Mid-Pleistocene transition in glacial cycles explained by declining CO₂ and regolith removal

Area of Science:

• Paleoclimatology
• Climate Dynamics
• Earth System Science

Background:

• Quaternary glacial-interglacial cycles are paced by Earth's orbital variations (Milankovitch cycles).
• The precise mechanisms translating orbital forcing into global climate shifts, particularly ice age cycles, are not fully understood.
• Understanding these mechanisms is crucial for predicting future climate change.

Purpose of the Study:

• To investigate the coevolution of climate, ice sheets, and the carbon cycle over the past 3 million years.
• To identify the key factors driving the transition in glacial-interglacial cycle periodicity.
• To reconstruct past atmospheric CO2 concentrations and global temperature variations.

Main Methods:

• Transient climate simulations integrating ice sheet and carbon cycle dynamics.
• Modeling Earth's climate system over the past 3 million years.
• Analysis of simulated climate variability and its relationship with orbital forcing and CO2 levels.

Main Results:

• A gradual decrease in atmospheric CO2 and regolith removal are essential for simulating Quaternary climate variability.
• Long-term CO2 decline initiated Northern Hemisphere glaciation and amplified glacial-interglacial cycles.
• The combined effects of CO2 decline and regolith removal explain the shift from 41,000-year to 100,000-year cycles.

Conclusions:

• Atmospheric CO2 levels over the past 3 million years have not exceeded current concentrations.
• Global temperatures during the Quaternary period did not surpass preindustrial levels by more than 2°C.
• Orbital forcing alone is insufficient; internal Earth system feedbacks, particularly the carbon cycle, are critical for glacial-interglacial dynamics.