As the holiday gift-buying frenzy picks up, no one really knows whether online shopping hurts or helps the environment. The nonprofit Center for Energy and Climate Solutions says such shopping may be an environmental plus, citing the benefits of delivery trucks and warehouses over the multiple car trips and energy-intensive retail space necessary for traditional in-person shopping. But Carnegie Mellon’s Green Design Initiative, in its case study “Harry Potter and the Ozone Layer,” says it may be less environmentally efficient to ship books individually to customers, often overnight by plane, than for customers to buy books in-person that were sent to bookstores by the crate load. Researchers at the New Jersey Institute for Technology found that buying a computer online was worse for the environment. Meanwhile, some catalogue and online retailers are experimenting with reducing the environmental impact of their packaging.