An increase in air temperature leads to an increase in evaporation as warmer air is able to hold more moisture. Incredibly, this means that since 1950, there is more moisture in the atmosphere, to the tune of about 2kg or 2 litres per every square metre of earth's surface. The total volume of water that has been evaporated is equivalent to twice the volume of Lake Erie - in other words, climate change has essentially boiled of Lake Erie twice over.
What does this mean? This means more humid summers and more likelihood of increasing heat index above danger levels.