Context for interpreting equilibrium climate sensitivity and transient climate response from the CMIP6 Earth system...

Area of Science:

• Climate Science
• Earth System Modeling
• Atmospheric Physics

Background:

• Coupled Model Intercomparison Project Phase 6 (CMIP6) models exhibit a broad range of equilibrium climate sensitivity (ECS), from 1.8°C to 5.6°C.
• The transient climate response (TCR) range in CMIP6 is similar to previous generations, yet ECS shows unprecedented variability.

Purpose of the Study:

• To review and synthesize recent developments in ECS and TCR values within CMIP.
• To compile and analyze the reasons provided by modeling groups for current ECS and TCR values.
• To identify future research directions for climate modeling.

Main Methods:

• Analysis of CMIP6 model outputs for ECS and TCR.
• Synthesis of information provided by modeling groups regarding model behavior.
• Review of scientific literature on climate feedback mechanisms.

Main Results:

• CMIP6 models display the largest range of ECS observed since the 1990s.
• The TCR range for CMIP6 models is only marginally wider than in CMIP3 and CMIP5.
• Cloud feedbacks and cloud-aerosol interactions are identified as primary drivers for the increased ECS range in CMIP6.

Conclusions:

• The significant increase in ECS range in CMIP6 is largely attributed to advancements and uncertainties in representing cloud feedbacks and aerosol interactions.
• Further research into these processes is crucial for refining climate projections and reducing uncertainty in climate sensitivity estimates.