At some point in late 2015, the world got its one millionth plug-in vehicle. The IEA said this was, "a significant milestone," but albeit the current stock [of EVs] is still small compared to the ambitious aim of deploying over one billion electric vehicles by 2050 to achieve the 2°C goal."
The "2°C goal" is the idea that, "global warming of more than 2°C would have serious consequences" and that the world needs to take action to keep global warming from rising that high. The main leader for the 2C goal should be cities, the IEA says, because they're the ones that have, "up to two-thirds of the potential to cost-effectively reduce global carbon emissions." Thankfully, the IEA's Energy Technology Perspectives 2016 (PDF) shows that there are two green energy technologies that are "on track" for helping the world achieve a maximum two-degree (C) increase in average temperature: electric cars and solar/wind energy. Luckily, those technologies work well together.
Last year, the 2015 xEV Industry Insider Report predicted that plug-in vehicles (EVs and PHEVs) would grow from their 350,000 count in 2014 to 1.4 million in 2020. After that, the prediction is for things to just ramp up. In just eight US states (the ones that are leading in the EV deployment race), the expectation is that there will be 3.3 million EVs by 2025.