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Climatology

Of ice and elephants

Nature volume 404, pages 23–24 (2000)Cite this article

What caused the great ice ages? Accurate dating of the end of one of these ice ages makes us reconsider which part of the climate system drives severe glaciation.

For over a century, geologists have turned to astronomy for explanations of the cause of ice ages during the Pleistocene epoch (the past 1.6 million years). In the 1870s, James Croll1 first suggested that ice ages were caused by changes in the amount of solar irradiance received at the poles as a result of changes in the shape (with a frequency of about 100,000 years), tilt and wobble (with frequencies of about 40,000 and 20,000 years) of the Earth's orbit around the Sun. Despite the success of this astronomical theory, some fundamental questions remain. We still don't know how subtle changes in the pattern of solar irradiance are amplified to produce such spectacular changes in climate — cooling the deep ocean almost to the freezing point and extending ice sheets thousands of kilometres towards the Equator. And we don't understand why ice ages occur in both hemispheres simultaneously when the changes in solar irradiance from orbital variations have opposite effects in the north and south.

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Figure 1: Timescale of ice ages during the late Pleistocene.

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  1. Department of Earth and Planetary Sciences, Laboratory for Geochemical Oceanography, Harvard University, 20 Oxford Street, Cambridge, 02138, Massachusetts, USA

    Daniel P. Schrag

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  1. Daniel P. Schrag
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Correspondence to Daniel P. Schrag.

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Schrag, D. Of ice and elephants. Nature 404, 23–24 (2000). https://doi.org/10.1038/35003667

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