A new study from Princeton University suggests that countries around the world are significantly underreporting greenhouse gas emissions from wastewater systems, raising concerns about gaps in climate data and policy planning.
Published in February in the journal Nature Climate Change, the research finds national inventories may underestimate emissions of methane and nitrous oxide by between 19% and 27%. The discrepancy is largely attributed to outdated accounting methods and the omission of sources such as latrines and untreated sewage.
Researchers point to continued reliance on 2006 guidelines from the Intergovernmental Panel on Climate Change (IPCC), rather than updated methodologies introduced in a 2019 refinement, as a key factor behind the undercount.
Z. Jason Ren, a civil and environmental engineering professor at Princeton who led the study, said more accurate data is critical for both public reporting and effective climate action.
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“If you don’t know exactly how much emissions you have, then it’s really difficult to make effective policies or technologies or methods to reduce the emissions,” Ren said in an article published by Princeton Engineering.
Wastewater systems are a major but often overlooked source of greenhouse gases, particularly methane and nitrous oxide, which have significantly higher global warming potential than carbon dioxide. On a CO₂-equivalent basis, emissions from the sector are comparable to those from industries such as aviation and commercial shipping.
Despite their impact, wastewater emissions have received less attention than sectors like transportation and power generation, where carbon dioxide reduction strategies have been studied for decades. Ren said this presents an opportunity: wastewater systems could offer substantial emissions reductions if better understood and managed.
The study analyzed data from 38 countries, including Canada, across five continents, and examined both developed and emerging economies. Researchers compared national reports with updated estimation techniques and found that key emission sources were frequently excluded.
As a result, an estimated 94 to 150 million metric tons of carbon dioxide equivalent may be missing from global emissions totals each year due to gaps in wastewater accounting, the research warns.
The findings are accompanied by a policy paper urging governments and the IPCC to adopt more accurate standards when compiling national inventories. Ren emphasized that improving emissions estimates is not just a technical issue, but a long-term investment in climate decision-making.
Wastewater infrastructure, he noted, is built to last for decades, meaning today’s design and technology choices will shape emissions well into the future.
“If you don’t have an accurate accounting, it’s hard to make good and right decisions, yet such decisions can have long-lasting impacts,” Ren said.
