Greenhouse gases influence the climate because they interact with flows of heat energy in the atmosphere. The main greenhouse gases that are affected by human activities and are relevant to agriculture are carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O).
These gases vary in their potency or effect on the atmosphere, with methane being 21 times more potent than carbon dioxide, and nitrous oxide being 310 times more potent than carbon dioxide. This means that one molecule of methane has the same effect on global warming as 21 molecules of carbon dioxide. The reason some gases are more potent than others is a complex combination of factors including among other things, the gas’s longevity in the atmosphere and its molecular structure which determines its ability to trap or reflect heat.
All greenhouse gases are measured in global warming potential units known as Carbon Dioxide Equivalents (CO2-e). This simply means that one molecule of carbon dioxide is 1 CO2-e, one molecule of methane is 21 CO2-e and one molecule of nitrous oxide is 310 CO2-e.
According to the CSIRO or The World Meteorology, the atmospheric level of CO2 rose from around 280 parts per million (ppm) in 1800, to 386 ppm in 2009, and is increasing at nearly 2ppm per year. To have a chance of keeping human induced, average global warming below 2°C, cumulative emissions need to stay below one trillion tonnes of carbon. The world has already emitted more than half of this amount since the industrial revolution, and (at current growth rates for CO2 emissions) the rest will be emitted by the middle of this century.1
Carbon dioxide, methane and nitrous oxide are all emitted by agriculture. Jump to the climate change and agriculture page for more detail.
For a more detailed explanation of greenhouse gases and their actions in the atmosphere, click here to read the relevant chapter from the CSIRO publication Climate Change: Science and Solutions for Australia.