Around 56 million years ago, the climate warmed at nearly the same rate as today, with an explosive rise in CO2 levels, resulting in prolonged disruption of terrestrial ecosystems. Ferns replaced conifers as the dominant vegetation, and there was widespread erosion and wildfires. These findings have been reconstructed by researchers from NIOZ and Utrecht University following analyses of pollen and other sediment traces from the so-called Palaeocene–Eocene Thermal Maximum (PETM) period in the Norwegian Sea (PNAS, 19 January). ‘Ecosystems on land were disrupted for thousands of years; an increase in charcoal shows that more wildfires occurred. An increase in clay minerals in the marine sediment also indicates that entire stretches of land were washed into the sea through erosion’, says biologist and lead author Mei Nelissen in an accompanying press release.
The layered sediments in the drill cores collected in 2021 make it possible to reconstruct in detail – and even season by season – what happened 56 million years ago when the world warmed by five degrees in a short space of time. Within at most three hundred years of the onset of the explosive rise in CO2, the conifer-dominated vegetation disappeared and an enormous spike in fern spores emerged. These were predominantly representatives of the fern family Gleicheniaceae, which are characteristic of disturbed and fire-prone environments. ‘CO2 emissions are now rising some two to ten times as fast’, warns Nelissen. ‘In geological terms, such a rate is unprecedented.’ Earlier research has already established that during the PETM the oceans acidified dramatically, causing particular problems for marine organisms that form calcareous skeletons or shells.