Climate Change: Science and Solutions for Australia

  1. Overview
  2. Foreword
  3. Contents, List of authors, Acknowledgements
  4. Introduction
  5. Chapter 1: Observations of global and Australian climate
  6. Chapter 2: Climate and greenhouse gases
  7. Chapter 3: Future Australian climate scenarios
  8. Chapter 4: Climate change impacts
  9. Chapter 5: Adaptation: reducing risk, gaining opportunity
  10. Chapter 6: Adapting to heatwaves and coastal flooding
  11. Chapter 7: Adapting agriculture to climate change
  12. Chapter 8: Greenhouse gas mitigation: sources and sinks in agriculture and forestry
  13. Chapter 9: Mitigation strategies for energy and transport
  14. Chapter 10: Reducing energy demand: the imperative for behavioural change
  15. Chapter 11: Responding to a changing climate
  16. Endnotes, Index

Chapter 2: Climate and greenhouse gases

Page 6 of 16

Landscape with chimney stacks.

By Dr Michael Raupach and Dr Paul Fraser

Greenhouse gases influence the Earth’s climate because they interact with flows of heat energy in the atmosphere.

The atmospheric level of carbon dioxide (the most important greenhouse gas influenced by human activities) rose from about 280 ppm in 1800 to 386 ppm in 2009, and is currently increasing at nearly two ppm per year.

Overview

The main greenhouse gases influenced directly by human activities are carbon dioxide (CO2) methane, nitrous oxide, ozone, and synthetic gases. Water vapour, although an important GHG, is not influenced directly by human activities.

CO2 levels are rising mainly because of the burning of fossil fuels and deforestation. Over half of this CO2 input to the atmosphere is off set by natural CO2 sinks in the land and oceans, which constitute a massive natural ecosystem service helping to mitigate humanity’s emissions.

To have a 50:50 chance of keeping human-induced average global warming below 2 °C, it will be necessary to stop almost all CO2 emissions before cumulative emissions reach one trillion tonnes of carbon. The world has already emitted more than half of this quota since the industrial revolution, and (at current growth rates for CO2 emissions) the rest will be emitted by the middle of this century.

Climate change is a risk management issue – the longer we take to act and the weaker our actions, the greater the risk of dangerous outcomes.

Discover more about Climate and greenhouse gases:

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Climate Change - Dr Michael Raupach

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Transcript

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For the CSIRO climate book Paul Fraser and I wrote a chapter called Climate and Greenhouse Gases, and the first thing we discuss is the fact that certain gases in the Earth’s atmosphere interact with radiation, and therefore are called greenhouse gases, because they act like an insulating blanket that warms the Earth. The most important of these gases are carbon dioxide, methane, nitrous oxide, some artificial gases like CFC’s, and additionally water vapour. All of those, except for water vapour, are strongly influenced by human activities. Water vapour’s a bit different, it responds to the temperature of the Earth’s system, rather than responding directly to human influence.

If we look at the most important of the greenhouse gases that are influenced by human activities, that’s carbon dioxide, we find that its concentration has risen since the start of the industrial revolution around 1800, from about 280 parts per million, to around nearly 390 parts per million at present, and it’s rising now at nearly two parts per million per year – a very rapid rate of rise. And the major reason for this rapid increase in carbon dioxide concentration is emissions of CO2 from human activities, largely the burning of fossil fuels, and to some extent deforestation, the chopping down of forests, now happening mostly in tropical regions.

Finally we can ask how much carbon dioxide can we emit in order to have a reasonable chance of avoiding major risks from dangerous climate change. The question of what’s a major risk is a value judgement, but it’s widely agreed that a threshold of two degrees centigrade of warming above pre-industrial temperatures marks the point at which risks from climate change start to become significant and accelerate substantially.

In order to stay below this two degree threshold we can emit a total of one trillion tonnes of carbon dioxide since the start of the industrial revolution back in 1800. Up to now we’ve emitted well over half a trillion tonnes, and at present growth rates for atmospheric carbon dioxide emissions, this means that the rest of that one trillion tonne quota will be emitted in a timeframe of 30 to 40 years. That means that the need to act on climate change, the need to reduce emissions is urgent, because if we don’t we’ll have lost the chance to get into... to avoid substantial risks from dangerous climate change.

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