Science 7–10 · Years 9–10

Reading the carbon dioxide record: Kennaook / Cape Grim and Mauna Loa

Science understanding: Earth and space sciences (NSW Stage 5 focus areas Environmental sustainability and Data science 2)

Practical, model not builtLow risk

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The idea

Two long records of carbon dioxide in clean air show the same accelerating rise, and a yearly wave from plant growth that is large at Mauna Loa in the northern hemisphere and small at Cape Grim in Tasmania.

What you need

the Kennaook / Cape Grim monthly baseline carbon dioxide file (CSIRO and Bureau of Meteorology, release of September 2026, May 1976 to August 2026)
the NOAA Mauna Loa monthly mean file (March 1958 to August 2026 at the time of writing)
a spreadsheet, or graph paper, a ruler and a calculator

How to do it

Plot the monthly values of both stations against time on one set of axes.
Calculate annual means for complete years and the average rise per year for 1980 to 1990 and for 2010 to 2020.
Fit a straight line through the Cape Grim annual means for 2015 to 2025 and read its gradient.
Remove the trend by subtracting a 12-month centred running mean, then average the leftovers by calendar month for 2015 to 2024 to get each station's seasonal wave.
Compare the size and timing of the two waves and explain them from where most land plants grow.
Record the month the Cape Grim record first reached 400 ppm and 420 ppm.

What you should see

Cape Grim annual means: 336.53 ppm (1980), 350.98 (1990), 386.20 (2010), 409.84 (2020) and 422.88 (2025). The average rise was 1.45 ppm per year in the 1980s and 2.36 ppm per year in the 2010s, and the least-squares line through 2015 to 2025 has a gradient of 2.45 ppm per year. Mauna Loa's annual mean was 315.98 ppm in 1959 and 427.35 ppm in 2025, 4.47 ppm above Cape Grim. The detrended seasonal wave for 2015 to 2024 is about 6.7 ppm from peak to trough at Mauna Loa (highest in May, lowest in September and October) and about 1.0 ppm at Cape Grim (highest in August and September, lowest in February and March). Cape Grim first reached 400 ppm in May 2016 and 420 ppm in June 2024. The learner knows it worked when their gradients agree with these within 0.1 ppm per year.

What changes

This activity lists no variables to change, measure and keep the same.

Common misconceptions

Each of these ideas is wrong, and the activity is a chance to test it.

The yearly wiggle in the record is measurement error; it is plants taking up carbon dioxide in their growing season and releasing it in winter.
Carbon dioxide is higher over Australia because of local pollution; Cape Grim measures background air and reads slightly lower than Mauna Loa.
The rise is slowing down; the average rate has grown decade by decade.

Safety card

Low riskLearners carry it out

Hazards

No hazard is listed.

Controls

No control is listed.

Note

Screen-based model with no practical hazard; follow the school's guidelines for device use.

Curriculum references

The NSW syllabus outcomes and Australian Curriculum v9 codes this activity supports. They are references, not a verified or complete curriculum alignment.

Science 7-10 Syllabus (2023), NSW Education Standards Authority (implemented from 2026; codes read at curriculum.nsw.edu.au on 22 and 23 September 2026)SC5-ENV-01 SC5-DA2-01 SC5-WS-05 SC5-WS-06
Australian Curriculum v9AC9S9U03AC9S10U04AC9S10I04AC9S10I05

Sources

The pages the author read to write this activity.

All Concept Studio activities