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Abstract Detail

Past Presidents' Symposium: Biodiversity: Past, Present, and Future

Floristic change during a global greenhouse event 56 million years ago: what can we learn about the future?

The Paleocene-Eocene Thermal Maximum (PETM) was an ~200,000-year-long period of rapid carbon release and warming that occurred ~56 million years ago, at the beginning of the Eocene Epoch. The PETM is analogous to extreme scenarios for future anthropogenic global warming in both the amount of carbon released and the increase in global temperature.
Plant fossils, both palynological remains and macrofossils, have been collected from sedimentary rocks deposited during the PETM in many places around the world, with the best-studied and most extensive macrofossil record coming from the Bighorn Basin, in Wyoming, USA. Bighorn Basin plant fossils show radical floristic change during the PETM that was caused by local or regional extirpation of mesophytic plants, notably conifers, and colonization of the area by thermophilic and dry-tolerant species, especially Fabaceae. Hotter and drier conditions during the PETM have also been inferred from fossil soils and geochemical indicators. At the close of the PETM, as climate in the region became cooler and wetter, the floristic change largely reversed itself, with most of the common Paleocene species once again abundant in post-PETM fossil assemblages and most of the PETM immigrant species absent. A few PETM immigrants persisted, however, and some Paleocene species never returned to the region. Less detailed records from other parts of the world show regional variation in floristic response, but are mostly consistent with the Bighorn Basin trends.
The geological record documents that carbon released during the PETM caused major climate change, which in turn caused major changes in where plants lived. The plant fossil record shows geologically rapid extirpation of long-persistent populations, as well as rapid dispersal and establishment of immigrant plant populations. In spite of these rapid changes in range, there appears to have been little extinction during the PETM, suggesting the rate of climate change did not exceed the dispersal capacity of terrestrial plants. Best estimates of the rate of climate change during the PETM are that it was about a tenth as fast as the rate of anthropogenic warming predicted in the centuries to come. Because of its slower rate the PETM likely provides a minimum estimate of extinction levels that might be induced by anthropogenic climate change.

Broader Impacts:

1 - Smithsonian Institution, Dept. of Paleobiology NHB 121, PO Box 37012, WASHINGTON, DC, 20013-7012, USA

Keywords:
global change
climate
Paleobotany
extinction.

Presentation Type: Symposium or Colloquium Presentation
Session: SY12
Location: Grand Ballroom A/Riverside Hilton
Date: Wednesday, July 31st, 2013
Time: 2:45 PM
Number: SY12003
Abstract ID:228
Candidate for Awards:None