In large urban cities, tropospheric ozone is a pollutant that is capable of forming thick smog. Increases in tropospheric ozone can lead to warming because it is a greenhouse gas. Warming of the planet will probably lead to more water vapor in the atmosphere. The increased water vapor has the potential to lead to further warming. The amount of water vapor in part determines the types and distribution of clouds that form in the atmosphere.
Clouds can lead to cooling by reflecting incoming solar radiation.
Increased water vapor and clouds may act as positive or negative feedbacks in future greenhouse-warming scenarios. The potential affect of increased water vapor remains uncertain. The most obvious consequence of an enhanced greenhouse effect is that of increasing temperature. Records of average temperature change show an increase over the past century. The global increase is not steady but erratic.