Evaluate the evidence used to reconstruct climate change

The command word is ‘evaluate’, requiring you to assess the relative importance or validity of the evidence. Therefore, your conclusion should include a judgement, for example, of the most or least important or reliable method, or how one line of evidence alone is insufficient to reconstruct climate change. The key words to note are ‘evidence’ and ‘climate change’. A definition of climate change would help focus your answer. You should show an awareness of a range of evidence, both instrumental, consisting of in situ temperature measurements, and ‘proxy’ evidence, physical characteristics or indicators that stand in for direct measurements. A good way to approach this may be to structure your answer by time-scales, using evidence for long-term, medium-term and short-term climate change. At longer timescales, you could consider evidence from ice cores, pollen analyses, landforms indicating sea level change, and ocean sediment cores. Consider the advantages and disadvantages – for example, ice cores can become contaminated following drilling and handling, despite providing an indication of past climate extending back 800,000 years. Medium-term climate change can be inferred by historical records and dendrochronology. Yet consider issues such as subjectivity, in the historical records, and length of the record, with dendrochronology only extending back 8,000 years. More recently, you could assess modern meteorological measurements, which started to be taken from c.1850, and analysis of changing ecosystems. An evaluation of such evidence may lead to the conclusion that a ‘multi-proxy’ approach is favourable – where multiple methods and lines of evidence are used to increase the validity of the climate reconstructions.