The Impact of Global Warming on Marine Boundary
Layer Clouds over the Eastern Pacific
A. Lauer1, K. Hamilton1, Y. Wang1, V. Phillips2, and R. Bennartz3
1IPRC, 2U.
Hawaii, 3U. Wisconsin
The local cloud feedback parameter λ
computed from simulations with 15
global
coupled
ocean–atmosphere
climate models and iRAM (lower right
panel).
λ is calculated from the differences in net
cloud forcing (ΔCFnet) between the end of
the 21st century (IPCC SRES A1B scenario)
and present-day conditions.

CFnet  W 


Tsurface  m 2 K 
State-of-the-art global climate models (GCMs) display a wide range of temperature sensitivity to largescale climate forcings. This variation in global climate sensitivity is largely attributable to differences in
cloud feedbacks, especially the feedbacks of low-level clouds. The eastern Pacific with its two large and
persistent stratocumulus decks is particularly important in determining the cloud-climate feedback. The
IPRC regional atmospheric model (iRAM) performs much better in reproducing observed cloud fields in
this region than current GCMs. When forced by boundary conditions from a global warming scenario
iRAM shows a distinct thinning of the low clouds and reduction in cloud coverage. This makes a strong
positive contribution to the global cloud climate feedback.