Natural causes of climate change

Milankovitch cycles (long term)

Changes in Earth's orbit alter how much sunlight reaches different latitudes and seasons (NASA):

• Eccentricity: the orbit varies from more circular to more elliptical over about 100,000 years.
• Obliquity (axial tilt): varies between 22.1 and 24.5 degrees over about 41,000 years; it is now about 23.4 degrees and slowly decreasing.
• Precession: the wobble of the axis; combined precession averages about 23,000 years.

Glacials occurred about every 41,000 years between one and three million years ago; about 800,000 years ago the cycle lengthened to about 100,000 years.

Feedbacks

Orbital changes are small, so feedbacks amplify them:

• Ice-albedo feedback: more ice reflects more sunlight, causing further cooling; melting ice exposes darker surfaces, causing further warming.
• Lower tilt gives milder seasons with cooler summers, so snow survives and builds up at high latitudes.
• Warming oceans release CO2, which adds to the warming (and cooling oceans absorb it).

Solar output and volcanoes (medium and short term)

• Solar output varies with the 11-year sunspot cycle and longer cycles. NASA notes that solar radiation has decreased somewhat over the last 40 years, and that since 1750 greenhouse warming from fossil fuels is over 50 times greater than extra warming from the Sun.
• Volcanic eruptions inject sulphur dioxide into the stratosphere, forming sulphate aerosols that reflect sunlight (global dimming), cooling the surface for a year or two. The June 2025 examiners credited global dimming, not CO2 warming, for this answer.

Why natural causes cannot explain recent warming

NASA gives several reasons:

• Milankovitch cycles act over tens of thousands of years; recent warming has occurred over decades.
• Orbital positions now would favour slow cooling.
• The surface and lower atmosphere are warming while the stratosphere cools, the pattern expected from greenhouse gases rather than the Sun.

Worked example

Explain how a large volcanic eruption can cause short-term global cooling.

1. The eruption injects sulphur dioxide high into the stratosphere.
2. It forms sulphate aerosols that spread around the globe.
3. These reflect incoming sunlight back to space (global dimming), so surface temperatures fall for one to two years.

Answer: Stratospheric sulphate aerosols reflect sunlight, cooling the surface briefly.

Check yourself

1. Earth's axial tilt varies between 22.1 and 24.5 degrees. What is the range of variation in degrees?
   Show answer

   2.4 degrees. 24.5 - 22.1 = 2.4 degrees.

2. Glacial cycles of about 41,000 years became cycles of about 100,000 years. By what factor did the cycle length increase? Give your answer to 2 decimal places.
   Show answer

   2.44. 100,000 / 41,000 = 2.44.

3. Which Milankovitch cycle has the shortest period?
   • Precession
   • Eccentricity
   • Obliquity
   • The sunspot cycle
   Show answer

   Precession. About 23,000 years, against 41,000 and 100,000.

4. Large explosive eruptions cool the climate mainly because
   • they release large amounts of CO2
   • lava cools the oceans
   • ash melts glaciers
   • sulphate aerosols in the stratosphere reflect sunlight
   Show answer

   sulphate aerosols in the stratosphere reflect sunlight. Global dimming: aerosols reflect solar radiation.

5. Why can Milankovitch cycles NOT explain the warming of recent decades?
   • They stopped 800,000 years ago
   • They operate over tens of thousands of years, far too slowly
   • They only affect the Southern Hemisphere
   • They cause warming only in winter
   Show answer

   They operate over tens of thousands of years, far too slowly. Recent warming has happened over decades (NASA).

6. According to NASA, since 1750 warming from fossil-fuel greenhouse gases compared with extra warming from the Sun is
   • about the same
   • half as large
   • unknown
   • over 50 times greater
   Show answer

   over 50 times greater. NASA: greenhouse warming is over 50 times the slight solar contribution.

7. Explain how the ice-albedo feedback amplifies a small orbital cooling.
   Show answer

   Cooling lets more ice and snow build up; ice has a high albedo so it reflects more sunlight, which causes further cooling and more ice.. More ice reflects more sunlight, causing more cooling and more ice.

Practise with instant feedback Print this lesson

Sources

• Pearson Edexcel International Advanced Subsidiary/Advanced Level in Geography specification (Issue 3, September 2025)
• NASA Science: Milankovitch (orbital) cycles and their role in Earth's climate (updated 22 October 2024)
• NASA Science: Why Milankovitch (orbital) cycles can't explain Earth's current warming (updated 23 October 2024)
• Pearson principal examiner report, WGE01 Global Challenges, June 2025
• Pearson WGE01 mark scheme, June 2025 (copy hosted by Physics and Maths Tutor)

Last updated 8 November 2026. Spotted a mistake? Tell us.