Effects of Rapid Global Warming at the Paleocene-Eocene Boundary on Neotropical Vegetation

Hot Tropical Explosion The Paleocene-Eocene Thermal Maximum (PETM), 55 million years ago, was a unique episode of rapid global warming (∼5°C), often used as an ancient analog for future global climate change. Climate alteration during the PETM has been extensively studied in the marine realm, and from a few temperate to polar terrestrial localities, but little is known about how the tropics responded to the high temperatures and high levels of CO2. Using evidence from pollen analysis, Jaramillo et al. (p. 957) show that rapid tropical forest diversification occurred during the PETM, without plant extinction or regional aridity. Unexpectedly, diversity seemed to increase at higher temperatures, contradicting previous assumptions that tropical flora will succumb if temperatures become excessive. Palynology shows that tropical forests persisted under conditions of rapid climate warming 55 million years ago. Temperatures in tropical regions are estimated to have increased by 3° to 5°C, compared with Late Paleocene values, during the Paleocene-Eocene Thermal Maximum (PETM, 56.3 million years ago) event. We investigated the tropical forest response to this rapid warming by evaluating the palynological record of three stratigraphic sections in eastern Colombia and western Venezuela. We observed a rapid and distinct increase in plant diversity and origination rates, with a set of new taxa, mostly angiosperms, added to the existing stock of low-diversity Paleocene flora. There is no evidence for enhanced aridity in the northern Neotropics. The tropical rainforest was able to persist under elevated temperatures and high levels of atmospheric carbon dioxide, in contrast to speculations that tropical ecosystems were severely compromised by heat stress.