From a theoretical perspective, the effect of international climate policy on individual willingness to take up climate protection efforts is ambiguous. An effective international climate policy may motivate individuals to increase their voluntary efforts to mitigate global warming (crowding-in). However, if individuals perceive international climate policy to be effective, they may decide to scale back their own voluntary climate protection activities (crowding-out). Relying on data from representative household samples from Germany and the US, this article empirically explores the relation between individual perceptions of climate policy and their planned adoption of six climate protection activities. It also tests the effects of a ‘warm glow’ motivation and whether this effect varies with the perceived effectiveness of international climate policy. The econometric analyses provide suggestive evidence that higher perceived justification and effectiveness of international climate policy crowd in voluntary individual climate protection activities in the US and Germany. In both countries, these activities are also positively related to the warm glow indicator, confirming that feelings which go beyond pure altruism help explain individual voluntary climate protection efforts. For the German (but not the US) sample, the effect of warm glow is stronger when international climate policy is believed to be ineffective. Key policy insights More effective international climate policy is expected to spur additional voluntary climate protection activities by individuals. Enhancing people’s trust in the outcomes of international climate policy likely raises their engagement in voluntary actions. In some cases, policy failure may be somewhat compensated for by greater individual action, motivated by warm glow.