Addressing Cumulative Environmental Effects under the Canadian Environmental Assessment Act

Operational Policy Statement

Original: March 1999
Update: November 2007


This guide is for information purposes only. It is not a substitute for the Canadian Environmental Assessment Act (the Act) or any of its regulations. In the event of any inconsistency between this guide and the Act or regulations, the Act or regulations, as the case may be, would prevail.

This document provides guidance on environmental assessment under the provisions of the Canadian Environmental Assessment Act as amended on July 12, 2010. It has not been updated to reflect changes to the process introduced in the Canadian Environmental Assessment Act, 2012. To ensure that you have the appropriate versions of the Act and regulations, please consult the Department of Justice website.


This operational policy statement provides clarification to responsible authorities on how cumulative environmental effects should be considered in environmental assessments conducted under the Canadian Environmental Assessment Act (the Act). It also highlights differences between the Cumulative Effects Assessment Practitioners Guide (the Practitioners Guide), the Act and previous Agency guidance on this subject. Finally, this document updates the Agency's position on the assessment of cumulative environmental effects as described in the 1994 Reference Guide.


Subsection 16(1) of the Act requires every environmental assessment to include consideration of the environmental effects of a project, including "any cumulative environmental effects that are likely to result from the project in combination with other projects or activities that have been or will be carried out."

Responsible authorities must determine appropriate means to satisfy this requirement as part of screenings and comprehensive studies.

Detailed guidance for doing so can be found in the following documents:

The Agency recommends that responsible authorities consult these documents when determining how to take cumulative environmental effects into account as part of the environmental assessment of a project.

Cumulative Effects Practitioners Guide

The Agency sponsored and funded the development of the Practitioners Guide by an independent multi-stakeholder committee. It was the subject of broad consultations among federal authorities, other practitioners and the public prior to being finalized and published.

The Practitioners Guide offers a "best practices" perspective on cumulative environmental effects assessment with emphasis on the assessment of cumulative biophysical effects. It is intended to be broadly applicable across Canadian jurisdictions and to projects of varying size and complexity in different industrial and development sectors.

The Practitioners Guide was not developed solely in reference to the assessment of cumulative environmental effects under the Act. Accordingly, with respect to projects undergoing a federal environmental assessment, responsible authorities should take the following information into account.

Definition of Cumulative Environmental Effects

"Cumulative environmental effects" are defined more narrowly in the Practitioners Guide than under the Act. While the Practitioners Guide is limited to cumulative biophysical effects, assessments of cumulative environmental effects under the Act can extend to the effects of such changes on health and socio-economic conditions, physical and cultural heritage, and other matters described in the definition of "environmental effects" in section 2 of the Act.

Responsible authorities should consider whether these factors, as well as biophysical effects, need to be examined in the cumulative environmental effects assessment.

Identifying Future Projects to Include in Cumulative Environmental Effects Assessment

According to the Practitioners Guide, the selection of future actions to consider in a cumulative environmental effects assessment should reflect "the most likely future scenario." Emphasis is given to projects with greater certainty of occurring; however, hypothetical projects might be discussed on a conceptual basis in some cases.

As stated above, the Act refers to the consideration of "any cumulative environmental effects that are likely to result from the project in combination with other projects or activities that have been or will be carried out." Accordingly, in identifying future projects to include in the cumulative environmental effects assessment, responsible authorities should consider projects that are "certain" and "reasonably foreseeable", as recommended by the Practitioners Guide. The Act does not require consideration of hypothetical projects, but responsible authorities may choose to do so at their discretion. Information concerning the cumulative environmental effects of the project under assessment combined with hypothetical projects may contribute to future environmental planning; however, it should not be the determining factor in the environmental assessment decision under the Act.

The Agency's 1994 Reference Guide advised that the assessment of cumulative environmental effects in relation to future projects should focus exclusively on imminent projects, that is, projects that have been approved but not yet implemented or proposals awaiting planning or other formal approval. It is now recognized that this approach may not always be adequate to understand the implications of development activities on the future well-being of the environment. Also, it may limit the ability of cumulative environmental effects assessment to contribute to informed environmental planning and decision making in the future in the project area.

To better reflect the broad objectives of the Act, the Agency position has evolved to include "certain" and "reasonably foreseeable" projects and, where appropriate those projects that are "hypothetical". This position is also consistent with the "best practices" approach of the Practitioners Guide.

Responsible authorities will need to exercise judgment in distinguishing between projects that are certain, reasonably foreseeable and hypothetical. The following definitions from the Practitioners Guide (p.18 and 19) can assist responsible authorities in this regard. Additional details are found in section of the Practitioners Guide.


The action will proceed or there is a high probability the action will proceed.
Reasonably Foreseeable
The action may proceed, but there is some uncertainty about this conclusion.
There is considerable uncertainty whether the action will ever proceed. The conjecture is based on currently available information.

Level of Effort

The Practitioners Guide emphasizes approaches and issues associated with the cumulative environmental effects assessment of large projects; however, it also notes that this framework can be scaled down and adapted for use with smaller projects.

The level of effort directed to the assessment of cumulative environmental effects should be appropriate to the nature of the project under assessment, its potential effects and the environmental setting. For example, the practitioner should give particular attention to the selection of future projects to be considered in the cumulative environmental effects assessment where:

  • certain and reasonably foreseeable projects may have an impact on the same valued ecosystem components as the project under assessment;
  • rapid development of the project area is anticipated; or
  • particular environmental sensitivities or risks are involved.

Regional Studies

Amendments to the Act that took effect in October 2003 recognize the use of regional studies as an important tool for the consideration of cumulative environmental effects. The Act now specifies, in section 16.2, that the results of a study of the environmental effects of possible future projects in a region may be taken into account, particularly for the consideration of any cumulative environmental effects that are likely to result from the project in combination with other projects or activities - past, present and future.

The Act encourages federal authorities to cooperate with provinces, land claim bodies or Aboriginal self-governing bodies in regional studies outside the scope of the Act.

Additional Information

For more information on this operational policy statement or on the requirements of the Act, please contact the Agency office in your region.

Additional Agency policies and guidance can be found on the Agency's Web site.

© Her Majesty the Queen in Right of Canada, 2008.

This publication may be reproduced for personal or internal use without permission, provided the source is fully acknowledged. However, multiple copy reproduction of this publication in whole or in part for purposes of distribution requires the prior written permission from the Minister of Public Works and Government Services Canada, Ottawa, Ontario K1A 0S5 or

Catalogue No.: 978-0-662-47682-5
ISBN: En106-76/2008E

This document has been issued in French under the title: Aborder les effets environnementaux cumulatifs en vertu de la Loi canadienne sur l'évaluation environnementale.

This document is also available in Adobe's Portable Document Format [PDF - 48 KB].

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