The increased warmth allows the atmosphere to hold more water vapour so that total atmospheric density increases and the atmospheric greenhouse effect strengthens. (newclimatemodel.com)
Therefore it will cause more evaporation, leading to more water vapour which is also a greenhouse gas. (realclimate.org)
As the climate warms, warmer temperatures and more open water will mean more water vapour entering the atmosphere — itself a powerful greenhouse gas. (newscientist.com)