Ancient CO2 Rise Caused Catastrophic Forest Dieback

A significant dieback of forests occurred approximately 56 million years ago, triggered by a rapid and substantial rise in atmospheric carbon dioxide (CO2) levels, according to research published online on August 13, 2026, in the journal Nature. This ancient event, known as the Paleocene-Eocene Thermal Maximum (PETM), saw global temperatures increase by 5-8 degrees Celsius and atmospheric CO2 concentrations surge to levels comparable to or exceeding those projected for the near future. The study, which analyzed fossilized plant evidence from various locations, indicates that this abrupt warming and elevated CO2 had catastrophic consequences for forest ecosystems worldwide, leading to widespread vegetation stress and mortality.

The research highlights that the rapid increase in CO2, estimated to have occurred over a period of thousands of years, overwhelmed the adaptive capacity of many plant species. Evidence from fossilized leaves shows signs of stress, such as reduced stomatal density and altered growth patterns, suggesting that plants struggled to cope with the combined effects of higher temperatures and increased CO2. While elevated CO2 can, under certain conditions, stimulate plant growth, the study emphasizes that the speed and magnitude of the PETM's CO2 rise, coupled with extreme heat, created an environment where the negative impacts far outweighed any potential benefits. This led to a significant decline in forest cover and biodiversity, with some regions experiencing near-total ecosystem collapse.

Scientists draw direct parallels between the PETM event and contemporary climate change. Today's atmospheric CO2 levels are rising at an unprecedented rate, driven by human activities, and are projected to reach levels seen during the PETM within this century. The current warming trend, although driven by different mechanisms, is also leading to increased global temperatures and associated climate stresses such as droughts, heatwaves, and altered precipitation patterns. The findings from the PETM study serve as a stark warning about the potential vulnerability of modern forests to rapid climate shifts. The research suggests that current forest ecosystems may face similar widespread dieback and ecological disruption if atmospheric CO2 continues to rise unchecked.

The implications of this ancient event for modern plant life are profound. The study underscores that the rate of environmental change is a critical factor in ecosystem resilience. Forests that are already stressed by pollution, habitat fragmentation, and other human impacts may be particularly susceptible to the effects of rapid climate change. Understanding the mechanisms of forest dieback during the PETM can help scientists predict how current forest ecosystems will respond to future climate scenarios and inform conservation strategies aimed at enhancing forest resilience. The research, published with the DOI 10.1038/d41586-026-02544-y, provides a long-term perspective on the devastating impact of rapid greenhouse gas increases on the planet's vegetation.