5.3.1Unit 5: Respiration, Internal Environment, Coordination and Gene Technology
Evidence for Climate Change — IAL Edexcel Linear Revision Notes & Topical Questions
5 min read 5 parts Lesson 23 of 36 Unit quiz
Section 1 of 5Records of Greenhouse Gases and Temperature
Direct and indirect records show that the planet has warmed.
Carbon dioxide
- Atmospheric carbon dioxide rose from about 280 ppm before the Industrial Revolution to over 400 ppm today.
Ice cores
- Bubbles of ancient air trapped in ice show past carbon dioxide levels, with deeper ice being older.
Temperature records
- Instrument records show the average global temperature has risen by just over 1 °C.
Correlation
- Temperature and carbon dioxide have tended to rise together, but correlation alone is not proof of cause.
Section 2 of 5Indirect Evidence
Indirect Evidence
Pollen in peat
- Pollen survives in acidic waterlogged peat, and its types show which plants grew in each period.
Dendrochronology
- Tree rings are wider in warm, wet growing seasons and narrower when conditions are poor.
Other signs
- Retreating glaciers, rising sea level and loss of sea ice agree with a warming trend.
Species ranges
- Many species have shifted to higher latitudes or altitudes as temperatures rise.
| Evidence | Shows | Limitation |
|---|---|---|
| Ice cores | Past CO₂ levels | Resolution falls with depth |
| Pollen | Past vegetation | Indirect link to temperature |
| Tree rings | Past growth conditions | Affected by drought and pests |
Section 3 of 5Interpreting a Tree Ring
Rings give a record of conditions in each year.
1
Each year a tree adds a layer of new wood, forming a ring.
2
Wide rings suggest favourable growth conditions such as warmth and adequate water.
3
Narrow rings suggest poor conditions, so a pattern of rings reflects climate over time.
4
Rings from different trees and old timbers are matched to extend the record back many years.
Section 4 of 5Evaluating the Evidence
Several sources
- Agreement between independent sets of data makes the conclusion stronger.
Validity
- The data must measure what is claimed, for example temperature, not another variable.
Time scale
- Long records separate climate trends from short-term weather changes.
Causation
- Evidence of warming is separate from evidence that human emissions cause it.
Section 5 of 5Exam Checklist & Tips
5.3.1 – Key Points for the Exam
- Climate The average weather conditions in a region over many years.
- Greenhouse gas A gas such as CO₂ or methane that traps heat in the atmosphere.
- Dendrochronology The study of tree rings to date events and investigate past climates.
- Ice core A cylinder of ice drilled from an ice sheet that holds trapped air from past times.
Common Mistakes
- Confusing weather, which changes day to day, with climate.
- Claiming that correlation proves that carbon dioxide caused warming.
- Saying pollen records show temperature directly; they show vegetation, from which climate is inferred.
- Assuming that one cold year disproves a long-term warming trend.
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