Renewable energy sources may eventually render fossil fuels irrelevant in energy generation, but when will the switch between the two energy sources occur?
It's a question that fosters much debate among policymakers, environmental advocates, and financial analysts.
For its part, ExxonMobil believes fossil fuels—notably including coal—will endure for at least the next two decades and perhaps much longer.
DON'T MISS: Electric-car market share in 2020: estimates vary widely
A report recently released by the oil giant forecasts that the fossil-fuel status quo will remain in place until 2040, according to The Guardian.
Despite growing global concern over climate change and increased competition from less expensive renewable energy, the report predicts that coal, oil, and natural gas will have roughly the same share of the energy-generating mix 25 years hence as they do today.
Coal will still account for 20 percent of global energy usage in 2040, the report projects, only slightly lower than the 24 percent predicted for 2025.
2017 Nissan Leaf
Renewable sources will provide 17 percent of global energy in 2040, up from 13 percent today, Exxon's report estimates, while nuclear power will account for 18 percent.
In the automotive sector, ExxonMobil predicts "small, shorter-range electric cars" will account for more than 10 percent of the U.S. new-car market in 2040, but that the vast majority of cars on world roads will still have internal-combustion engines.
However, the oil company's report predicts the world's fleet will be more fuel-efficient, averaging 50 mpg globally.
MORE: Renewable energy growth accelerating, says International Energy Agency (Nov 2016)
While ExxonMobil remains optimistic about the future of fossil fuels and pessimistic about widespread electric-car adoption, other analyses take the opposite view.
In its Medium-Term Coal Market Report, published in December, the International Energy Agency noted a downward slide for coal.
The IEA predicts coal's share in the energy-generation mix will drop to 36 percent by 2021, down from 41 percent in 2014.
BMW DesignworksUSA solar carport concept
The agency previously wrote that renewable energy surpassed coal in 2015 and is now the largest source of newly-installed generating capacity in the world.
Continued robust growth, the IEA expects, will make renewable energy 28 percent of the energy-generating mix in 2021, up from 23 percent in 2021.
In separate reports, the IEA also calculates that the number of electric cars on world roads exceeded 1 million for the first time in 2015 and that electric cars sold that year alone saved 33 million barrels of oil.
It's also worth noting that the future prospects for coal may be tied as much to the availability of other fossil fuels, especially cheaper natural gas, as it is to renewable-energy growth.
Unexpected issues—a crisis in the Middle East, a decrease in U.S. oil and gas extraction through fracking, and others—could increase the price of those fuels, an oil-industry source told this site.
That in turn could lead to a spike in the use of coal to fill the gap in demand, as its price would have remained constant as even as oil and gas rose suddenly.
[hat tip: Brian Henderson]