Future historians “may look back on 2015 as the year that the renewable energy ascendancy began, the moment when the world started to move decisively away from its reliance on fossil fuels,” author and academic Michael T. Klare suggests in a recent post on Grist.

Nobody realistically expects to phase out fossil fuels overnight, he writes. “For the first time, however, it appears that a shift to renewable energy sources is gaining momentum. If sustained, it will have momentous implications for the world economy—as profound as the shift from wood to coal or coal to oil in previous centuries.”

Although Saudi oil minister Ali Al-Naimi described fossil fuels as “our most enduring energy source” as recently as April 2013, “oil’s dominance may not prove as ‘enduring’ as imagined,” Klare writes, citing energy analyst Nick Butler’s observation that “rapidly spreading solar technology could change everything. There is growing evidence that some fundamental changes are coming that will over time put a question mark over investments in old energy systems.”

Writing in The Financial Times, Butler notes that solar has made the transition “from being a niche supplier to being a major regional competitor” with fossil fuels, adding that “the direction of change is clear.”

Klare gives four reasons to expect the low-carbon transition to continue and pick up steam: Concern over climate change, a “sea change” in China’s energy behaviour, the rise of clean energy in developing countries, and falling renewable energy costs.