Fact check: Global warming caused by greenhouse gas emissions, not mysterious ocean warming
The claim: It's more likely oceans are causing global warming than CO2
A Dec. 28, 2022, article circulating on Facebook speculates that CO2 is "only very very slightly" warming the Earth.
"It is much more likely that oceanic warming is causing the problem," reads the article from cfact.org. "IF SO IT IS A NATURAL OCCURRENCE, THAT DEMANDS ADAPTATION, NOT ECONOMIC AND FREEDOM SUICIDE."
The author then speculates that ocean warming is being caused by "geothermal sources" such as underwater volcanos.
The article garnered more than 300 interactions on Facebook, according to Crowdtangle, a social media analytics tool. It was also linked on Twitter.
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Our rating: False
Earth's oceans are indeed warming. However, multiple lines of evidence show that this warming and other elements of modern climate change are caused by greenhouse gases, such as CO2, released by human activity. Geothermal activity does not warm ocean water enough to account for the observed changes in global temperatures, according to researchers.
Oceans and atmosphere warming because of human activity
There are a number of ways that scientists know greenhouse gas emissions released by human activity are causing global warming, Josh Willis, a NASA climate scientist, told USA TODAY.
Scientists have long known that CO2 is a greenhouse gas, which warms the lower atmosphere by slowing the escape of heat into space.
"The amount of warming we see matches what we expect based on the increased CO2 we've added," he said in an email. "The timing of the warming matches the timing of the CO2 increase caused by people. Not only that, the timing of global sea level rise matches the CO2 increase."
Further, researchers can tell that the excess CO2 build-up in Earth's atmosphere comes from burning fossil fuels, he said. This is because the type of carbon found in atmospheric CO2 – its isotopic signature – matches the carbon found in fossil fuels.
Fact check: Warming varies across oceans and atmosphere, doesn't contradict climate change
Human-caused CO2 is the only explanation for global climate change that accommodates all the evidence, Willis said.
"Scientists have looked for other sources of heat, cycles of the sun, volcanos on the sea floor and pretty much everything else you can think of," he said. "Nothing besides humans burning fossil fuels can explain all of these things."
Geothermal activity cannot account for recent ocean warming
Earth's oceans have warmed. In fact, ocean warming is a major driver of sea level rise, because water expands as it warms, according to NASA.
However, the oceans are not self-heating. They are warming for the same reason the rest of the Earth is warming – greenhouse gas emissions, Tim Boyer, a National Oceanic and Atmospheric Administration oceanographer told USA TODAY.
"The thermal energy increase in the upper ocean – as well as the atmosphere – seen over the last 60 years is almost exclusively due to incoming solar radiation and ... heat energy trapped within the Earth's system," he said in an email.
The oceans have absorbed about 90% of Earth's "excess" heat associated with greenhouse gas emissions, he said.
Fact check: Plymouth Rock has been moved, not an accurate gauge of sea level rise since 1620
While geothermal energy does heat Earth's oceans, it cannot explain the magnitude or distribution of observed ocean heating, according to researchers.
"We know quite well that geothermal activity has not been a substantial driver of global warming," Kyle Armour, a physical oceanography professor at the University of Washington, told USA TODAY in an email. "Geothermal activity has not been changing rapidly enough to cause the climate warming we’ve seen."
Further, observed ocean warming is mostly occurring near the surface, not in the deep ocean where geothermal activity takes place, Timothy DeVries, a professor of ocean science at the University of California Santa Barbara, told USA TODAY in an email.
"If geothermal heating were responsible for ocean heating, then most of the ocean warming would be concentrated in the deep ocean," he said. "However, ocean temperature observations show that the vast majority of ocean warming has occurred near the surface."
This shows the ocean is being warmed from above, said DeVries.
USA TODAY reached out to the article's author for comment.
Our fact-check sources:
Timothy DeVries, Jan. 17, Email exchange with USA TODAY
Josh Willis, Jan. 17, Email exchange with USA TODAY
Tim Boyer, Jan. 17, Email exchange with USA TODAY
Kyle Armour, Jan. 18, Email exchange with USA TODAY
NASA Vital Signs of the Planet, accessed Jan. 17, Sea level
NASA Vital Signs of the Planet, accessed Jan. 17, Carbon dioxide
NASA Vital Signs of the Planet, accessed Jan. 17, Global Temperature
NASA Vital Signs of the Planet, accessed Jan. 17, Is the sun causing global warming?
NASA Vital Signs of the Planet, accessed Jan. 17, Ocean warming
Australian Department of Climate Change, Energy the Environment and Water, accessed Jan. 17, 2023, Understanding climate change
NOAA, Oct. 12, 2022, How do we know the build-up of carbon dioxide in the atmosphere is caused by humans?
NOAA, Jan. 22, 2020, Ocean heat content rises
The Conversation, July 31, 2020, John Tyndall: the forgotten co-founder of climate science
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This article originally appeared on USA TODAY: Fact check: Global warming is caused by CO2, not ocean warming