ATM 623: Climate Modeling

Brian E. J. Rose, University at Albany

Lecture 12: Orbital variations, insolation, and the ice ages

About these notes:

This document uses the interactive IPython notebook format (now also called Jupyter). The notes can be accessed in several different ways:

• The interactive notebooks are hosted on github at https://github.com/brian-rose/ClimateModeling_courseware
• The latest versions can be viewed as static web pages rendered on nbviewer
• A complete snapshot of the notes as of May 2015 (end of spring semester) are available on Brian's website.

Many of these notes make use of the climlab package, available at https://github.com/brian-rose/climlab

Contents

1. The ice ages
2. Introducing the astronomical theory of the ice ages
3. Ellipses and orbits
4. Past orbital variations
5. Using climlab to calculate insolation for arbitrary orbital parameters
6. Past changes in insolation: investigating the Milankovitch hypothesis
7. Understanding the effects of orbital variations on insolation
8. Summary

%matplotlib inline
import numpy as np
import matplotlib.pyplot as plt
from climlab import constants as const

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1. The ice ages

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Recent Earth history (past few million years) has been dominated by the repeated growth and retreat of large continental ice sheets, mostly over the land masses of the Northern Hemisphere.

Extent of glaciation

The images below show typical maximum extents of the ice sheets during recent glaciations (grey) compared with present-day ice sheets (black)

from IPython.display import display, Image
url = []
url.append('http://upload.wikimedia.org/wikipedia/commons/thumb/e/ef/Iceage_north-intergl_glac_hg.png/480px-Iceage_north-intergl_glac_hg.png')
url.append('http://upload.wikimedia.org/wikipedia/commons/thumb/4/44/Iceage_south-intergl_glac_hg.png/480px-Iceage_south-intergl_glac_hg.png')

for u in url:
    display(Image(u))

Hannes Grobe/AWI, http://commons.wikimedia.org/wiki/File:Iceage_north-intergl_glac_hg.png

Pacing of ice ages: evidence from ocean sediments

This figure shows a global record of oxygen isotopes recorded in the shells of marine organisms. This record tells us primarily about variations in global ice volume -- because the net evaporation of water from the oceans to build up the ice sheets leaves the oceans enriched in heavier isotopes.

The x axis is plotted in Thousands of years before present (present-day is at zero on the left).

Image('../images/Lisiecki_Raymo_Fig.4top.png', width=800)