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Climate Change – Causes and Effects: The natural causes of climate change – are they to blame?

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20 minutes

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Methodology & teacher’s notes

  1. Earth’s climate has changed throughout its history. During the Quaternary period, the oscillation between glacial (colder) and interglacial (warmer) periods are due to three cycles: eccentricity, precession, and axial tilt. Combined, these are known as the ‘Milankovitch Cycles’. Two other natural influences on Earth’s climate are solar irradiance (energy from the sun) and volcanic activity.
    1. Students to complete the match up activity. Answers are below:

     

Going into depth about the Milankovitch Cycles is not necessary and is rather complex, but if you or some students wish to explore further, these interactive tools and videos are worth a play:

The biggest factor in changing Earth’s climate is thought to be axial tilt. Larger axial tilt angles tend to coincide with interglacial periods (the melting and retreat of glaciers and ice sheets). This is because most of the planet’s snow and ice is found towards the poles, so there is more overall summer insolation, and more insolation at the higher latitudes, which melts more of the previous winter’s snow and ice.

  1. The graph underneath the match-up is for reference only, to demonstrate how the Milankovitch cycles come together. If you decided to stretch some students by looking at the links above, writing some notes as annotations on this graph might be one way to record their ideas.              Source: E. Generalic
  2. Begin to show this video, which explores the reason for Earth’s climate change in modern times: and pause at 2:04 (just after the host states “…and all of these affect Earth’s climate”).
    1. Ask the students to guess to what extent do they think natural causes – Milankovitch cycles, volcanic eruptions, and sun activity – are responsible? You could simply get them to call out ‘a little, half of it, most of it…’ etc or even a percentage if they wish – nothing scientific, just to think about the extent today’s climate change is natural vs human. When you have collected guesses, continue the video
    2. Pause the video again at 3:00. What do they think now? (NB: The solar radiation line is not on the graph: while slightly rising on average, it cycles up and down around that zero-degree line. Students will get to see the plot for solar radiation in the next activity.)
    3. Pause at 3:40, with the red ‘greenhouse gasses’ line clearly showing the strongest explanation for observed warming (black line). In short, natural causes have very little influence compared to human causes.
    4. The rest of the video (from 3:40 onwards) is optional, but worth the watch if you have time. If you do, you may wish to play it again from the start to consolidate the messages that might have been lost in the constant pausing.

References, sources & credits

Eccentricity, tilt and precession images: Skeptical Science

Milankovich cycles graph: E. Generalic

Volcanic eruption impact on climate: Hong Kong University

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