Greenhouse gases (GHG) is the collective term for all gases that raise the temperature of the earth via the greenhouse effect. There are many such gases, but in carbon accounting, we consider the most impactful ones, which are defined in Kyoto Protocol:

How much a specific gas contributes to warming depends on its capacity to trap heat and how long it stays in the atmosphere before breaking down.

Global warming potential, or GWP, helps to compare how much different gases contribute to global warming. The GWP for CO2 is a baseline and set to 1. To define the GWP of other greenhouse gases, it is compared to CO2. If a gas causes X times more warming than the same amount of CO2, the GWP of that gas is X.

Not all gases stay in the atmosphere for the same amount of time. Some gases break down quickly and stop warming the Earth sooner. Others stay for longer, continuing to warm the planet over time. That's why we measure GWP over specific time frames, like 10, 20, or 100 years. The most common time frame is 100 years, known as GWP-100.

For example, GPW100 of methane is 30. This means one kg of methane released into the air has the same global warming impact over 100 years as 30 kg of CO2.

Each company activity emits different amounts and types of greenhouse gases. To standardize the comparison of these emissions, the tool calculates them in terms of carbon dioxide equivalent more commonly known as CO2e.

To calculate the CO2e for an activity, the amount of emitted greenhouse gas is multiplied by its GWP. This gives us the CO2e, showing how much environmental impact the gas has compared to CO2.

For instance, if an activity emits 30 kg of methane, and methane has a GWP100 of 30, then it corresponds to 30 kg * 30 = 900 kg CO2e. This means its impact on global warming is the same as that of 900 kg of CO2.

When an activity emits several gases, each is converted to CO2e as described above. To calculate the activity's full carbon footprint, these impacts are summed up. The final figure shows the total kg CO2e caused by the activity.