There are more than 30 different greenhouse gases and so in order to create a common language to understand the impact that these gases have we convert them into the most common greenhouse gas; Carbon Dioxide.
Except that it isn’t carbon dioxide at all! So we use Carbon Dioxide equivalent to show that a conversion has occurred from the original gas. This is shortened to CO2e, which is what you will see throughout the Carbonhound App.
The “exchange rate” of these other greenhouse gases into CO2e is defined by the assessment reports that are released by the IPCC. These change over time as the science gets better at understanding their impact. The technical term for this “exchange rate” is the Global Warming Potential (GWP).
Basically if you emit 1 tonne of methane (CH4) then this is equal to the emission of 28 tonnes of CO2. So we would call this 28 tonnes CO2e.