Ancient Climate Secrets Found in Microscopic Shells

Researchers from University of Utah have made significant strides in understanding past climate changes by studying a period between 59 and 51 million years ago, during the transition from the Paleocene to the Eocene epochs. During this time, Earth experienced both gradual and sudden warming periods, known as hyperthermals, driven by massive emissions of carbon dioxide (CO2) and other greenhouse gases. The study, published in the Proceedings of the National Academy of Sciences, explores how these ancient warming events can help predict the impacts of current human-induced climate change.

Lead author Dustin Harper, a postdoctoral researcher in the Department of Geology and Geophysics, emphasizes that these ancient events provide valuable analogs for understanding future climate changes. By analyzing microscopic fossils from drilling cores taken from an undersea plateau in the Pacific, the team reconstructed past sea surface temperatures and atmospheric CO2 levels. They focused on two significant hyperthermals: the Paleocene-Eocene Thermal Maximum (PETM), 56 million years ago, and Eocene Thermal Maximum 2 (ETM-2), 54 million years ago.

Their findings reveal a close link between rising atmospheric CO2 levels and increasing global temperatures. Gabriel Bowen, a co-author and professor of geology and geophysics, notes that the study highlights the sensitivity of the climate system to CO2 changes. Despite some variations, the overall climate response to CO2 increases remains consistent over long-term shifts.

Today, human activities are releasing carbon 4 to 10 times faster than during these ancient events. However, the total amount of carbon released in these ancient hyperthermals is comparable to current projections for human emissions. This suggests that studying these ancient periods might offer insights into what might lie ahead.

The researchers used fossilized remains of foraminifera, single-celled organisms with shells, to estimate past oceanic CO2 levels. These shells, which accumulated boron, provide a proxy for ancient CO2 concentrations. By analyzing the boron chemistry, the team was able to reconstruct past CO2 levels and temperatures, offering a detailed view of the climate system during the PETM and ETM-2.

The study utilized cores from the Shatsky Rise in the North Pacific, an ideal location for preserving ancient ocean-bottom sediments. These sediments offer a clear record of past sea surface conditions, making them invaluable for understanding ancient climate change.

Harper concludes that these findings help to establish new CO2 and temperature records for key ancient climate events, providing a long-term perspective to better understand modern climate change.