Climate change: causes and evidenceEdexcel A-Level Biology A: Mind map

Exam questions on Climate change: causes and evidence

1. A palaeoecologist extracts a vertical core from a peat bog in northern England. Peat is waterlogged, acidic and contains very little oxygen. She identifies the pollen grains in each layer of the core under a microscope and dates the layers using radiocarbon dating. Moving from the deepest layers to the surface, the proportion of birch and pine pollen decreases while the proportion of oak and hazel pollen increases. Birch and pine tolerate colder conditions than oak and hazel.
   Suggest two reasons why pollen from a single peat core may not give a reliable record of past temperature.2 marks
2. A forestry researcher takes thin cores from the trunks of living oak trees and from oak beams in medieval buildings. Each core shows a series of annual rings, and the width of each ring depends on how much new wood the cambium laid down in that year. Over a 150-year period, she finds that the ring width in the living oaks has a positive correlation with mean summer temperature (r = +0.81).
   A newspaper claims that this correlation proves that higher summer temperatures cause wider rings. Explain why the correlation alone does not prove this.2 marks
3. Scientists drill ice cores in Antarctica. Each layer of ice formed from snow that fell in a particular year and trapped tiny bubbles of air. Analysis of the bubbles shows that over the last 800 000 years the carbon dioxide concentration varied between about 180 and 280 parts per million (ppm). Direct measurements of air at the Mauna Loa Observatory in Hawaii show that the concentration rose from 316 ppm in 1959 to 421 ppm in 2022.
   Describe how ice cores can be used to find the carbon dioxide concentration of the atmosphere in the past.3 marks