Latitude and energy balance

The two main features of the Earth's energy balance are that:

  • there is a net gain of solar energy in the tropical latitudes and a net loss towards the poles
  • tropical latitudes receive more of the Sun's energy than polar regions

You can see in the graph below that there is a surplus of energy between 35˚ North and 35˚ South. In this region, incoming insolation exceeds outgoing radiation.

Radiation intensity (Joules) graph

There's an energy deficit between 35˚ North and the North Pole, and between 35˚ South and the South Pole. Here the outgoing radiation exceeds incoming insolation.

Insolation rises sharply from approximately 50 joules at the poles to 275 joules at the equator. Terrestrial radiation varies less, from 120 joules at the poles to 200 joules at the equator.

Energy is transferred from lower latitude energy surplus areas to higher latitude energy deficit areas by atmospheric circulation. If there was no atmospheric circulation, lower latitudes would get hotter and hotter and higher latitudes colder and colder.

The diagram below tells us that tropical areas get more insolation than polar regions.

Sun's rays spreading out to show different levels of insolation. High latitudes and low latitudes are also shown.