A team of scientists, including climatologists and an astronomer, have used a better computer model to recreate the pattern of ice ages (periods of extreme cold) that occurred 1.6 to 1.2 million years ago. They found that the cycles of ice ages were mainly caused by astronomical forces, but in a different way than what's happening today. This research will help us learn more about the history, current state, and future of ice sheets and the Earth's climate.
The Earth's position and orientation with respect to the Sun and other planets change over time due to gravity. These changes affect the environment on Earth by altering the amount and distribution of sunlight and changing the seasons. As a result, ice sheets on Earth are influenced by these changes, leading to a cycle between cold and warm periods called glacial and interglacial periods.
Scientists have been studying the changes in the Earth's climate over a long period of time. They have found that the Earth's orbit and spin axis orientation change slowly due to the pull of gravity from the Sun, Moon, and other planets. These changes cause differences in the amount of sunlight that reaches different parts of the Earth and result in cycles of glacial and interglacial periods. In the past, the cycle of ice ages changed more rapidly than it does today, and scientists have been trying to understand why. Recent advancements in research have allowed them to investigate the role of astronomical forces in more detail.
A group led by Yasuto Watanabe from the University of Tokyo used a better computer model to study the early Pleistocene Epoch between 1.6 and 1.2 million years ago. The team included the most current theory of astronomical forces in their simulations. Their simulations were large and accurately replicated the 40,000-year glacial cycle seen in geological record data from the early Pleistocene.
The research team has discovered three key facts about how astronomical forces caused changes in the climate during the early Pleistocene Epoch. Firstly, the cycle between glacial and interglacial periods was influenced by small differences in the amplitude of variation of the Earth's spin axis orientation and orbit. Secondly, the timing of deglaciation was mainly determined by the position of the summer solstice on its orbit, which is at perihelion, and not just by the effect of the periodical change of the tilt of the Earth's axis. Lastly, the timing of the change in the Earth's spin axis orientation and the position of the summer solstice on its orbit affected the duration of the interglacial period.
Takashi Ito, a member of the research team and leader of the discussion on astronomical external forces, suggests that as new geological evidence emerges from older times, it is becoming increasingly evident that the Earth's climate in the distant past was different from what it is today. Ito adds that the numerical simulations carried out in this study not only accurately replicate the glacial-interglacial cycle of the early Pleistocene, but also explain the complex effects of how astronomical forcing drove the cycle at that time. This study can be seen as a starting point for studying glacial cycles beyond the present-day Earth.
These results appeared as Watanabe Y. et al. "Astronomical forcing shaped the timing of early
Pleistocene glacial cycles" in Communications Earth & Environment on May 15, 2023.