Other than your vehicles, you are likely to operate other engines that burn fossil fuel and emit CO2 into the atmosphere.
In a dive shop, those are typically your boat engines, any fuel engines powering your compressors and any generators.
All those engines can be treated in the same way.
What you need to do is
• Determine their annual fuel consumption
• Translate that consumption into metric tons of CO2
Following the guidelines of the Intergovernmental Panel on Climate Change, the commonly accepted ratios are:
CO2 emissions from gasoline = 19.4 pounds/gallon = 2.32 kg/liter
CO2 emissions from diesel = 22.2 pounds/gallon = 2.73 kg/liter
one metric ton is 1,000 kilograms, or one kilogram is 0.001 metric tons.
one kilogram is 2.20 pounds, or one 1 pound is 0.45 kilograms
one US liquid gallon is 3.79 liters, or one liter is 0.26 gallons
Additional resources concerning the specific Carbon footprint of vessels can be found here.
They obviously lead to the same results but in addition, they contain valuable tips on how to calculate your annual consumption and how to reduce the Carbon footprint of your boat.
By applying the above formulas, you can equally calculate the precise emissions of your Vehicles based on their annual fuel consumption rather than their mileage, however with this one caveat.
In addition to carbon dioxide, automobiles produce methane (CH4) and nitrous oxide (N2O) from the tailpipe, as well as HFC emissions from leaking air conditioners. The emissions of CH4 and N2O are related to vehicle miles traveled rather than fuel consumption, and the emissions of CH4, N2O, and HFCs are not as easily estimated from a vehicle as for CO2. On average, CH4, N2O, and HFC emissions represent roughly 5 – 6 percent of the GHG emissions from passenger vehicles, while CO2 emissions account for 94-95 percent, accounting for the global warming potential of each greenhouse gas. (These percentages are estimated from the EPA “Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990 – 2001”.)
To simplify this estimate, it is assumed that CH4, N2O, and HFCs account for 5 percent of emissions. You must thus multiply your CO2 estimate for your vehicle by 100/95 to incorporate the contribution of the other greenhouse gases.