It is Hard to Measure What Reduces CO2 More - So do not say "Please scam me" to Politicians

"Researchers find Nissan LEAF creates less CO2 than Toyota Prius hybrid in west US and Texas, but more in N. Midwest"

Regionally specific lifecycle CO2 emissions per mile traveled for plug-in hybrid electric vehicles (PHEVs) and battery electric vehicles (BEVs) in the US can vary widely based on grid emission factors (i.e., the “carbon footprint” of electricity production and use), according to a new study by researchers at Carnegie Mellon University. Under some conditions, the battery electric Nissan LEAF can produce higher emissions than a Toyota Prius hybrid. The paper is published in the ACS journal Environmental Science & Technology."
The team characterized the vehicle emissions across the United States under alternative assumptions for regional electricity emission factors, regional boundaries, and charging schemes. Among the findings were that:"

It is very difficult to tell which method reduces CO2 the most per dollar. So if you go along with  subsidies to green tech beyond basic research and/or cap and trade you telling your congressman "Please scam me."