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  • Rights: Crown Copyright 2020, CC BY-NC-ND 4.0
    Published 15 October 2020 Referencing Hub media

    James Renwick, Professor of Physical Geography at Victoria University of Wellington and climate change communicator, briefly explains climate change.

    Questions for discussion:

    • What are two ways of changing the climate?
    • Which way is backed up by scientific evidence?



    What’s going on at the moment is that the amount of energy within the Earth – that’s in the air and the water, the oceans and so on – is increasing. There’s more energy in the climate system, so everything is warming up and the cold things are melting, and that’s what people mean by climate change now.

    There are two ways to change the climate. Either the Sun becomes brighter or dimmer or the amount of greenhouse gas in the air goes up or down, because that’s the way that the Earth works.

    Sunlight comes into the Earth and the Earth absorbs that sunlight – mostly the oceans. And the Earth radiates heat energy back to space – the sort of energy our bodies put out – and that energy is absorbed into the atmosphere through greenhouse gases. And that’s very like having a blanket on a bed, and the blanket keeps you warmer because it traps some of that heat underneath. You put a thicker blanket on your bed, you get warmer. You put a thicker blanket of greenhouse gases on the Earth, and the Earth gets warmer. So that’s another way to warm the Earth – add greenhouse gas to the air or the Sun becomes brighter. Now we know the Sun is not becoming brighter – we measure that very accurately.

    It’s true that the climate has always been changing for billions of years. Geological records tell us the climate is actually sensitive. You tweak the amount of sunlight falling on the Earth a bit, you tweak the amount of greenhouse gases like carbon dioxide in the air a bit, and the temperature of the Earth, of the climate can change quite a lot.

    When the dinosaurs went extinct and further back in time, there have been some really rapid changes, but when you look as closely as we can, we’re still talking a thousand years minimum to see much of a change.

    So what’s happening today is that the amount of greenhouse gas in the air has gone up dramatically since the Industrial Revolution – a couple of hundred or getting on for 300 years ago now – when we started burning coal and oil for fuel.

    Greenhouse effect animation adapted from NASA animation What is the Greenhouse Effect?
    Ice core drilling footage from Drilling Back to the Future: Climate Clues from Ancient Ice on Greenland, Climate Central, released under CC BY-NC-ND 3.0
    Graphs of CO2 during the ice ages and CO2 emissions 1750–2019, courtesy of NOAA


    This resource has been produced with the support of the Ministry for the Environment and Stats NZ. (c) Crown Copyright.

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