Posts mislead on climate impact of human-caused CO2

A visual representing the proportion of carbon dioxide in the atmosphere is spreading in social media posts that misleadingly claim the gas does not have a major effect on Earth's climate. Most scientists agree CO2 is not "saturated" and has grown due to humans burning fossil fuels, thereby driving global warming.

"Co2 has negligible heat trapping effects. man's input (white spec) has no accurate measurable effect," says a September 15, 2024 X post, adding that CO2 levels have been saturated for decades and no longer induce warming.

The post includes a graphic with colors representing the composition of the atmosphere. Human-produced CO2, denoted by a small white box, equals a fraction of a percent.

Other posts have shared the same visual, including in French.

In pre-industrial times, naturally occurring greenhouse gases helped make Earth's climate habitable. Without CO2, the planet's average temperature would be below freezing.

The graphic shared online accurately shows greenhouse gases -- including CO2, methane, nitrous oxide and ozone -- make up a tiny fraction of the atmosphere at 0.04 percent. But they play a major role in trapping heat and warming the planet (archived here).

Scientists have repeatedly said human-caused emissions are consequential because they are not absorbed as part of the natural CO2 cycle, triggering larger environmental consequences as they stay in the atmosphere for years.

"The math is clear -- CO2 increases make a difference," said Gavin Schmidt, director of the NASA Goddard Institute for Space Studies (archived here).

A 2016 study found a mathematical model confirmed a link between Earth's temperature increases and rising CO2 concentration in the atmosphere (archived here).

Schmidt told AFP on September 23 that the X post misleads on "how much CO2 is human-caused" and is "wrong about it not mattering."

"All of the climate trends in recent decades are due to human drivers," he said, as shown in a NASA database (archived here).

'Saturated' CO2 levels?

Climate skeptics have long promoted the unsubstantiated theory that CO2 levels will eventually become "saturated," meaning the gas will no longer contribute to global warming.

"The saturation 'theory' assumes that CO2 is somewhat like a sponge so that it absorbs longwave radiation to some maximum capacity and then stops because it cannot absorb anymore," said Marilyn Raphael, director of the Institute of the Environment and Sustainability at the University of California-Los Angeles (archived here).

"This is not how it works."

She told AFP on September 24 that CO2 "absorbs longwave radiation, warming the atmosphere which re-emits longwave radiation in all directions, including towards the Earth, thereby increasing surface temperatures."

"This occurs constantly," Raphael said.

Research indicates CO2 "is nowhere near being saturated" (archived here), and scientists have demonstrated that adding more of the gas will make the greenhouse effect stronger regardless of saturation (archived here).

Raphael pointed to Venus, which she said is "often considered a twin of Earth." NASA describes the planet as "a hellish world" with a CO2 layer 90 times as thick as Earth's and temperatures that reach 864 degrees Fahrenheit (462 degrees Celsius).

"Is something like this what is being recommended?" she said.

Increase over time

NASA and the US National Oceanic and Atmospheric Administration (NOAA) have tracked the drastic acceleration of CO2 in Earth's atmosphere over the past half-century.

The concentration of the greenhouse gas has risen from around 280 parts per million (ppm) in the 1850s to 426 ppm (0.04 percent), per NASA data last updated in July 2024 (archived here).

Greenhouse gas concentrations hit record highs yearly (archived here and here). NOAA data show atmospheric CO2 has increased alongside a surge in human-caused emissions (archived here).

Such high concentrations of CO2 have not been recorded on Earth in the last 14-16 million years.

Six datasets from educational and governmental agencies (archived here) have tracked the resulting rise in global average temperature (archived here).

"Today we are increasing CO2 at a rate that may be faster than ever before in the geological record," said Bärbel Hönisch, a professor at Columbia University's Lamont-Doherty Earth Observatory (archived here). "This CO2 contributes to the greenhouse effect and warms our planet."

She previously told AFP on April 16 that climate models "cannot explain observed global temperature ranges without the addition of anthropogenic CO2."

The UN Intergovernmental Panel on Climate Change (IPCC) says it is "unequivocal that human influence has warmed the atmosphere, ocean and land" -- and that CO2 is the main culprit (archived here and here).

More of AFP's reporting on climate misinformation is available here.