Study Shows Historical CO2 Increases Linked to Past Climate Changes

Daniel Novakovič/STA

Original article (in Slovenian) was published on 13/5/2024; Author: Žan Premrov

According to a 2020 study published in the Proceedings of the National Academy of Sciences, the current rise in atmospheric carbon dioxide concentrations closely resembles the increase that occurred 56 million years ago, when average temperatures surged by 5 to 8 degrees Celsius.

On April 26, Triglav Media published an article entitled Climate alarm: truth or hoax? in which they shared a link to the documentary Climate: The movie (Cold truth). The claimed that the documentary “also shows that there is no evidence that changing CO2 levels (which have changed many times) have ever ’caused’ climate change in the past”. 

The Slovenian Environment Agency told Razkrinkavanje.si that carbon dioxide is “one of the most important causes of change in the Earth’s history, and the main driver of change since the Industrial Revolution”. They pointed out that global temperature changes over the last several hundred thousand years have coincided with changes in CO2 concentrations of the atmosphere. 

Direct measurements of atmospheric CO2 have been carried out since 1958, they explained, while historical temperature data, such as those from the Museum of Natural History in Washington, DC, are most often obtained by analysing oxygen isotopes in fossilized plankton. 

Fossilized plankton is suitable for calculating historical atmospheric CO2 levels, according to the authors of a study published in 2020 in the Proceedings of the National Academy of Sciences. They found that atmospheric CO2 concentrations more than doubled as a result of volcanic eruptions 56 million years ago, and average temperatures rose by 5 to 8 degrees Celsius during that period. 

The authors consider this event to be the best natural proxy for the current increase in CO2 levels caused by human activities. They also pointed out that the pace of change is much more rapid than it was 56 million years ago.

The impact of CO2 on climate change in the past was also determined by the authors of a study published in 2017 in the scientific journal Geology. According to their findings, CO2 and temperature also increased between 27 million and 22 million years ago. 

Triglav Media furthermore argued that the current level of CO2 in the atmosphere is extremely and unusually low compared to the last 500 million years. As we reported in January this year, current atmospheric CO2 concentrations are the highest since measurements began, and also the highest in two million years, according to the United Nations Intergovernmental Panel on Climate Change (IPCC).

In response to our queries, Triglav Media replied that there are different opinions among scientists “about whether we are actually in the midst of a ‘climate crisis’ and whether this ‘crisis’ is caused by human CO2 emissions”.

As we reported last August, a 2021 study by scientists at Cornell University in the US found that more than 99% of peer-reviewed scientific research published since 2012 confirm that climate is affected by human activity. The authors collected more than 88,000 such studies and finally analyzed a random sample of 2,718 papers, of which only four denied human influence on the climate.

Triglav Media’s claim that there is no evidence that changes in CO2 levels in the past have caused climate change is not true.