Americans have a long tradition of taking to the streets to protest or to advocate for things they believe in. New research suggests that when it comes to climate change, these marches may indeed have a positive effect on the public.

A team including Penn State researchers found that people tended to be more optimistic about people's ability to work together to address climate change and have better impressions of people who participated in marches after the March for Science and the People's Climate March in the spring of 2017.

Janet Swim, professor of psychology at Penn State, said the findings suggest that climate change marches can have positive effects on bystanders.

"Marches serve two functions: to encourage people to join a movement and to enact change," Swim said. "This study is consistent with the idea that people who participate in marches can gain public support, convince people that change can occur, and also normalize the participants themselves."

Swim added that recent research has shown that marches are becoming more prevalent in the US, not just for climate change but for many issues. She and her coauthors, Nathaniel Geiger from Indiana University, and Michael Lengieza from Penn State, were interested in learning more about whether marches are effective at changing psychological predictors of joining movements.

"There are several measures that predict people engaging and taking action in the future," Swim said. "One of those is collective efficacy -- the belief that people can work together to enact change. People don't want to do something if it's not going to have an effect. We were interested in whether marches increased this sense of efficacy, that once you see other people do something, you might think yes, it's possible."

For the study, the researchers recruited 587 bystanders -- people who did not participate in the march but observed it through the media. 302 participants completed a survey the day before the March for Science held on April 22, 2017, and 285 completed a survey several days after the People's Climate March held on April 29, 2017.

The surveys asked participants how much they knew about the marches, their impressions of the people who participated in the marches, and whether they believed people could work together to reduce climate change, among other measures.

"Activists are often seen negatively -- that they're arrogant or eccentric or otherwise outside of the norm," Swim said. "There's a fine line between marchers and other activists expressing themselves and raising awareness of their cause, while also not confirming negative stereotypes. So, one of our questions was whether marches increase or decrease people's negative impressions of marchers."

Because the researchers were also interested in how media coverage contributed to outcomes, they also noted the participants' preferred news sources and coded whether the sources were generally more conservative or liberal.

The researchers found that after the People's Climate March, study participants were more optimistic about people's ability to work together to address climate change -- referred to as collective efficacy beliefs. They also found that study participants had less negative opinions of marchers after the march.

Additionally, the researchers found that participants who regularly consumed news from conservative media had more collective efficacy beliefs and intent to take action after the marches. Those who regularly got news from liberal media tended to have less negative impressions of marchers, particularly among those who reported having heard about the marches.

Swim said that because they controlled for such factors as political affiliation and beliefs, these changes were likely due to the way their preferred media sources portrayed the marches before and after the events.

"If conservative news sources only talk the march after the fact, that might be why their viewers have more efficacy afterwards, because they didn't know about it before," Swim said. "Additionally, a more liberal news source may portray marchers as more sympathetic, which may be why their viewers had more favorable impressions of marchers."

In future, Swim said she would like to further study how news and other media sources contribute to people's beliefs about climate change. For example, a content analysis that helps tease apart whether it is how much coverage a march gets that contributes to changes in beliefs or whether it is how the marches and marchers are portrayed that matters.

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Nathaniel Geiger, Assistant Professor of Environmental Communications from Indiana University, Michael L. Lengieza, graduate student in Psychology from Penn State, and also participated in this work.