The practice of “carbon farming,” which once seemed like an idealist’s dream, is becoming a reality in Marin County. The California Coastal Conservancy has just announced a $200,000 grant to the Marin Resource Conservation District that will fund as many as 10 projects on local ranches and farms. At each project, landowners and the M.R.C.D. will take measures to capture atmospheric carbon, improve riparian habitat and optimize the use and retention of water. The use…