This is the lapse rate (the rate of change of the temperature in the gases in the atmosphere along different altitudes) of a mass of moist air as it rises in the atmosphere. This rate begins to slow as the dew point is reached and condensation forms. This rate of cooling goes from 4 degrees C/km all the way to 9 degrees C/km depending on humidity. Contrast with the dry adiabatic lapse rate which is 9. 8 degrees C per km of rise. The saturated lapse rate is always less than the dry rate because the lapse rate (cooling) is less for air that contains water vapor which releases its latent heat as it cools, suppressing the cooling.