Lets do some math:
According to
Wikipedia, the footprint for the factory is 3 km2, which is 300 hectares (about 742 acres).
CarbonNeutral.com estimates 100 - 300 metric tonnes (100,000 -300,000 kg, or 220,462 - 661,387 lbs) of CO2 sequestration per hectare per year.
On the
European Environmental Agency website, we learn that the average European car (9.35 km/L or 22 mpg) produces 95 g of CO2 per km on average (this is actually the 2021 target, but I felt that it's appropriate to use considering the built time of the factory. However, it's important to note that the 2020 target is 146 g of CO2 per km, so reaching 96 g a year later seems dubious).
Assuming 18500 km per year (11,500 miles per year), that's 1.76 metric tonnes of CO2 per car per year.
(300 hectares of land * 300 (max) tonnes of CO2 per hectare) / 1.76 tonnes of CO2 per car = 51136 cars per year.
Tesla needs to offset the carbon emissions of just over 51,000 average European ICE cars per year to break even on their carbon. Tesla plans 500,000 EV's per year from the Gigafactory. They're going to offset by a factor of 10.
Granted, this does not include the carbon associated with building the factory or the cars, but an order of magnitude gives a healthy amount of wiggle room...