Carbon Dioxide Today Is at Historically Low Levels in Earth’s Geological History

Some 4.5 billion years ago, Earth’s atmosphere was primarily composed of carbon dioxide, with a CO₂ concentration (as measured today) of approximately one million parts per million (i.e., 1,000,000 ppm) compared to about 420 ppm today. Some 500 million years ago, the CO₂ concentration fell to around 7,500 ppm, about eighteen times today’s levels. Between twenty-five million and nine million years ago, the CO₂ atmospheric concentration appeared to have varied between 180 and 290 ppm. With the inception of the Industrial Revolution, the air’s CO₂ content increased to above 400 ppm registered today.[1]

Daniel H. Rothman, a professor at the Department of Earth, Atmospheric, and Planetary Sciences at MIT, published an important paper in the Proceedings of the National Academy of Sciences in 2002.[1] His research established that over most of the geologic record of the past 500 million years, Earth’s CO₂ concentration fluctuated between values two to four times greater than those of today. However, over the past 175 million years, the data shows a long-term decline in the air’s CO₂ content. Again, we encounter an inherent problem with time-series analysis. What is the proper period to identify the actual trends the data reflects? Since the inception of the industrial age CO₂ levels in the atmosphere have risen. Yet, the trend if we look back over the past 175 million years is different. If we look back over the past 175 million years, the CO₂ levels in the atmosphere have continued to drop, including through today.

Still, IPCC adherents want to blame global warming and climate change disasters on human beings burning increasing amounts of  hydrocarbon fuels since the dawn of the industrial age. The argument demands that IPCC adherents can establish CO₂ levels today are at historically high levels.  From the evidence just presented, this argument fails when we examine the scientific evidence of atmospheric CO₂ concentrations over the history of geological time. As we have just noted, the scientific evidence is not clear the industrial age burning of hydrocarbon fuels has caused a rise in atmospheric CO₂ levels. Looking over the past 175 million years, CO₂ levels today have continued to drop, such that the recent rise since the industrial age does not change the trend curve when the time-series analysis extends back millions of years. In other words, to make their argument work, IPCC adherents fall into a classic trap of time-series statistics by choosing a time period for their analysis that is nonrepresentative of the data as a whole.  Clearly, with the historical record of CO₂ in Earth’s atmosphere going back 4.5 billion years, the trend curve of CO₂ concentrations dropping over the past 175 million years receives further confirmation.

[1] Daniel H. Rothman, “Atmospheric carbon dioxide levels for the past 500 million years,” Proceedings of the National Academy of Sciences of the United States of America (PNAS), Volume 99, Number 7 (April 2, 2020), pp. 4167-4171, https://www.pnas.org/content/99/7/4167.

[1] Data on carbon dioxide concentrations in Earth’s atmosphere over geological time are summarized here: C.D. Idso, R.M. Carter, and S.F. Singer, editors, Climate Change Reconsidered II: Physical Science (Chicago, Illinois: The Heartland Institute, 2013), p. 151. Contemporary readings of CO₂ concentrations are drawn from NOAA research at the Mauna Loa Observatory. See: NOAA Research News, “Carbon dioxide peaks near 420 parts per million at Mauna Loa Observatory,” Research.NOAA.gov, June 7, 2021, https://research.noaa.gov/article/ArtMID/587/ArticleID/2764/Coronavirus-response-barely-slows-rising-carbon-dioxide.