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Ice Ages and Climate Change – Milankovitch Cycles, the Sun, Volcanoes and CO₂

GeographyWeather & ClimateAges 15–16

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Switch each climate driver on or off: the three Milankovitch cycles (eccentricity about 100 000 years, axial tilt about 41 000 years, precession about 23 000 years), changes in solar output, volcanic aerosols and fossil-fuel CO₂. Compare the modelled temperature and CO₂ with an ice-core-style record over the last 800 000 years (glacial and interglacial periods) and over the last 2000 years. Adding fossil-fuel CO₂ shows today's level far outside the natural range. Record each experiment in a table.

Lesson: Causes of climate change: Milankovitch cycles, glacial and interglacial periods, ice-core evidence, solar output, volcanic eruptions and human CO₂ emissions

What it shows

Earth's climate has swung between cold glacials and warm interglacials for the last 800 000 years. Slow changes in Earth's orbit – its shape (eccentricity), the tilt of its axis (obliquity) and the wobble of the axis (precession) – change how much summer sunshine reaches high northern latitudes. Ice sheets grow when summers are weak and melt when they are strong, and CO₂ falls and rises with them, amplifying the change. The Sun and volcanoes cause smaller, shorter changes. Since about 1850, burning fossil fuels has pushed CO₂ far above its natural range.

How to use

Choose a Time window, then tick or untick Eccentricity, Axial tilt, Precession, Changes in solar output, Volcanic aerosols and Fossil-fuel CO₂. Compare the blue model line with the grey record and read r below. Drag Selected time or along the graphs, or press Play, to follow the orbit and the ice sheets. Press Record to save each experiment in the table.

Parameters you can change

  • Time window Last 800 000 years, Last 150 000 years, Last 2000 years
  • Eccentricity cycle (~100 000 years)
  • Axial tilt (obliquity) cycle (~41 000 years)
  • Precession cycle (~23 000 years)
  • Changes in solar output
  • Volcanic aerosols
  • Fossil-fuel CO₂
  • Show ice-core-style record

Questions to explore

  1. Which orbital cycle can only change the climate when Earth's orbit is not a circle, and why?
  2. Why do ice sheets take tens of thousands of years to grow but melt in only a few thousand?
  3. How far is today's CO₂ level outside the range recorded in ice cores, and which switch is needed to explain it?

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