@oo1
I think that you have been working to make the paper clearer. So i am using your definition draft and adding a section after the "Abstract". It goes like so:
Unit of measure
Exposed data are annual throughput of carbon-dioxide equivalent emissions. The unit is giga-tonnes of CO2-equivalent/year, or Gt/year for short. For any greenhouse gas, the number represents the mass of carbon dioxide that would warm the earth over a hundred years as much as the mass of the gas newly-sent.