Fifty-six million years ago, Earth entered a truly extreme phase of rapid global warming. This uncomfortably warm stretch is called the Paleocene-Eocene Thermal Maximum (PETM). Temperatures skyrocketed like never before during this extreme event. The main culprit was the enormous influx of carbon into the atmosphere and oceans. This unprecedented period of climatic change will alter the world of plants radically. It will similarly take a toll on animal pollinators, demonstrated by an exceptional fossil record found in Wyoming.
During the PETM, Earth’s global temperatures quickly increased by about 6°C and stayed that high for more than 100,000 years. This era is an especially important reference point with which to compare today’s climate changes. That’s because the carbon release during the PETM was gradual. By comparison, the current human-driven climate change is occurring at least 10 times faster.
Causes of the Paleocene-Eocene Thermal Maximum
The PETM was triggered by large geological changes, including intense volcanic activity and the release of methane from ocean sediments. In these last 5,000 years, an enormous amount of additional carbon has poured into the atmosphere. This increase has caused a greenhouse effect—human-induced warming—that has fundamentally altered the planet’s climate.
Science shows that the carbon levels in the atmosphere at this time were exponentially different than what we see today. Today’s concentrations of carbon dioxide, methane, and nitrous oxide are the highest they have been in over 2.5 million years. Through the past century and a half, human endeavors have increased atmospheric CO2 levels by over 40%. This concentration increase has already contributed to global warming of more than 1.3°C.
Importantly, the pace at which carbon was released during the PETM is much slower than the rate we’re currently emitting carbon today. This unique historical perspective allows scientists to identify the potential long-term effects of today’s climate actions.
Impacts on Flora and Fauna
The warming connected with the PETM allowed plants from dry tropical climates to spread into new landscapes. This change in plant distribution had damning effects on animal life—especially for pollinators. As re-vegetation took place, pollinators followed, evolving with the bloom of the plants on which they relied on for food.
Fossil evidence from places like the Bighorn Basin in Wyoming capture these changes in stunning detail. Today, that topography has revealed the rich badlands of the region, full of fossilized sediments that have preserved clumps of pollen. This fossil pollen provides a crucial window into past climate. It provides insight into how plants and their pollinators evolved in response to extreme climatic shifts during the PETM.
“Clumps of pollen recovered from the Bighorn Basin, Wyoming, USA.” – The Conversation
This monumental evidence reflects how ancient ecosystems experienced extreme changes from climate change. It argues that pollinator species were able to rapidly evolve in step with new environments as their plant relatives moved to meet their needs.
Lessons for Today’s Climate Crisis
The Paleocene-Eocene Thermal Maximum is an important touchstone in our understanding of the connection between climate change and biodiversity. For the first time, modern humans are rapidly increasing the amount of greenhouse gases in our atmosphere. Climatologists are making comparisons between what happened then and what’s happening now.
As it is now, the current rate of rise in atmospheric carbon dioxide concentrations already endangers our ability to recreate past warming trajectories. Owing to the great pace of change, many species will likely experience struggles just like those they went through in the PETM. The ability of pollinators to be resilient and adapt will be crucial in figuring out how ecosystems are able to cope with these fast-paced changes.
Pollinators are key to our planet’s ecological balance and agricultural productivity. By understanding their past-adaptive responses to climate change, we might better inform our conservation strategies. That knowledge will lead us to better strategies for protecting these essential species as temperatures continue to rise.