What natural processes drive climate change and how do we know past climates?
Explain natural causes of climate change and the proxy evidence for past climates
A focused answer to the WACE Year 12 Earth and Environmental Science dot point on natural climate change. Covers Milankovitch cycles, solar and volcanic forcing, feedbacks, and proxy records from ice cores, sediments and tree rings, with examples.
Reviewed by: AI editorial process; not yet individually human-reviewed
Have a quick question? Jump to the Q&A page
What this dot point is asking
SCSA wants you to explain the natural drivers of climate change and the proxy evidence used to study them. A strong answer links each driver to how it changes energy balance and names the proxy that records each kind of change. This sets up the human-caused change examined in the next dot point.
Earth's energy balance
Climate reflects the balance between energy arriving from the Sun and energy radiated back to space. Anything that changes incoming solar energy, how much is reflected, or how much heat is trapped by the atmosphere acts as a climate forcing. Natural forcings have driven ice ages and warm periods long before humans.
Natural drivers of climate change
- Milankovitch cycles: slow, regular changes in the shape of Earth's orbit, the tilt of its axis and the wobble (precession) of that axis alter how sunlight is distributed across the planet over tens of thousands of years. These cycles pace the ice ages.
- Solar variation: the Sun's output changes slightly over time, altering incoming energy.
- Volcanic eruptions: large eruptions inject ash and sulfate aerosols into the upper atmosphere, reflecting sunlight and causing short-term cooling for a few years.
- Greenhouse gas changes: natural shifts in carbon dioxide and methane, for example from oceans warming and releasing gas, change how much heat is trapped.
- Plate tectonics: over very long timescales, moving continents alter ocean currents and weathering, affecting climate.
Feedbacks amplify change
Feedbacks can magnify a small forcing.
- Ice-albedo feedback: warming melts reflective ice, exposing darker land and ocean that absorb more heat, causing further warming. Cooling works the reverse way.
- Water vapour feedback: warmer air holds more water vapour, itself a greenhouse gas, adding warming.
- Carbon feedbacks: warming oceans release dissolved carbon dioxide, adding more warming.
These feedbacks explain how modest orbital changes can trigger full glacial cycles.
Proxy evidence for past climates
Because instruments only record the last century or two, scientists reconstruct earlier climates from proxies.
- Ice cores from Antarctica and Greenland trap ancient air bubbles, giving direct samples of past atmospheric carbon dioxide and methane, while the ice chemistry indicates past temperature. Cores extend records back hundreds of thousands of years.
- Ocean sediment cores contain the shells of microorganisms whose chemistry records past ocean temperature, plus layers that reveal past conditions.
- Tree rings record year-by-year growth, with ring width reflecting temperature and rainfall.
- Pollen preserved in lake and bog sediments shows which plants grew, indicating past climate.
- Coral and speleothems (cave deposits) add further dated records.
Multiple proxies that agree give confidence in a reconstruction.
Exam-style practice questions
Practice questions written in the style of SCSA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
WACE 20217 marksDescribe the natural causes of climate change and explain how proxy records such as ice cores allow scientists to reconstruct past climates beyond the instrumental record.Show worked answer →
A 7 mark answer needs the natural drivers plus how proxies extend the record.
- Natural causes
- Milankovitch cycles (orbital eccentricity, axial tilt and precession) redistribute sunlight and pace the ice ages over tens of thousands of years; solar output varies slightly; large volcanic eruptions inject reflective aerosols causing short-term cooling; natural shifts in greenhouse gases (oceans releasing carbon dioxide) change heat trapping; and over very long times plate tectonics alters currents and weathering. Feedbacks (ice-albedo, water vapour, carbon) amplify these.
- Proxies
- Instruments only cover the last century or two, so proxies stand in for earlier measurements. Ice cores trap ancient air bubbles giving direct samples of past carbon dioxide and methane, while ice chemistry indicates past temperature, extending records hundreds of thousands of years. (Sediment cores, tree rings, pollen and coral add corroborating records.)
- Link
- Because multiple proxies agree, scientists can reconstruct past climate confidently and show carbon dioxide and temperature have long been closely linked.
Markers reward several natural drivers and a clear account of how ice cores provide direct gas samples and temperature indicators back beyond the instrumental era.
WACE 20236 marksDistinguish between a climate forcing and a climate feedback, and use ice-albedo feedback to explain how a small natural forcing can produce a large climate change.Show worked answer →
A 6 mark answer needs the forcing-feedback distinction applied to ice-albedo.
Distinction. A forcing is a factor that initiates a climate change by altering the energy balance (for example an orbital change reducing high-latitude summer sunlight). A feedback is a response to that change which either amplifies it (positive) or dampens it (negative).
Ice-albedo feedback. Suppose an orbital forcing causes slight cooling so a little extra ice forms. Ice is bright and reflective (high albedo), so it reflects more sunlight back to space, reducing absorbed energy and cooling the surface further, which forms yet more ice. This positive feedback loop amplifies the small initial cooling into a much larger change, helping turn a modest orbital nudge into a full glacial period (and the reverse on warming).
Markers reward the initiate-versus-respond distinction and a correct positive-feedback loop (more ice, more reflection, more cooling, more ice) showing amplification.