5.3.2Unit 5: Respiration, Internal Environment, Coordination and Gene Technology
Anthropogenic Climate Change — IAL Edexcel Linear Revision Notes & Topical Questions
5 min read 6 parts Lesson 26 of 36 Unit quiz
Part 1 of 6The Greenhouse Effect
Be precise with termsthe greenhouse effect is the natural process, while global warming is the extra temperature rise caused by raised gas levels.
Incoming energy
- Sunlight warms the Earth, and the warmed surface then re-radiates energy outwards as infrared radiation.
Greenhouse gases
- Gases such as carbon dioxide and methane absorb some of this infrared radiation and so slow its escape into space.
A natural process
- The greenhouse effect is natural and keeps Earth warm enough for life, with far smaller swings in temperature than a planet without it.
Enhanced effect
- More greenhouse gas in the air traps more radiation, so the average temperature of the lower atmosphere rises.
Part 2 of 6Where the Extra Carbon Dioxide Comes From
Where the Extra Carbon Dioxide Comes From
Fossil fuels
- Burning coal, oil and gas for transport, electricity and industry releases carbon that was locked away for millions of years.
Deforestation
- Clearing forests removes trees that were absorbing carbon dioxide and often releases carbon when the wood is burned or rots.
Soils and peat
- Draining or harvesting peat bogs and degrading soil exposes stored carbon to decay, which releases it as carbon dioxide.
Warming oceans
- Warmer water holds less dissolved gas, so a warming ocean can release carbon dioxide rather than absorb it.
Part 3 of 6Methane Sources
1
Methane (CH₄) is a hydrocarbon and the main component of natural gas, and it is also a greenhouse gas.
2
Intensive farming of ruminant animals such as cattle raises methane levels because microbes in their guts release it.
3
Waterlogged rice paddies provide anaerobic conditions where bacteria produce methane that escapes into the air.
4
Landfill sites release methane as buried organic waste is broken down by microorganisms without oxygen.
5
Extracting fossil fuels releases methane, and warming can thaw permafrost and release the methane trapped in frozen ground.
Part 4 of 6Reading the Evidence
Trend
- Carbon dioxide has risen from about 280 ppm before industrialisation to above 400 ppm today, alongside rising mean temperature.
Correlation
- Matching trends show a correlation, but correlation alone does not prove that one variable causes the other.
Stronger case
- The link is supported by the known ability of carbon dioxide to absorb infrared radiation and by many independent data sets.
Other factors
- Temperature also fluctuates when carbon dioxide is steady, so other influences such as volcanic activity are involved.
Part 5 of 6Worked Example
Question
- Carbon dioxide rose from 280 ppm to 420 ppm.
- Calculate the percentage increase.
- Find the change420 − 280 = 140 ppm.
- Divide by the original value140 ÷ 280 = 0.5.
- Multiply by 100 to give a percentage.
Answer 50% increase.
Part 6 of 6Exam Checklist & Tips
5.3.2 – Key Points for the Exam
- Greenhouse gas A gas that absorbs infrared radiation re-emitted from the Earth and so traps energy in the atmosphere.
- Anthropogenic Caused by human activity.
- Carbon sink A store that takes in more carbon than it releases, such as forests, soils, peat and the oceans.
- Permafrost Ground that stays frozen throughout the year.
- ppm Parts per million, a unit for the concentration of a gas in air.
Common Mistakes
- Using greenhouse effect and global warming as if they mean the same thing, when the first is natural and the second is the enhanced rise.
- Saying that carbon dioxide levels were constant before humans;
- they have always varied naturally, but never as quickly.
- Writing that a correlation proves causation; say only that the data are consistent with it.
- Forgetting methane, which is a different gas from carbon dioxide and has its own human sources.
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