Can someone rephrase this for me? Thank you.

To take into account the emission of other greenhouse gases when calculating the level of greenhouse gas emissions, scientists have devised an equivalent measure – CO2e (which literally means carbon dioxide equivalent).

There's nothing wrong with the way it's written. I think it's pretty self-explanatory. Could you specify what is unclear?

The calculation:

Basicaly, scientists are using CO2e is a common standard unit which is equivalent to a volume or quanity of CO2 emission. So, for instance, if the greenhouse gas was water vapor, H2O, so the molecular weight is 18. The molecular weight of CO2 is 44, therefore, 1 CO2e = 44 molecular weight.

So the CO2e of water vapor is 18/44 = 0.41