Climate impact of EV's
Zero emission is often mentioned as an inherent attribute of EV's. However this only refers to the tailpipe emission which is obviously zero. Opponents to this thought refer to the "long tailpipe" which is to illustrate the fact that electricity plant also pollute, it is just in another place than the car. The chimney of the power plant thereby constitutes an imaginary extension of the tailpipe.
It is certainly true, that part of the world's electricity productions is done with less clean technologies so electricity in general cannot be considered "green" without caution.
Watch this video to learn about CO2 emissions:
One might argue that electricity consumed by EV's is marginal and should thus be judged by the worst available electricity source (marginal cost approach). On the other hand EV's are very flexible energy consumers and can thus be used to promote fluctuating renewable energies such as wind or solar. They may also provide a stabilizing service to the grid which is valuable for other consumers.
The most commonly accepted way of dealing with this is to take average of the pollution arising from regional electricity production and put a proportionate part of this pollution on the EV. Thereby the net emissions will depend on the region where the EV is operated.
In EU the average CO2 footprint of an electric car is about 75 g/km. That is better than even the most efficient fossil fuel cars which are currently at around 100 g/km. The electricity production in EU is getting significantly greener in future years. Fuels will only see marginal improvements due to admixing of biofuels to gasoline and diesel.
What about biogas?
Biogas is a very special case in automotive fuels. In some countries the conditions are such that biogas can actually be produced with a negative CO2 footprint. However even under ideal conditions biogas will not be able to supply more than 5 - 10 % of the vehicles in EU.
What about hydrogen?
Hydrogen works in principle just like a battery. It stores energy from other sources and releases it at the desired time. Hydrogen outperforms batteries in terms of capacity and refueling time. At the moment however hydrogen technology is much more expensive and less energy efficient compared to batteries.