carbon emissions: Carbon released when many substances — particularly fossil fuels such as oil, gas, and coal — are burned by vehicles and planes; by the manufacturing processes of many consumer goods; and by the heating, cooling, and electricity for your home.

carbon footprint; ecological footprint: The amount of land needed to support a person’s consumption of goods and resources. It describes the amount of land required to farm a person’s food, mine their energy sources, transport their goods and services, and hold their waste.

carbon neutral : The state of reducing a person’s carbon emissions as much as possible and balancing the remaining carbon emissions by offsetting them with processes that consume carbon.

carbon offsets; carbon credits : Paying for or participating in programs that reduce the carbon in the atmosphere. Purchased “shares” go toward reducing the same amount of environmental costs that an activity expends. Carbon offset programs or projects often involve tree planting because trees have a huge capacity to absorb carbon from the atmosphere. Other programs involve everything from supporting solar and wind power to replacing fossil fuel–burning stoves in developing countries with more sustainable energy sources.

carcinogen : A cancer-causing substance.

carpooling : Reducing the number of vehicles going to the same destination by having two or more people ride in the same vehicle. In most cases, carpoolers take turns being the driver and using their own vehicles.

car-sharing : A system in which a person pays a fee that gives them access to a vehicle (or a pool of vehicles), usually parked in an easily accessible location. Car-sharing can eliminate the need for a personal vehicle.

climate change; global warming: Changes in the concentrations of various gases in the atmosphere that are affecting the planet’s climate. Many scientists believe that the increase of carbon dioxide is a primary contributor to global warming, which occurs when gases trap warmth in the earth’s atmosphere instead of letting the atmosphere release it.

compact fluorescent (CFL) bulbs : Fluorescent light bulbs that fit into a standard light bulb socket and use a fraction of the energy of their incandescent counterparts.

compost: Decayed plants and other organic matter that breaks down into rich soil.

core aerating: Poking small holes in the top few inches of lawn to encourage the flow of air, water, and nutrients.

corporate social responsibility : Principles adopted by a business to make sure that its operations harm no one and instead benefit everyone around it and involved in it.