A group of climatologists and an astronomer have collaborated on a research project to gain a deeper understanding of the glacial periods that occurred 1.6 to 1.2 million years ago. By utilizing an enhanced computer model, they have successfully replicated the cycle of ice ages during that time period. Surprisingly, their findings reveal that the glacial cycle was primarily influenced by astronomical forces in a manner distinct from the mechanisms observed in the present era. This breakthrough will significantly contribute to our comprehension of past, present, and future ice sheets and Earth’s climate.
Over time, the Earth’s orbit around the sun and its spin axis undergo gradual changes due to the gravitational pull exerted by celestial bodies such as the sun, moon, and other planets. These astronomical forces impact our environment by altering the distribution of sunlight and seasonal variations. Notably, ice sheets exhibit sensitivity to these external forces, leading to alternating periods of glaciation and interglacial periods.
The current glacial-interglacial cycle spans approximately 100,000 years. However, during the early Pleistocene era, roughly 800,000 years ago, the glacial cycle shifted more rapidly, occurring in cycles of approximately 40,000 years. While it was previously acknowledged that astronomical forces were responsible for this alteration, the specific mechanisms behind it remained elusive. Recent advancements in geological data analysis and theoretical research have facilitated a more detailed exploration of the role played by astronomical forces.
Under the leadership of Yasuto Watanabe from the University of Tokyo, the team focused on the early Pleistocene epoch spanning 1.6 to 1.2 million years ago. Employing an improved climate computer model, they incorporated state-of-the-art astronomical forces based on modern theories into their simulations. These extensive numerical simulations successfully replicate the 40,000-year glacial cycle observed in the geological records from the early Pleistocene period.
Through their analysis of the simulation results, the research team has unveiled three significant insights into the mechanisms by which astronomical forces influenced the climate during that era.
- The glacial cycle’s characteristics were determined by subtle disparities in the Earth’s spin axis orientation and orbital variations.
- The timing of deglaciation was primarily dictated by the position of the summer solstice on the Earth’s orbit, particularly when it coincided with perihelion. This timing was not solely influenced by the periodic changes in the Earth’s axis tilt.
- The duration of the interglacial period was determined by the timing of the changes in the spin axis orientation and the position of the summer solstice on the Earth’s orbit.
Takashi Ito, a member of the research team from the National Astronomical Observatory of Japan, emphasized the importance of comprehending the role of astronomical forcing in the Earth’s distant past, as evidence from older geological periods sheds light on different climatic regimes.
The numerical simulations conducted in this study not only successfully replicated the glacial-interglacial cycle of the Pleistocene era but also provided a comprehensive understanding of the intricate effects of astronomical forcing during that time. This work marks a crucial starting point for the investigation of glacial cycles that extend beyond the Earth’s present-day conditions.
The findings of this study have been published in the journal Communications Earth & Environment.