Carbon dioxide is one of the gases generally known as “greenhouse” gases because of their propensity to capture heat within the troposphere, the lowest layer of our atmosphere. Without greenhouse gases, our planet would freeze over (see above).
Water vapour is, in fact, a more potent greenhouse gas than CO2 and one that we can see and feel in action virtually every day. When there are no clouds (water vapour), the day is generally warmer. In fact, we can feel the difference when a cloud passes in front of the Sun. We can feel the temperature drop, even if just for a short time. We are in the shadow of the cloud as it absorbs the heat. Conversely, cloud at night keeps the atmosphere warmer than on a cloudless night. It traps the heat radiating out from the surface of the Earth.
Can a tiny amount of a gas in the atmosphere affect temperature on Earth? Water vapour does.
But can humans affect climate?
I lived in London for four years when I was in my 20s. Winter in England is cold and, in some ways, bleak. Snow falls through most of the country in winter. But it rarely snows in London itself. In fact, while I was there, Australians celebrated – to the amusement of locals – when we saw snow in London. It was a rare excitement. Yet snow falls regularly in the surrounding counties of Kent, Essex, Middlesex and Surrey. Why not often in London? The city – as many cities – generates an enormous amount of heat from the buildings, lights, business and sheer amount of humanity throughout the year. The heat is so great that it increases the ambient temperature immediately above and around. The phenomenon even has a name, the urban heat island.
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