6.3.2Global Challenges
The Greenhouse Effect — OCR Gateway GCSE Combined Science A J250 - Chemistry Revision Notes & Topical Questions
5 min read 10 parts Lesson 9 of 12
Part 1 of 8Energy balance of the Earth
Incoming
- Incoming the Earth receives most of its thermal energy as thermal radiation from the Sun
Outgoing
- Outgoing the Earth emits its own thermal radiation
Wavelengths
- Wavelengths the Sun emits mainly short-wavelength radiation and the Earth emits longer-wavelength infrared
- The difference is caused by their different surface temperatures
Rates
- Rates part of the incoming radiation is reflected back into space, part is absorbed, and the Earth emits radiation from its surface and atmosphere
Stable temperature
- Stable temperature the average temperature is stable when energy absorbed equals energy emitted
Part 2 of 8How the greenhouse effect works
Greenhouse gases
- Greenhouse gases water vapour, methane and carbon dioxide absorb the long-wavelength infrared radiation from the Earth
Re-emission
- Re-emission they emit it in all directions, including back towards the surface
Result
- Result less energy escapes directly into space, so the Earth is warmer than it would be without these gases
Atmosphere
- Atmosphere largely transparent to incoming visible light but absorbs outgoing infrared
Part 3 of 8Size of the natural effect
Without greenhouse gases
- Without greenhouse gases the average surface temperature would be about −18 °C
With greenhouse gases
- With greenhouse gases the temperature stays at a reasonable level for life, about 30 °C warmer
Part 4 of 8The enhanced greenhouse effect
Carbon dioxide
- Carbon dioxide added by burning fossil fuels and by deforestation
Methane
- Methane released by livestock farming, rice paddies and landfill
Effect
- Effect more greenhouse gas absorbs more outgoing infrared and returns more to the surface, so the average temperature rises
Terms
- Terms the rise is global warming and the resulting change in climate is climate change
Part 5 of 8Equilibrium temperature
Balance
- Balance the temperature settles where the rate of emission equals the rate of absorption
More absorption
- More absorption if the atmosphere absorbs more outgoing radiation the surface warms until emission rises enough to restore the balance
General rule
- General rule if absorption exceeds emission the temperature rises, and if emission exceeds absorption it falls
Part 6 of 8Consequences
Sea level
- Sea level melting polar ice and glaciers and thermal expansion of oceans raise sea level
Weather
- Weather more extreme weather such as droughts, heatwaves, floods and storms
Living things
- Living things changes in habitats, loss of species and effects on crop growth
Part 7 of 8Evidence and responses
Evidence
- Evidence air bubbles in polar ice record past atmospheres, and direct measurements show carbon dioxide rising since industrial times
Temperature records
- Temperature records thermometers, buoys and satellites show a rising trend in global average temperature
Reducing emissions
- Reducing emissions renewable energy, nuclear power, energy efficiency, electric vehicles and carbon capture
Adapting
- Adapting sea defences and drought-resistant crops
Part 8 of 8More from the specification
More from the specification
Thermal Conduction in Solids and Metals
- Thermal conduction is the transfer of heat through a substance without net movement of the material itself;
- metals are excellent thermal conductors because free delocalised electrons rapidly transfer kinetic energy through the lattice when the metal object is heated.
Convection Currents in Fluids
- Convection occurs in liquids and gases (fluids) where heated fluid expands, becomes less dense,
- and rises,
- while cooler, denser liquid or gas sinks to take its place, establishing continuous convection circulation transfers.
Thermal Radiation and Surface Emission Experiments
- All warm objects emit infrared thermal radiation;
- experimental comparisons using Leslie's cube demonstrate that dull, matte black surfaces are the most effective emitters and absorbers of radiant heat,
- whereas shiny metallic surfaces reflect infrared radiation.
Thermal equilibrium
- Constant temperature because energy is absorbed and lost at equal rates
Potassium permanganate
- A purple compound used to show convection currents in water.
Convection
- Transfer of thermal energy by the movement of a heated fluid
Conduction
- Transfer of thermal energy by lattice vibrations and free electrons
Liquid
- State with a fixed volume that takes the shape of its container.
Conductor
- Material that allows current to flow.
Lattice
- The regular arrangement of atoms in a solid.
Solid
- State with a fixed shape and a fixed volume.
Vibration
- A repeated backwards and forwards movement.
Energy transferred
- W = V Q, in joules.What the symbols mean: E or W = energy transferred (J) · Q = charge (C) · V = potential difference (V) · I = current (A) · t = time (s)
Key terms
| Term | Meaning |
|---|---|
| Greenhouse gas | Gas such as carbon dioxide, methane or water vapour that absorbs infrared from the Earth |
| Greenhouse effect | Warming of the Earth because gases absorb and re-emit its infrared radiation |
| Global warming | Rise in the average temperature of the Earth |
| Thermal equilibrium | Constant temperature when absorption and emission rates are equal |
| Infrared radiation | Long-wavelength thermal radiation emitted by the Earth |
Avoid these mistakes
1
Saying the greenhouse effect is entirely harmful — the natural effect keeps the Earth habitable.
2
Giving only pollution as the problem of fossil fuels — name carbon dioxide or another greenhouse gas.
3
Saying greenhouse gases reflect infrared — they absorb it and re-emit it in all directions.
4
Mixing up the radiation received and emitted — the Sun gives short wavelengths, the Earth gives long-wavelength infrared.
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