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Shortwave forcing and feedbacks in Last Glacial Maximum and Mid-Holocene PMIP3 simulations
Pascale Braconnot1, Masa Kageyama2
1Laboratoire des Siences du climat et de l'Environnement, Orme des Merisiers, bât. 712, Gif-sur-Yvette Cedex 91191, France pascale.braconnot@lsce.ipsl.fr.
Summary
Simulations of past climates reveal that cloud and surface albedo feedbacks significantly impact climate model results. Differences in feedback strength across climate periods hinder direct comparisons of past and future climate sensitivity.
Area of Science:
- Paleoclimatology
- Climate Modeling
- Earth System Science
Background:
- Climate simulations of past periods like the Last Glacial Maximum and Mid-Holocene offer insights into climate dynamics.
- Understanding climate feedbacks is crucial for improving future climate projections.
Purpose of the Study:
- To analyze climate feedbacks during radically different past climate states.
- To investigate the role of model physics and biases in simulating past climates.
Main Methods:
- Simulating the Last Glacial Maximum (21,000 years ago) and Mid-Holocene (6,000 years ago) climates.
- Analyzing cloud, surface albedo, land-surface, and vegetation feedbacks across different climate models.
- Comparing model results with observational data for the Mid-Holocene using IPSL model versions.
Main Results:
- Shortwave cloud feedback is a primary driver of inter-model differences.
- Land-surface feedback shows significant disparities among models, while sea-ice and snow feedbacks are consistently positive.
- Vegetation feedback exhibits high model sensitivity and regional variability, influenced by model complexity and biases.
Conclusions:
- Direct comparison of past and future climate sensitivity is limited by differing feedback strengths across climate periods.
- Past climate simulations, particularly the Mid-Holocene, can be used to assess model biases and physics.
- Model intercomparison highlights the 'fingerprint' of model physics on simulated climate changes.
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