Past warming trend constrains future warming in CMIP6 models.

Area of Science:

• Climate Science
• Earth System Science
• Environmental Modeling

Background:

• Global warming estimates have historically shown consistency across assessments.
• Recent climate models, specifically the Sixth Coupled Model Intercomparison Project (CMIP6), simulate significantly higher warming trends, creating a discrepancy with prior evaluations.

Purpose of the Study:

• To reconcile the divergent warming projections between CMIP6 models and previous assessments.
• To constrain future global warming estimates using observed warming trends from recent decades.

Main Methods:

• Correlating projected future warming with simulated warming trends from recent decades across CMIP5 and CMIP6 models.
• Constraining CMIP6 model outputs based on their consistency with observed historical warming.

Main Results:

• Projected future warming is strongly correlated with simulated recent warming trends across both CMIP5 and CMIP6 models.
• Observationally constrained CMIP6 median warming is substantially lower than raw projections, particularly under high emissions scenarios.
• By 2050, constrained CMIP6 warming is over 16% lower in high emissions scenarios and 14% lower in mitigation scenarios compared to raw CMIP6 median.
• By 2090, constrained CMIP6 warming is over 14% lower in high emissions scenarios and 8% lower in mitigation scenarios.

Conclusions:

• Observationally constrained CMIP6 warming aligns with previous CMIP5 assessments.
• In ambitious mitigation scenarios, the constrained CMIP6 warming range is consistent with achieving the Paris Agreement target.