Surface measurements find more downward infrared radiation warming the planet's surface. (skepticalscience.com)
As far as water vapor in the tropics, they even say» In the humid equatorial regions, where there is so much water vapour in the air that the greenhouse effect is very large, adding a small additional amount of CO2 or water vapour has only a small direct impact on downward infrared radiation.» (climateaudit.org)
Detailed studies of the energy balance and ablation of the Zongo and Chacaltaya glaciers support the importance of air temperature increase, and identify the increase in downward infrared radiation as the main way that the effect of the warmer air is communicated to the glacier surface [Wagnon et al. 1999; Francou et al, 2003]. (realclimate.org)