Talking Climate · The Wilkes Center for Climate Science and Policy

25: Climate Sherlocking: Turning Up Clues from Past Global Warming Events

·34 min·3 clips

Dustin Harper explains how ancient warming triggered carbon feedbacks from sediments and methane, just like today.

Host Ross Chambliss interviews marine geologist Dustin Harper about using ancient climate events to understand modern global warming. Harper is a postdoctoral researcher at the University of Utah who co-authored a study on past hyperthermal events. Their conversation explores how geology provides crucial context for today's anthropogenic climate change. The episode focuses on the Paleocene-Eocene Thermal Maximum, a warming event 56 million years ago where temperatures rose 4-5°C over millennia. Harper and professor Gabe Bowen analyzed microscopic shell fossils from ocean drilling cores to reconstruct past sea surface temperatures and CO2 levels. They studied two hyperthermals, the PETM and a subsequent Eocene event, which serve as analogs for current carbon release but at a rate 4 to 10 times slower than today. A leading hypothesis involves volcanism from the North Atlantic Igneous Province as an initial trigger. Harper's research indicates volcanic activity alone couldn't explain the carbon release, pointing to feedback loops involving organic carbon and methane from sediments. These feedbacks, where warming unlocks more greenhouse gases, created a positive warming cycle. The team used geochemical proxies from the shells of single-celled calcifying organisms to measure past seawater chemistry and temperature. Scientific ocean drilling expeditions, involving international crews on two-month voyages, recovered these core samples from the deep Pacific. One key finding is a climate sensitivity estimate of about 5°C of warming for each doubling of atmospheric CO2 during these abrupt events. This sensitivity was higher during the short-term hyperthermals than over longer multi-million-year periods influenced by tectonic shifts. The PETM world featured palm trees in Antarctica and average ocean surface temperatures exceeding 40°C in some regions. While not a mass extinction, the events stressed deep-ocean calcifiers due to acidification and coincided with mammalian diversification. Harper describes the work as detective work, piecing together evidence from decades of research to solve ancient climate mysteries. He emphasizes that while past events are informative, the current rate of change is unprecedented in the geological record. The discussion offers perspective, noting that human activity is compressing changes comparable to the PETM into centuries rather than millennia. Harper also shares his personal path from a pre-med student to a geologist captivated by fieldwork and chemistry. The tone is educational and conversational, structured as an interview that blends scientific explanation with personal narrative. It maintains a serious but curious atmosphere, focusing on evidence and discovery without being alarmist. Listeners interested in climate science, Earth's deep history, or paleoclimatology will find this episode fascinating. Those seeking solely contemporary policy debates or immediate climate solutions might find the deep-time perspective less directly applicable.

As heard by us

A careful look at deep-time climate evidence and what it says about today.

Talking Climate treats the Paleocene-Eocene thermal maximum as a detective story built from ocean-floor cores and tiny shell fossils. Dustin Harper walks through how statistical models turn geochemical measurements into a picture of past environments, and he keeps the…

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You want a detective story about 56-million-year-old warming that still speaks to modern carbon release.

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