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Understanding the evidence for past and present climate change — and the methods used to project future change — is a core requirement of the AQA A-Level Geography specification. This lesson examines proxy records, instrumental data, natural causes of climate variability, and the IPCC's latest scenarios and projections.
Direct instrumental records of temperature extend back only to the mid-19th century. To reconstruct earlier climates, scientists use proxy records — natural archives that preserve information about past environmental conditions.
| Proxy | What It Records | Temporal Range |
|---|---|---|
| Pollen analysis (palynology) | Vegetation assemblages, indicating climate zones | Up to ~1 million years |
| Coral growth bands | Sea surface temperature, ocean chemistry | Up to ~500 years per colony; fossil corals extend range |
| Speleothems (cave formations) | Temperature, rainfall via δ¹⁸O and growth rates | Up to ~600,000 years |
| Historical records | Harvest dates, frost fairs, diary entries | Centuries (varies by region) |
| Lake sediments (varves) | Seasonal deposition patterns, pollen, diatoms | Up to ~50,000 years |
Milutin Milankovitch (1920s-1940s) identified three orbital variations that affect the amount and distribution of solar radiation reaching Earth:
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