Dickson Despommier is a public health professor at Columbia University in New York City. His area is environmental health sciences. One day nine years ago, he and his students developed an idea. They imagined people in cities growing crops inside a tall building. Tomatoes could grow on one floor of the skyscraper, potatoes on the next, small animals and fish on the floor above. You get the idea. This vertical ( 垂直的 ) farm, or “farmscraper”, could have space for restaurants and other places that serve food, like schools or hospitals. They could serve foods that are truly locally grown. The building could even produce its own energy. It could have wind turbines ( 涡轮机 ) on top. But why would anyone want to build a farm indoors in a city? Dickson Despommier believes it will become necessary. The world needs to find places to produce enough food to feed the growing population. Space, he says, is an all important issue. The professor also points to problems of traditional farms. They use a lot of fresh water. Their fertilizer ( 肥料 ) and animal waste can pollute water resources. And their growing seasons can be limited. But inside the vertical farm, crops could grow all year. And there would be no wind to blow away soil. Farmers would not have to worry about too much or too little rain, or about hot summers, freezing winters or insects. And without insects there would be no need for chemicals to kill them. Farm machines that use fossil fuels, like plows and tractors, would not be needed either. And water could be recycled for drinking. “The vertical farm reuses everything, so there is no waste,” says Professor Despommier. Even buildings could be saved. Old buildings could become new farms and provide jobs. The professor has been actively proposing the idea to cities as far away as Dubai and Canada. But so far it exists only in plans and drawings, and a model at the Museum of Science and Industry in Chicago. Critics say building a farmscraper would cost too much, especially considering the price of land in many cities. Dickson Despommier estimates the cost at about twenty to thirty million dollars. But he says the building would not have to be very tall. And his graduate students have found many empty lots and unused buildings in New York City that could provide space.