Milankovich cycles

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• Environmental Systems and Societies (DP ESS)
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Milankovich cycles

Are we getting another ice age?

Topic 6: Atmosphere & Climate Change

6.1: Introduction to the atmosphere

(HL content)

Prior knowledge: summers and winters

Source: https://www.lpi.usra.edu/education/skytellers/seasons/

What defines the Earth´s seasons?

A

The distance between the Earth and the Sun

B

The tilt of the Earths axis

C

Answer C

D

Answer D

Currently, is the overall temperature on Earth increasing or decreasing?

A

Increasing

B

Decreasing

C

Answer C

D

Answer D

What is the main cause of global warming?

A

Human emission of greenhouse gases

B

Astronomical Milankovich cycles

C

Answer C

D

Answer D

Milankovich cycles

• Astronomical variations in Earth's orbit and axis

• Control the distribution and intensity of solar radiation on the Earth´s surface

• Drive long-term climate change and are linked to the occurence of ice ages and interglacial periods

--> We are currently in an interglacial phase; and the next ice age is likely more than 50,000 years away. According to Milankovitch cycles alone, the Earth should be showing a very slow long-term cooling trend right now.

Milankovich cycles

• Eccentricity (~ 100,000-year cycles)

  • Changes in the shape of Earth's orbit from circular to more elliptical

  • Slightly changes the total amount of insolation of the Earth´s surface

• Obliquity (~ 41,000-year cycles)

  • Changes in axial tilt of the Earth between about 22.1° and 24.5°

  • Affects the strength of the seasons (more tilt -> stronger seasons)

• Precession (~ 26.000-year cycles)

  • Slow wobble of Earth's rotational axis, changing its orientation in space

  • Shifts the timing of seasons relative to Earth’s orbital position, making them more or less extreme.

Take home message

The shape, tilt and wobble of Eath´s movement, over thousands of years, affects long-term climate.






Milankovich cycles would eventually cause another ice age, in about 50.000 years. But... on a much smaller time schale, human-caused greenhouse gas emissions are currently causing the Earth to warm up instead.
Source: https://s3.amazonaws.com/medill.wordpress.offload/wp-media-folder-medill-reports-chicago/wp-content/uploads/sites/3/2020/10/fixed.medill.milankovitch-1.gif

Exam question (paper 2: data-based)

Figure 1. Variations in Earth's eccentricity, obliquity, and precession, and their combined effect on insolation over the last 800 000 years. (Source: https://www.researchgate.net/figure/Variation-in-eccentricity-obliquity-and-precession-over-the-past-800-ka-and-their_fig1_329346514

Use figure 1, showing Milankovitch cycles and their combined effect on insolation (solar radiation reaching Earth), to answer the questions below.

1a. Identify the three Milankovitch cycles shown in Figure 1 and state the approximate periodicity of each cycle. [3 marks]

1b. Describe the relationship between the three Milankovitch cycles and the combined insolation curve shown in Figure 1. [4 marks]

1c. Compare and contrast the causes, timescales, and environmental impacts of climate change driven by Milankovitch cycles and climate change driven by human activities. [6 marks]

MARKSCHEME 1a

1a. Identify the three Milankovitch cycles shown in Figure 1 and state the approximate periodicity of each cycle. [3 marks]

Eccentricity: ~100 000 years (or 400 000 years)
Obliquity: ~41 000 years
Precession: ~23 000 years

Figure 1. Variations in Earth's eccentricity, obliquity, and precession, and their combined effect on insolation over the last 800 000 years. (Source: https://www.researchgate.net/figure/Variation-in-eccentricity-obliquity-and-precession-over-the-past-800-ka-and-their_fig1_329346514

MARKSCHEME 1b

1b. Describe the relationship between the three Milankovitch cycles and the combined insolation curve shown in Figure 1. [4 marks]

• Combined insolation is influenced by all three cycles.

• The cycles have different periodicities or timeframes.

• Peaks and troughs occur when the effects of the cycles reinforce or oppose each other.

• Higher insolation is generally associated with warmer (interglacial) periods, while lower insolation is associated with cooler (glacial) periods.

Figure 1. Variations in Earth's eccentricity, obliquity, and precession, and their combined effect on insolation over the last 800 000 years. (Source: https://www.researchgate.net/figure/Variation-in-eccentricity-obliquity-and-precession-over-the-past-800-ka-and-their_fig1_329346514

MARKSCHEME 1c

1c. Compare and contrast the causes, timescales, and environmental impacts of climate change driven by Milankovitch cycles and climate change driven by human activities. [6 marks]

Compare (similarities):

• Both can change global climate patterns and temperatures.

• Both can affect biodiversity and species distributions.

• Both can be predicted by models based on past climate data.

Contrast (differences):

• Milankovitch cycles are caused by astronomical variations, wheras human-caused climate change by the emission of greenhouse gases.

• Milankovitch cycles are very slow (100 - 100 000 years), whereas human-caused climate change is much faster (10-100 years).

• Milankovitch cycles are driving glacial/interglacial periods, whereas human-caused climate change is mostly linked to sea-level rise, ocean acidification, and increased extreme weather.

Figure 1. Variations in Earth's eccentricity, obliquity, and precession, and their combined effect on insolation over the last 800 000 years. (Source: https://www.researchgate.net/figure/Variation-in-eccentricity-obliquity-and-precession-over-the-past-800-ka-and-their_fig1_329346514

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