In Norway’s case, its $890 billion pension fund — the largest sovereign wealth fund in the world — will begin divesting itself of its stakes in coal companies. The move, approved by Parliament on June 5, offered a powerful endorsement of a tactic its backers say has the potential to reduce carbon consumption and in that way limit harmful greenhouse gas emissions.

The fossil fuel divestment movement, begun on the campus of Swarthmore College in Pennsylvania in 2011, has gathered force in only four years. AXA, the French insurance group, said it would sell $560 million in coal investments. The Rockefeller family said its enormous philanthropic arm would sell fossil fuel investments, starting with coal. And the endowments of several universities, including Stanford and Syracuse, have purged coal company stocks.

The logic of the campaign is that diminishing support from the markets will create financial hardship and ultimately lead fossil fuel producers to change. But there is an open secret: For all its focus on stock holdings, the true impact of divestment campaigns has nothing to do with a company’s investor base, share price or creditworthiness.

The most exhaustive study on the subject was conducted by researchers at Oxford, Mr. Caldecott among them. Their report, published in late 2013, examined previous divestment movements — like those against the government of South Africa in protest of apartheid, and against companies that sell tobacco, alcohol or pornography. It also looked closely at the emerging fossil fuel campaign, analyzing the targeted companies and their shareholders. The study concluded that even if every public pension fund and university endowment joined the movement and sold its fossil fuel stock, the effect would be negligible.

“The maximum possible capital that might be divested by university endowments and public pension funds from the fossil fuel companies represents a relatively small pool of funds,” the study found.

Moreover, few institutions vote with their dollars. During a three-decade divestment campaign against tobacco companies, only about 80 of organizations and funds ever sold stock to support the cause.

“Divestment in itself is neither here nor there,” Atif Ansar, one of the study’s authors and a professor at Saïd Business School at Oxford, said in an interview. “On its own, it’s not going to generate any real impact.”

That is, for all of the noise divestment campaigns create, they do little to affect the supply-and-demand economics that would undercut the business of mining, drilling for and refining fossil fuels. Even in the case of coal, the stocks of those companies are down not because of divestment, but because shale mining and cheap natural gas have reduced demand for coal.

But that does not mean divestment campaigns have no consequences. What they do best is good old-fashioned public shaming.

The Oxford researchers found that the negative publicity can create reputational headaches.

“It becomes much harder for stigmatized businesses to recruit good people, to influence policy and, occasionally, to raise capital,” Mr. Caldecott said.

Divestment campaigns also give activists a focused — and easy to understand — object for their outrage.

“The goal is not to bankrupt the fossil fuel industry. We can’t do that with divestment alone,” said Bill McKibben, whose group, 350.org, is a leader in the divestment movement. “But we can help politically bankrupt them. We can impair their ability to dominate our political life.”

Critics argue that damaging the reputations of coal and oil companies does nothing to reduce reliance on those fossil fuels.

“I’m very supportive of aggressive climate policies,” said Robert Stavins, director of the Environmental Economics Program at the Harvard Kennedy School of Government. “But the message from the divestment movement is fundamentally misguided.”

He contends that the problem is not investment in energy companies; it is an economy that remains dependent on fossil fuel production and consumption. While clean energy production is growing, Western economies would grind to a halt tomorrow without fossil fuels. And the divestment movement has focused on Western companies, while India and China have continued to mine and burn huge amounts of coal. Norway, now a leader in the movement, amassed its gargantuan sovereign fund by drilling for oil and gas in the North Sea.

“Divestment comes at the expense of meaningful action,” said Frank Wolak, director of the Program on Energy and Sustainable Development at Stanford. “It will do nothing to reduce global greenhouse emissions. It will not prevent these companies from raising capital.”

A more effective use of activists’ energy, Mr. Wolak and Mr. Stavins said, would be to work on putting a price on carbon emissions through a carbon tax or a cap-and-trade system.

“What we need to do is focus on actions that will make a real difference,” Mr. Stavins said, “as opposed to actions that may feel or look good, but have very little real world impact.”

For divestment campaigners, moving markets is not really the point, despite their focus on stockholdings. Instead, they are more than happy to provoke companies like Exxon Mobil and Peabody Energy.

“If it polarizes the debate, it does so in a helpful way,” Mr. McKibben said. “Left to their own devices, a sense of concern is inadequate to move the fossil fuel industry to action.”