The central aim of the United Nations Paris Agreement on climate change is to strengthen the global response to the threat of climate change by keeping a global temperature rise this century well below 2 ^oC above pre-industrial levels and to pursue efforts to limit the temperature increase even further to 1.5 ^oC.  Most of the attempts to achieve this focus either on reducing the amount of carbon dioxide entering the atmosphere by for example substituting diesel and gasoline vehicles with electric vehicles and/or removing some of the existing carbon dioxide by sequestration. Scientists at Stanford University in the USA have proposed a novel approach in a recent article in Nature which, if implemented, would actually increase the concentration of carbon dioxide in the atmosphere but lower global warming.

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Option C (sub-topic C.5 Environmental impact – global warming) covers the science behind global warming and relates the concentrations of different greenhouse gases in the atmosphere with their global warming potential, GWP. Water and carbon dioxide are the most abundant greenhouse gases in the atmosphere. The concentration of carbon dioxide is currently approximately 415 ppm, up by some 45% of pre-industrial levels. Methane is much less abundant having a concentration of 1866 ppb  a rise of some 2.5 times its pre-industrial level of 722 ppb.  However methane has a much greater GWP than carbon dioxide. GWP is measured over a specific time period (so different sources quote different values) but over a twenty year period methane has a GWP approximately 80 times that of carbon dioxide.  Methane is formed by the anaerobic decomposition of organic matter and much comes from farmed wetland crops (e.g. rice) and ruminant animals so is difficult to reduce at source.

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Both wetlands and Highland cattle are sources of atmospheric methane

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What the Stanford scientists are proposing is to trap existing methane in the atmosphere using zeolites (see sub-topic A.3 Catalysts in Option A). The trapped methane is then converted into carbon dioxide. Although this would increase the carbon dioxide concentration it would considerably lower the overall greenhouse effect of all the gases in the atmosphere. They calculate that if about 3.2 billion tons of methane is removed from the atmosphere it could restore the methane concentrations to pre-industrial levels. This would have the effect of eliminating approximately one-sixth of all causes of global warming to date.