Humans are responsible for a significant amount of CO2 in the atmosphere | Fact check
The claim: CO2 is 0.04% of the atmosphere and humans have contributed only 3% of that
A May 26 Instagram video (direct link, archive link) shows an Australian broadcaster talking about climate change and economic policy on a talk show.
"How much carbon dioxide is the problem," he asks. "How much carbon dioxide is in the atmosphere? It's 0.04%. And of that 0.04%, human beings around the world create 3%. And of that 3%, Australia creates 1.3%. So, for the 1.3% of the 3% of the 0.04%, we then decide to have a national economic suicide."
The video was liked more than 8,000 times in four weeks.
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Our rating: Partly false
The atmosphere is roughly 0.04% CO2, but humans have contributed about 33% of that, not 3%, since 1850. Australia has contributed around 1.4% of accumulated human CO2 emissions during that timeframe ? similar to the number stated in the video. However, that's 1.4% of around 33%, not 1.4% of 3% (or 1.3% of 3%) as claimed in the video. The overall proportion of CO2 in the atmosphere is relatively small, but researchers say the total amount of CO2 is more important than its proportion as it relates to climate change.
Humans responsible for significant portion of CO2 in the atmosphere
CO2 levels in the atmosphere have reached 421 parts per million, or 0.0421%, according to NASA. That's similar to the amount the person in the video claims is in the atmosphere.
However, the claim that humans are only responsible for 3% of that CO2 is wrong, according to Gavin Schmidt, a NASA climate scientist and director of the Goddard Institute of Space Studies.
In 1850, the atmospheric CO2 concentration was about 280 parts per million. The increase to the current level of 421 parts per million is all a result of human activity, Schmidt told USA TODAY in an email.
So roughly a third, not 3%, of the CO2 currently in the atmosphere has been contributed by humans since 1850.
Fact check: Global temperatures and atmospheric CO2 levels are correlated, contrary to claim
Australia was responsible for about 1.4% of human emissions between 1850 and 2021, according to Carbon Brief. This is close to what is stated in the video. But, again, that's 1.4% of one-third of the amount of CO2 currently in the atmosphere, not 1.4% of 3% (or 1.3% of 3%) as claimed in the video.
Additionally, between 1990 and 2019, Australia's per capita CO2 emissions from industry, land use change and agriculture were among the highest in the world, outpacing the U.S., China and Russia, according to Climate Watch.
For climate change, total amount of CO2 is more important than proportion of CO2
The video implies the relatively small proportion of CO2 in the atmosphere can't drive climate change.
However, in the context of climate change, the proportion of CO2 in the atmosphere is less relevant than the total amount of CO2 in the atmosphere, Grant Petty, a professor at the University of Wisconsin-Madison and author of two textbooks on atmospheric physics, told USA TODAY in an email.
That's because atmospheric CO2 molecules trap heat in the atmosphere by intercepting energy released from Earth's surface. The molecules then re-emit the energy, but some emit it back toward Earth instead of allowing it to escape into space.
"The ability to trap infrared heat depends on the probability of a photon (energy) from the surface encountering a greenhouse gas molecule – so the more molecules, the more trapping," Schmidt said. "Thus, it is the total amount of CO2 that matters, not so much its concentration. On Mars, for instance, the air is 95% CO2, but there is much less air – 150 times less than the amount on Earth – so the greenhouse effect is much less."
Humans contributed more than 1 trillion metric tons of CO2 to the atmosphere through fossil fuel emissions and land use changes between 1850 and 2022, according to the 2022 Global Carbon Budget.
Fact check: Climate change theory compatible with laws of thermodynamics
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."
Global warming causes global sea level rise because warming ocean water expands. Additionally, melting glaciers and ice sheets have increased the amount of water in the oceans.
USA TODAY reached out to the Instagram user who shared the post for comment but did not immediately receive a response.
The claim was also debunked by AFP.
Our fact-check sources:
Gavin Schmidt, June 7, Email exchange with USA TODAY
Grant Petty, June 7, Email exchange with USA TODAY
Pierre Friedlingstein, June 12, Interview with USA TODAY
Josh Willis, Jan. 17, Email exchange with USA TODAY
Simone Alin, June 9, Email exchange with USA TODAY
Rob Jackson, June 12, Email exchange with USA TODAY
Pep Canadell, June 11, Email exchange with USA TODAY
European Union, Dec. 5, 2019, Trends in atmospheric concentrations of CO2 (ppm), CH4 (ppb) and N2O (ppb), between 1800 and 2017
USA TODAY, Dec. 5, 2021, Fact check: Human-generated CO2, not water vapor, drives climate change
The Australian, accessed June 2, Alan Jones
NOAA, June 3, 2022, Carbon dioxide now more than 50% higher than pre-industrial levels
NOAA, accessed June 8, Carbon Cycle
NOAA, May 12, Climate Change: Atmospheric Carbon Dioxide
NASA Vital Signs of the Planet, accessed June 2, Carbon dioxide
NASA Vital Signs of the Planet, accessed June 8, Ice sheets
NASA, July 15, 2021, How Much Carbon Dioxide Are We Emitting?
NASA, Oct. 9, 2019, The Atmosphere: Getting a Handle on Carbon Dioxide
NASA, accessed June 8, Understanding sea level thermal expansion
Our World in Numbers, accessed June 2, Cumulative CO2 emissions by world region
The Conversation, July 31, 2020, John Tyndall: the forgotten co-founder of climate science
Carbon Brief, Dec. 13, 2017, Analysis: Why scientists think 100% of global warming is due to humans
Carbon Brief, Oct. 5, 2021, Analysis: Which countries are historically responsible for climate change?
Carbon Brief, April 28, 2021, Melting glaciers drove ‘21% of sea level rise’ over past two decades
Global Carbon Project, 2022, Global Carbon Budget 2022
National Geographic, accessed June 8, Carbon sources and sinks
Australian Government Department of Climate Change, Energy and Environment and Water, accessed June 8, Understanding climate change
MIT Climate Portal, Jan. 4, 2022, How much carbon dioxide does the Earth naturally absorb?
Our World in Data, Oct. 1, 2019, Who has contributed most to global CO2 emissions?
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This article originally appeared on USA TODAY: Humans have significant impact on atmospheric CO2 | Fact check
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