Water and Carbon Footprints of Electricity Are Sensitive to Geographical Attribution Methods

Environmental
footprinting methods provide a means to relate the
environmental externalities of electricity production to electricity
consumers. Although several methods have been developed to connect
the environmental footprint of electricity generation to end users,
estimates produced by these methods are inherently uncertain due to
the impossibility of actually tracing electricity from the point of
generation to utilization. Previous studies rarely quantify this uncertainty,
even though it may fundamentally alter their findings and recommendations.
Here, we evaluate the sensitivity of water and carbon footprints estimates
among seven commonly used methods to attribute electricity production
to end users. We assess how sensitive water and carbon electricity
footprint estimates are to attribution methods, how these estimates
change over time, and the main factors contributing to the variability
between methods. We evaluate and make available the water and carbon
footprints of electricity consumption for every city across the contiguous
United States for all assessed methods. We find significant but spatially
heterogeneous variability in water and carbon footprint estimates
across attribution methods. No method consistently overestimated or
underestimated water and carbon footprints for every city. The variation
between attribution methods suggests that future studies need to consider
how the method selected to attribute environmental impacts through
the electrical grid may affect their findings.