Challenges simulating the AMOC in climate models.

Area of Science:

• Climate Science
• Oceanography
• Atmospheric Science

Background:

• The Atlantic Meridional Overturning Circulation (AMOC) is projected to decline this century, but with low confidence in magnitude.
• Model biases in mean climate state impact AMOC's state, variability, and climate change response.
• Reducing model biases is critical for accurate AMOC change predictions and impact assessments.

Purpose of the Study:

• To discuss how model biases, particularly salinity biases, influence the AMOC and deep convection.
• To analyze biases in the UK HadGEM3-GC3-1 climate model and their dependence on resolution.
• To highlight priorities for improving climate model representation of key oceanographic processes.

Main Methods:

• Review of existing research on AMOC and climate model biases.
• Analysis of salinity biases and their impact on deep convection.
• Examination of model resolution effects on AMOC biases in the HadGEM3-GC3-1 model.

Main Results:

• Salinity biases significantly influence AMOC and deep convection.
• Model biases in the HadGEM3-GC3-1 model are sensitive to resolution.
• Ongoing model development aims to address identified biases.

Conclusions:

• Understanding and reducing model biases, especially salinity-related ones, is essential for improving AMOC projections.
• Improved representation of processes like North Atlantic Current position and eddy dynamics is needed.
• Addressing biases in climate models will reduce uncertainty in future AMOC changes and climate impacts.