Climate Change: Science and Solutions for Australia
Chapter 2: Climate and greenhouse gases
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.
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.
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