The United States is the second largest emitter of greenhouse gases (GHGs) in the world, behind only China. In 2013, U.S. GHG emissions totaled 6,870 million metric tons of carbon dioxide equivalent (MMTCO2e), accounting for about 16 percent of global emissions that year.

Since 1990, U.S. GHG emissions have grown by about 10 percent. This increase is largely due to a growing economy and population, as well as increased demand for energy. The transportation, industry, electricity generation, and commercial and residential sectors are the largest contributors to U.S. GHG emissions.

U.S. GHG emissions are divided into three categories, or scopes, based on where the emissions take place.

Scope 1 emissions are directly emitted by a company from its own sources. For example, scope 1 emissions from a power plant come from the combustion of fossil fuels to generate electricity.

Scope 2 emissions are indirect emissions that occur as a result of the production and consumption of electricity, heat, or steam purchased by a company. For example, scope 2 emissions from an office building come from the scope 1 emissions of the power plant that generates the electricity the office consumes.

Scope 3 emissions are all other indirect emissions that are a result of activities of a company, but that take place outside of its own direct operations. For example, scope 3 emissions from a manufacturing company include the emissions associated with the transportation and disposal of its products.

In general, scope 1 and 2 emissions are under the control of a company, while scope 3 emissions are not. Therefore, companies often focus their GHG reduction efforts on scope 1 and 2 emissions. However, scope 3 emissions can sometimes be reduced indirectly through scope 1 and 2 reduction efforts, such as by improving the energy efficiency of a manufacturing process.

Which scope of emission is the most important for a company to focus on?

It depends on the company and its goals. For example, a company that is trying to reduce its overall GHG emissions might focus on scope 1 and 2 emissions, because those are the emissions that it can directly control. Alternatively, a company that is trying to reduce its carbon footprint might focus on scope 3 emissions, because those are the emissions associated with its products and services. Ultimately, it is up to the company to decide which scope of emission is most important for it to focus on.