Enhancing perceived effectiveness can increase climate policy acceptance

Public acceptance is crucial for the successful implementation of climate policies; hence, it is essential to understand its determinants and how to boost it. In this research, we aim to test the causality of perceived effectiveness on policy acceptance. For this purpose, we experimentally manipulated perceived effectiveness by providing information about the objective effectiveness of a climate policy. In a preregistered experiment (N = 953; T1), participants were asked about the perceived effectiveness and acceptance of a speed limit on German highways. Beforehand, participants in the information condition were given details about the speed limit's effectiveness in terms of CO₂ reductions, whereas those in the control condition were not. Participants were asked about the perceived effectiveness and policy acceptance again 1.5 years later (n = 334; T2). We found that providing vs. not providing such information led to higher perceived effectiveness but not greater policy acceptance at T1. However, among those participants without prior knowledge of the speed limit's effectiveness, providing the information positively affected both perceived effectiveness and policy acceptance at T1. Among those people who learned about the effectiveness of the policy at T1, perceived effectiveness and policy acceptance were higher when they could (vs. could not) recall the effectiveness information after 1.5 years (i.e., at T2). Our results suggest that perceived effectiveness causally affects policy acceptance in the climate domain. Explaining the objective effectiveness of climate policies—and doing so in such a way that people can remember the information over time—thus offers a promising approach for policymakers to increase public acceptance of climate policies.