We’re used to hearing about humangenerated carbon dioxide contributing to the greenhouse effect, but the major greenhouse gas in Earth’s atmosphere is actually water. A planet’s temperature is determined by the balance between the incoming solar energy and the heat that’s radiated away. If our atmosphere didn’t contain any water, the energy flowing in and out would be balanced at an average temperature of -18°C. Water vapour in the atmosphere diverts some of the outgoing heat (via the greenhouse effect), and shifts the balance point to a far more pleasant 14°C. Human-generated greenhouse gases are now nudging the average temperature even higher.
Water helps our planet stay at a balmy average of 14°C