Unless we change course, the US agricultural system could collapse | Tom Philpott

Our food supply comes from an environmentally unsustainable system that is going to unravel

Picture an ideal dinner plate. If you're like most Americans, it features a hearty portion of meat, from animals fattened on midwestern corn and soybeans, and a helping of vegetables, largely trucked in from California. The unique landscapes we rely on to deliver this bounty - the twin jewels of the US food system - are locked in a state of slow-motion ecological unravelling.

California's agricultural sector has flourished from decades of easy access to water in one of the globe's biggest swaths of Mediterranean climate. The Sierra Nevada, the spine of mountains that runs along California's eastern flank, captures an annual cache of snow that, when it melts, cascades into a network of government-built dams, canals and aqueducts that deliver irrigation water to farmers in the adjoining Central Valley. In light-snow years, farmers could tap aquifers that had built up over millennia to offset the shortfall.