About 700,000 years ago, a “warm ice age” caused a permanent change in Earth’s climate cycles. This extremely hot and humid phase coincided with the significant expansion of the polar ice caps. A team of European researchers, including geophysicists from the University of Heidelberg, used recently available geological data and computer models to decipher this seemingly paradoxical relationship. The researchers suggest that this massive change in Earth’s weather patterns led to changes in climate cycles and marks a significant advance in our planet’s subsequent climate history.

Geological ice ages – the so-called ice ages – are characterized by the development of large ice sheets in the Northern Hemisphere. During the last 700,000 years, the phases alternated between distinctly glacial and warm periods approximately every 100,000 years. But before that, Earth’s climate was dominated by 40,000-year cycles with shorter and weaker ice ages. A change in climate cycles occurred during the Middle Pleistocene transition period, which began about 1.2 million years ago and ended about 670,000 years ago.

“The mechanisms responsible for this critical shift in global climate rhythm are largely unknown. They cannot be related to changes in orbital parameters that determine Earth’s climate,” explains Dr. Andre Bar, associate professor of Heidelberg University Earth Sciences Institute. “However, the ‘warm ice age’ recently described, which caused the accumulation of excess continental ice, played a crucial role.”

Long-term expansion of Mediterranean forests and increased precipitation, as well as intensification of the East Asian summer monsoon, associated with increased Atlantic moisture supply and its northward migration. Paradoxically, the ice age was warmer and wetter than the previous interglacial period. Author: Andre Bar

For their research, the researchers used new climate data from a drilling core near Portugal and loess records from the Chinese Plateau. It was then submitted to computer simulation.

The models show a long-term trend of warming and wetting in both subtropical regions over the last 800,000-670,000 years. Concurrent with this last ice age of the middle Pleistocene transition, sea surface temperatures in the North Atlantic and tropical Pacific were higher than in the previous interglacial period between the two ice ages.

This led to increased moisture production and precipitation in southwestern Europe, expansion of Mediterranean forests, and increased summer monsoons in East Asia. Moisture also reached the polar regions of northern Eurasia, where it contributed to the expansion of the ice sheets. These continued for some time and predicted a permanent and extensive glaciation phase of the Ice Age that lasted until the Late Pleistocene. This expansion of continental glaciers was necessary for the transition from the 40,000-year cycles to the 100,000-year cycles we have today, and it was crucial to the later evolution of Earth’s climate,” says Andre Bar.