Electric and hybrid cars are often promoted as a partial solution to help reduce carbon emissions and decrease global warming. While it is true that increasing the mileage of cars and reducing the amount of fuel burned are both helpful, it is still unclear that the use of electric cars en masse is significantly helpful, if not somewhat damaging.
First of all, replacing the entire fleet of gasoline and diesel powered cars would take decades, and the energy and materials cost of manufacturing so many cars would be massive. It is by no means clear that this would result in a net reduction of energy use or greenhouse gas emissions. The gains from low emission automobiles would have to be balanced with the massive emissions generated in the production of so many cars, including the extraction and transportation of the raw resources, and the industrial processes of their manufacture. This includes not just the cars themselves, of course, but also their batteries.
A second issue is that while the electric cars themselves may not generate emissions, the energy used to charge them comes from the general electric grid, which is largely powered by coal or natural gas burning plants which produce massive emissions. Coal alone accounts for about half of all electricity production. Some does come from nuclear or hydroelectric sources, but neither of these sources can be increased rapidly (and there is a large debate over whether nuclear should be increased at all).
Another problem with electric cars and hybrids is that many of them cost far too much money to be widely used, with the cost of the batteries (both to replace and dispose of) making this worse. I pointed out a particularly bad example a few days ago. Even worse is that many hybrids don't provide particularly good mileage compared to other similar gasoline or diesel powered vehicles. There already exist many small affordable vehicles (gasoline or diesel) that can provide better mileage than hybrids. The technology already exists to make cars with mileage as high as 100 MPG. This can be done using existing plants, without requiring extensive new technology or retooling. Even better, it is possible to convert many existing vehicles to have much higher mileage, which removes the need to manufacture as many new cars.
The idea of using electric cars on a large scale is also based on the idea of maintaining (or even expanding) the existing system of highways and roads. This system requires a massive amount of resources and energy to maintain. A great deal of fossil fuels are needed to build and maintain these roads, and the asphalt itself is composed of oil-based products. This is a hugely wasteful and inefficient system of transportation. While this system cannot be eliminated anytime in the near future, new construction can be halted and the system can be scaled back, allowing maintenance to focus on a smaller area.
In order to compensate for the above, electrified rail, which is one of the most energy-efficient transportation methods, can be expanded both for cargo and passenger transportation. Eventually this can be used to eliminate the use of most long haul trucking. Not only would this reduce emissions in itself, it would reduce damage to roads and highways, dramatically decreasing the the maintenance required. Trucks would still be required on a local level, however, to transport goods to and from local train depots. For passengers, expanding public transportation can help provide a link from the rail network to local destinations.
The main point here is that electric and hybrid cars are not a mass solution, but that doesn't mean they are useless. In fact, electric cars can provide a great benefit. Lightweight efficient electric trucks can be used to replace gasoline or diesel trucks for local delivery of goods to warehouses and to and from train depots. Other smaller vehicles can be used for local delivery to homes, especially if their routes and schedules are designed to maximize efficiency. This can often be much more energy efficient than having many individuals each use personal vehicles to drive to stores to buy products. On the personal level, small electric vehicles can also be used for local transportation in an urban or rural setting where public transportation is lacking or impractical. For shorter distances, electric bicycles can also fill an important niche.
We should continue to develop and improve the technology for building efficient, long lasting, and easily recyclable electric cars. They can serve a very important role in helping to reduce emissions, other types of pollution and general energy use. This smaller scale use of electric vehicles makes it much easier and more practical to use renewable energy sources, such as wind, or small-scale hydroelectric, to charge these vehicles. But the idea of replacing gas-powered cars with electric ones on a one-to-one basis, leaving the existing road system intact, is counter-productive and environmentally destructive.