Research from a team of scientists led by Dr Rieneke Weij from the Human Evolution Research Institute (HERI) at the University of Cape Town (UCT), and Dr Kale Sniderman from the University of Melbourne, shows past ice ages across much of the Southern Hemisphere were wetter than today and may have been ideal environments for plants, animals, and early humans over the last 350,000 years.
The work, published in the renowned journal Nature, challenges long-held assumptions that ice age climates were cold, dry and inhospitable periods during which life struggled to survive.
The findings are based on data derived from Uranium-Thorium dating of speleothems, or cave carbonates such as stalagmites and stalactites, from two cave sites in southern Australia. These benchmarks were then compared with other reliable climate records from southern Australia, southern Africa, and South America.
The results revealed surprising yet consistent trends over the last 350,000 years, with wetter times occurring within cooler, glacial periods (ice ages), and interglacial periods being consistently dry in the subtropical regions of the Southern Hemisphere (from 20° to 40° south).
“This suggests that, for these regions, glacial periods were relatively stable environments with abundant water resources, which may have supported the lives of plants, animals and early humans,” says Weij.
The team also studied fossil pollen trapped within the speleothems. That work revealed confirming evidence that moisture-demanding plants thrived during these glacial periods but were suppressed during interglacial periods.
Understanding past changes in climate and the environment of the Southern Hemisphere has historically been limited by a lack of well-dated and long-term records. This research not only adds new data but debunks long-held assumptions about what ice age environments were like.
Indeed, for over 50 years glacial environments have globally been characterised as cold, dry and inhospitable for many life forms, including humans. This was based on evidence from the Northern Hemisphere showing huge ice sheets spread across the northern parts of Europe, northern Asia, and North America during glacial periods, while large areas south of the ice were covered with tundra.
“We now know that the Southern Hemisphere subtropics did not follow this Northern Hemisphere concept, which calls for a paradigm shift in how we view past ice age environments across the Earth,” says Weij.
For southern Africa, with its rich record of human evolution, this kind of big picture climate data is essential for painting an accurate picture of the past, says HERI co-Director Dr Robyn Pickering.
“Dr Weij and her team have shown that the Southern Hemisphere is not simply an inverted version of the Northern Hemisphere, with distinct and much more complex reactions to global ice ages, which until now were not fully recognised,” says Pickering.
“Because our species, Homo sapiens, appeared during this time, understanding more about our distant relatives' world is a vital piece of the puzzle of how we came to be the diverse and successful species we are today.”
Publication:
Weij, R., Sniderman, J.M.K., Woodhead, J.D., Hellstrom, J., Brown, J.R., Drysdale, R.N., Reed, E., Bourne, S. & Gordon, J. (2024). Elevated Southern Hemisphere moisture availability during glacial periods. Nature. 626(7998), 319-326. https://doi.org/10.1038/s41586-023-06989-3