Most greenhouse gas emissions from transportation are carbon dioxide (CO₂) emissions resulting from the combustion of petroleum-based products, like gasoline and diesel fuel, in internal combustion engines. The largest sources of transportation-related greenhouse gas emissions include passenger cars, medium- and heavy-duty trucks, and light-duty trucks. These sources account for over half of the emissions from the transportation sector.

The building sectors include all homes and commercial businesses (excluding municipal operations, agricultural and industrial activities). Greenhouse gas emissions from this sector come from direct emissions including fossil fuel combustion for heating and cooling needs, management of waste and wastewater, and leaks from refrigerants in homes and businesses, as well as indirect emissions that occur offsite but are associated with use of electricity by homes and businesses.

Greenhouse gas emissions from industry primarily come from burning fossil fuels for energy, and greenhouse gas emissions from certain chemical reactions necessary to produce goods from raw materials. Industrial emissions are the third largest source of direct emissions.

Greenhouse gas emissions from agriculture come from livestock such as cows, agricultural soils, and production.

Natural lands provide clean air and water, wildlife habitat, carbon sequestration, recreational opportunities, and wood production, among other benefits. These land uses pull CO2 out of the atmosphere in a process called carbon sequestration. Sequestration of CO2 and emissions of other greenhouse gasses can occur from the management of lands. Land use and forestry activities can result in more removal of CO2 from the atmosphere than emissions.

Waste emissions include carbon dioxide, methane, nitrous oxide, and fluorinated gas emissions from anthropogenic activities other than those created by fossil fuel combustion including solid waste management, landfills, composting and anaerobic digestion, and municipal waste combustion that does not generate electricity, wastewater treatment, including septic tanks, wastewater treatment plants, and effluent management.

The electric power sector involves the generation, transmission, and distribution of electricity. Carbon dioxide makes up the vast majority of greenhouse gas emissions from the sector, but smaller amounts of methane and nitrous oxide are also emitted. These gases are released during the combustion of fossil fuels, such as coal, oil, and natural gas, to produce electricity.