This month's chart comes from a paper published last year in Nature Climate Change examining the potential to reduce greenhouse gas emissions from faecal sludge. It is topical this month because of the US and EU pledge to reduce methane emissions by 30% by 2030 (see The List overleaf). The water sector contributes to methane emissions largely because of inadequate wastewater treatment. Emissions from faecal sludge in cities in low-income countries where there is no sewerage are particularly problematic. The chart illustrates the overall global warming potential of combined methane, nitrous oxide and carbon dioxide, according to different faecal sludge management practices. The authors of the paper, led by Gavin McNicol of Stanford University, argue that off-site composting can reduce the per capita emissions of slum dwellers by as much as 126Kg CO_2e per year. Overall, it might be possible to mitigate 13-44% of the sanitation sector's CH_4 emissions in this manner.
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