Assessing global impacts at sector and project levels

The assessment of global impacts must account for effects that would be insignificant on their own, but which may be highly significant in combination with many others like them. This can in principle be dealt with by requiring that any adverse impact by fully mitigated, either within the action being assessed or in conjunction with other activities. More commonly, global impacts are not mitigated fully, and so some measure is needed of the extent to which an impactʹs magnitude is consistent with global sustainability objectives. This may be achieved by defining a time-dependent target for the overall impact and apportioning it, using criteria of global equity for apportionment between countries, and simple measures of project benefit for apportionment between individual projects. Quantified significance criteria can then be derived. Examples are given for greenhouse gas emissions and habitat loss in industrial and developing countries.