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  • Rights: Thin Ice/University of Waikato
    Published 11 April 2017 Referencing Hub media

    Professors Jane Francis and Matt Huber explain how fossilised plants are one of several proxies used to form a picture of past climates and ecosystems.


    Professor Jane Francis

    The really important thing is to use the multi-proxy approach so to get as much evidence about the ancient environment and the climate as we can from all different kinds of sources to back up the interpretations. So the nearest living relative, how its nearest living relative lived. Some of the analysis we do on the wood and the leaves by looking at specific anatomical characteristics of the wood and leaves that we know are specific features that are adapted to climate today – temperature, rainfall and things like that.

    Professor Matthew Huber

    Over the past couple of hundred thousand years, we can go to ice core records, but if you want to go further back into the past, you have to rely on entirely different kinds of approaches. We have a variety of different paleo-PCO2 proxies, different proxies for atmospheric carbon dioxide concentrations.

    One of them depends on the number of stomata on a leaf. So leaves obviously take in carbon dioxide as part of the normal process of a plant living, and they have developed a very carefully controlled system by which they open and close their stomata – the little holes in the leaf that control how much water vapour and CO2 enter and leave a leaf. These are very sensitive indicators of past CO2, and people who have a lot of time on their hands sit down with a little microscope and actually count the number of stomata within a centimetre of a leaf and look at the density of stomata on fossil leaves. You can use that technique with leaves from an herbarium so you can actually look at leaves that were living in the past hundred years and that are sitting in the collections of botanical institutes and validate that, yes, over the past hundred years, these leaves are reproducing the CO2 change that we know happened. And then you can use these same records to go back much further – 50 million years ago if you want.


    This video is an extract from Thin Ice – The Inside Story of Climate Science, a David Sington/Simon Lamb film.

    The full documentary film is available by emailing The link for streaming is available free of charge. The DVD is also available to New Zealand schools for $20 to cover costs.

    © Thin Ice/University of Waikato

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