The baseline (or reference) is the state against which change is measured. It might be a ‘current baseline,’ in which case it represents observable, present-day conditions. It might also be a ‘future baseline,’ which is a projected future set of conditions excluding the driving factor of interest. Alternative interpretations of the reference conditions can give rise to multiple baselines.

Intergovernmental Panel on Climate Change (IPCC) 2012 1

A description of existing conditions to provide a reference (e.g. pre-project condition of biodiversity) against which comparisons can be made (e.g. post-impact condition of biodiversity), allowing the change to be quantified.

Adapted from Business Biodiversity and Offsets Programme (BBOP) 2012 2