Fact check: Global temperatures and atmospheric CO2 levels are correlated, contrary to claim
The claim: Greenhouse effect is a hoax, global warming uncorrelated with CO2 levels
A Dec. 17 Facebook post (direct link, archive link) claims a CO2-driven greenhouse effect is not causing modern climate change.
"The greenhouse effect is a hoax," reads the post's caption. "There is no correlation between a higher level of CO2, and higher temperature. The year 1998 was warmer than 2013, although the atmosphere had less CO2."
The post also features a video that describes four purported mismatches between CO2 concentrations and global temperatures since 1887. A narrator in the video then claims that, based on this evidence, global CO2 levels and temperature are not correlated.
Our rating: False
Global temperature and CO2 levels are correlated and both have risen overall since the late 1880s, according to researchers. However, the Earth's average temperature fluctuates from year to year due to natural variability in Earth's climate systems. This means that it's possible for a certain year to be cooler than a previous year, even if CO2 concentrations have risen. The greenhouse effect has repeatedly been verified in experiments since at least the 1800s.
USA TODAY reached out to the Facebook user who shared the post for comment.
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Greenhouse effect repeatedly proven through experiments and observations
The greenhouse effect is the process by which energy from the sun ultimately gets trapped on Earth. It begins when the sun's energy strikes the Earth, which then warms and releases heat, Howard Diamond, a climate scientist at National Oceanic and Atmospheric Administration, told USA TODAY.
"Greenhouse gases in the atmosphere 'capture' some of this heat, then re-emit it in all directions – including back to the Earth's surface," he said in an email.
This process slows the escape of heat into space, warming the planet.
Experiments demonstrating the greenhouse effect and proving that CO2 is a greenhouse gas date back to at least the late 1800s.
A simple lab experiment can be conducted to demonstrate the phenomenon, Josh Willis, a NASA climate scientist, previously told USA TODAY. In the experiment, two tanks, one filled with CO2 and one filled with oxygen, are exposed to radiation.
The tank with CO2 retains the most heat, he said.
"The theory and mathematics of radiation passing through gases are clearly defined," Michael Roman, a planetary scientist at the University of Leicester, told USA TODAY in an email. The greenhouse effect has "been verified by laboratory experiments and meteorological observations."
Fact check: Human-generated CO2, not water vapor, drives climate change
Clear correlation between CO2 levels and modern global warming
Over the long term, CO2 and other greenhouse gases are causing global warming by slowing the escape of heat into space. However, shorter-term global warming and cooling also occur because of natural climate cycles such as the El Ni?o–Southern Oscillation, according to National Oceanic and Atmospheric Administration.
"Within any given decade ... the temperature bounces around between warm and cool years," reads the agency's website. "The warmest years are usually El Ni?o years, when the eastern and central tropical Pacific is warmer than average. The coldest years are generally La Ni?a years, when that same part of the tropical Pacific is cooler than average."
The fact that 1998 was warmer than 2013 – as stated in the social media post – was largely due to a very powerful El Ni?o event, according to NOAA.
However, global temperatures have clearly increased overall – as have CO2 levels. The two aren't always perfectly in step because global warming due to CO2 is "superimposed" on this natural variability, said Roman.
"It's messy because many complicated natural factors in the Earth system are in play and producing effects at the same time," said Roman. "However, we cannot escape the simple physics – increasing CO2 will inevitably trap more heat in the lower atmosphere, producing an upward trend in surface temperatures overall."
Fact check: Climate change caused by humans, celestial 'magnetic state' not cause of extreme heat
Our fact-check sources:
Howard Diamond, Dec. 29, 2022-Jan. 2, Email exchange with USA TODAY
Michael Roman, Jan. 2-3, Email exchange with USA TODAY
NASA, accessed Dec. 29, 2022, Carbon dioxide
NASA, accessed Dec. 29, 2022, Global temperature
USA TODAY, March 31, 2022, Fact check: Short term global temperature fluctuations do not negate climate science, overall warming
USA TODAY, March 9, 2022, Fact check: Misleading data used in claim alleging a global cooling trend
NASA, accessed Dec. 29, 2022, Causes
NASA, accessed Dec. 29, 2022, World of Change: Global temperatures
Columbia Climate School, Feb. 25, 2021, How Exactly Does Carbon Dioxide Cause Global Warming?
Australian Department of Climate Change, Energy the Environment and Water, accessed Dec. 29, 2022, Understanding climate change
NASA, accessed Dec. 30, 2022, Graphic: The relentless rise of carbon dioxide
NOAA, May 5, 2014, What is the El Ni?o–Southern Oscillation (ENSO) in a nutshell?
Geophysical Research Letters, March 25, 2021, Observational Evidence of Increasing Global Radiative Forcing
Josh Willis, Nov. 23, 2021, Phone interview with USA TODAY
USA TODAY, Dec. 3, 2021, Fact check: Climate change theory compatible with laws of thermodynamics
NASA, March 25, 2021, Direct observations confirm that humans are throwing earth's energy budget off balance
NOAA, Sept. 4, 2018, Did global warming stop in 1998?
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 temperatures and atmospheric CO2 levels correlated
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