Greenhouse Effect & Global Warming

Question 1

Where does our energy come from? Write down as many sources as possible.

Answer 1

The majority of energy comes directly or indirectly from the sun.
For example:
1. Solar power comes
from the sun.
2. Biomass uses photosynthesis
to convert sunlight into sugars.
3. Wind is caused by the sun heating
the planet and causing movement of air.
4. Wind subsequently generates waves as it passes over the oceans (Wave power).
5. Rainfall comes from solar evaporation which supplies hydroelectric power.
6. The energy in fossil fuels, ultimately comes from the sun.

Question 2

Are there any exceptions to where energy typically comes from? What are they?

Answer 2

Yes, these are:
1. Nuclear power (heat generated by radioactive decay of matter) mass of atoms is converted into energy by Einstein’s equation.
2. Geothermal (do not confuse with GSHPs as Heat pumps are collect heat from just under the surface so are still indirectly supplied by the sun). Geothermal is drilled much deeper into the ground or a natural phenomenon where heat comes from the core of the planet (accretion) and by nuclear reactions. It is the gravitational potential energy from the formation of the planet (space dust) was trapped as heat in the earth’s core.
3. Tidal - gravitational and potential energy from the moon & sun

Question 3

How much solar electromagnetic radiation is reflected back into space vs what reaches the atmosphere?

Answer 3

50% goes back into space

Question 4

True or false: Hot air is more dense than cool air.

Answer 4

False - less dense

Question 5

How much energy does the world consume in a year?

Answer 5

595 exajoules = 595 x 10^18 J

Question 6

Why does not all energy from the sun (that enters the earth’s atmosphere) not reach the surface? What 4 main optical processes are involved?

Answer 6

The earth has to maintain an energy balance:
Energy in = energy out

Processes involved include:
1. Radiation
2. Absorption
3. Scattering
4. Emission

Question 7

What is direct and indirect radiation?

Answer 7

Direct Radiation - light does not interact with the atmosphere (direct from the Sun and will cast a shadow) e.g. intense sunlight

Indirect radiation - light that is scattered in the atmosphere (does not cast a shadow) e.g. overcast

Question 8

What is absorption?

Answer 8

Light energy is taken in by the molecules in the atmosphere. The energy is transferred to electrons within the molecules usually resulting in the generation of heat and possibly re-emission.

Question 9

What makes photovoltaics unique in terms of absorption?

Answer 9

Most materials when they absorb light generate heat but not always. For photovoltaic materials they generate electricity rather than heat.

Question 10

What is scattering?

Answer 10

Any process that can alter the direction that light is travelling e.g. reflection and refraction.

Question 11

What is emission?

Answer 11

Electromagnetic radiation radiates from all objects. The amount and wavelength of the radiation emitted by an object depends upon its temperature. e.g. The sun is very hot so emits a lot of UV, visible light & infrared.

Question 12

What parameters are involves in absorption & scattering and how does this link to the greenhouse effect?

Answer 12

Parameters:
1. Refractive index
2. Reflectance
3. Transmission
4. Absorbance

These all vary as a function of wavelength. The variation in these properties at different wavelengths is what causes the greenhouse effect.

Question 13

Name the 3 types of scattering in order of particle size.

Answer 13

1. Rayleigh scattering
2. Mie scattering
3. Geometric scattering

Question 14

What is Rayleigh scattering?

Answer 14

This is the smallest in terms of particles compared to wavelength of light (wavelength to the power of -4)
e.g. Refractive index n fluctuations in atmospheric gases.

These shorter wavelengths are more scattered than longer wavelengths and are seen more in the daytime.

Question 15

In the sky, is blue or red the longer/less scattered wavelength?

Answer 15

Red - which is why it appears when the sun is close to the horizon as it has to pass through a longer physical distance through the atmosphere to reach our eyes.

Question 16

What equations describe the scattering processes reflection and refraction at an interface between 2 materials?

Answer 16

Fresnel’s equation

Question 17

What equations are used to describe absorbance?

Answer 17

Beer Lambert Law

Question 18

What does the amount absorbed depend on?

Answer 18

The wavelength (length it has to travel through). All the energy will be absorbed at some
wavelengths and none will be absorbed at others.

Question 19

On a molecular level, what determines what wavelengths can be absorbed?

Answer 19

This is dependent upon the electronic energy levels within that molecule.
1. When light (i.e. a photon) is absorbed the energy has to go somewhere.
2. Molecules contain electrons and absorbing a photon usually results in the excitation of a electron. That is the electron has more energy (electronic potential energy). This excitation can only happen if there is a suitable energy level for the electron to be excited into (e.g. metals).
3. The excited electron may then convert its energy into heat or re-emit it as light (not necessarily at the same wavelength).

Question 20

True or false: Cool objects emit less radiation at longer wavelengths

Answer 20

True

Question 21

True or false: Clouds (H2O) are strong absorbers and emitters of infrared radiation, so on clear nights the Earth’s surface can cool down faster than on cloudy nights.

Answer 21

True

Question 22

What is the greenhouse effect?

Answer 22

The greenhouse effect is a complex combination of wavelength dependent atmospheric absorption and emission effects.

Overall, the atmosphere acts like the glass in a greenhouse – it lets visible sunlight in. Objects and life on earth absorb this visible light and re-emit IR, because we are much cooler than the sun. But this IR emission does not get back out again.

This is blocked by
Greenhouse gases (GHGs) in the atmosphere. These increase absorption and re-emit infrared radiation, but they do not absorb the visible sunlight. They allow incoming visible light in but block the IR radiated from the Earth.

Question 23

What 2 process are prevalent at shorter wavelengths when visible light enters the atmosphere? With reference to the solar spectrum.

Answer 23

1. Oxygen & ozone absorption
2. Rayleigh scattering

Question 24

What other components/elements make up the solar spectrum?

Answer 24

1. Water vapour
2. CO2
3. Methane
4. NOx

Question 25

How can the impact of greenhouse gases be seen on the solar spectrum?

Answer 25

The ‘notches’ out of the re-emitted curve should match up with those seen with water vapour. This is good because it allows IR to be emitted back into space. However, when we can see that there are small peaks on the CO2 and methane spectrums, this is letting less IR get back out so it stays within the atmosphere.

Question 26

What is the main greenhouse gas?

Answer 26

Water - lots of it all over the planet. This absorbs at lots of different wavelengths.

Question 27

List the greenhouse gases.

Answer 27

CO2, H2O, CH4, O3, N2O, sulfur hexafluoride SF6, hydroflurocarbons, perflurocarbons and chloroflurocarbons.

Question 28

Is CO2 or methane the most significant anthropogenic greenhouse gas?

Answer 28

Methane traps more radiation but we re-emit more CO2 therefore, CO2 is the most significant.

Question 29

What is the rise in CO2 in the atmosphere attributed to?

Answer 29

1. Fossil fuel combustion
2. Deforestation

Question 30

In what period did the planet experience the highest CO2 levels?

Answer 30

The Cretaceous period.
- 100 million years ago
- One of the warmestperiodsin the history of Earth
- Average temperaturesof up to 35 °C in the oceans
- No permanent ice caps
- Higher sea levels ~ 60 m above current
- CO2 levels at ~ 8 times pre-industrial levels

Question 31

What climate change events occur because of the changing composition of gases in the earth’s atmosphere?

Answer 31

1. Sea level rise
2. Global temperature rise
3. Warming oceans
4. Glacial retreat
5. Declining Arctic sea ice
6. Shrinking land ice sheets
7. Extreme events
8. Ocean acidification
9. Decreased snow cover

Question 32

What are thought to be the combined effects that have caused rising global temperatures?

Answer 32

1. Irregular El Nino
2. Sulphate aerosols emitted in volcanic eruptions
3. Solar cycle activity
4. Anthropogenic changes (changing land use, pollution, GHG emission)

Question 33

What is energy used for across the world?

Answer 33

1. FOOD production, transportation, preservation and preparation
2. POWER for healthcare
3. Development and
   constructing HOUSING
4. LIGHTING, HEATING, and COOLING our homes
5. TRANSPORTING people and goods
6. COMMUNICATIONS
7. PRODUCTION of goods

Question 34

Why is there disparities in energy use across the world?

Answer 34

1. Population growth - this causes energy demand to grow by 2% each year
2. Wealth - developed countries cause the anthropogenic contributors to climate change so should lead the way in fixing it
3. Developing countries need to become more developed, which involves industrialisation and social development - need energy to support this.

Question 35

What is the lifetime of carbon in the atmosphere?

Answer 35

200-300 years

Question 36

Why does burning fossil fuels release so much carbon?

Answer 36

A lot of carbon is stored in the ocean since this is ancient biomass which has decayed and transformed over millions of years.

Therefore, extracting and burning it releases carbon from this store.

Question 37

What are the 9 stages of the carbon cycle?

Answer 37

1. Plants absorb CO2 to grow through photosynthesis. They also release CO2 as they decompose.
2. Iron-rich dust from industry is blown by the wind into the ocean. This disturbs the basis of marine ecosystems & stimulate phytoplankton blooms.
3. CO2 is exchanged between the sea and the air.
4. Phytoplankton in the sea absorb CO2 to grow.
5. Zooplankton eat phytoplankton and respire CO2.
6. Some carbon sinks to the bottom of the ocean in the form of decaying biota and fecal pellets.
7. Most of the carbon is recirculated back to the surface over 100 - 1000 years by the ocean.
8. Over millions of years, carbon becomes embedded in rocks or is turned into hydrocarbons.
9. Rocks are eventually uplifted onto land and weathered to release carbon to the soil and the atmosphere.

Question 38

What are the 2 types of CO2 emission?

Answer 38

1. Static - such as power plants, ethanol plants, cement manufacturing, petroleum & gas processing, etc.
2. Mobile - mostly the transport sector

Question 39

True or false: It is easier to capture CO2 emissions from mobile sources

Answer 39

False - static

Question 40

List 6 different sectors that produce emissions starting with the largest emitter.

Answer 40

1. Electricity & heat production
2. Agriculture, forestry & other land use
3. Industry
4. Transportation
5. Other energy
6. Buildings

Question 41

How can the emissions produced by mobile sources be reduced? What are the associated issues?

Answer 41

Electric (or hydrogen) vehicles (short-term).

However, this just transfers the CO2 burden back to the power generation sector.

It is also going to take time to implement since existing cars will have to come out of use.

A lot of engineering is also required to implement carbon capture on mobile sources.

This amplifies the importance pragmatic CO2 solutions for power generation.

Question 42

List the order of static sources in order of the highest emitting carbon source.

Answer 42

1. Power plants
2. Residential buildings
3. Deforestation
4. Cement & lime manufacturing
5. Agriculture
6. Iron & steel production
7. Chemical & petrochemical

Question 43

Give 3 carbon abatement technologies can be implemented to reduce emissions? What are the issues associated with each?

Answer 43

1. Higher Efficiency Conversion Process – more efficient use of fossil fuels can cut emissions from 10 – 30 %. However, this is not enough to make a meaningful difference alone.
2. Medium term : CO2 capture and Storage (CCS) – in which carbon in fossil fuel is captured (as CO2) either before or after the combustion and committed to long term storage in geological formations. However, this will likely be needed to keep to global warming below 1.5°C, especially for CO2 intense industries.
3. Longer term: Fuel Switching to Low Carbon Alternatives – replacement of coal fired generation with natural gas, biomass co-firing, renewable energy supplies. However, this is happening faster than point (2) due to increased use of wind and solar.

Question 44

How can Higher Efficiency Conversion Processes be used to reduce carbon emissions?

Answer 44

In modern power plants, new materials and designs allows the cycle temperature and pressure to be increased which help increase efficiency. This in turn makes better use of fossil fuels used.