In the race to replace the internal combustion engine that propels most of the world's cars, trucks and buses with vehicles powered by electricity, one country stands out, and it might not be one that immediately comes to mind.

It's not China, even though the sheer number of new plug-in electric vehicles sold there in 2017, 605,500, was the highest in the world, accounting for 2.6 percent of all vehicles purchased in the country. It's certainly not the United States, where EV sales checked in last year at just 1.1 percent. The undisputed leader is Norway, where fully 35 percent of new vehicles sold in 2017 -- and 52 percent of those sold in December alone -- were EVs.

Looking at Norway's figures, one might believe that EVs are on a fast track to upend the century-long reign of fossil fuels as the dominant vehicular power source. That may very well be the case in Norway, where almost all electricity is generated from hydropower, EVs are exempted from most taxes, and their owners enjoy a range of benefits that can be worth thousands of dollars a year, including free recharging and use of toll roads along with free or subsidized parking. But what about the rest of the world? Experts' predictions are truly all over the map.

Bloomberg New Energy Finance, for example, forecasts that "adoption of emission-free vehicles will happen more quickly than previously estimated because the cost of building cars is falling so fast." Electric cars, Bloomberg predicts, will outsell fossil-fuel-powered vehicles within two decades, turning the global auto industry upside down and creating economic turmoil for oil-exporting countries.

That's a conservative forecast compared to the predictions of Tony Seba, author of the 2014 book Clean Disruption of Energy and Transportation, who argues that much larger forces are in play than just the cost of the vehicles. He says that the combination of digital and electricity-generating technologies will put an end to the conventional atom-based energy and transportation industries. His forecast: By 2030 all new mass-market vehicles will be electric and all new energy will be provided by solar or wind.

  More than most in the EV forecasting game, both Bloomberg and Seba focus on near-horizon advances in technology as the major factor affecting adoption rates. But there are many other forces at work. A 2015 report prepared for the University of Hawaii provides a range of EV adoption-rate forecasts for that state -- between 6 percent and 15 percent by 2040 -- based on numerous internal and external factors. Internal factors, as described in the report, are those under the control of vehicle manufacturers and include characteristics of the EV itself: not only purchase price but also battery costs, driving range and charging time. External factors include fuel prices, consumer characteristics, availability of charging stations, travel distance, public visibility, vehicle diversity and governmental policy incentives.

EV support policies, regulations and incentives linked to California's decades-long campaign to improve its air quality are clearly the major factors underlying its leading position among the states for EV sales - 5 percent last year. Despite these efforts, however, the state still has the nation's worst health impacts from air pollution. Ramping up the state's air-quality campaign, last month Gov. Jerry Brown issued an executive order setting a new target of five million zero-emission vehicles by 2030. He proposed an eight-year, $2.5 billion initiative to help bring 250,000 electric-vehicle charging stations and 200 fueling stations for hydrogen-powered vehicles to the state by 2025.

California already is home to about half of all EVs that have been sold in the U.S. Its continuing and intensifying efforts to build a strong EV market should serve as a model for other states and regions -- and perhaps even countries -- that want to improve their air quality and reduce their greenhouse-gas emissions.

But whether California could ever come close to matching Norway's amazing EV sales numbers is anybody's guess. Perhaps Norway's success will turn out to be an exception, fueled by a unique set of circumstances in a small economically advantaged country. Or maybe, as the leading early adopter of EVs, it will provide the roadmap for the rest of the world. One thing is for sure: Anyone interested in the future of EVs will want to keep an eye on a small Scandinavian country where these vehicles seem poised to rule the roads.