The International Energy Agency, an advisory council to energy-consuming countries, released a new report forecasting that by 2030, the world will have 125 million electric cars on the road.

That would amount to 10 to 12 percent of the world's cars running on electricity in a little over a decade.

The report, publicized by CNBC, says that while battery prices are coming down, the main driver for electric-car growth is still public policy—mandates and incentives for automakers to sell large numbers of electric cars.

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Those 125 million electric cars would be about 40 times the number on the road last year, which is already up 54 percent from a year earlier. 

Unlike other polls, which examine the sales of new electric cars, the IEA tracks the growth of the cars on the road, including used cars.

While 125 million is a big number, the IEA notes that the number of electric cars in the world could grow to 220 million if countries take a more aggressive approach to fighting climate change and reducing pollution.

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The Agency notes that in the Unites States in particular, electric cars are likely to grow on two different paths, with faster growth in California and other states that require electric car sales, and slower growth elsewhere in the face of lower gas prices and possibly lower emissions standards. 

In Germany and Japan, both of which have strict emissions standards and high fuel taxes, sales of electric cars jumped 72 percent from 2016 to 2017.

By 2030, higher fuel taxes and tightening emissions standards are expected to boost sales of electric cars to 23 percent of the European market.

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In China, which has become a leader in electric cars, sales surged 72 percent from 2016 to 2017. The IEA expects electric cars to account for 25 percent of the market in China by 2030.

The IEA also measured what type of plug-in vehicles consumers in various countries preferred.

Consumers in China, France, and the Netherlands favored pure electric cars, while those in Japan, Sweden, and Britain gravitated toward plug-in hybrids.

In Norway, where electric cars accounted for 34 percent of new car sales last year, sales and market share actually fell between 2013 and 2017, because tax incentives for plug-in hybrids ended, and because of changes in how company cars are treated for tax purposes.