Crossing the ocean twice costs less than half a kg of CO2 per kg of book. Rail is almost as efficient and goes smaller distances. The truck portion is probabl

Crossing the ocean twice costs less than half a kg of CO2 per kg of book. Rail is almost as efficient and goes smaller distances. The truck portion is probably the biggest factor in shipping but it's still not that much. And it's the part that's hardest to remove from the supply chain.