Learn about cumulative effects

What are cumulative effects?

There are many definitions of cumulative effects, varying across jurisdictions. For example:

The Canadian Council of Ministers on the Environment developed the following definition in 2014: “cumulative effects are defined as the changes in the environment caused by multiple interactions among human activities and natural processes, which accumulate across time and space.”
The Impact Assessment Agency of Canada states that “cumulative effects are defined as changes to the environment, health, social and economic conditions as a result of a project’s residual effects combined with the existence of other past, present and reasonably foreseeable physical activities.”
The Metlakatla Cumulative Effects Monitoring program defines cumulative effects as “changes to the environment or human well-being from past, present and future development projects and human activities.”
The Nunavut Impact Review Board defines cumulative effects as “the accumulation of changes to the environment caused by human activities (e.g., past, existing and proposed activities, including activities associated with the project under assessment). These changes occur over space and time and can be brought about by environmental effects that are additive or interactive. For example hunting, oil spills and loss of habitat, commercial fishing pressure on prey species, can affect marine mammals in the Arctic.”

Some definitions consider only cumulative environmental effects, while others also include cumulative socio-economic and health effects. Some definitions include only human activities, while other also include natural processes. Some focus on adverse effects, while others consider both positive and adverse effects. Generally, they all refer to effects that are individually minor, but collectively significant.

In a world of increasing development pressures and changing natural processes, it is important to be able to assess and manage cumulative effects for the environment, socio-economic condition and human health.

The following video developed by Environment and Climate Change Canada provides a brief introduction to cumulative effects, using effects to water quality as a primary example.