Actually, similar to the Christian eco-books that I have from twenty years ago, this book isn't what I'd call 'tepid' in its assertion that there exist a profound necessity for the growth of a robust environmental consciousness among Christians. Thus, even if you don't agree with it's religious thrust, this book isn't a shallow treatment of the subject.
Alright. I understand somewhat your complaint in all of this and I think you already know that I've had to hear various criticism of my 'own form' of Christian faith, such as it is, philosophically conceived in the eclectic and inter-denominational expansiveness that I promote. I will say that this book by Daniel L. Brunner, Jennifer L. Butler, and A.J. Swoboda does address sin, and it does so on some level that is not cutting itself off from basic Evangelical notions of faith.
HOWEVER, at the same time, in perusing the book, these three authors seem to want to instill a much wider spiritual conscience into their readers by infusing some much needed reorienting of perspective, even in regard to how we address and manage our theology of sin. Since you mentioned sin, I took the liberty to further quickly peruse this book, and I came upon the following (moderately lengthy) quote that I think is one for us to consider in this thread, and not just as it applies to Environmental concerns, but to many of them

:
A second way to conceptualize personal sin is as relational. From this standpoint, sin is primarily understood as broken relationships, as estrangement or alienation. It is a view more attuned to Eastern Orthodoxy, in which salvation, becomes the process of restoring broken relationships through the life, death, and resurrection of Jesus Christ. Bryant Myers delineates the extent of this relational estrangement, stating that people experience broken, unjust relationships “with ourselves, with our community, with those we call 'other,' with our environment, and with God.” Instead of a healthy sense of self, our belovedness, and our vocation, our relationship with ourselves is marred by self-deprecation and a poverty of being. Instead of a reciprocated connectedness with our community, we exploit our neighbors and isolate ourselves. Instead of justice and shalom with “others,” we dominate and oppress those not like us. Instead of being rooted in and caring for our created environment, we overuse the land and its resources. Instead of a dynamic spiritual relationship with God, we fall prey to the idolatry of consumerism and substitue gods. (p. 128)
REFERENCE
Brunner, Daniel L., Jennifer L. Butler, and A. J. Swoboda.
Introducing Evangelical Ecotheology: Foundations in Scripture, Theology, History, and Praxis. Baker Academic, 2014.