The key answer of exercise 4

The root cause of the extreme weather is basically water: too much water. The oceans are the main source of the water in the atmosphere, of clouds and rain. The sun causes water from the oceans to evaporate. The water becomes a vapour, a kind of gas, that surrounds the earth. More heat means more evaporation, which in turn means more energy building up in the atmosphere and thus more possibility of extreme weather.