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Exploring the Effects of Atmospheric Forcings on Evaporation: Experimental Integration of the Atmospheric Boundary Layer and Shallow Subsurface

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Observational and model evidence for positive low-level cloud feedback.

Amy C Clement¹, Robert Burgman, Joel R Norris

¹Rosenstiel School of Marine and Atmospheric Sciences, University of Miami, Division of Meteorology and Physical Oceanography, MSC 362, 4600 Rickenbacker Causeway, Miami, FL 33149, USA. aclement@rsmas.miami.edu

Science (New York, N.Y.)

|July 25, 2009

Summary

This summary is machine-generated.

Low-level clouds create uncertainty in climate models. This study found observed clouds act as a positive feedback, with one model supporting this, showing reduced cloud cover with increased greenhouse gases.

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Area of Science:

Atmospheric science
Climate modeling
Ocean-atmosphere interactions

Background:

Low-level clouds are a major source of uncertainty in global climate model projections.
Understanding cloud feedbacks is crucial for accurate climate change predictions.

Purpose of the Study:

To examine changes in low-level clouds over the Northeast Pacific using observations and climate models.
To test the realism of cloud simulations in current climate models.

Main Methods:

Analysis of decadal fluctuations in multiple, independent low-level cloud datasets.
Correlation of observed cloud cover changes with local temperature structure and large-scale circulation.
Evaluation of climate models based on their ability to reproduce observed cloud-meteorological relationships.

Main Results:

Decadal fluctuations in low-level cloud cover were identified in independent observational datasets.
Observed cloud cover changes were linked to regional temperature structure and large-scale atmospheric circulation.
One climate model successfully reproduced observed relationships, simulating reduced Pacific cloud cover under increased greenhouse gases.

Conclusions:

Observations indicate low-level clouds act as a positive feedback on decadal timescales in the Northeast Pacific.
The study provides a method for testing climate model realism regarding cloud feedbacks.
Modeling evidence suggests a positive low-level cloud feedback mechanism in a warming climate.