Antarctica had a subtropical climate, suggest scientists who have pulled up proof that palm trees once grew there. Study of pollen and spores and the remains of tiny creatures have given a climatic picture of the early Eocene period, about 53 million years ago.
The early Eocene was a period of atmospheric CO2 concentrations higher than the current 390 parts per million (ppm )- reaching at least 600ppm and possibly far higher.
The study published in Nature suggests Antarctic winter temperatures exceeded 10C, while summers may have reached 25C.
“There are two ways of looking at where we’re going in the future. One is using physics-based climate models; but increasingly we’re using this ‘back to the future’ approach where we look through periods in the geological past that are similar to where we may be going in 10 years, or 20, or several hundred,” James Bendle of the University of Glasgow, a co-author of the study, told BBC News.
Drilling research carried out in recent years showed that the Arctic must have had a subtropical climate.
But looking for similar evidence in Antarctic has been a challenge. Glaciation 34 million years ago wiped out much of the sediment that would give clues to past climate, and left kilometres of ice on top of what remains.
Now, the Integrated Ocean Drilling Program (IODP) has literally got to the bottom of what the Eocene Antarctic was like, dropping a drilling rig through 4km of water off Wilkes Land on Antarctica’s eastern coast.
The rig then drilled through 1km of sediment to return samples from the Eocene. With the sediment came pollen grains from palm trees and relatives of the modern baobab and macadamia.
Crucially, they contained also the remnants of tiny single-celled organisms called Archaea.
The creatures’ cell walls show subtle molecular changes that depend on the temperature of the soil surrounding them when they were alive. The structures are faithfully preserved after they die.
They are, in essence, tiny buried thermometers from 53 million years ago.