Unsettled

In order to study the climate, we also have to study the atmosphere, the ocean, the cryosphere and the biosphere. Weather and climate are not the same; as the early 20th century saying goes: ‘Climate is what you expect, weather is what you get’. In order to illustrate the difference between weather and climate, the author provides the example of a person who moves from Wisconsin to southern Arizona. Being familiar with the climates of the two areas will help them decide whether to install an air conditioner or a heater in their home, and whether to plant cacti or water-loving plants in their garden. It will not help them decide whether to take an umbrella when they go out for a walk; that is what the weather forecast is for.

The weather changes all the time, sometimes more predictably than others, and can vary during the course of the same day, from one day to the next, through the seasons, and even from one year to another. The climate of an area, on the other hand, is determined by looking at the average weather in a given place over several decades.

The climate therefore changes much more slowly than the weather, and sometimes with very small variations. The climate also varies from place to place depending on a number of factors, including latitude, since it is colder at the poles; altitude, because it is colder in the mountains; proximity to water; and the influence of ocean currents. Urban agglomerations and their size are also variables that can lead to local climate change.