On the face of it, environmentalist Bill McKibben's international climate campaign to have universities divest fossil fuel assets had limited success. Only a handful of institutions pledged to divest and it didn't affect the stocks of fossil fuel companies.

But a new study by University of Michigan sustainable enterprise professor Andy Hoffman and Temple University's Todd Schifeling, a former postdoc with U-M's Erb and Graham institutes, shows McKibben's activism might have been successful in another way. Their analysis of media coverage of climate change during McKibben's 350.org effort shows that it influenced the public debate.

Ideas that were once on the margins became more mainstream, due to what's known as the "radical flank effect." That is, when there are two entrenched sides on an issue, the appearance of a new idea perceived as more extreme can move previously marginalized ideas to the center.

"A lot of people said that what McKibben did was a waste of time," said Hoffman, the Holcim (US) Inc. Professor of Sustainable Enterprise at the Ross School of Business and School of Environment and Sustainability. "But he had a tremendous effect on the climate change debate in this country and still does."

Hoffman and Schifeling examined 300 newspapers from 2011 to 2015, which totaled about 42,000 articles. Using text analysis, they created a network map of key actors and issues and examined the changes over that time.

They found that certain liberal issues that were considered marginal—in particular a carbon tax, severe weather and carbon pollution—moved toward the center of the network map over time, indicating more mainstream press coverage. The scores on their scale for traditionally liberal climate change issues grew 97 percent, on average. The carbon tax score increased 134 percent, on average.

Adding the divestment idea to a polarized debate drew greater attention to other liberal ideas. It also attracted more attention to financially themed issues such as stranded assets and unburnable carbon. Those are still considered more radical ideas but they, like McKibben, adopted the language of financial risk.

"When McKibben's ideas were discussed in news outlets, it took these previously marginal issues and made them mainstream," Hoffman said. "Before that, few journalists were writing about issues such as stranded assets or cap-and-trade. They had limited appeal. But the introduction of the divestment issue brought attention to these other economic policy instruments."

Their findings suggest that activists waging what look like uphill battles can have a significant effect on public discourse and perception.

"We see that radical actors within a movement can shift the entire ecology of a debate, so I think we need to pay more attention to the indirect effects of these activists," he said.

Their study, "Bill McKibben's Influence on U.S. Climate Change Discourse: Shifting Field-Level Debates through Radical Flank Effects," will be published in a future edition of the journal Organization & Environment.

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