What the evidence shows

This study asks a question that's directly relevant to protest strategy: does an individual's willingness to show up at a climate protest depend on how many other people they expect to attend? Two competing dynamics are possible — "strategic complementarity" (people are more likely to join when they expect a bigger crowd) or "strategic substitutability" (people free-ride and are less likely to join when they expect a bigger crowd, since their individual presence feels less pivotal or less distinctive).

The researchers used the Third Global Climate Strike (20 September 2019) as a natural experiment. They surveyed a general-population sample (not committed activists) in Germany's four largest cities across three waves — before, immediately before, and after the protest — and randomly gave a subset of respondents truthful information about how many other people planned to attend locally. This lets them isolate the causal effect of updated beliefs about turnout on actual participation, rather than just observing a correlation.

Key Findings

• Participation decisions are strategic substitutes, not complements. A 1 percentage point (pp) increase in a person's belief about how many others will attend reduces their own probability of participating by roughly 0.7 pp.

• The substitution effect was driven by expectations about adults aged 30–69, not younger adults (18–29). Beliefs about the older cohort had a significant negative effect on participation; beliefs about the younger cohort did not.

• Protesters differed demographically from non-protesters: younger (under 50), more highly educated, higher-income, and holding stronger environmental attitudes.

Stand-out data points

• 11%: average actual protest participation rate among study respondents across the four cities, versus much higher stated pre-event intentions.

Examples of how Understories uses this research

• Solution focus: doesn't strongly apply here in the usual sense (this isn't about pairing a problem with a remedy), but the paper does offer a structural insight: the "solution" to weak turnout isn't more enthusiasm, it's better information design, communicating conservative estimates rather than relying on optimistic buzz.

• Actionability: offers a concrete, testable recommendation (communicate conservative rather than triumphant turnout estimates pre-event).

• Beneficence: this research helps advocates avoid an unintended backfire — publicizing large expected crowds may suppress turnout among the general public. Using it well means organizers can calibrate mobilization messaging for genuine impact rather than optimism bias.

• Non-Maleficence: there is a real misuse risk here worth flagging. The finding could be used to justify deliberately understating expected turnout to manipulate potential participants — a tactic that shades into dishonest framing. Understories should flag that the appropriate use is "communicate realistically and conservatively," not "mislead people about turnout to manufacture urgency."

— non exhaustive.

Key quote

“It seems advisable to communicate conservative estimates to the media in the run-up to another Global Climate Strike."

© The Author(s) 2023 — CC BY 4.0. 

Last update: 8 July 2026

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