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- Scientific research has revealed how climate change is placing added strain on water in California and the Western United States.
- In a new study, scientists estimate the role of carbon dioxide emissions from more than 100 of the world’s largest fossil fuel companies.
In the last few years, multiple studies have shown that global warming is intensifying drought and worsening water scarcity in California and the Western United States.
Now, scientists have found that a group of polluters is responsible for a large share of this drying.
In their study, published this week in the journal Communications Earth & Environment, the researchers estimated that climate change shrank the peak annual snowpack in 11 Western states by 36% between 2014 and 2024, and reduced the flow of rivers and streams in spring and summer by 13% compared to a world without human-caused warming.
They found that nearly half of those declines were caused by the planet-heating gases released into the atmosphere by 122 of the world’s largest fossil fuel and cement companies.
New research shows global warming has become the dominant driver of worsening drought in the western United States.
This group, which researchers refer to as the “carbon majors,” includes big producers of oil, gas and coal, both private corporations and state-owned enterprises in countries such as Russia, China and Saudi Arabia.
“Collectively, they constitute a really big source of human-caused climate change,” said Emily Williams, the lead author and a climate scientist at UC Merced.
The researchers used climate models to examine the effects of the companies’ carbon dioxide emissions since 1950.
They also found that global warming, by drying out soil and making crops soak up more water, has increased irrigation water demand by 4%, and that this group of companies is responsible for about half of that.
With days left in the legislative session, California lawmakers are considering several high-stakes energy and environment bills.
The remainder of planet-warming gases are released by smaller fossil fuel companies, livestock agriculture, deforestation, landfills and other activities, according to the study.
Even without rising temperatures caused by the use of fossil fuels, heavy water use is putting major strain on the West’s rivers, streams and groundwater aquifers, Williams said.
“Climate change is taking what has been a precarious situation already and turning it into a crisis,” she said.
Agriculture uses much of the water throughout the West. In California’s Central Valley, chronic overpumping of water from wells has caused major declines in groundwater levels. The scientists estimated in the study that at least 20% of the groundwater loss can be attributed to global warming.
A spokesperson for the American Petroleum Institute, the largest oil and gas trade association in the country, did not respond Wednesday to a request for comment about the study.
The research is based on sound scientific principles and methods, said Rob Jackson, a climate scientist at Stanford University’s Doerr School of Sustainability, who was not involved in the study.
“Climate change is making our water problems systematically more challenging,” Jackson said. “We can no longer manage our water resources without thinking about how the atmosphere is changing, and how snowpack is changing.”
According to a new report, California groundwater regulations threaten to put many small farms out of business.
It’s also important to consider, he said, that “a relatively small number of companies and sources have been responsible for most of the pollution in the air, and that some of those companies are still fighting the consensus on climate change and fighting climate action.”
At the federal level, there is a heated political debate over climate lawsuits against oil and gas companies. Republican members of Congress are proposing to grant the fossil fuel industry immunity from lawsuits based on studies like this one, while Democrats oppose such legislation.
In recent years, a growing body of research has focused on analyzing the role of climate change in worsening droughts, floods, heat waves and wildfires. Some studies have also examined the role of large oil and gas companies.
For example, a 2023 study estimated that nearly 40% of the forest area burned by wildfires in the Western U.S. and southwestern Canada in the last 40 years can be attributed to the carbon emissions of the world’s largest fossil fuel producers and cement makers.
A 2025 study found that the carbon dioxide released by such companies and their products has substantially worsened heat waves since 2000.
In other research, scientists found that the last quarter-century has probably been the driest in 1,200 years in Western North America, and that global warming is responsible for about 40% of the drought’s severity.
Even after a year and a half of wet weather, research shows the American West has experienced the driest 25-year period in 1,200 years. When might the megadrought end?
Researchers have estimated that climate change is linked to about half of the decline in the flow of the Colorado River, which provides water for seven states and Mexico. This year, the river’s largest reservoirs have fallen lower than ever before.
Record-breaking heat this winter and spring left mountains across the West with very little snow, and scientists recently determined in other research that climate change made such a snow drought four times more likely than before the rise of industry started releasing more carbon dioxide and driving global warming.
In the latest study, the researchers said they focused on emissions since the 1950s because during that decade some companies began to have access to research indicating the use of oil, gas and coal could lead to dangerous climatic changes.
Carly Phillips, a co-author and senior scientist at the nonprofit Union of Concerned Scientists, said that’s why research focusing on the role these companies play in the climate crisis is important.
“Despite recognizing this science internally, they poured resources into a campaign of deception and obstruction to protect their profits,” she said.
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