Global temperatures have been both much higher and much lower than the current average, and understanding paleoclimatic variations is important as they provide valuable analogues for models of future climate change.
This study examines two transient warming events—the Paleocene-Eocene Thermal Maximum (PETM) and the Eocene Thermal Maximum (ETM2)—in which the temperature increased by 4-8°C for periods of less than 200,000 years each.
Applying pollen and spore microfossil analyses of marine sediment cores from nearly 400 metres below the Arctic Ocean seabed, researchers reconstructed the terrestrial vegetation of PETM and ETM2. Using a bioclimatic analysis of GBIF-mediated occurrences of modern living relatives assumed to have similar climatic niches, the authors then derived climate parameters during the two events.
Based on pollen taxa present and bioclimatic reconstructions, the study provides evidence of Arctic broad-leaved swamp forests during both PETM and ETM2. PETM mean annual temperatures and mean winter temperatures were both ~2 to 3.5°C warmer than the late Paleocene.