NIWA monitors the amount of carbon dioxide in the atmosphere by passing air through an infra-red analyser at Baring Head, to the east of Wellington Heads. 'Clean' air is sampled during southerly winds. This is because in these conditions, air has come off the sea and originates far away in the Southern Ocean. It provides a good representation of the air in the entire southern hemisphere. In northerly winds, the air has passed over the southern North Island before reaching Baring Head. This means that it is contaminated by local emissions from factories and vehicles and does not represent air from the whole of the southern hemisphere.

Study the graph below.

Graph 1. Graph showing the 'mole fraction' or 'mixing ratio' of carbon dioxide in the air at Baring Head since 1971. (Click for enlargement)

The blue dots show individual data points.

The green (wavy) line shows this data once it has been 'smoothed', and includes seasonal variations.

The red line shows the trend on an annual basis since 1970.

The vertical scale is measured in 'parts per million' i.e. the number of molecules of carbon dioxide in every million molecules in the air.

The graph below 'zooms in' on carbon dioxide readings since 1999.

Graph 2. Graph showing the 'mole fraction' or 'mixing ratio' of carbon dioxide in the air at Baring Head since 1999. (Click for enlargement)

Questions

1. Study graph 1. What has happened to the amount of carbon dioxide in the air over the last 30 years?
2. By how many 'parts per million' has the amount of carbon dioxide increased since 1970?
3. Calculate your answer to question 2 as a percentage of the total amount of carbon dioxide in the air at the start of 2005.
4. Study graph 2. Looking at the green (more wavy) line, in which year did the amount of carbon dioxide increase the most?
5. In which year did it increase the least?
6. By how much has the amount of carbon dioxide increased, on average, each year since 1999?
7. Suggest why some of the blue points are quite a way from the lines on the graph.
8. During which season does the amount of carbon dioxide decrease? Why do you think this happens?
9. Before the industrial revolution in the mid 1800s, the level of carbon dioxide had been stable at about 280ppm for most of the last 10,000 years. What has caused carbon dioxide to increase so markedly in the atmosphere since then?
10. Computer models predicting the climate in the future refer to the 'doubling of carbon dioxide compared with pre-industrial times'. This would correspond to a level of carbon dioxide in the atmosphere of about 560ppm. Work out when the doubling of carbon dioxide might occur, assuming that the rate of increase remains roughly as it is at present.
11. A large amount of carbon dioxide is produced when fossil fuels are burned. Combustion uses up another gas in the atmosphere. What is this gas? If you were shown a plot of the amount of this gas in the atmosphere over the last 30 years, what would the shape of the plot look like?