While that is often true, it isn't always the case. If you are using a lot of gas (driving a lot, high consumption), replacing it with an electric car can very quickly be more environmental friendly. If you are not using a lot of gas, like only driving your car infrequently, keeping your old car running might be better though.
What would very quickly mean? Do you have some data perhaps on the breakpoints regarding this? I'm not dismissive of your statement, just want to see some data.
