Bright clouds are probably caused by gases such as methane rising in the atmosphere and condensing into highly reflective clouds of methane ice. (keckobservatory.org)
CO2 is of course particulary insidious as it stays clear, it doesn't condense out forming reflective clouds as H2O does. (realclimate.org)
«The increased breaks in the clouds, fewer clouds and less reflective clouds produced the amount of warming we were looking for.» (sciencedaily.com)