Lesson 2 – Major climate controls

Factors affecting insolationObjectives:

Know what is meant by insolation and heat budget

Understand the factors that affect insolation

Starter: Insolation is the energy received by the earth as incoming short wave solar radiation. This energy controls our planet’s climate and weather and is converted by photosynthesis to support all forms of life. But what affects how much incoming radiation is received by the earth? What happens to this insolation when it reaches the earth’s surface?

Working as a class, produce a mindmap on the whiteboard to show your ideas for answers to these questions.

Task 1: The atmospheric heat budget depends on the balance between incoming solar radiation (insolation) and outgoing radiation from the planet.

Read the following extract from ‘Geography – An Integrated Approach’ by D Waugh (1990). Highlight/underline key words and concepts:

‘Since the earth is neither warming up nor cooling down, there must be a balance between incoming insolation and outgoing terrestrial radiatin. There is a net gain in radiation everywhere on the earth’s surface except in polar latitudes, which have high albedo surfaces. There is a net loss in radiation throughout the atmosphere. After balancing the incoming and outgoing radiation there is a net surplus between 35 ̊S and 40 ̊N and a net deficit to the poleward side of those latitudes.

There is therefore a positive heat balance within the tropics and a negative heat balance both at high latitudes (polar regions) and high altitudes, so two major transfers of heat take place to prevent the tropical areas from overheating:

1. Horizontal heat transfers – to prevent the Equator from becoming increasingly hot and the poles becoming colder, heat is transferred away from the tropics. Winds are responsible for 80% of this transfer and ocean currents for 20%.

2. Vertical heat transfers – so that the earth’s surface does not get hotter and the atmosphere colder heat must be transferred vertically. This is achieved through radiation, conduction, convection and the transfer of latent heat.’

This excerpt is from the 1990 version of this textbook. How do you think it may have changed in more recent editions? Can you find a more recent edition to check your ideas out?

Task 2: Write a sentence next to each of the heat budget diagrams shown below to explain what they show.

Task 3: Read the following excerpt from ‘Geography – An Integrated Approach’ by D Waugh (1990). Convert the information into a series of diagrams in the spaces on the next page.

Long term factors

Short term factors

Local influences

Plenary: Peer assess each other’s diagrams using two stars (good) and a wish

(what could be done better):

Homework : Answer the exam question below by __________.

1. Figure 1 shows the average annual latitudinal pattern of solar radiation.

a) Define the terms insolation and albedo (7 marks)

b) Explain why the amount of solar radiation absorbed by the Earth’s surface varies from place to place (8 marks)

c) Explain why the amount of solar radiation absorbed by the Earth’s surface varies from time to time (10 marks)