Pets — some of life's greatest sources of joy, love and, at times, frustration — can add up to a large carbon [paw]print. Since the pet products market has expanded from collars, food and litter to apparel, accessories, baked goods, fitness classes and much more, the impact pets have on the environment has grown. Become a green pet owner with MNN's tips and ideas in the articles below. (Photo: Flickr)