Before you can buy shoes that fit, you need to measure your feet. Before you can shrink your carbon emissions, you need to measure your carbon footprint.Your Carbon Footprint describes the annual amount of greenhouse gas emissions you produce, based on the energy you consume, whether you’re an individual, organization, business or country.Greenhouse gas emissions are gases that retain heat energy in the atmosphere, preventing that energy from radiating into space. The primary greenhouse gas is carbon dioxide (CO₂). Methane (CH₄) and Nitrogen Oxide (N₂O) are the next most significant. These gases are much less prevalent in the atmosphere than is CO₂, but their molecular structure enables them to retain more heat than CO₂. The global warming potential of these different greenhouse gases are standardized in tonnes (t) of CO2_e (see below).  For example, over the course of a century, one tonne of methane in the atmosphere will trap the same amount of heat as 25 tonnes of carbon dioxide. One tonne of CH₄ is therefore calculated as: 25 t CO_2e.

A carbon footprint is typically the sum of three different classes of emissions:

• Scope 1 Emissions: Emissions that come from using fuels under your direct control are considered Scope 1. They come, for example, from burning fossil fuels in vehicles, furnaces, and boilers. Scope 1 emissions can be calculated using fuel consumption data (natural gas bills, gas station receipts/company card tracking) and fuel emissions factors. These factors can be found on the EPA website or in Canada’s National Inventory Report. Scope 1 emissions are the most controllable, therefore are the first place you will look to shrink your carbon footprint.
• Scope 2 Emissions: Emissions that come from using energy produced by someone else are considered Scope 2. For example, a coal power plant will produce emissions as a by-product of generating electricity. The emissions are produced at the plant, but you use the electricity at your home or business. For most, Scope 2 emissions come only from using electricity but can also come with purchased heat or steam. Scope 2 emissions are calculated using electricity consumption data from utility bills and region-specific emissions factors, which can be found on the EPA website or in Canada’s National Inventory Report.
• Scope 3 Emissions: Emissions that are embodied in the products and services you purchase from others, are considered Scope 3. These include emissions from products in a supply chain as well as emissions associated with employee commuting, air, train or bus travel. Scope 3 emissions are much harder to calculate. A detailed analysis is required at each step, working in conjunction with suppliers to determine specific emissions factors in their products. For some Scope 3 emissions, such as commuting or travel, there may be standard emissions factors you can use. More detail on Scope 3 emissions can be found in the GHG Protocol’s Scope 3 guidance.

You will most likely measure your carbon footprint with Scope 1 & 2 emissions. Where standard factors are available, such as for travel, you can also measure Scope 3 emissions. However, Scope 1 and Scope 2 emissions are the most controllable. It is with these, that you will most easily understand the size of your carbon footprint. Once you understand your carbon footprint, it is easiest to shrink it by reducing your Scope 1 and 2 emissions.