Photo credit: Brines.org
There is a huge variety of food available throughout the year in grocery stores in the US. In most places, this is due to several factors: far distant farms situated in temperate climate regions; varieties of plants that have been bred to produce food that will ripen slowly and be hardy enough to withstand the rigors of packaging and shipping; and a transportation infrastructure that brings them to our stores. Unless you live in a southern state, much of the produce in your local stores right now is being shipped from far away.
All that shipping has an associated cost (financial cost as well as energy use and carbon release). Locally grown food has many adherents. There are hundreds of farms operating as community supported agriculture (CSA), where people buy memberships in the farm and receive a share of produce (usually on a weekly basis). CSA farms are wonderful for getting food locally, but they are usually tied to the local growing season, meaning that they don't have produce during the winter. But other options can allow even more extension of the growing season.
Even in cold-weather climates, for example, it is possible to grow some vegetables year round. In my area, a local farmer operates a zero-energy greenhouse with which he grows a range of cold-tolerant greens ("various lettuce, spinach, arugula, claytonia, mache, carrots, leeks, cress, tatsoi, pac choi, mizuna, and kale to name a few") throughout the winter. These are sold at the local farmers' market on weekends. (Interestingly, on cold winter days at the market, he often keeps the greens in an insulated cooler – not to keep them cool, but rather to keep them warm and prevent them from freezing.) The Brines Farm hoop house uses a frame covered with greenhouse film to create an enclosure to admit sunlight and retain heat in order to maintain a suitable growing environment. The project is well documented, and they have also produced a pamphlet with instructions for individuals who are interested in setting up similar enclosures for themselves. The pamphlet says a 12' x 12' greenhouse can be built for $200 or so.
A more unusual possibility has researchers have looked at the possibilities for a compost heated greenhouse. Composting gives off heat as the organic material is broken down. However, composting also releases carbon dioxide into the atmosphere. While plants require carbon dioxide for growth, in one test case, the CO2 created from composting was 6 times as much as the plants in the greenhouse required, and other by-products were also many times more than what was needed for a balanced system.
Supporting and choosing locally produced food reduces the carbon footprint for the food we do eat. For the DIY-inclined, building a hoop house is an easy project that makes it possible to have an extended growing season and be able to have locally produced food of their own.