So, unfortunately, there is no easy answer. It really depends from vehicle to vehicle, not only the vehicle that you're currently driving that you would be replacing but also, the vehicle that you would replacing it with. The U.S. government came out with a (https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2F%2Fforum%2Fcopies%2FRTEmagicC_747px-Benz-velo.jpg.jpg&hash=c10d6d0766b3b6d038728a2f5eae8dea)model for figuring out the energy as to make a vehicle called, ‘GREET.’ And basically, it tells you how many BTUs it takes to build a car. The manufacturing of the average car is roughly equivalent to 880 gallons of gasoline, in terms of the energy that’s used. If a new car will save at least as much gas, it definitely makes sense to get rid of the old car. If we’ve seen that your old car has around 100,000 miles left on it with good maintenance, your new car would need to be at least 6 miles per gallon better to make up for the emissions for manufacturing. That means that if your old car gets less than 24 miles per gallon makes environmental sense to get a new car that gets 30 miles per gallon or better. Not only can you feel better about your environmental impact, but you also get a £2000 discount on your new car.
Average CO2 emissions for new cars sold in the UK fell to a record low of 167.2g/km in 2006
You wrote: "How do I save carbon with a new car?" First, you need a way to collect and store it. I don't think even JC Whitney has such a device. And what would you do with it once you had it? Put it in a safe deposit box?
Oh, I read about that...
A little box you could attach under your car to pick up all the CO2.
http://www.reuters.com/article/idUSL1847347220070719
I now have a 30 yr old PICKUP, Made in the USA, that gets 45 MPG.
There were several small Diesel pickups made in the Mid 80's.
Ford sold a Ford Ranger Diesel. Mazda had a Diesel Pickup. Chevy Luv Diesel Pickup. Most of them got in the mid 30's for MPG.
In fact, I believe the Chevy was actually made in Japan!!
VW had a little pickup called the VW Rabbit Pickup based on their Rabbit line. Made in New Stanton, Pennsylvania from 1979 to 1982. The factory ran from 1978 to 1988 at which point it was packed up and shipped to South Africa. Or at least the American version of the Caddy and Rabbit ended up there.
It isn't very big, but for a little commuter work truck, 45 mpg isn't too bad.
While similar models have been made in Europe, South Africa, and Brazil (by VW), only the old ones are available in the USA.