We use CO₂e as a common scale to measure the climate effects of all greenhouse gases. It takes into account the Global Warming Potential (GWP) of all greenhouse gases (i.e. how much energy a gas will absorb over a period of time), making it a more accurate measurement than CO2 alone.
For instance, over a period of 100 years, methane (CH4) is estimated to trap more heat than CO2, giving it a GWP of 27-30.