Half the diesel fuel in California is made not from unsustainable petroleum but from renewable biomass such as waste and plant oils. Soon all our diesel will be biofuels. This is particularly good for the environment if the fuel is made from wastes and residues, but it’s much less so if it’s made from crops that use energy and land but don’t produce food.
It also harms watersheds, disrupts Indigenous communities and causes a raft of other social and environmental problems. If what happened in California stayed in California, we wouldn’t be so concerned. Global vegetable oil producers probably could replace California’s remaining fossil-fuel-based diesel without much additional harm. But other jurisdictions that have adopted or are considering policies like California’s are watching the state carefully.