Non-communicable diseases, such as hypertension, diabetes, or depression, result from an interplay of physiological, genetic, behavioral, and environmental aspects. Together with climate change, they are arguably among the most significant challenges mankind faces in the 21st century. Additionally, the bidirectional influences of climate change and health on each other are undisputed. Behavioral changes could curb both climate change and the spread of non-communicable diseases. Much effort has been put into information campaigns in both fields, but success has been limited. In the following, the knowledge action gap is compared and analyzed in healthy and climate-friendly behavior from a practical point of view and the supporting theoretical models are highlighted. The analysis shows that self-efficacy plays an essential role in both areas of research for effecting behavioral changes. The models of ‘Planned Behavior’ and ‘Stages of Change’ seems helpful and can be applied and adapted to explain behavioral changes in health and climate changes settings. We compared two previously unrelated research fields to uncover new avenues for further study and stimulate fruitful transdisciplinary discussion. Future directions on how behavioral medicine and climate change research can learn from each other are discussed.