Climate scientists rubbish claim humans not responsible for rising CO2 levels

"For the net zero zealots," Craig Kelly posted to his 118,000 followers on X on December 29, 2023.

Kelly, a member of the United Australia Party, has repeatedly spread misinformation about the pandemic.

"The Coronavirus lockdowns led to the biggest fall in global energy demand in 70 years. Global air passenger traffic fell an unprecedented 65%. There are the things the Net Zero zealots dream of achieving," he added.

Net zero refers to cutting emissions of greenhouse gases -- such as carbon dioxide from coal-fired power stations and methane from belching cattle -- to as close to zero as possible.

Any remaining carbon pollution from human sources must be absorbed from the atmosphere by forests, for example, or through experimental technologies that suck CO2 from the air.

Kelly's post compares a graph from the National Oceanic and Atmospheric Administration (NOAA) showing a gradual increase in atmospheric carbon dioxide levels over the past decade, to International Air Transport Association (IATA) figures showing a dramatic drop in air passenger traffic between 2019 and 2020 (archived links here and here).

He concludes: "Perhaps unsurprising as anyone that follows the science understands that 97% of C02 emissions come from natural sources and have nothing to do with fossil fuels."

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Screenshot of the misleading X post, captured on January 18, 2024

Other posts on X and Facebook here and here shared the same claim, prompting comments from social media users who appeared to believe it was true.

"We will stop the fake climate scam agenda," read one comment.

"Stand up to the net zero zealots," read another.

But there is overwhelming scientific consensus that human activity is causing climate change.

The United Nations' Intergovernmental Panel on Climate Change (IPCC) reported in 2021 that "it is unequivocal that human influence has warmed the atmosphere, ocean and land" (archived link).

Oil, gas and coal are responsible for the bulk of heat-trapping greenhouse emissions and scientists say the world must ditch these fossil fuels in order to limit global warming.

'Plain wrong'

Andy Pitman, a climate science professor at the University of New South Wales in Australia, said that while carbon dioxide is emitted from natural sources, human-induced emissions have overwhelmed the planet's ability to absorb carbon through natural processes. 

Humans emit around 40 billion tonnes of additional CO2 per year, which is only partly absorbed by the land and oceans (archived link).

"Those natural systems cannot keep up," he explained.

University of Melbourne climate science professor Malte Meinshausen added that emissions from natural sources "do not lead to warming" and that Kelly's comparison was "plain wrong". 

Scientists also said a temporary decline in carbon emissions from air traffic during the pandemic would not have an impact on carbon dioxide levels in the atmosphere.

"The CO2 in the atmosphere is cumulative over time, so the concentrations do not reflect only emissions during that period of observation, but an accumulation," said Daniel Clarke, a researcher from the Organisation for Economic Co-operation and Development (OECD).

Meinshausen said CO2 levels kept rising during the pandemic because "CO2 in the atmosphere does not disappear but accumulates in the atmosphere, biosphere and the oceans."

Furthermore, aviation only contributes to a small percentage of human-induced carbon dioxide emissions.

"Air traffic is not a large source of atmospheric CO2. Therefore any reduction in air traffic won't show up in the graph," said Hamish McGowan, professor of atmospheric and climate sciences at the University of Queensland.

Aviation was responsible for two percent of global energy-related carbon dioxide emissions in 2022, according to the International Energy Agency (IEA) (archived link).

While global energy-related carbon emissions fell by 5.8 percent in 2020 as the pandemic kicked in, this was not enough to lower CO2 levels in the atmosphere (archived link).

"If we stop emissions completely to zero, then the concentration is going to fall. But if we keep emissions at today's level, or just slightly decreased -- or even at half of today's level -- then CO2 concentration keeps increasing," Meinshausen said.

AFP has previously debunked misinformation about CO2 emissions and climate change here, here and here.