Let's start this article busting a myth. Pollution and global warming aren't caused only by cars, even if it seems to be like that. Governments, organisations, et cetera have taken actions predominantly against cars, but various researches show how cars pollute only for the 15% of the total, and all transports for the 25-30%. House-heatings pollute almost for the 50%.
Then let's distinguish pollution and global warming. Global warming isn't caused by pollution; or better, the only molecule responsible of global warming is CO2, that is, with the water, one of the products of the combustion reactions - the chemicals reactions happening in ICEs (internal combustion engines). Instead pollution comes from the presence of heavy metals and impurities in the fuels. Therefore there will be some other products in the combustion reactions, and these products are pollutants if they are harmful for human's health and for the environment.
In the common opinion, the most polluting engine, among the most common ones, is the diesel. But the diesel is also one of the cleanest if we consider the CO2 released; if in the combustion reaction we have a larger number of other products, the quantity of CO2 will be less. Everyone thinks that the biggest problem for diesel is the production of NOxs; but these molecules are not considered as pollutants, and they can become pollutants if they react with volatile hydrocarbons, because this reaction creates ozone, that is classified as an irritant. However, governments are always reducing the levels of emissions allowed for diesels, and it's becoming more and more expensive producing and mantaining them. That's why the diesel engine is going to die.
The most entertaining engine, the petrol engine, is the one that produces most CO2. However, with the most recent technologies, the level of CO2 produced by petrol engines has decreased considerably, and motor companies, such as Mazda with the Skyactiv X, are going to create and develop devices able to cut those emissions.
The most controversal engine is the electric. The big questions is: is it worth switching from the oil-fueled engines to the electric, building all the infrastructures and spending all the money required? My answer is: it could be not necessary. Why all motor companies are developing electric cars? Because it's easier building something that has zero emissions on its own than staying within the limits. Switching to the electric would mean move the emissions from the 15% of cars to the production of energy (I know, there are also renewables sources, but that should require further investments).
I think that it could be smarter finding a way to reduce the CO2 in the atmosphere than making a massive change in mobility. The most recent researches (as vox.com reported) showed that with the 1991 massive eruption of the volcano Pinatubo in the Philippines the global temperature decreased of about 0.5°C. Scientists have found that this decreased is attributable to the action of CaCO3 (calcium carbonate), that reacts with CO2 producing a non-greenhouse gas. Therefore a way to reduce CO2 could be putting in the atmosphere great quantities of calcium carbonate.
Sources: Quattroruote, Automoto.it, Vox.com