1. (a) Suggest why the first measurements of CO2 levels were taken at Mauna Loa in Hawaii and at the South Pole.
2. (b) Explain the annual fluctuations in CO2 levels at Mauna Loa.
3. (c) Identify two different means by which CO2 can be removed from the atmosphere naturally and give balanced equations for both of these.
4. (d) Suggest how the depletion of tropical forests can lead to an increase in CO2 levels.