We present the design, the set-up, and results of research of which difficult or special physics concepts students of environmental sciences identify as threshold concepts, in the physics course for environmental sciences of their undergraduate e-learning programme. More specifically, which characterizations –, transformativity, irreversibility, integrativity, counter-intuitivity, and boundedness – are applicable in their view, and what they did to overcome these threshold concepts. The data are gathered by analyzing a reflection assignment of the students at the end of the course. The pattern observed in earlier threshold concepts research, computer science and mathematics, that very few threshold concepts are mentioned by a vast majority of the students, while all the other threshold concepts were mentioned by very few student, is also investigated. Finally, we analyzed to what extend the use of the physics concepts increased their knowledge of environmental topics. As results we report as the highest scoring threshold concepts: Carnot cycle, radiation enforcement, quantum theory, and electromagnetism. This is indeed in accordance with the earlier mentioned pattern in computer science and mathematics that a few high scoring threshold concepts are mentioned and many low scoring threshold concepts. The highest scoring characteristics are transformative, irreversible, and integrative. The most frequently mentioned ways of overcoming a threshold concept are: studying the physical concept again and working with it (exercises) or using it (applications). The least mentioned way is consulting external resources, such as internet and literature. The benefit of knowing physics concepts in oder to better understand the environmental topics is on the average judges as 4.5 on a 5-points-scale, which is interpreted as that understanding physical concepts has highly improved their understanding.