A recent extensive study indicates that the Earth’s current levels of carbon dioxide, attributed to human activities, have not been consistently observed in the atmosphere for approximately 14 million years. Published in the journal Science, the research spans from 66 million years ago to the present, employing biological and geochemical data to reconstruct the historical CO2 levels with unprecedented accuracy. Lead author Baerbel Hoenisch emphasizes the uniqueness of contemporary human-induced CO2 emissions, highlighting the significant deviation from Earth’s historical patterns.
The analysis reveals that the last instance of atmospheric carbon dioxide reaching 420 parts per million (ppm) occurred between 14-16 million years ago, a period marked by the absence of ice in Greenland and the early transition of human ancestors from forests to grasslands. This timeframe significantly predates previous estimations of 3-5 million years. Prior to the late 1700s, atmospheric CO2 stood at around 280 ppm, indicating a 50 percent increase due to human activities, resulting in a 1.2 degrees Celsius rise in global temperatures since the industrial era.
Hoenisch underscores the brief evolutionary timeline of Homo sapiens, emphasizing our species’ adaptation to the existing sea levels, warm tropics, cool poles, and temperate regions with abundant rainfall. Projecting into the future, the study warns that if global CO2 emissions persist, levels could reach 600-800 ppm by 2100. Such concentrations were last witnessed 30-40 million years ago during the Eocene, a time before Antarctica was ice-covered, and the planet hosted a vastly different array of flora and fauna.
The research, conducted over seven years by an international consortium of 80 researchers across 16 countries, consolidates existing data into an updated consensus within the scientific community. Employing proxies such as the chemical composition of ancient leaves, minerals, and plankton, the study provides insights into carbon levels beyond the reach of traditional ice core analyses.
The study confirms that Earth’s warmest period occurred 50 million years ago when CO2 levels spiked to 1,600 ppm, resulting in temperatures 12 degrees Celsius higher. This was followed by a prolonged decline. About 2.5 million years ago, carbon dioxide stabilized at 270-280 ppm, initiating a series of ice ages. This relatively stable level persisted until the advent of large-scale fossil fuel burning by modern humans.
Anticipating a potential doubling of CO2 and its long-term impacts, the research estimates a warming of 5-8 degrees Celsius over hundreds of thousands of years. The study underscores the relevance of its findings for policymakers, emphasizing the potential for prolonged consequences similar to Earth’s past experiences, unless effective measures are taken to sequester carbon dioxide and curb emissions promptly.
