Chart of historical carbon dioxide levels misleadingly shared by climate change sceptics

The chart was shared here on Facebook on October 30, 2023, in a group called "Australian Climate Sceptics Group" with nearly 7,000 members.

The graph's title and caption both read: "Our current geologic period (Quaternary) has the lowest average CO2 levels in the last 600 million years."

It appears to show historical concentrations of carbon dioxide spanning from the Cambrian period about 541 million years ago, to the current Quaternary period, which began 2.58 million years ago (archived links here and here).

The graph shows the highest carbon dioxide levels during the Cambrian period and the lowest during the most recent span of time.

It includes the logo of a US-based lobby group, CO2 Coalition, which denies human-caused emissions lead to climate change (archived link). AFP has debunked misleading claims by the group's members here.

The same graph has been shared by the group on its official social media accounts since July 2022.

Image

Screenshot of the misleading post, taken November 20, 2023.

The UN's IPCC climate expert panel said in a 2021 report it was "unequivocal" that human influence has warmed the atmosphere, ocean and land -- leading to deadly floods, heatwaves and storms (archived link).

With temperatures soaring and 2023 expected to become the warmest year so far in human history, scientists say the pressure on world leaders to curb planet-heating greenhouse gas pollution has never been more urgent.

Image

Graphs of temperature change since 1850 and simulations including and excluding human influence, and of CO2 concentrations in the atmosphere over the last 400,000 years. ( AFP / Eléonore HUGHES, Jean-Michel CORNU, Simon MALFATTO, Jonathan WALTER)

But the graph of carbon dioxide concentrations continued to be shared more than 300 times in Australia here, here and here, as well as in the United States and Britain, with some users believing it disproved climate change.

"Global warming, end of the world scenarios are the biggest hoax ever played on man kind," read one comment.

"Climate change is the biggest scam ever foisted upon the western population," said another.

Graph 'not too relevant'

The chart made by the CO2 Coalition includes text that reads "Berner 2001" and credits the data to an essay by Robert Berner and Zavareth Kothavala published in the American Journal of Science in 2001 (archived link).

The pair of Yale scientists used proxy data to model atmospheric carbon dioxide on Earth starting from about 541 million years ago to the present, finding that levels of the gas fluctuated throughout the planet's history.

However, Ashleigh Hood of the University of Melbourne's School of Earth Sciences said the graph is "not a very good representation of our current knowledge" that uses a now-outdated model (archived link).

"So yes, CO2 is low today compared to much of Earth's history," Hood said, but emphasised that this "is not really the point".

"The climate and CO2 has never changed as rapidly as today, and this is the real problem."

Her comments echo the IPCC's warning that the scale of recent changes across the climate system as a whole "are unprecedented over many centuries to many thousands of years" (archived link).

According to NASA, human activities have raised carbon dioxide levels by 50 percent in less than 200 years -- greater than the natural increase observed at the end of the last ice age 20,000 years ago (archived link).

Hood said the rapid rate of change left life on Earth with little space or time to adapt, causing all life forms to suffer.

Climate scientist James Renwick of the Victoria University of Wellington told AFP that humans are used to the climate of the past 10,000 years, but our activities have caused the composition of the atmosphere to change rapidly and affect food security as well as the availability of other resources, such as land (archived link).

"All the rules of life we’ve been used to for thousands of years are changing. Concerning," he said on November 10.

AFP has previously debunked similar claims that high carbon dioxide concentrations in the atmosphere of Earth hundreds of millions of years ago showed climate change was part of a natural cycle.

However, Hood said those prehistoric carbon levels could not sustain humans and only single-celled life was present at the time.

'Intolerable future'

According to The Lancet Countdown, a major annual assessment carried out by leading researchers and institutions, the world's still-increasing use of fossil fuels could lead to five times more people dying in extreme heat in the coming decades.

Around 520 million more people will experience moderate or severe food insecurity by mid-century, while mosquito-borne infectious diseases will spread to new areas, according to the projections published on November 14.

UN Secretary-General Antonio Guterres responded to the report by saying that "humanity is staring down the barrel of an intolerable future".

"We are already seeing a human catastrophe unfolding with the health and livelihoods of billions across the world endangered by record-breaking heat, crop-failing droughts, rising levels of hunger, growing infectious disease outbreaks, and deadly storms and floods," he said in a statement.