Observationally Constrained Cloud Phase Unmasks Orbitally Driven Climate
Feedbacks
Abstract
The mechanisms which amplify small orbitally driven changes in
insolation and drive the glacial-interglacial cycles of the past 2.7
million years are poorly understood. Previous studies indicate that
cloud feedbacks oppose ice sheet initiation at times when orbital
configuration supports ice sheet growth. A recent study in which cloud
phase was observationally constrained by satellite measurements provides
evidence for a weaker opposing cloud feedback than previously found in
response to carbon dioxide doubling (Tan et al., 2016). We
observationally constrain cloud phase in the Community Earth System
Model. We find a weaker cloud phase feedback, which unmasks water vapor
and cloud feedbacks that extend cooling to lower latitudes. Snowfall
accumulation and ablation metrics also support ice sheet expansion as
seen in proxy records. Our results indicate that well understood cloud
and water vapor feedbacks are the amplifying mechanism driving orbital
climates.