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Petrochemical fuels produce CO2 when burned. The total amount is based upon the volume of fuel. A US gallon of gasoline produces about 20# of CO2 when burned in an ICE. Diesel and jet fuel are roughly the same. So if goods are being transported locally in very fuel efficient vehicles that amount is spread over more miles. If heavy transportation is used that amount is likely spread over a larger volume or weight of goods transported per mile.

New Zealand has been running a lot of adverts and information recently to point out that even with transportation costs from NZ their products often have less carbon associated with them than domestic products.

oil pollution.. where does all the oil go when you change it? Probably most of it goes into the sea when people pour it down stormwater drains. Also the process of building cars causes waste products which probably are pollutants. Battery acid probably leaches into the ground also when they are dumped. Hope this helps...