The Pacific Institute, a non-profit research organization, estimates that the energy used in the production and use of plastic bottles, such as water bottles, is equivalent to filling the plastic bottles one-quarter full with oil. Oil affects global warming by producing high quantities of greenhouse gases when it is burned. The manufacture of one pound of PET -- polyethylene terephthalate -- plastic can produce up to three pounds of carbon dioxide. Processing plastic resins and transporting plastic bottles are major contributors to a bottle's carbon footprint. The Beverage Industry Environmental Roundtable estimates that one 500-milliliter (0.53 quarts) plastic bottle of water has a total carbon footprint equal to 82.8 grams (about 3 ounces) of carbon dioxide.
Transportation of Raw Materials
Plastic bottles are made of resins derived from oil or refined petroleum and natural gas. Refined petroleum and natural gas are sometimes transported long distances to the plastic manufacturers, using fossil fuel and producing emissions of greenhouse gases. The size of the carbon footprint depends on the mode of transportation and the distance raw materials have to travel. For example, truck transportation causes more carbon dioxide emissions than rail shipping. When long distances are involved, transportation energy expenditures can approach that of plastic manufacturing and can represent as much as 29 percent of a plastic bottle's carbon footprint.
Making Plastic Resins
The manufacture of plastic resins is associated with the greatest amount of carbon emissions, according to the U.S. Environmental Protection Agency. During processing, hydrocarbons in petroleum and natural gas are heated to extremely high temperatures to break down the large hydrocarbon molecules into smaller ones. The small hydrocarbons are then combined in different ways to make various types of plastic. PET resin, resembling grains of rice, is the source material for plastic PET bottles. The energy to produce PET resin represents about 30 percent of the total carbon footprint of a 500-milliliter plastic bottle.
Plastic Bottle Production
Energy is needed to convert the plastic resin into plastic bottles. Plastic resin, such as PET resin, is melted and injected into a mold, and then heated and formed into the desired bottles. This final process represents about eight percent of a plastic bottle's carbon footprint.
Cleaning, filling, storing and packaging plastic bottles also uses energy. Waste generation, including carting plastic bottles to landfills, add to the plastic bottle's carbon footprint. The total of these processes can represent 33 percent of the plastic bottle's carbon footprint.
Carbon Footprint Calculators
Carbon footprint calculators for individuals, businesses and even children are available online. Some carbon footprint calculators are free, such as the one by The Nature Conservancy. Calculators for individuals usually address general lifestyle activities and their estimated greenhouse gas emissions. Results from different calculators may vary, because different variables and assumptions are used.
Given that production of plastic resin is usually the major contributor to the carbon footprint of a plastic bottle, recycling can reduce the carbon dioxide and other greenhouse gasses by an estimated 30 to 70 percent. Other methods to reduce the carbon footprint are to use less plastic for bottles, making a lighter bottle, reducing transportation distances and other energy intensive processes. Research into other types of plastics and material that is not derived from fossil fuel could lead to a smaller carbon footprint of the plastic bottle.