We came across the following post on the social media site X:

The post features a video of Dr. Patrick Moore, who is described as a ‘Greenpeace co-founder’, being interviewed about climate change, during which he states that ‘we are replenishing the CO2 (carbon dioxide) back to the air and water, where it came from in the first place’, suggesting that human activity is restoring carbon dioxide to natural levels. Greenpeace is an independent organisation that was founded in Canada to raise awareness and advocate for environmental causes.

Further expanding on his claims, Moore says that ‘carbon dioxide is lower now that it has been for almost the entire history of the Earth, and it is colder now—it is called the Pleistocene Ice Age for a reason—it is colder now that it has been through almost the entire history of the Earth’.

Moore adds that CO2 levels were at 6,000 ppm (parts per million) historically, and that it gradually reduced to 180 ppm during the most recent glacial maximum, only 30 ppm above CO2 levels that would cause the death of plants.

‘There is no evidence whatsoever that carbon dioxide is the control knob of the Earth’s climate’, Moore asserts.

An Old Tale

When we did a keyword search on the topic, we found that similar claims have been circulating on the Internet, which may be expected given the proliferation of conspiracy theories around climate change, including some that we have debunked.

We found a Reuters Fact Check from January 2024 which investigated a claim originally circulated by a US-based climate sceptic group in 2022, and which later resurfaced on Facebook. The claim suggested that ‘Carbon dioxide is the lowest it’s been in 600,000,000 years’.

Reuters Fact Check, which determined that the claim was misleading, found that the claim ‘omits the rise in human-driven CO2 levels over the past 150 years and simplifies Earth’s climate history to provide a misleading account of current climate challenges’.

Charting Historical CO2 Levels

Moore’s statement that the Earth’s atmospheric CO2 levels reached 6,000 ppm historically is within the range of scientific estimates, though it is not as relevant to climate change today as he makes it out to be.

When we investigated the claim, we found studies from 1997 and 2001 by the scientist Robert Berner of Yale University and other scientists that indicated that atmospheric CO2 was estimated to be over 20 times current levels around 500 million years ago.

With atmospheric CO2 above 300ppm at the time of the studies, this would mean that atmospheric CO2 was estimated to be about 6,000ppm 500 million years ago.

The Earth at the time cited was very different from it is today. During the Cambrian period (542 to 485.4 million years ago), global temperatures were about 10 degrees higher than they are today. During the Ordovician period (488.3 to 443.8 million years ago), sea levels were as much as 220 metres higher than they are today.

Exact calculations of past CO2 levels are not possible, with the estimates becoming more uncertain the further back in time we look. Robust evidence for the calculation for atmospheric CO2—which requires surviving ice cores containing trapped air bubbles—exists for only as far back as 800,000 years ago.

Moreover, Homo Sapiens only arrived on the Earth 400,000 years ago at the earliest, and the first species in the Homo line—Homo Habilis, arrived on Earth 2.8 million years ago, when the atmospheric CO2 concentration was between 200 to 300ppm.

Using the Right Measure

When measured against a timeline for which strong evidence exists for the atmospheric carbon dioxide levels, it is clear that present-day CO2 levels are unnatural and do correlate strongly with the Earth’s temperatures.

These are demonstrated on charts available on a NASA webpage, which show that carbon dioxide levels and Antarctic temperatures in the last 800,000 years follow similar trends.

Another chart by NASA demonstrates how current atmospheric CO2 levels are far above any level encountered in the last 800,000 years.

Current measurements find CO2 to measure 425.79 ppm. The last time CO2 levels were this high was 3 million years ago, when temperatures were 2 degrees higher than they are today.

While it is true that temperatures now are lower than they have been for much of the Earth’s history, current projections suggest that climate change will cause temperatures within the next few decades to exceed anything experienced for millions of years.

Paul Olsen, a geologist at Columbia University, emphasises that while life on Earth experienced far higher levels of CO2 and temperatures than they do today, it does not mean that the current trends are natural or sustainable.

‘Throughout most of the Earth’s history, carbon dioxide levels have generally changed very slowly. That gave organisms and their ecosystems sufficient time to adapt to climate change through both evolution and migration’, he said.

While the carbon dioxide in the atmosphere, including from the burning of fossil fuels, originates from natural sources, the changes caused by human activity would likely have taken thousands of years to occur, and humans are emitting carbon dioxide far faster that the Earth’s natural sinks are able to remove it.

In essence, humans have returned millions of years of sequestered carbon to the atmosphere in less than 300 years.

Not a Greenpeace Expert

We investigated Moore’s background due to the claim that he was a Greenpeace co-founder and environmental expert. In doing so, we found that like his claims, his credentials were also misleading.

A Snopes fact-check from 2019 found that while Moore was one of Greenpeace’s ‘earliest and more influential members’, he did not co-found the organisation. He left the group in 1986 as his views diverged from the rest of the organisation, and has since been paid to represent several entities or causes that Greenpeace opposes.

Greenpeace also issued a statement in 2010 indicating that Moore ‘does not represent Greenpeace’ and that he exploits his former ties with the organisation to misrepresent himself to the media as an environmental expert or as an environmentalist. Greenpeace also detailed instances where Moore had provided inaccurate information regarding the nuclear industry, for which he was a paid spokesperson.

In recent times, Moore has gained prominence after opposing the Green New Deal proposals that call for public policy in the US to address climate change. His views were found to have gained an audience with the former president and current presidential candidate Donald Trump.

Climate Change—The Details Matter

To conclude, we find that while Moore’s claims contain some elements of truth, they are highly misleading, and that the core of his claim that climate change is returning CO2 levels to historical levels natural for humans is false.

Human activity is changing the atmosphere far faster than it has changed throughout history, and the high CO2 levels experienced in the past, while ‘natural’, are unlike anything that humans have experienced or survived.