O - Energy and matter *03

Question 1

what radiation does the sun emit?

Answer 1

electromagnetic radiation

mostly; visible light, UV radiation and infrared radiation

Question 2

what happens when radiation from the sun reaches the earth’s atmosphere?

Answer 2

most of the UV and IR is absorbed by atmospheric gases, and some radiation is reflected back into space from clouds

Question 3

What happens to the energy that reaches the earth’s surface?

Answer 3

mainly visible light and UV

some of this radiation is reflected back into space by light-coloured, shiny surfaces
—> ice and snow

the rest is absorbed by the earth, which causes it to heat up

Question 4

what happens to the energy which is absorbed by the earth?

Answer 4

the earth then radiates energy back towards space as infrared radiation

Question 5

what happens to the IR radiation radiated by earth?

Answer 5

some of this IR radiation escapes (‘IR window’ –> the range of frequencies not absorbed by atmospheric gases)

But various gases in the TROPOSPHERE (lowest layer of the atmosphere) absorb other infrared radiation

• –> then re-emit it in all directions (Including back to the earth - keeping us warm)
• –> this is the GREENHOUSE EFFECT

Question 6

what is the greenhouse effect?

Answer 6

when infrared radiation emitted by earth is absorbed by gases in the troposphere and re-emitting it all directions including back to earth
—> keep us warm

Question 7

why is the greenhouse effect important?

Answer 7

without this absorption and re-emission of heat by ‘greenhouse gases’ the average surface temperature on Earth would be about 30 degrees cooler than it is

and we wouldn’t survive

Question 8

what are greenhouse gases?

Answer 8

carbon dioxide
methane
water vapour

greenhouse gases because their molecules absorb IR radiation to make the bond in the molecule vibrate more

Question 9

how can greenhouse gases transfer energy?

Answer 9

through collisions

1. greenhouse gases absorb IR radiation and bonds in molecules vibrate more
2. this extra vibrational energy is passed onto other molecules in the air by collisions, giving the other molecules more kinetic energy and so raising the overall temperature

Question 10

what does the contribution to the greenhouse effect of a molecule depend on?

Answer 10

how much radiation one molecule of the gas absorbs

how much of that gas there is in the atmosphere

• water vapour greater contribution than carbon dioxide
• methane traps far more heat than one carbon dioxide molecule but there’s much less methane in the atmosphere so overall contribution to the greenhouse effect is less

Question 11

what causes global warming

Answer 11

an enhanced greenhouse effect

Question 12

what has caused an enhanced greenhouse effect?

Answer 12

1. over the last 150 years human population has grown massively and become more industrialised
   - to supply our energy needs we’ve been burning fossil fuels at an ever-increasing rate, releasing tons and tons of CO2 into the atmosphere
   - also been copping down forests which absorb CO2 by photosynthesis
2. not just CO2 also METHANE, grow more food —> cows and paddy fields
3. these human activities have caused a rise in greenhouse gas concentrations, which enhances the greenhouse effect

Question 13

what is the enhanced greenhouse effect?

Answer 13

human activities have caused a rise in greenhouse gas concentration

this enhances the greenhouse effect as less IR can escape

so now too much heat is being trapped and the Earth is getting warmer
—> this is global warming

Question 14

what does global warming lead to?

Answer 14

sea-levels rising

climate change

Question 15

climate change - naturally

Answer 15

climate change has happened naturally throughout the earth’s history on various different timescales

1. regular changes in the earth’s orbit around the sun are linked to ice age cycles
   - –> long periods of cold with warmer periods (interglacials) in between
2. various changes in the sun’s activity (sunspots every 11 years) also cause warming or cooling
3. not all-natural changes are caused by regular cycles
   - –> huge volcanic eruptions or meteor impacts have thrown vast amounts of smoke or dust into the air and caused significant global cooling