1. The problem statement, all variables and given/known data The air is at 50% humidity and the temperature of the surface of the ocean and the air is 20degrees C. What are the two critical processes that must occur to ensure there is continued evaporation in the absence of external energy sources? 2. Relevant equations Relative humidity = partial pressure of water vapour in air / vapour pressure 3. The attempt at a solution I am sure that there would be net evaporation of water until the equiilibrium is reached so that the relative humidity becomes 100%. Surface of ocean and the air is at same temperature so I assume that the temeperature of water must increase so that the relative humidity just above the surface becomes lower but since there is no external energy source, I have no idea... Please help!