A Small Group of Fossil-Fuel Giants Tied to a Third of California's Groundwater Loss

Emissions from a small group of the world's largest fossil-fuel and cement producers are responsible for roughly one-third of the climate-related groundwater loss in California's Central Valley between 2003 and 2024, according to a study published in Communications Earth & Environment. The same emissions have reduced the West's spring mountain snowpack by enough water to fill Lake Mead, the largest reservoir in the United States.

The study focused on the "Carbon Majors," a group of 122 corporations identified as the world's largest producers of oil, gas, coal and cement. Researchers used two methods, a simple proportional calculation and a more detailed approach built on physics simulations, to estimate how much of the water crisis across the Western United States, the area west of 105 degrees longitude, can be linked to these companies' emissions. Both methods produced similar results.

Since 1950, Carbon Majors emissions have reduced warm-season streamflow in the region by 6% while raising irrigation demand by 2.4%, together accounting for 40% to 64% of the human-driven climate change measured in the area. The same emissions drove a 15% drop in spring mountain snowpack across the West, a loss of about 35 billion cubic meters of snow every year. The Pacific Northwest and California were hit hardest in absolute terms, losing 27.0 and 5.1 cubic kilometers of snowpack respectively.

Warming has also reshaped the seasons, pushing peak river flows to arrive 5.6 days earlier on average and up to 30 days earlier on the western slopes of Washington's Cascade Range. In the Upper Colorado River Basin, rivers have grown drier in both winter and summer.

The researchers say the proportional method tends to overestimate snowpack loss while underestimating crop water demand, even though it produced results similar to the more detailed approach. States and counties pursuing lawsuits and climate superfund legislation against fossil-fuel producers need this kind of evidence to link emissions from specific companies to water losses in specific places.