Last Glacial Maximum pattern effects reduce climate sensitivity estimates

Area of Science:

• Paleoclimatology
• Climate Modeling
• Earth System Science

Background:

• Equilibrium climate sensitivity (ECS) quantifies global warming from greenhouse gases.
• ECS feedbacks depend on spatial temperature patterns, known as "pattern effects."
• Understanding LGM cooling patterns is key to constraining modern climate sensitivity.

Purpose of the Study:

• To use Last Glacial Maximum (LGM) data to constrain equilibrium climate sensitivity (ECS).
• To account for "pattern effects" in LGM climate reconstructions and models.
• To refine ECS estimates for future global warming predictions.

Main Methods:

• Combining data assimilation reconstructions with atmospheric models.
• Analyzing spatial patterns of surface temperature during the LGM.
• Quantifying how LGM cooling patterns differ from modern warming feedbacks.

Main Results:

• The climate system is more sensitive to LGM forcing due to ice sheet amplification of extratropical cooling.
• Accounting for LGM pattern effects yields a median ECS of 2.4°C (1.7°–3.5°C).
• Integrating LGM evidence with other data refines the best ECS estimate to 2.9°C (2.4°–3.5°C).

Conclusions:

• The LGM provides a robust constraint on ECS when pattern effects are considered.
• This study significantly narrows uncertainty in ECS estimates compared to recent assessments.
• Refined ECS estimates improve predictions of future global warming.