BERKELEY, Calif. (August 25, 2026) — A new peer-reviewed study published today in Nature’s Communications Earth and Environment journal by the Union of Concerned Scientists (UCS) and University of California, Merced (UC Merced) quantifies how the world’s largest climate polluters are responsible for nearly 50% of the climate change-driven impacts on the western United States water crisis due to their heat-trapping emissions since 1950. This study is the first of its kind to evaluate how worsening drought conditions attributable to the “Carbon Majors,” the world’s 122 largest fossil fuel producers and cement manufacturers, are harming U.S. communities, ecosystems and agriculture.
Between 2014 and 2024, climate change impacts in the western United States caused by the Carbon Majors made people, and especially farming communities dependent on water for food production, more vulnerable to drought by shrinking snowpack by 15%, decreasing stream flow by 6%, and increasing irrigation demand by 2.4%. Ultimately, this reduction in water availability exacerbates a widening seasonal gap between when water is available and when it is needed most.
“Emissions traced to the Carbon Majors are intensifying an already dire water crisis across the western United States,” said Dr. Angel Fernández-Bou, co-author and bilingual senior 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.”
The research used climate and hydrological models and found that west of the Continental Divide, Carbon Majors’ emissions since 1950 have led to a reduction in snowpack and warm season streamflow that totals a loss of more than 40 million acre-feet of water, a volume comparable to nearly six times the annual water use of all California’s cities. Similarly, a 2.4% increase in irrigation demand due to higher temperatures led to additional water consumption equivalent to roughly 150% of the total water used by the city of Los Angeles annually.
The timing of water flows is also changing substantially due to these emissions, creating a growing divergence between supply and demand. The study found that on average, the midpoint of annual streamflow now occurs more than 5 days earlier in basins across the region and up to 30 days earlier in some mountainous regions. This creates challenges particularly for agricultural communities that depend on reliable water access to accurately time planting and harvesting.
“People living in the western United States have been paying the price for climate-change-fueled droughts and fires with their health, livelihoods and wallets,” said Dr. Emily Williams, lead author of the study and a postdoctoral scientist at UC Merced. “In particular, our dwindling snowpack and hotter, thirstier summers have spelled disaster for our water resources. These corporate climate emissions are bleeding us dry.”
The worsening of the western U.S. water crisis did not have to be this way. But when fossil fuel companies like BP, Chevron, ExxonMobil and Shell understood as early as 1959 how their products would devastate the climate at people’s expense, they chose to launch a decades-long coordinated campaign to deceive the public, deny the science, and delay climate action. Communities such as those in California and Oregon have increasingly sought to hold these companies accountable for the harms caused by their disinformation, and now the fossil fuel industry is lobbying Congress for a blanket immunity bill introduced by Sen. Ted Cruz and Rep. Harriet Hageman earlier this year.
“Legislation and lawsuits to hold big polluters accountable are essential pathways to justice that must be protected,” said Dr. Carly Phillips, study co-author and senior scientist at UCS. “Communities deserve the opportunity to recoup the costs of climate change inflicted by fossil fuel companies that prioritize profits over people and the planet. To limit the worst effects of the already unfolding fossil-fueled water crisis in the western United States, policymakers must ensure a rapid and equitable transition away from fossil fuels to clean energy and invest in climate resilience.”