In his 2015 book Wages of Rebellion: The Moral Imperative of Revolt, journalist Chris Hedges describes the research of two academics who have investigated the determinants of success for rebellious movements. He writes:
"Maria J. Stephan and Erica Chenoweth examine 100 years of violent and nonviolent resistance movements in their 2008 article "Why Civil Resistance Works: The Strategic Logic of Nonviolent Conflict." They conclude that nonviolent movements succeed twice as often as violent uprisings. Nonviolent movements appeal to those employed within the power structure, especially the police and civil servants, who are cognizant of the corruption and decadence of the power elite and are willing to abandon them. And, the authors point out, with as little as 3.5 percent of the population who are organized and disciplined, it is possible to bring down even the most ruthless totalitarian structures." (p. 84)
As far as I can tell, the claim about 3.5 percent of the population doesn't come from that paper, but from Erica Chenoweth's 2013 TEDxBoulder talk: "The success of nonviolent civil resistance" (See also: "Peaceful protest is much more effective than violence for toppling dictators").
Regardless of the precise source, there's an appealing symmetry to that 3.5% figure, when placed alongside the conviction that the atmospheric concentration of CO2 must be kept below 350 parts per million (ppm) if we are to avoid the worst effects of climate change.
Three and a half percent means three and a half per hundred. Three and a half per hundred is the same as thirty five thousand per million, since one million is ten thousand times one hundred. If Stephan and Chenoweth are right, achieving 350 parts per million in the atmosphere may require 35,000 active people per million.
That's about 92,000 active people in Toronto; about 350,000 people active in Canada; and about 256 million people around the world. 3.5% of Toronto, Canada, and the world is a much larger fraction of Torontonians, Canadians, and humans than I would guess are presently strong supportive of moving beyond fossil fuels to climate-safe forms of energy. Nonetheless, it doesn't seem an impossible fraction to motivate, as the global impacts of burning fossil fuels are felt more keenly and universally. After all, last month 10,000 people marched in Toronto for climate justice, and forty times as many marched in New York in September 2014.
The idea that the 3.5% can drag along the 96.5%, even in the face of determined opposition from an entrenched few, is both encouraging and a challenge to some common theories of change. It challenges the view that victory depends on convincing a tiny global elite: that the richest and most powerful stratum of global society will come to its collective senses and realize how climate change threatens to eradicate its prosperity (to say nothing of the impact on the rest of us). It also challenges some perspectives on mass mobilization, in which new consciousness for the great bulk of society leads to them overturning the global social order. Stephan and Chenoweth present one possibility for how much the climate justice movement needs to grow before it can succeed, as well as some usefully empirically-grounded recommendations about tactics and strategies that can help get us there.