Hare's two-level ("Kantian") utilitarianism, animal welfare and animal rights philosophies (especially how empirical science informs their application), environmental ethics, philosophical issues in environmental law
VARNER, G. E.
(1991).NO HOLISM WITHOUT PLURALISM. Environmental Ethics: an interdisciplinary journal dedicated to the philosophical aspects of environmental problems.
13(2), 175-179.
book
Newman, J. A., Varner, G., & Linquist, S.
(2017).Defending Biodiversity. Cambridge University Press (CUP).