Investigating Science 11–12 · Year 11
Testing trend models for carbon dioxide on Cape Grim data
Module 3: Scientific Models
This site has no interactive model of its own. Where a step or a material names a Concept Studio model, simulation or tool, it has not been built; an external simulation a step names (for example PhET) is not part of this site.
The idea
Different mathematical models can fit the same past data almost equally well yet predict differently, so a model is judged by how well it predicts data it was not fitted to.
What you need
- computer with a spreadsheet
- the CSIRO and Bureau of Meteorology monthly baseline carbon dioxide file for Kennaook / Cape Grim, Tasmania (CapeGrim_CO2_data_download.csv)
How to do it
- Download the file and calculate the annual mean for each complete year.
- Fit a straight line, a quadratic and an exponential rise above 280 ppm to the annual means from 1977 to 2015 only.
- Use each model to predict 2020, 2024 and 2025, and calculate the difference from the measured values.
- Calculate the mean growth rate for each decade.
- Decide which model to use for a 2030 projection and state the assumption it makes about the future.
What you should see
Computed from the file released in September 2026: the annual mean was 331.70 ppm in 1977, 397.46 ppm in 2015 and 422.88 ppm in 2025. Fitted to 1977–2015, the straight line predicts 411.2 ppm for 2025 (11.7 ppm too low), the quadratic 419.7 ppm (3.2 ppm too low) and the exponential rise above 280 ppm 427.1 ppm (4.2 ppm too high). The mean growth rate rose from 1.44 ppm a year over 1977–1987 to 2.54 ppm a year over 2015–2025, which is why the straight line fails although it fitted the training years well.
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.
- A model that fits past data well will predict the future well.
- Carbon dioxide is rising at a steady rate.
- Seasonal ups and downs mean the trend is uncertain.
Safety card
Hazards
No hazard is listed.
Controls
No control is listed.
Note
Screen-based model with no chemicals, heat or apparatus: no practical risk assessment is triggered beyond the school's normal classroom procedures.
Curriculum references
The NSW syllabus outcomes and Australian Curriculum v9 codes this activity supports. They are references, not a verified or complete curriculum alignment.
- Investigating Science Stage 6 Syllabus (2017), NESA; currentINS11-10INS11/12-2INS11/12-3INS11/12-4
- Australian Curriculum v9No Australian Curriculum v9 code is listed.
Sources
The pages the author read to write this activity.
- www.nsw.gov.au/education-and-training/nesa/curriculum/science/investigating-science-stage-6-2017
- www.csiro.au/en/research/natural-environment/atmosphere/latest-greenhouse-gas-data
- capegrim.csiro.au/GreenhouseGas/data/CapeGrim_CO2_data_download.csv
- education.nsw.gov.au/teaching-and-learning/curriculum/science/science-curriculum-resources-k-12/science-11-12-curriculum-resources/investigating-science-year-11-and-12