Ice Age Data and CO2 Levels Debunked in Climate Skeptic’s Claim

ice age data and co2 levels debunked in climate skeptic s claim.jpg Science

In the midst of heated debates on climate change, a recent post on social media platform X, formerly known as Twitter, has sparked controversy. The post features a video of Ian Plimer, a known climate change skeptic with connections to the mining industry, downplaying the significance of current atmospheric CO2 concentrations. Plimer’s statement, quoted in the video’s caption, claims that "six of the six great ice ages started when we had more carbon dioxide in the atmosphere than now", suggesting that a decrease in CO2 levels would lead to the extinction of all plant and animal life. The post has since been shared widely, with over 300 shares on Facebook in seven weeks and more than 9,000 reposts on X.

However, the veracity of Plimer’s claim is under scrutiny. While it’s true that plants and animals have existed in periods where CO2 levels were half of what they are today, the assertion about the "six great ice ages" is more complex. The post doesn’t specify which periods these ice ages refer to, and while there have been times when the Earth’s climate cooled despite high CO2 levels, the Quaternary glaciation, considered by some scientists as a "major ice age", is believed to have started when atmospheric CO2 concentration was lower than today’s levels. In the world of paleoclimatology, the term "ice age" can refer to a range of events, adding another layer of confusion to Plimer’s statement.

Debunking the Myths about CO2 Levels and Ice Ages

A recent video making rounds on social media, featuring Ian Plimer, a climate change skeptic with mining industry ties, has sparked significant conversation. Plimer claims that six of the ‘great ice ages’ began when atmospheric CO2 was higher than today and warns of a potential mass extinction if CO2 levels were cut in half. This article aims to explore the validity of these claims, based on expert opinions and scientific findings.

Examining the ‘Great Ice Ages’ Argument

Plimer’s assertion of ‘six great ice ages’ happening when CO2 levels were higher is difficult to assess, primarily because he doesn’t specify which ice ages he is referring to. This term varies in its usage among scientists, as it can denote long periods with significant ice cover or specific times within these periods when the ice volume was larger.

Ashleigh Hood, a sedimentologist and paleo-environmental scientist at the University of Melbourne, states that it’s challenging to reconstruct deep past climates accurately. According to her, the best climate records available only cover the last hundreds of thousands to millions of years.

Yige Zhang, a paleoclimatologist at Texas A&M University, points out that the Quaternary glaciation, considered by some as a ‘major ice age’, started approximately 2.6 million years ago when CO2 concentrations were lower than today.

What About CO2 Concentrations?

The claim that atmospheric CO2 levels have been as high as 20% in the past is not definitively proven. If such high CO2 levels ever existed, it would have been billions of years ago, according to Hood. If CO2 concentration rose to 20% today, "the oceans would likely boil," says Marcus Lofverstrom, a hydrology and atmospheric science professor at the University of Arizona.

The Impact of Lower CO2 Levels on Life

The video also claims that halving present-day CO2 levels (about 420 ppm) would cause all plant and animal life to die. However, history shows that life has survived in lower CO2 atmospheres. For instance, during the Last Glacial Maximum, around 21,000 years ago, CO2 concentration was approximately 185 ppm, yet life continued.

The Importance of the Rate of Change

While it’s true that CO2 levels have varied throughout Earth’s history, the current rapid increase due to human activities is causing significant global warming. This fast rate of change does not afford ecosystems enough time to adapt, leading to increased heat waves, sea level rise, and polar and glacial ice melt. As Hood notes, rapid environmental and climate changes in Earth’s history are typically associated with mass extinction events.


This examination shows the importance of scrutinizing sweeping claims, especially those related to complex systems like Earth’s climate. While it’s true that CO2 levels have varied across history, it’s crucial to consider the rate of change and the specific conditions present during different eras. Moreover, the survival of life at lower CO2 levels in the past invalidates the claim of a mass extinction at half of today’s CO2 concentration. Lastly, it’s essential to remember that the current rapid rise in CO2 due to human activity is a significant concern that requires immediate attention.

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