Abstract
Cities dominate greenhouse gas emissions. Many have generated self-reported emission inventories, but their value to emissions mitigation depends on their accuracy, which remains untested. Here, we compare self-reported inventories from 48 US cities to independent estimates from the Vulcan carbon dioxide emissions data product, which is consistent with atmospheric measurements. We found that cities under-report their own greenhouse gas emissions, on average, by 18.3% (range: −145.5% to +63.5%) – a difference which if extrapolated to all U.S. cities, exceeds California’s total emissions by 23.5%. Differences arise because city inventories omit particular fuels and source types and estimate transportation emissions differently. These results raise concerns about self-reported inventories in planning or assessing emissions, and warrant consideration of the new urban greenhouse gas information system recently developed by the scientific community.
Highlights
A necessary element in urban emissions mitigation is the development of a numerical accounting of greenhouse gas (GHG) emissions following a standardized method[6]
We have investigated 48 SRIs published online by cities in the USA and compare these to urban extractions from our recently completed, research-driven Vulcan version 3.0 estimate of US fossil fuel carbon dioxide (FFCO2) emissions
The mean relative difference (RD) between the two emission datasets is +18.3% (Vulcan > SRI; calculated as [(Vulcan – SRI)/ average(Vulcan, SRI)]) with a mean absolute relative difference (MAD) of 29.1% (Fig. 1). This is in the context of a mean RD 95% confidence interval of +5.2%/+31.7% for the Vulcan urban emissions
Summary
Differences arise because city inventories omit particular fuels and source types and estimate transportation emissions differently These results raise concerns about self-reported inventories in planning or assessing emissions, and warrant consideration of the new urban greenhouse gas information system recently developed by the scientific community. There is no systematic, peerreviewed assessment of SRI quality or accuracy in spite of their importance to establishing baseline emissions, urban mitigation target setting, and mitigation outcome assessment Given this assessment gap, we have investigated 48 SRIs published online by cities in the USA and compare these to urban extractions from our recently completed, research-driven Vulcan version 3.0 estimate of US fossil fuel carbon dioxide (FFCO2) emissions. The omission of sub-sector elements in the SRI (e.g., individual fuels within a sector, individual factories in the city domain), rarely documented, are considered part of the comparison in this analysis, and not adjusted for (see “Methods”)
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