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    • Rights: Crown Copyright 2020, CC BY-NC-ND 4.0
    Published 15 October 2020 Referencing Hub media
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    Climate1 expert James Renwick explains how detective chemistry provides the evidence2 that humans are responsible for climate change3.

    Questions for discussion:

    • How much have greenhouse gas4 levels increased from the pre-industrial level?
    • What does James mean by the phrase ‘detective chemistry’?

    Transcript

    DREW BINGHAM

    It’s very clear that humans are causing climate change right now. Just the weight of evidence we’ve accumulated over the years show that it is from humans.

    PROFESSOR JAMES RENWICK

    We do know that it’s caused by humans, by us. And that’s what people mean by climate change now. So what’s happening today is that the amount of greenhouse gas in the air is going up dramatically, and we measure that very carefully as well, and we know that greenhouse gas levels, carbon dioxide5 especially, has gone up nearly 50% in the last couple of hundred years from what we call the pre-industrial level.

    And then, we can look at the chemistry of that carbon dioxide and methane6 and so on, and we can tell that most of the increase comes from what we call fossil carbon7. Human activity, industrial activity releases carbon dioxide into the air – we burn fossil fuels8. There are radioactive9 isotopes10, there’s a chemical signature to the carbon dioxide that we breathe out every day, and there’s a chemical signature to the carbon that comes from a source that’s been underground for a very long time such as coal and oil. So if you dig up that old carbon and burn it and put carbon dioxide in the air, what you see is these little trace bits of radioactivity11 going down, so the carbon in the atmosphere12 is becoming less radioactive. It’s a tiny fraction, but it’s there, we can measure it.

    It’s a bit of detective chemistry really, but the numbers all add up. We know that the amount that’s going into the atmosphere and the oceans matches up with the amount that we burn every year. So it’s pretty conclusive that it’s human burning of fossil fuels that’s mostly changing the climate.

    Acknowledgements
    Drew Bingham, Ministry for the Environment
    Professor James Renwick, Victoria University of Wellington
    Baring Head, and Principal Technician Gordon Brailsford collecting and analysing air samples, NIWA
    Mass spectrometry13 screengrabs, Gordon Brailsford, NIWA
    Graph CO2 concentrations at Baring Head, NIWA

    Acknowledgement

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

    1. climate: The weather conditions of an area averaged over a series of years, usually 30 or more.
    2. evidence: Data, or information, used to prove or disprove something.
    3. climate change: The large-scale, long-term increase in the Earth’s average temperatures, with associated changes in weather patterns. There is significant scientific evidence that warming is due to increased quantities of greenhouse gases in the atmosphere, with most of the rise due to human activity.
    4. greenhouse gases: A natural or manmade gas that traps heat in the Earth's atmosphere and contributes to the greenhouse effect. The main greenhouse gases are water vapour, carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), ozone and industrial gases such as chlorofluorocarbons (CFCs). These gases in the Earth's atmosphere trap warmth from the Sun and make life possible. An overabundance of greenhouse gases leads to a rise in global temperatures – known as the greenhouse effect.
    5. carbon dioxide: CO2 is a colourless, odourless, incombustible gas. It is a product of cellular respiration and combustion and is an essential component in photosynthesis.
    6. methane: CH4, a gas that contributes to the greenhouse effect.
    7. carbon: A non-metal element (C). It is a key component of living things.
    8. fossil fuel: Materials such as coal, oil and natural gas formed from the fossilised remains of plants that lived many millions of years ago. Often burned as fuel – although this releases large amounts of CO2, which contributes to global warming. Fossil fuels are also not renewable – there is a limited amount.
    9. radioactive: Giving off energy as a result of the breaking up of nuclei of atoms. Something undergoing radioactive decay, the process by which an unstable atom emits radiation.
    10. isotope: Different forms of atoms of the same element. Within the nucleus, there is the same number of protons but a different number of neutrons, giving each isotope a different atomic mass.
    11. radioactivity: The spontaneous emission of radiation from an atom’s nucleus.
    12. atmosphere: 1. The layer of gas around the Earth. 2. (atm) A non-SI unit of pressure equivalent to 101.325 kPa.
    13. mass spectrometry: An analytical technique measuring the characteristics of individual molecules by converting them to ions.

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    • ARTICLE

    What is climate change?

    Climate change is defined as a long-term change to the Earth’s climate. But what does this mean? To understand climate change, we need to understand what makes up our climate. Rights: Crown ...

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      climate

    1. + Create new collection

      2. The weather conditions of an area averaged over a series of years, usually 30 or more.

      greenhouse gases

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      3. A natural or manmade gas that traps heat in the Earth's atmosphere and contributes to the greenhouse effect. The main greenhouse gases are water vapour, carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), ozone and industrial gases such as chlorofluorocarbons (CFCs). These gases in the Earth's atmosphere trap warmth from the Sun and make life possible. An overabundance of greenhouse gases leads to a rise in global temperatures – known as the greenhouse effect.

      carbon

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      4. A non-metal element (C). It is a key component of living things.

      isotope

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      5. Different forms of atoms of the same element. Within the nucleus, there is the same number of protons but a different number of neutrons, giving each isotope a different atomic mass.

      mass spectrometry

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      6. An analytical technique measuring the characteristics of individual molecules by converting them to ions.

      evidence

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      7. Data, or information, used to prove or disprove something.

      carbon dioxide

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      8. CO2 is a colourless, odourless, incombustible gas. It is a product of cellular respiration and combustion and is an essential component in photosynthesis.

      fossil fuel

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      9. Materials such as coal, oil and natural gas formed from the fossilised remains of plants that lived many millions of years ago. Often burned as fuel – although this releases large amounts of CO2, which contributes to global warming. Fossil fuels are also not renewable – there is a limited amount.

      radioactivity

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      10. The spontaneous emission of radiation from an atom’s nucleus.

      climate change

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      11. The large-scale, long-term increase in the Earth’s average temperatures, with associated changes in weather patterns. There is significant scientific evidence that warming is due to increased quantities of greenhouse gases in the atmosphere, with most of the rise due to human activity.

      methane

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      12. CH4, a gas that contributes to the greenhouse effect.

      radioactive

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      13. Giving off energy as a result of the breaking up of nuclei of atoms. Something undergoing radioactive decay, the process by which an unstable atom emits radiation.

      atmosphere

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      14. 1. The layer of gas around the Earth.

      2. (atm) A non-SI unit of pressure equivalent to 101.325 kPa.

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