Study Traces Half the West's Climate-Driven Water Loss to 122 Fossil Fuel Companies

A study published Aug. 25 in Communications Earth & Environment attributes 40% to 64% of the climate-driven decline in western US water supply to emissions from 122 fossil fuel and cement producers, the group the research literature calls the Carbon Majors.

Emily L. Williams and colleagues traced the effect of emissions released by those producers since 1950. Across 2014 to 2024, the authors assign to those emissions a 15% reduction in April 1 snow water equivalent, the amount of water held in the snowpack, or about 35 cubic kilometers a year. They also assign a 6% decline in April-to-September streamflow, about 15 cubic kilometers a year, and a 2.4% rise in irrigation demand, about 0.89 cubic kilometers a year. Those figures are 40% to 64% of the change the authors attribute to all human-caused climate change, not of the total decline in western water.

For California's Central Valley, the paper puts the same emissions at about a third of the groundwater loss it attributes to climate change over 2003 to 2024.

The numbers are modeled attributions rather than measured differences. The authors compare simulations that carry the producers' emissions against counterfactual runs without them, so each figure depends on the emissions inventory and on the hydrological modeling chain used to convert it into snow, streamflow and groundwater.