Strategic environmental assessment
One of the most significant limitations in project-level EA has been in the assessment of the effects of a number of different developments within the same geographical area or economic sector. Project-level EA systems have tended to focus on specifically defined types of project which by virtue of their size and location are considered likely to have significant environmental effects. This approach has the disadvantage that many small individual projects, which in themselves have relatively minor impacts, are not the subject of EA, even though their collective effects may be significant. The established use of EA has also tended to exclude those impacts which are distant (in time or space) from the project itself, for example the additive or synergistic effects arising from existing or other proposed developments. Additive effects generally refer to situations in which the magnitude of an impact is directly proportional to its size, whereas synergistic effects arise when the resulting environmental impact is greater than the sum of its constituent inputs. Project-level EAs have also often ignored those secondary developments which may arise as a result of an initial project, for example the proliferation of retail and housing developments which follow on from the opening of a new road. The process of cumulative effects assessment (CEA) seeks to address these deficiencies and, with the exception of the analysis of the cumulative impacts of a single project, is more appropriately performed within the scope of an SEA.