B.2 Greenhouse Effect

Question 1

Emissivity (e)

Answer 1

How close to a black body an object is

Question 2

Emissivity formula not in book

Answer 2

power radiated per unit area of a object / power radiated per unit area of a black body at the same temperature.

Question 3

Max emissivity

Answer 3

1.0 for a black body

Question 4

Albedo (a)

Answer 4

Proportion of incident radiation that is reflected/scattered

Question 5

a = 1

Answer 5

All incident radiation is reflected

Question 6

a=0

Answer 6

All incident radiation is absorbed

Question 7

Earth’s albedo

Answer 7

Changes daily but usually 0.3

Question 8

What does Earth’s albedo depend on?

Answer 8

Cloud formation and latitude

Question 9

Solar constant

Answer 9

The amount of solar energy that falls per second on an area of 1m^2 above the earths atmosphere (average value 1360Wm-2)

Question 10

Why is the amount of power that arrives per m^2 on earth much lower than the solar constant?

Answer 10

Due to the radiation absorbed by the atmosphere/reflected by the clouds

Question 11

What is the proportion of the radiation that reaches the earths surface?

Answer 11

It depends on weather but typically 45% of that falling on the upper atmosphere

Question 12

Why do different parts of the Earth’s surface receive different amounts of solar radiation per m^2?

Answer 12

They are at different latitudes so receive different amounts of solar radiation due to variations in the angle at which the Sun’s rays strike the surface and the thickness of the atmosphere through which the radiation travels.

Question 13

Give two examples of why the radiation received would be less?

Answer 13

Longer distance needing to travel through atmosphere, shallower angle means energy is more spread out

Question 14

Why is the average intensity incident to Earth’s upper atmosphere 1360Wm^-2 while the average intensity incident to Earth’s entire upper atmosphere 340 Wm^-2?

Answer 14

Upper atmosphere - earth viewed from sun as a disc and so energy is 1360xpiR^2

Entire atmosphere - energy is spread out over the surface of the atmosphere (1360piR^2/4piR^2

Question 15

Greenhouse effect

Answer 15

Earth’s atmosphere warming the planet’s surface

Question 16

Sun’s radiation onto Earth

Answer 16

Sun’s incoming radiation is mostly in the ultraviolet and visible regions, which is absorbed and causes the earth’s surface to heat up. Because of the temperature, infrared light is reflected.

Question 17

Greenhouse gas examples

Answer 17

Methane, water vapour, carbon dioxide, nitrous oxide

Question 18

How do greenhouse gases increases Earth’s temperature?

Answer 18

The reflected infrared light is absorbed by greenhouse gases and is reflected in all directions. Some is absorbed by the surface, further heating up the earth.

Question 19

Why do greenhouse gases absorb infra-red radiation?

Answer 19

Frequency of the radiation is the same as the natural frequency (molecular energy level) as the green house gas particles vibrations.

Question 20

Resonant frequency

Answer 20

Natural frequency

Question 21

Resonance

Answer 21

Absorption of radiation at the same frequency

Question 22

Enhanced greenhouse effect

Answer 22

The increase of greenhouse gases in the atmosphere due to human activity

Question 23

Solar constant units

Answer 23

Wm-2