simple logic shows that any greenhouse agent (clouds, CO2, CH4, etc) would result in positive net gain. For example suppose clouds reflect 10% of heat. They will reduce sun induced heating by 10% during day (12hr) and decrease cooling by 10% during day and night (24hr). 10% * 12/24 = 5% 10% * 24/24 = 10% 5% < 10%