Feedbacks involving low-level clouds remain a primary cause of uncertainty in global climate model projections.  This issue is addressed by examining changes in low-level clouds over the NE Pacific in observations and models. Decadal fluctuations are identified in multiple, independent cloud datasets, and show that changes in cloud cover are linked to changes in both local temperature structure and large-scale circulation. This observational analysis indicates that clouds act as a positive feedback in this region on decadal timescales.
The observed relationships between cloud cover and regional meteorological conditions provide a more complete way of testing the realism of the cloud simulation in current generation climate models.
The only model that passes this test simulates a reduction of cloud cover over much of the Pacific when greenhouse gases are increased, providing modeling evidence for a positive low-level cloud feedback.