A simple rule to determine which insolation cycles lead to interglacials

Area of Science:

• Paleoclimatology
• Quaternary geology
• Climate dynamics

Background:

• Glacial-interglacial cycles of the Quaternary period (last 2.6 million years) are paced by astronomical changes in high-latitude insolation.
• The precise mechanism linking astronomical forcing to the sequence of interglacials remains unclear.

Purpose of the Study:

• To investigate how astronomical forcing translates into the observed sequence of interglacials during the Quaternary.
• To explain the shift in glacial-interglacial cycle frequency around one million years ago.

Main Methods:

• Analysis of insolation thresholds for deglaciation.
• Development of a statistical model to predict deglaciation events.
• Comparison of model predictions with paleoclimate records.

Main Results:

• Before one million years ago, interglacials occurred when summer insolation exceeded a 41,000-year threshold.
• Over the past million years, a rising deglaciation threshold led to skipped insolation peaks and longer glacial periods.
• A statistical model accurately predicts all deglaciations in the past million years.

Conclusions:

• The observed sequence of interglacials is one of a limited set of possibilities governed by insolation thresholds.
• Increased ice sheet size over the past million years resulted from a higher deglaciation threshold and more skipped insolation peaks.
• The model explains the shift from obliquity dominance to a different pacing around one million years ago.