The problem he is trying to point out is this one:
Let's say that we solve problem no. 1 for the environment: people stop buying new stuff when their old stuff still works. So you'll keep your car until repairing it would cost more than 30% of a new car.
Now, say I have 3-year-old efficient car, like a VW Polo BlueMotion, and assume my options are as follows:
1. Switch to an electric car
2. Keep the VW
How long does it take from today for Option 1 to have produced less total emissions (including manufacturing the electric car)? It comes out at around 7 years. As gasoline cars get more efficient, this quickly becomes >10 years. Now, what is the estimated life time of a battery pack for an electric car? That's right, about 10 years. What happens when the battery pack is dead? Buying a new battery pack costs more than the car is worth at that point, so you're going to buy a brand new electric car, that's what.
Extrapolating further: if gasoline car emissions are reduced by another 40% over the current VW Polo, and the Polo lasts for 20 years, you never pollute less by going for the electric car.