Starbucks announced this week that it will pay an extra 10 cents per pound for coffee beans that are grown on environmentally and socially responsible farms. The announcement, which was made at a growers conference in Costa Rica, comes at a time when a world coffee surplus has depressed wholesale prices to 40 cents per pound, with devastating effects on many growers. Starbucks, which pays at least $1.20 per pound and buys about 1 percent of the world’s coffee and 15 percent of specialty coffee, said it would reward suppliers who conserve water and energy, reduce pesticide use, recycle, provide safe working conditions, and comply with local wage and benefit laws. The group Conservation International will help to oversee third-party verification of the suppliers. However, critics say that until the company publicly discloses information about its suppliers, the announcement amounts to little more than a P.R. stunt.