The “warm ice age” that reshaped climate cycles

Earth scientists have identified a pivotal step in the Earth’s subsequent climatic evolution.

Roughly 700,000 years ago, the “Warm Ice Age” caused a permanent shift in Earth’s climate cycles. This unusually hot and humid period coincided with a significant expansion of the polar glaciers.

A team of European researchers, including geoscientists from the University of Heidelberg, used newly obtained geological data and computer models to decipher this seemingly paradoxical relationship. The researchers suggest that this massive shift in Earth’s weather patterns led to changes in climate cycles and marked a major advance in the subsequent climatic history of our planet.

The research vessel “Joides Resolution” – here in the port of Lisbon – has been used since 1985 as part of the International Ocean Discovery Program for scientific prospecting. The drill samples used in the current “Warm Ice Age” study were taken during an expedition in the Gulf of Cadiz and off southern Portugal. Credit: Andre Bahr

Geological ice ages – called ice age periods – are characterized by the development of large ice sheets in the northern hemisphere. In the past 700,000 years, phases have shifted between distinct glacial and warm periods every 100,000 years. Before then, Earth’s climate was governed by 40,000-year cycles with shorter, weaker glacial periods. The change in climate cycles occurred in the Middle Pleistocene transition, which began approximately 1.2 million years ago and ended about 670,000 years ago.

The mechanisms responsible for this critical change in the global climate rhythm are still largely unknown. It cannot be attributed to differences in the orbital parameters that govern the Earth’s climate,” explains Associate Professor Dr. Andre Barr of the Institute of Geosciences at the University of Heidelberg. “But the recently identified warm ice age, which caused the accumulation of continental ice excess, also played a role. decisive.”

Long-term expansion of Mediterranean forests and increased precipitation as well as an increase in the summer monsoon in East Asia associated with the northward increase and migration of a moisture source in the Atlantic Ocean. Ironically, the glacier was much warmer and wetter than in the previous Ice Age. Credit: Andre Bahr

In their investigations, the researchers used new climate records from core drilling off Portugal and loess records from the Chinese plateau. Then the data was entered into computer simulations.

The models show a long-term trend of warming and wetting in both subtropical regions over the past 800,000 to 670,000 years. Concurrent with this last glacial period of the Middle Pleistocene transition, sea surface temperatures in the North Atlantic and northern equatorial Pacific were much warmer than in the preglacial period, the stage between the two ice ages.

This has led to increased moisture production and precipitation in southwestern Europe, expansion of Mediterranean forests, and an increase in the summer monsoon in eastern Asia. Moisture has also reached the polar regions, where it has contributed to the expansion of the ice sheets in northern Eurasia.

“They persisted for some time and ushered in the phase of continuous and far-reaching glaciation of the Pleistocene that lasted until the late Pleistocene. Such an expansion of continental glaciers was necessary to bring about the shift from the 40,000-year cycles to the 100,000-year cycles we see today, which were crucial to the evolution of the climate Earth later,” Andre Barr stated.

Reference: “Wet and Warm Conditions in Eurasia During the Last Glacial Phase of the Middle Pleistocene Transition” By María Fernanda Sanchez Goni, Thomas Exeter, Josey M. Polanco Martinez, Coralie Zorzi, Teresa Rodriguez, Andre Parr, May 10, 2023, Available Here. Nature Communications.
DOI: 10.1038/s41467-023-38337-4

Scientists from Germany, France, Spain and Portugal contributed to the research. The work was funded by the German Research Foundation.