This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Climate change was once something scientists warned us about, and now it's a reality we are living in. In California's Central Valley, about one-third of climate-related groundwater loss between 2003 and 2024 can be attributed to emissions from the same actors.
Scientists call them the "Carbon Majors," a group of 122 corporations that are the world's largest producers of oil, gas, coal and cement. A recent study found that emissions from the Carbon Majors caused a significant reduction in spring snowpack across the Western United States—enough lost snow water to fill Lake Mead, the largest reservoir in the country. For years, climate change has been discussed as a broad, global problem, often making it difficult to trace its effects to individual companies.
This study sought to make that connection quantifiable by measuring the Carbon Majors' contribution to changes in water supply, water demand and groundwater across the Western United States (west of 105°W). Published in Communications Earth & Environment, the research tested one simple mathematical method and a detailed approach involving physics simulations to calculate how much climate change can be linked to individual companies. Both methods told a similar story.
Since 1950, emissions from the Carbon Majors have reduced warm-season streamflow by 6% while increasing irrigation demand by 2.4%. Taken together, these changes accounted for 40% to 64% of human-driven climate change in the region. As streamflow kept falling and irrigation demand kept climbing, water grew scarcer just when farmers and communities needed it most during warm seasons.
The Western United States is one of the driest parts of the country, and much of its water comes from mountain snowpack, which acts as a natural reservoir. Snow accumulates during winter and melts gradually through summer, supplying more than half of the river water that supports the region's multibillion-dollar agricultural industry. As temperatures rise, that system is being disrupted: Snow melts earlier, the air becomes drier and farmers are forced to rely more heavily on groundwater pumped from deep underground to grow crops.
Groundwater laws can limit how much farmers pump, but they cannot stop climate-driven changes that reduce water supplies. That has led states and counties across the Western United States to pursue lawsuits and climate superfund legislation against major fossil fuel producers. To bring those cases, they need solid scientific evidence linking emissions from specific companies to water losses in specific places.
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