CO2 is 0.04% of the atmosphere. That doesn't mean climate change is a 'hoax' | Fact check

The claim: Climate change is a 'hoax' because CO2 is only 0.04% of the atmosphere

A Feb. 7 Instagram post (direct link, archive link) shows Rep. Doug LaMalfa of California questioning a panel of transportation and construction experts about carbon dioxide at a congressional hearing.

LaMalfa asks what percentage of the atmosphere is comprised of CO2, and the panelists offer guesses ranging from 5% to 8%.

"The answer is .04%," LaMalfa says. "Not 1%. Not a half of a percent. It's .04%. It's gone up from .03 over the last couple decades. This is what we're being all contorted into doing, is this tiny change in CO2. If we get below .02, plant life starts dying off."

The post's caption includes the hashtag #climatechangeisahoax.

The post was liked more than 1,500 times in about two weeks.

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While it's true that carbon dioxide is about 0.04% of the atmosphere, scientists said that doesn't mean climate change is a hoax or is insignificant. There are multiple lines of evidence that show modern global warming is caused by rising atmospheric levels of CO2.

CO2 figure used to mislead on climate change, scientists say

The video in the post shows LaMalfa, a Republican, questioning witnesses at a March 28, 2023, House Transportation and Infrastructure Committee hearing on the implementation of the Infrastructure Investment and Jobs Act.

LaMalfa's carbon dioxide figure is right. CO2, a greenhouse gas, makes up about 0.042% of the atmosphere. But scientists say this fact has been used to mislead people about climate change, and it ignores the link between the rising concentration of CO2 in the atmosphere and a warming planet.

"This is one of the silliest of the climate denier talking points," Michael Mann, a leading climate scientist and professor at the University of Pennsylvania, said in an email. "Yes, CO2 today is about 420 parts per million in the atmosphere. That might sound like a small amount, but a relatively minute amount of a very potent substance can have a huge impact."

The concentration of CO2 in the atmosphere is 50% higher than the pre-industrial level of 280 parts per million, Mann said. This increase in carbon dioxide levels has already warmed the planet nearly 2 degrees Fahrenheit, causing dramatic loss of ice, sea level rise and more extreme weather events, he said.

"The impacts will get that much worse if we continue to burn fossil fuels," Mann said.

Scientists understand that modern global warming is largely caused by human activities because they have long-observed how CO2 is a greenhouse gas that slows the escape of heat into space, according to the National Oceanic and Atmospheric Administration.

Fact check: 'Overwhelming' evidence of climate change regardless of weather map colors

"We know from both its rapid increase and its isotopic 'fingerprint' that the source of this new carbon dioxide is fossil fuels, and not natural sources like forest fires, volcanoes, or outgassing from the ocean," the NOAA website says.

There are multiple lines of evidence that show these emissions have caused modern climate change, Josh Willis, a NASA climate scientist, previously told USA TODAY.

"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."

Kristie Boering, a chemistry and Earth and planetary sciences professor at the University of California, Berkeley, called arguments downplaying the meaning or significance of small concentrations of things "ridiculous."

To illustrate the point, Boering pointed to California's laws governing driving under the influence. It is illegal for people over 21 to drive with a blood alcohol concentration of 0.08% or higher. The legal limit drops to 0.04% for people driving passengers for hire or people driving a vehicle that requires a commercial driver's license.

"So, clearly small concentrations of things in our blood can have a huge effect on our bodies and brains," Boering said in an email. "Alcohol, medications to relieve pain or kill bacteria. By analogy, so too can small concentrations of things in the atmosphere have huge impacts on temperatures."

LaMalfa also claims in the video that plant life will start dying off if atmospheric CO2 levels drop below 0.02%. USA TODAY previously reported that there have been times plants and animals lived in atmospheric levels at that point or lower.

The Instagram user who shared the video did not immediately respond to a request for comment.

PolitiFact debunked a similar version of the claim.

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This article originally appeared on USA TODAY: CO2 percentage used to mislead on global warming | Fact check