Researchers have long wondered how our planet's climate shifted 700,000 years ago from 40,000-year long climate cycles to the current 100,000-year long climate cycles. A new study identifies a 'warm' glacial period that would have allowed the accumulation of ice necessary for this important transition.

Our planet has been submitted during the last 700,000 years (ka) to alternating phases of marked glacial and interglacial periods spanning circa 100 ka. The glacials are characterized by the development of large ice-sheets in the northern hemisphere. Prior to 700 (ka), the Earth's climate was governed by 40,000-year cycles with shorter and weaker glacials. The shift between the two cyclicities occurred at the end of a period, called the Middle Pleistocene Transition, dated between 800 and 670 ka. This interval is composed of two interglacial periods interspersed with an ice age. The mechanisms accounting for this key change of cyclicity remain largely unknown as they cannot be attributed to variations in the orbital parameters governing the Earth’s climate.  

Discovery of a warm glacial period which changed the Earth’s climate cyclicity.

In a new study published in the journal Nature Communications that included Teresa Rodrigues, researcher from CCMAR and IPMA, the reasons behind this change in climate cycles during the Middle Pleistocene Transition were uncovered. By combining new climatic records from the South-West Iberian margin with loess records from the Chinese Plateau and model simulations, the study identified a similar long-term warming and wetting trend in the two subtropical regions from 800 to 670 ka.

The study revealed that sea surface temperatures in the North Atlantic and tropical North Pacific Oceans were, at the Middle Pleistocene Transition, paradoxically warmer during the glacial compared to the precedent interglacial, leading to higher moisture production and rainfall, stronger Western Mediterranean forest expansion and enhanced East Asia summer monsoon. This climatic configuration resulted in a supply of oceanic moisture from both oceans to higher latitudes which fed the ice caps and critically contributed to the expansion of Eurasian and North American ice-sheets. Such expansion was necessary to trigger the shift from the 40,000-year cycles to the 100,000-year cycles we experience today, which was critical for the Earth's climate evolution.

Check out the full article here: https://doi.org/10.1038/s41467-023-38337-4

Figure 1 – Long-term increase in Mediterranean forest and precipitation and in the East Asian summer monsoon associated with the increase and northward migration of the Atlantic moisture source. The glacial climate is warmer and wetter than the previous interglacial.