A study in Communications Earth and Environment attributes about half of climate-driven water loss in the American West to emissions from 122 fossil fuel companies and cement producers.
Between 2014 and 2024, climate change removed more than a third of the region’s typical annual snowpack and cut streamflows by about 13 per cent, the authors found. Emissions from the group known as carbon majors account for roughly half of those losses, according to Inside Climate News.
The volume involved runs to trillions of gallons, close to the full capacity of Lake Mead, the largest reservoir in the United States. Carly Phillips, a senior research scientist at the Union of Concerned Scientists and a co-author, said millions of people rely on those water resources. “The consequences of these changes are really evident for people on the ground,” she said.
How the attribution works
The team drew on the Carbon Majors database, compiled by the think tank InfluenceMap, which estimates that 178 entities have emitted the equivalent of 1.44 trillion tons of carbon dioxide since the Industrial Revolution. The authors subtracted the carbon majors’ share from total emissions for 2014 to 2024, then modelled each case against a hypothetical world without climate change.
Attribution science of this kind has grown steadily. Warmer air shifts precipitation from snow to rain and melts what snow falls earlier, which scrambles water forecasts. Less snow also means less reflected sunlight, so more heat reaches the surface and more moisture evaporates from soil, plants and groundwater.
The Colorado basin stands out
The Pacific Northwest and California’s Central Valley lost the most snow water equivalent and peak streamflow by volume. In the lower Colorado basin the absolute losses were smaller, though far more severe in proportion. Snow water equivalent there fell by 76 per cent over the decade, while streamflow declined by 21 per cent.
Demand moved the other way. Irrigation demand across the West rose by over four per cent between 2014 and 2024, and carbon majors’ emissions drove just over half of that increase. Phillips said 97 per cent of those emissions have occurred since the 1950s.
What it means for the courts
Dozens of US states and cities have sued oil and gas companies over damages linked to their products. Nevada sued the federal government this week over its plan for managing the Colorado River, which supplies water to 40 million people.
Graham Fogg, professor emeritus of hydrogeology at the University of California, Davis, was not involved in the research. He called the work “a groundbreaking paper” and said it should prompt follow-up studies that refine the estimates.
Phillips said the findings support plaintiffs seeking to attach a price to climate damages. Some producers understood the risks of their products in the 1950s, she said, “but instead of taking action to warn the public and inform policymakers, they engaged in a campaign of delay and denial and deception to cast doubt on the science”.
