This session covers core content knowledge taught in Grades 10-12, focusing on Energy Exchange.

By the end of the session participants should be able to:

• Describe how is energy supplied and added to the system?
• Explain how is energy transformed through various processes? (e.g. moisture in the atmosphere)
• Explain how is energy transferred across the system? (e.g. Earth’s energy balance and the global air circulation)
• Outline energy transfer (e.g. pressure belts, cold and warm fronts, high and low pressures) *

Energy from the sun enters the Earth System in the form of short-wave radiation. When it enters the atmosphere, some of this solar energy is reflected, scattered and absorbed. Only about half of the radiation arrives at the Earth’s surface. The atmosphere, which is made up of gases such as carbon dioxide and water vapour which re-radiates energy back into the atmosphere and then back towards the Earth. This exchange of energy is usually referred to as the ‘greenhouse effect’ because it causes the warming of the Earth.

Source: EPA (2012)

The role of global circulation in the Earth’s energy balance

More solar energy is received at the equator and less at the poles, this process causes a global circulation system. The movement of the Earth around the sun affects when and where different amounts of energy are received. The Tri-Cellular Model (Hadley cell, Ferrel cell and the polar cell) shows how energy is redistributed across the globe and ensures there is not a surplus at the equator and deficit at the poles, which would be caused by the differential heating of the Earth’s surface by the Sun. South Africa is a relatively dry country, with an average annual rainfall of about 464 mm due to its subtropical location.

Watch the Video explaining the Tri-cellular Global Circulation model, pressure and wind belts.

You can teach about the physical drivers of climate change by making links to other sections of the CAPS Geography curriculum, for example:

• The Earth’s changing structure (Grade 10, term 3) – Volcanic eruptions emit large quantities of ash, which can add to the greenhouse effect (through particles and ash scattering or reflecting energy, or by absorbing some of the energy and re-radiating it). You can briefly reflect on the impact of volcanic eruptions on past climates and climate variability.

• The role of water in the energy balance in the atmosphere (Grade 10, Term 1) – Energy transfer by water occurs in two dimensions: Firstly, the vertical transfer of energy by evaporation, condensation and cloud development, and latent heat transfer when energy changes phases from gas-liquid-solid and the horizontal transfer of energy through large ocean bodies by warm and cold currents, and how they influence climate (e.g. El Niño) (Grade 11 Africa’s weather and climate).

Below are some readings that you might find interesting.

• For a very good explanation of the role of radiation in the energy balance, including some basic physics, see Focus Geography Learner Book, Grade 10, 2011, 88-89).
• The climate-energy system
• The general circulation
• The role of global circulation in the Earth’s energy balance (Platinum Series, 2011 Learner’s Book, p.76)
• The three-cell model that results from differential heating, the Earth’s rotation, and the fluid dynamics of the atmosphere, see https://www.metoffice.gov.uk/weather/learn-about/weather/atmosphere/global-circulation-patterns