Clouds reduce downwelling longwave radiation over land in a warming climate

Area of Science:

• Climate Science
• Atmospheric Physics
• Earth System Science

Background:

• Clouds significantly impact Earth's energy balance, influencing climate predictions.
• Cloud radiative feedback is a major source of uncertainty in climate models.
• Understanding land-based cloud feedback is crucial for accurate climate projections.

Purpose of the Study:

• To observationally constrain surface longwave cloud feedback over land.
• To quantify the impact of cloud changes on downwelling longwave radiation.
• To provide a benchmark for validating climate model performance over land.

Main Methods:

• Utilized direct, long-term observations of spectrally resolved downwelling longwave radiance.
• Applied an optimal spectral fingerprinting method to isolate cloud feedback.
• Analyzed data from the Southern Great Plains site and validated with reanalysis and satellite datasets.

Main Results:

• Identified a local negative surface longwave cloud feedback over land.
• Quantified a change of -1.77 ± 1.15 W m⁻² per decade in downwelling longwave radiation due to this feedback.
• Demonstrated that negative surface longwave cloud feedbacks are common over land, linked to decreasing low cloud cover.

Conclusions:

• Cloud changes, particularly decreased low cloud cover, can partially offset warming over land.
• The findings provide a critical observational benchmark for climate model evaluation.
• This research improves our understanding of radiative forcing and feedback mechanisms on land.