Thermal Energy Transfer and the Sun

Thermal Energy and Climate

Without a climate system, Earth would be much colder (world ave -20oC) , the climate system moderates Earth’s temperature by trapping and storing energy from the Sun and distributing it around the world, as a result the air temperature remains relatively constant day and night and the poles are less cold and the equator is less hot (world average +14.7oC)

Thermal Energy Transfer

BACKGROUND INFO: All things are made up of molecules When things get heated, they absorb

heat energy With more energy, molecules are

able to move faster When molecules move faster, the

temperature rises

What is Thermal Energy??? Thermal Energy is energy resulting from

the motion of particles It is a form of kinetic energy and is

transferred as heat Thermal Energy Transfer can occur by

three methods:▪ Conduction▪ Convection▪ Radiation

View the following animation to get an overview of these processes: heat transfer

Conduction

Conduction is the transfer of thermal energy through direct contact between particles of a substance, without moving the particles to a new location

Usually occurs in solids

Conduction

View: Conduction in Solids When heat is supplied to one end,

molecules at that end start to move more quickly

In the process, they bump into their neighbours, transferring the kinetic energy

And so on, and so on……

Why is this less likely in liquids and gases?

Convection

Convection is the transfer of thermal energy through movement of particles from one location to another

Usually occur in fluids (liquids and gases)

Convection

Example with boiling water: Water at bottom of pan is heated first Heated water expands and density

decreases Heated water begins to rise Cooler water with higher density from

the sides of the pan rush down to take its place

The cooler water gets heated and the cycle repeats

We call these Convection Currents

Radiation

Radiation is the emission of energy as waves or particles or rays Radiation does not require a medium

to transfer energy Radiant energy is either reflected or

absorbed by matter Energy that is absorbed increases the

kinetic energy of the object▪ This increases the temperature of the object

Radiation

Example … the Sun Sun radiates energy in form of solar

radiation When this energy reaches Earth, it is

absorbed by matter (air, water, land) Absorbed radiant energy increases

kinetic energy of the matter, raising its temperature

Radiation

The Sun is an emitter It gives out heat

The Earth is an absorber It takes in the heat

Balance of Energy on Earth

Almost all energy on Earth comes from the sun

Electromagnetic spectrum, including infrared radiation and UV radiation

Earth Absorbs Energy from the Sun

When solar radiation contacts a particle of matter, one of three things happens:

1. Radiation is absorbed by a particle, causing the particle to gain energy

2. Radiation is transmitted through the particle

3. Radiation is reflected off the particle

Net Radiation Budget

Break down of the Radiation that reaches Earth (by percentage):

30% reflected back into space by clouds, atmosphere and Earth’s surface

30% of remaining 70% is absorbed by the atmosphere

The rest (40% of 70%) warms the Earth’s surface: Returns heat to atmosphere as infrared radiation,

thermal energy and water vapour

Net Radiation Budget

Net Radiation Budget the difference between the amount of incoming radiation and the amount of outgoing radiation

Net radiation budget = incoming radiation – outgoing radiation

= zero (theoretically)

Do all regions on Earth have a zero net radiation? Explain! Not all regions have a balanced radiation budget (but Earth

as a whole does) E.g. polar regions have less incoming than outgoing radiation E.g. tropics have more incoming than outgoing radiation

Factors Affecting Radiation

1. ALBEDO Colour of the surface Albedo is the percentage of the incoming solar

radiation that it reflects Albedo of Earth is about 30% Light-coloured, shiny objects reflect more solar

radiation and have a high albedo (ice, snow, sand)

Ice and snow reflect heat because they are white. They reflect so much of the Sun’s energy that it is hard for these locations, like the Arctic, to get very warm.

Darker, dull objects absorb more solar radiation and have a low albedo (forests, soils)

Factors Affecting Radiation

2. Surface Temperature• The higher the surface temperature,

the higher the rate of transfer

3. Surface Area• The larger the surface area, the higher

the rate of transfer

In Summary

Three methods of Heat Transfer Convection, conduction, and radiation

Earth’s Net Radiation Budget = “zero” Factors affecting radiation:▪ Albedo▪ Surface temperature▪ Surface Area

Homework Page 1 of 21. The amount of the energy the Earth absorbs is equal to the amount

of energy it radiates. Why is this important? Explain. [Knowledge]

2. The Sun shines continuously on Earth. Explain why Earth does not keep warming up. [Thinking]

3. a) Describe what happens to the Sun’s energy once it reaches Earth. [Knowledge]b) Describe what happens to the energy Earth emits. [Knowledge]

4. What would you expect to happen to the temperature of Earth if [Thinking]a) the amount of energy radiated by Earth increased but the amount of energy coming from the Sun stayed the same?b) the amount of energy radiated by Earth decreased but the amount of energy coming from the Sun stayed the same?

5. State two reasons why you would expect the climate in Nigeria to be warmer than the climate in Greenland. [Thinking/Application]

Homework Page 2 of 2

6. Explain why the greenhouse effect is important to life on Earth. [Knowledge]

7. Describe how the greenhouse effect in the atmosphere works and draw a diagram illustrating it. [Thinking]

8. a) Write a definition, in your own words, of “greenhouse gas”. [Knowledge]b) Name the two most important greenhouse gases that occur naturally in the atmosphere. [Knowledge]

9. If forests serve as important sinks for greenhouse gases, describe how past ice ages might have affected the concentration levels of carbon dioxide in the atmosphere. [Application]

10. Give one natural source for each of the following greenhouse gases: [Application]a) carbon dioxideb) methanec) nitrous oxided) water

Just For Fun

Go to the Ecokids.ca Climate Change Games and Activities. Spend ~ 5minutes playing each of the games listed as “Intermediate”. Identify one new thing you learned by playing the games that surprised you about climate change. Why were you surprised?