Carbon Emissions intensify Western US water crisis as a new attribution study links roughly half of the water-supply impacts of human-caused climate change in the semi-arid Western United States to emissions from 122 fossil fuel producers and cement manufacturers. Published August 25, 2026, in Communications Earth & Environment, the study found that emissions since 1950 have reduced snow and warm-season streamflow while increasing irrigation demand across the region.
Researchers from the Union of Concerned Scientists and the University of California, Merced, estimated that emissions from these companies account for 40-64% of water-resource impacts attributable to human-caused climate change. The findings also show that the effects are not evenly distributed, with particularly strong disruption in the Pacific Northwest and northern California.
Emissions Have Reduced Snow and Streamflow
The study examined emissions from 1950 onward and their influence on several measures of water availability and demand. Over the past decade, those emissions were associated with 35 cubic kilometres less April 1 snow water equivalent, 15 cubic kilometres less warm-season streamflow and 0.9 cubic kilometres more irrigation demand each year across the Western US.
The scale of the changes is substantial. The researchers say the annual reduction in April snow water equivalent linked to these emissions is roughly equivalent to the maximum capacity of Lake Mead, the largest human-made reservoir in the United States. The additional irrigation demand represents about one-third of California’s annual residential water use.
Water impact | Estimated annual change linked to emissions since 1950 |
|---|---|
April 1 snow water equivalent | -35 km³/year |
Warm-season streamflow | -15 km³/year |
Irrigation demand | +0.9 km³/year |
Share of anthropogenic climate-change impact | 40-64% |
The researchers found that these changes are widening the seasonal mismatch between when water is available and when demand is highest. Less mountain snow means less water stored naturally for release during the warmer months, while higher temperatures increase demand for irrigation.
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California Groundwater Faces Additional Pressure
The Central Valley illustrates how the changing balance can affect groundwater.
- Between 2003 and 2024, human-caused climate change accounted for 64% of the climatically driven decline in groundwater, according to the study.
- Emissions from the 122 carbon majors accounted for 34% of that climate-driven decline.
- The researchers estimate those contributions correspond to at least 20% and 10%, respectively, of total observed groundwater loss during the period.
- As surface water becomes less reliable, communities and agricultural producers can become more dependent on groundwater, reservoirs and water-transfer infrastructure.
The study identified two major hotspots of hydrological disruption in the Pacific Northwest and northern California, where declines in snow and streamflow occurred alongside rising irrigation demand.
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Water Stress Could Affect More Than Agriculture
The study comes as governments and communities face growing questions about who should bear the economic costs associated with climate impacts. Researchers say quantifying the contribution of major industrial emitters could help inform climate-risk disclosure, economic damage assessments and potential future liability frameworks.
The analysis does not suggest that the 122 companies alone caused the Western US water crisis. Rather, it estimates their contribution to water-resource changes associated with human-caused climate change. The researchers note that roughly 70% of global industrial CO₂ emissions since 1854 can be traced to these carbon majors, with 97% of their emissions occurring after 1950.
As drought and water scarcity remain persistent challenges across the American West, the findings add a specific measure to a problem that has often been discussed only in broad climate terms. Carbon emissions intensify the Western US water crisis by altering both the amount of water available and the amount demanded, creating a gap that becomes harder to manage as temperatures continue to rise.
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