MESS stands for Multivariate Environmental Similarity Surfaces. It is an index of similarity reporting the closeness of a point described by a set of environmental attributes to the distribution of these attributes within a population of reference points. The MESS approach has been proposed by Elith et al (2010). It works as BIOCLIM does but provides negative values which allows one to differentiate levels of dissimilarity. This is particularly valuable when considering points associated to values lying outside the range of the reference points.