Electric cars don't reduce release of CO2 unless the electricity used to recharge them is generated by hydroelectric, geothermal, wind, solar, or nuclear power plants. At present only a fraction of power in the US is from those sources, so electric cars don't reduce CO2 emissions much. To be practical at all electric cars must have lithium ion batteries. Widespread use of electric cars will put a strain on the supply of lithium. It is possible that we would run out of lithium before we run out of fossil fuel. Here is an article about electric cars.