Confusion with Carbon Calculators

So, we are trying to calculate the carbon footprint for the annual Westfield River Canoe Race. Using two online calculators we get two different emission for the same car.  What gives?

For example from

TerraPass

I get this

7,768 lbs CO₂ per year


Carbon Footprint Ltd.

I get this

3.73 metric tons:

12000 miles in a USA 2005 TOYOTA COROLLA 1.8, Auto(L4)