To cite the envirem package in publications, use:

Title P.O., Bemmels J.B. 2018. ENVIREM: an expanded set of bioclimatic and topographic variables increases flexibility and improves performance of ecological niche modeling. Ecography. 41:291–307.

Corresponding BibTeX entry:

  @Article{,
    title = {ENVIREM: An expanded set of bioclimatic and topographic
      variables increases flexibility and improves performance of
      ecological niche modeling},
    author = {PO Title and JB Bemmels},
    journal = {Ecography},
    year = {2018},
    volume = {41},
    pages = {291-307},
  }