A landmark study in Communications Earth & Environment links half of the western US water crisis to emissions from 122 fossil fuel and cement companies.
Since 1950, these carbon majors drove up to 64% of climate-related impacts, including snowpack loss equal to Lake Mead’s capacity and one-third of Central Valley’s groundwater decline, bolstering emerging climate liability and “superfund” debates.
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.
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.
The results imply an increased reliance on groundwater, surface water storage, and conveyance systems to capture surface flows when available, thus foreshadowing persistent issues with regional water availability and storage as temperatures continue to rise.
“Emissions traced to the carbon majors are intensifying an already dire water crisis across the western United States,” said Angel Santiago Fernández-Bou, co-author and climate scientist at UCS.
“Taxpayers, states, municipalities and communities are paying for the harms and costs associated with these climate impacts, and our study’s findings provide further scientific evidence on how the fossil fuel industry is responsible for those harms,” Fernández-Bou added.
The effects of changing water supply and increasing water demand extend beyond agriculture, initiating a cascade of impacts across the WUS with implications for wildfire, ecosystem health, and the overall resilience of regional water systems and associated sectors.
The study provides both methodological advances and scientific evidence and comes in the wake of emerging liability cases and climate ‘superfund’ legislation.
Many individual entities within the carbon majors knew about the projected climate effects of their products as early as the 1950s. The detrimental impacts to WUS water availability that the study identified highlight the consequences of the carbon majors’ continued fossil fuel and cement production in recent decades.
By quantifying the role of major industrial emitters in worsening regional water stress, the study offers further evidence to inform economic damage attribution, climate risk disclosure, and future liability frameworks.
On October 5, 2026, the Supreme Court will hear Suncor Energy (U.S.A.) v. Commissioners of Boulder County. The case will decide whether federal law bars state-law claims seeking relief for injuries allegedly caused by the effects of interstate and international greenhouse-gas emissions on the global climate.