.

While U.S. forests do not absorb all U.S. emissions, researchers say forest preservation and regeneration are important strategies for removing excess carbon dioxide from the atmosphere to lessen global warming.

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Greenhouse gas emissions from human activity drive modern global warming

Modern climate change is occurring because humans are amplifying Earth's "greenhouse effect" by adding additional CO2 and other greenhouse gases into the atmosphere. These gases have long been known to slow the escape of heat into space.

"The physics of the greenhouse effect has been well understood for decades," Dargan Frierson, an associate professor of atmospheric sciences at the University of Washington, told USA TODAY. "This same physics was used by Exxon’s own scientists in the 1970s to predict decades of global warming well before it happened."

Researchers can tell the increased CO2 in the atmosphere is due to human activity because a type of carbon found in excess in the atmosphere is the same type found in fossil fuels, Josh Willis, a NASA climate scientist, previously told USA TODAY.

Additionally, "the amount of warming we see matches what we expect based on the increased CO2 we've added," he said. "The timing of the warming matches the timing of the CO2 increase caused by people."

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Water vapor from undersea volcanoes does not drive sustained global warming

However, the video claims that modern global warming is caused by El Niño and a build-up of atmospheric water vapor from undersea volcanoes. There are several ways researchers know that is wrong.

It is possible for undersea volcanoes to vaporize water, which ends up in the atmosphere. However, while water vapor is a powerful greenhouse gas that contributes significantly to global warming, it behaves differently than CO2 in the atmosphere and does not drive global warming, Mark Zelinka, an atmospheric scientist at Lawrence Livermore National Laboratory, told USA TODAY in an email.

While CO2 released by humans easily builds up in the atmosphere over time, the long-term average amount of water vapor in the atmosphere can only change if the temperature of the atmosphere changes first. Otherwise, a random surge of water vapor into the lower atmosphere from an undersea volcano would just condense and rain out after a short period of time.

"Water vapor cannot just decide to change its concentration in the atmosphere," Zelinka said. "Its concentration is constrained by temperature. But when CO2 increases, the atmosphere warms and water vapor can invade the atmosphere – exponentially – causing substantial heating."

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The eruption of the Hunga Tonga-Hunga Ha’apai volcano in the South Pacific in early 2022 was unusual in that it projected enormous amounts of water vapor into a layer of the upper atmosphere called the stratosphere, Howard Diamond, a climate scientist with the National Oceanic and Atmospheric Administration, told USA TODAY. In this layer, water vapor is retained for longer than in the troposphere − the layer of the atmosphere closest to Earth's surface where most water vapor from volcanoes would end up.

This specific eruption is expected to increase global temperatures, but the effect should be "short-lived relative to anthropogenic climate change," Ben Liley, an atmospheric scientist at New Zealand's National Institute of Water and Atmospheric Research, told USA TODAY in an email.

Finally, while the rate of global warming has doubled since 1981, there is no evidence that undersea volcanic activity has escalated over that timeframe, according to Gregory Johnson, who co-leads the NOAA Pacific Marine Environmental Laboratory's Global Observations of Biogeochemistry and Ocean Physics program.

He also noted that many volcanic eruptions actually temporarily slow warming by emitting sulfur dioxide into the atmosphere, which reflects the sun's energy back into space.

"Hunga Tonga did inject a substantial amount of water vapor into the stratosphere and much less sulfur dioxide than usual, but it was a very unusual event," Johnson said.

El Niño doesn't doesn't drive modern global warming

There is also no mechanism by which the El Niño-Southern Oscillation − a natural circulation pattern in Earth's atmosphere and oceans − could drive the sustained global warming that has been observed since the late 1800s, Willis previously told USA TODAY.

El Niño has "been going on for thousands of years and human-caused warming has only been happening for the last 150," he said.

The El Niño-Southern Oscillation does cause periodic and temporary global average temperature rise due to warmer water on the ocean surface. And the related cold phase − called La Niña − causes temporary cooling due to colder surface water.

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Diamond previously told USA TODAY that these climate fluctuations work off the planet's baseline average temperature, which is increasing due to human greenhouse gas emissions.

"When an El Niño comes around, it is going to increase temperatures in line with that higher baseline, but it does not cause the higher baseline," he said.

Graph shows El Niño-Southern Oscillation fluctuations overlaid on global temperature data from 1950-2021. Temperatures are increasing due to human greenhouse gas emissions.
Graph shows El Niño-Southern Oscillation fluctuations overlaid on global temperature data from 1950-2021. Temperatures are increasing due to human greenhouse gas emissions.

These cycles also affect how much heat Earth gains or loses, but Johnson said they tend to cancel each other out and have little if any impact on long-term warming.

USA TODAY reached out to Burguiere and Bastardi for comment but did not receive a response.

AFP also debunked the video.

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This article originally appeared on USA TODAY: False claim global warming from volcanoes and El Niño | Fact check