Rational decisions or moral obligations? A systematic review of TPB-NAM integration in understanding low-carbon behavior

Objective Understanding low-carbon behavior remains a significant challenge due to the complexity of environmental decision-making and the persistent intention–behavior gap. While the Theory of Planned Behavior (TPB) and the Norm Activation Model (NAM) are among the most widely applied frameworks for explaining environmental behavior, studies increasingly integrate these theories to capture both rational and moral dimensions of decision-making. This study systematically reviews TPB–NAM integration research to identify major research trends, theoretical integration approaches, and implications for understanding the psychological mechanisms underlying low-carbon behavior. Methods A systematic review was conducted using 225 peer-reviewed articles retrieved from the Web of Science Core Collection. Bibliometric and content analysis techniques were employed using Bibliometrix, VOSviewer, and Scimago Graphica to examine publication trends, research hotspots, application contexts, dependent variables, and integration pathways between TPB and NAM. Results The findings reveal a substantial increase in TPB–NAM integration studies since 2019, reflecting growing interest in environmentally responsible behavior. Sustainable consumption, waste management, and sustainable transportation emerged as the most frequently investigated contexts. Behavioral intention remained the dominant dependent variable, accounting for 85.4% of studies, whereas actual behavior received comparatively limited attention. Four major integration pathways were identified, namely awareness of consequences → attitude, subjective norm → personal norm, awareness of consequences → subjective norm, and social norm → personal norm. Furthermore, 62.0% of studies adopted a simple combination of TPB and NAM without establishing clear theoretical linkages between constructs. Conclusion The findings suggest that TPB and NAM represent complementary rather than competing perspectives for understanding environmental behavior. The identified integration pathways highlight the interaction of cognitive evaluation, social influence, and moral regulation in shaping low-carbon behavior. By synthesizing existing evidence, this review advances understanding of the psychological foundations of environmental behavior and provides directions for future research aimed at addressing the intention–behavior gap and promoting sustainable behavioral change.