We present a programmatic research line to test whether a longitudinal intervention aiming to increase key psychological correlates of pro-environmental behavior motivates young adults to take climate action. In five longitudinal studies, we will test and optimize a six-week, in-person intervention, exposing participants to interactive lessons and activities that were developed from existing psychological theories and interventions. The goal is to increase pro-climate behavior by leveraging 12 psychological correlates such as beliefs, attitudes and affect. Before and after the intervention, participants will complete surveys measuring the psychological correlates, and also report individual and collective pro-climate behaviors via Ecological Momentary Assessment (EMA). Each study will include a control group. The psychological correlates and behavior will be measured again after three months to assess the medium-term effectiveness of the intervention. The results and participant feedback from each study will be used to update the intervention for the following studies. Each study will target young adults at different life stages (studying or working) across two countries (Italy and the Netherlands). The longitudinal design, the intensive manipulations and EMA’s ecological validity are uniquely capable of revealing causal evidence that changes in beliefs, attitudes and affect lead to climate action across age groups and cultures. Hosted on the Open Science Framework