SA Forum is an invited essay from experts on topical issues in science and technology.

That day will come: the life-changing moment when renewable energy—wind, solar, geothermal and others still in development—replace fossil fuels as the principal source of world energy. Most analysts insist, however, that this day will not arrive for many decades to come—certainly well past the middle of the century. Fossil fuels are too entrenched, it is said, and renewables too costly or impractical to usurp existing systems. According to the International Energy Agency (IEA), the share of global energy provided by renewables—a mere 14 percent in 2012—will increase only slightly between now and 2040, rising to just 19 percent. But there are good reasons to believe that the transition to renewables will occur much faster than previously assumed, pushing that percentage higher and higher. Indeed, recent increases in wind and solar installations have been running at nearly twice the rate of the IEA’s projections for long-term capacity growth, suggesting that its projections of renewables’ share of global energy are much too low.

It is hardly surprising, of course, that many experts say we will witness a relatively drawn-out transition from fossil fuels to renewables, given what is known about previous energy shifts of this sort. Any new form of energy initially operates at a severe disadvantage, lacking the elaborate production, processing and distribution networks retained by the prevailing type; before it can overcome that disadvantage and become the new leader the upstart must create a duplicate infrastructure—something that typically requires many decades. “Energy transitions take a long time,” observed Vaclav Smil of the University of Manitoba in Scientific American. It took more than 50 years for coal to replace wood as the world’s leading source of energy and another 50 years for oil to overtake coal; the shift from fossil fuels to renewables, he argued, is not likely to occur any faster.

Under ordinary circumstances, Smil’s forecast would no doubt prove accurate. But these are not ordinary times: Growing concern over climate change is leading to increasingly strict controls on carbon dioxide and other greenhouse gas (GHG) emissions, while a continuing cascade of innovations in renewables technology is lowering their price and speeding their installation. (In a 2009 Scientific American cover story Stanford University engineering professor Mark Jacobson presented a detailed plan showing how the entire world could be powered by wind, solar and water sources by 2030.

There are, of course, many obstacles to the effective control of carbon emissions, as demonstrated by the unremitting efforts of U.S. coal companies and their congressional allies to block the imposition of new rules by the U.S. Environmental Protection Agency (EPA). Nevertheless, it is impossible to dismiss the progress being made at the local, regional and international levels to curb GHGs and promote the use of renewables. The European Union (E.U.), for example, is well on the way to achieving a 20 percent reduction in GHG emissions from 1990 levels by 2020, along with a 20 percent increase in the share of its energy obtained from renewables. In the U.S. upgraded fuel-efficiency standards for cars and light vehicles will reduce U.S. consumption by an estimated savings of 12 billion barrels over the next 10 years. And China, the world’s leading fossil fuel consumer, has pledged to cap the growth in its carbon emissions by 2030 and increase the share of nonfossil fuels in its primary energy consumption to around 20 percent by that time.

Despite such progress, it appears increasingly unlikely that the world will succeed in preventing the expected increase in global temperatures from exceeding 2 degrees Celsius—the maximum amount, most scientists agree, that the Earth can absorb without experiencing catastrophic climate events such as the melting of the Greenland and Antarctic ice sheets. This may mean we can expect an ever-expanding assault of droughts, heat waves, hurricanes, typhoons and other disasters. But this, in turn, will prompt governments to impose even tougher restraints on carbon emissions and to accelerate the installation of renewables.

The transition to renewables will be hastened by dramatic improvements in the pricing and performance of such systems. Due to steady increases in the efficiency of wind and solar systems, coupled with the savings achieved through large-scale manufacture, the price of renewables is falling globally. Deutsche Bank reports that the total module costs sustained by leading Chinese solar companies has decreased by 62 percent over the past few years, falling from $1.31 per watt in 2011 to $0.50 in 2014; further reductions, it says, will occur over the next few years. With prices dropping this fast, solar energy is now proving competitive with fossil fuels for generating electricity in many areas. As if to confirm this development, the Electricity and Water Authority of oil-rich Dubai recently awarded a $330-million contract to a Saudi firm for construction of a 200-megawatt solar electricity plant, touting its superior price for delivered power over oil and gas-fired plants.

This shift, says energy analyst Nick Butler of the Financial Times, provides “advance notice of a revolutionary development.” The collapse of solar module prices “has enabled solar to move from being a niche supplier to being a major regional competitor to [fossil fuels] and a potential disrupter of the whole power industry.”

The transition from fossil fuels to renewable energy will not occur overnight, and it will not escape recurring setbacks. Nevertheless, renewables are likely to replace fossil fuels as the dominant source of electrical power well before mid-century as well as make giant strides in other areas such as transportation. Yes, the titans of carbon will continue to rule for another decade or so but their days are numbered and the smart money will place increasing bets on the eventual triumph of renewables.

Michael Klare is professor of peace and world security studies at Hampshire College and author of several books on energy and geopolitics, most recently The Race for What’s Left: The Global Scramble for the World’s Last Resources.