Earth and Environmental Science 11–12 · Year 12
Tree rings as climate records: counting, measuring and cross-dating
Module 7: Climate Science
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The idea
A tree adds one ring a year whose width follows the growing conditions, so ring sequences from overlapping trees give a dated record of past climate.
What you need
- tree cookies (thin cross-sections of a small trunk) from a tree of known felling year, sanded; or the UCAR simulated tree-ring cores and ring image
- hand lens, millimetre ruler or a photograph with a scale, pins, spreadsheet
- a second cookie or scan from another tree of the same species and area
How to do it
- Count rings from bark to pith along two radii and record the age; resolve any disagreement between radii.
- Measure each ring width along one radius to 0.1 mm and plot width against year, counting back from the felling year.
- Mark the narrowest rings (drought or cold years) and the widest.
- Match the narrow-ring pattern to the second tree to cross-date it and extend the record.
- Compare the narrow years with a rainfall record for the district if one is available.
What you should see
The two radii are checked against each other once false and missing rings are resolved; ring width varies from year to year, and the same narrow-ring years appear in both trees, which allows cross-dating (UCAR Trees: recorders of climate change). The plot and the list of narrow years, with their calendar dates, is the deliverable.
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.
- One ring is always one year (false rings occur).
- Ring width shows temperature only (it responds to whatever limits growth that year, rainfall included).
Safety card
Hazards
- splinters
- sanding dust
Controls
- cookies pre-sanded
- wash hands
Note
No hazardous chemicals or heat sources: record the activity in the school's RiskAssess risk assessment, following the NSW Department of Education Science safety and compliance page; the Chemical Safety in Schools package is not triggered.
Curriculum references
The NSW syllabus outcomes and Australian Curriculum v9 codes this activity supports. They are references, not a verified or complete curriculum alignment.
- Earth and Environmental Science Stage 6 Syllabus (2017), NESA; current, replaced by the 11–12 Syllabus (2025) from 2028EES12-14EES11/12-1EES11/12-6EES11/12-7
- Earth and Environmental Science 11–12 Syllabus (2025), NESA; to be implemented from 2028, not yet taughtEES-12-03
- Australian Curriculum v9No Australian Curriculum v9 code is listed.
Sources
The pages the author read to write this activity.