Environmental impact assessment of projects was the starting point for SEA, but EIA and SEA have some key differences:
|Source: UNEP (2002) Environmental Impact Assessment Training Resource Manual, 2nd Edition, UNEP, Geneva. Amended from CSIR (1996)|
|EIA of Projects||SEA of Policies, Plans and Programmes|
|Takes place near the end of decision-making cycle: aims to minimise impacts||Takes place at earlier stages of decision-making cycle: aims to prevent impacts|
|Reactive approach to development proposal||Pro-active approach to development proposals|
|Considers limited number of feasible alternatives||Considers broad range of potential alternatives|
|Limited review of cumulative effects||Cumulative effects assessment is key to SEA|
|Emphasis on mitigating and minimizing impacts||Emphasis on meeting environmental objectives, maintaining natural systems|
|Narrow perspective, high level of detail||Broad perspective, lower level of detail to provide a vision and overall framework|
|Well-defined process, clear beginning and end||Multi-stage process, overlapping components, policy level is continuing, iterative|
|Focuses on standard agenda, treats systems of environmental deterioration||Focuses on sustainability agenda, gets at sources of environmental deterioration|
These differences account for one of the two main reasons for SEA:
1. SEA addresses limitations of project EIA
Because EIA takes place once many strategic decisions have already been made, it can often address only a limited range of alternatives and mitigation measures: those of a wider nature are generally poorly integrated into project planning.
Consultation in EIA is also limited and the contribution of EIA to the eventual decision regarding the project is unclear.
Although project EIA is widely used and accepted as a useful tool in decision-making, it largely reacts to development proposals rather than proactively anticipating them:
"At this [EIA] stage, the prior questions of whether, where and what type of development should take place are either decided or largely preempted by earlier policy making processes. Often, these decisions will have occurred with little or no environmental analysis. This foreclosure of the range of choice is partially countered by provisions to addressing project justification and alternatives in EIA. In reality, however, prior policy, technological and locational options are not open to serious environmental reexamination; neither is project-by-project EIA an effective way of doing so. Far preferable is the use of SEA or an equivalent approach to incorporate environmental considerations and alternatives directly into policy, plan and programme design." (Sadler and Verheem 1996)
Project EIAs are also generally limited to the project's direct impacts. This approach ignores a wide range of impacts, including:
- cumulative impacts: the environmental impacts of multiple plans, projects and other actions;
- global impacts: impacts that go beyond the local, project level, for instance climate change;
- indirect, secondary or induced impacts: impacts that occur several steps away from the original action, for instance new houses that generate more vehicle movements that increase air pollution that affect the flora in an area;
- synergistic impacts: where impact A + impact B have a total impact of more than A+B: for instance NOx emissions and ozone emissions which together cause smog, which has impacts over and above those of just the NOx + ozone.
The figure below illustrates how simply carrying out EIAs for individual projects will not address more strategic issues. It shows long-ago proposals for building a second ring road around London. The EIAs for the individual road links comprising the ring road would not have dealt with, for instance, long-distance traffic on the ring road, or the additional freight traffic caused by the sudden opening up of better links between the London ports and areas to the west of London.
SEA can deal with many of these difficulties, as it:
- incorporates environmental issues into project planning and decision making;
- considers alternatives or mitigation measures beyond project level; and
- involves consultation on more strategic issues.