Geronimo, it depends which study you read and who is behind it.
I guess I should have said "just as dirty" instead of dirtier.
The studies that say its worse to have IC are electric car companies like Tesla Motors or lobbyist agencies trying to push policies through state and federal governments to enrich their clients. The ones that say EHVs are worse are funded by petrolium companies. The ones that hedge their bets one way or another or are inconclusive are generally university funded (they want to say its better to have EHVs but can't quite get the definite numbers). And power generation is not the only issue here. Manufacturing, materials used, lingevity of service, waste disposal, and carbon footprint of manufacture is another item often overlooked.