Moderate climate sensitivity due to opposing mixed-phase cloud feedbacks.

Area of Science:

• Climate Science
• Atmospheric Science
• Earth System Science

Background:

• Earth's climate sensitivity, the temperature change from doubled atmospheric CO2, has an uncertainty range of 2.3°C to 4.7°C.
• The representation of clouds, particularly mixed-phase clouds, in climate models is a major source of this uncertainty.

Purpose of the Study:

• To adjust the climate sensitivity of contemporary climate models.
• To reduce biases in the representation of mixed-phase clouds using satellite observations.
• To reassess the role of mixed-phase cloud cover changes in climate sensitivity.

Main Methods:

• Utilized satellite observations to identify and correct biases in mixed-phase cloud representation within climate models.
• Adjusted the climate sensitivity parameters of individual climate models based on observational data.
• Analyzed the opposing responses of cloud liquid and cloud cover to CO2 doubling.

Main Results:

• A moderate average climate sensitivity of 3.63 ± 0.98°C was calculated after model adjustments.
• Increasing liquid proportion in cold clouds enhanced climate sensitivity through phase transitions.
• Increased reflective cloud cover significantly decreased climate sensitivity, counteracting other effects.

Conclusions:

• The study provides a refined estimate of climate sensitivity by addressing cloud representation errors.
• Opposing cloud responses, specifically cloud phase transitions and cloud cover changes, critically influence climate sensitivity.
• Reconsidering the impact of mixed-phase cloud cover changes is essential for accurate climate sensitivity assessments.