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Current methods for estimating sanitation emissions underestimate the significance of methane emissions from non-sewered sanitation systems (NSSS), which are prevalent in many countries. NSSS play a vital role in the safe management of fecal sludge, accounting for approximately half of all existing sanitation provisions. We analyzed the distribution of global NSSS and used IPCC accounting methods to estimate the total methane emissions profiles from these systems. Then, we examined the literature to establish the level of uncertainty associated with this accounting estimate. The global methane emissions from NSSS in 2020 was estimated to as 377 (22–1003) Mt CO 2 e/year or 4.7% (0.3%–12.5%) of global anthropogenic methane emissions, which are comparable to the greenhouse gas (GHG) emissions from wastewater treatment plants. NSSS is the major option for open defecation and is expected to increase by 55 Mt CO 2 e/year after complete open defecation free. It is time to acknowledge the GHG emissions from the NSSS as a non-negligible source. • The global distribution of NSSS was partially visualized. • The CH 4 emission from global NSSS was tentatively calculated. • The impact of temperature on the in-situ monitoring was briefly analyzed. • The carbon emissions from NSSS and WWTPs were generally compared. [ABSTRACT FROM AUTHOR]

Current methods for estimating sanitation emissions underestimate the significance of methane emissions from non-sewered sanitation systems (NSSS), which are prevalent in many countries. NSSS play a vital role in the safe management of fecal sludge, accounting for approximately half of all existing sanitation provisions. We analyzed the distribution of global NSSS and used IPCC accounting methods to estimate the total methane emissions profiles from these systems. Then, we examined the literature to establish the level of uncertainty associated with this accounting estimate. The global methane emissions from NSSS in 2020 was estimated to as 377 (22–1003) Mt CO 2 e/year or 4.7% (0.3%–12.5%) of global anthropogenic methane emissions, which are comparable to the greenhouse gas (GHG) emissions from wastewater treatment plants. NSSS is the major option for open defecation and is expected to increase by 55 Mt CO 2 e/year after complete open defecation free. It is time to acknowledge the GHG emissions from the NSSS as a non-negligible source. • The global distribution of NSSS was partially visualized. • The CH 4 emission from global NSSS was tentatively calculated. • The impact of temperature on the in-situ monitoring was briefly analyzed. • The carbon emissions from NSSS and WWTPs were generally compared. [ABSTRACT FROM AUTHOR]