by Chris Jack and Anna Taylor

The Earth’s climate is largely driven by radiation from the sun. The amount of radiation the earth receives from the sun varies through time according to differences in the earth’s orbit. Radiation from the sun interacts with the earth’s atmosphere, which is made up of a combination of gases. The main components are nitrogen, oxygen and argon, which remain the in same amounts over time and space. There are much smaller components, like carbon dioxide and water vapour, which vary considerably in amount over both space and time, but play an important role in influencing the climate.

The atmosphere:

  • reflects some incoming radiation back out into space
  • transmits some of the sun’s radiation down to the earth’s surface
  • absorbs radiation coming back out from the earth’s surface
  • emits some of this radiation back to the surface and some of it back out to space

All this is not happening equally across the surface of the earth at any given time. Differential heating causes air to move, resulting in atmospheric circulation. Hot air rises and moves towards the poles, cool air sinks and moves towards the equator. The earth’s rotation and the land mass of the continents complicate things even further. The result is the general circulation patterns that we observe.

The climate has natural variability over many time scales.

Short term variability is the weather that we see day to day, wherever in the world we are. Long term variability takes many forms and is driven by a complex set of processes, for example:

  • El Nino and La Nina periods, which correspond with variations in the temperature structure in the Pacific Ocean over a few years
  • Ice ages and warm “inter-glacial” periods, which correspond with cyclical variations in the orbit of the earth around the sun over many thousands of years