Half of the water crisis in the semi-arid western US (WUS) has been linked to 122 fossil fuel producers and cement manufacturers (carbon majors) according to the first ever attribution study published in the journal Communications Earth & Environment on August 25, 2026.
Emissions traced to the carbon majors have substantially reduced water supply and increased water demand across the WUS.
These changes have led to a widening seasonal gap between water supply and demand, with carbon majors’ emissions accounting for 1/3 of observed, climatically-driven groundwater loss in California’s Central Valley during 2003-2024.
The researchers from the Union of Concerned Scientists and University of California, Merced quantified impacts on western US water resources attributable to the carbon majors, and compared the results with a simpler, proportional approach.
This corresponds to 42 per cent, 47 per cent, and 56 per cent of the changes attributable to ACC, respectively.
Half of the water crisis in the semi-arid western US (WUS) has been linked to 122 fossil fuel producers and cement manufacturers (carbon majors) according to the first ever attribution study published in the journal Communications Earth & Environment on August 25, 2026.
Emissions traced to the carbon majors have substantially reduced water supply and increased water demand across the WUS. Emissions since 1950 (CM1950) account for roughly half (40-64 per cent) of the impacts attributable to anthropogenic climate change (ACC).
These changes have led to a widening seasonal gap between water supply and demand, with carbon majors’ emissions accounting for 1/3 of observed, climatically-driven groundwater loss in California’s Central Valley during 2003-2024.
The researchers from the Union of Concerned Scientists and University of California, Merced quantified impacts on western US water resources attributable to the carbon majors, and compared the results with a simpler, proportional approach.
Roughly 70 per cent of global industrial carbon dioxide (CO2) emissions since 1854 are traceable to the 122 carbon majors, and 97 per cent of these emissions occurred after 1950—a decade when many of these entities began to understand the consequences of their products.
CM1950 has led to 35 km3/year less April 1st snow water equivalent (SWEApr1), 15 km3/year less warm season streamflow (streamflowwarm), and 0.9 km3/year more irrigation demand across the WUS over the past decade. This corresponds to 42 per cent, 47 per cent, and 56 per cent of the changes attributable to ACC, respectively.
This means that the annual decline in SWEApr1 across the WUS due to CM1950 is roughly equivalent to the maximum capacity of Lake Mead (the largest human-made reservoir in the US), and the increase in irrigation demand due to CM1950 is 1/3 of the annual residential water use of California.
Hotspots of hydrologic disruption
The analysis revealed two hotspots of hydrologic disruption concentrated in the Pacific Northwest and northern California. In these areas, basins experienced a substantial decrease in SWEApr1 and streamflowwarm, along with an increase in total annual irrigation demand.
In these basins, anthropogenic forcing has led to a widening seasonal gap between water supply and demand, which has profound impacts on groundwater. In the Central Valley, researchers estimated that ACC accounts for 64 per cent of the climatically driven decline in groundwater from 2003 to 2024, while emissions from the CM1950 accounts for 34 per cent. This corresponds to at least 20 per cent and 10 per cent of total observed groundwater loss during this period.
