Cumulative effects, also referred to as cumulative environmental effects and cumulative impacts, can be defined as changes to the environment caused by the combined impact of past, present and future human activities and natural processes. Cumulative effects to the environment are the result of multiple activities whose individual direct impacts may be relatively minor but in combination with others result are significant environmental effects. The multiple impacts of different activities may have an additive, synergistic or antagonistic effect on one another and with natural processes. Cumulative effects can be difficult to predict and manage due to inadequate environmental baseline data, complex ecological processes, and the large scale at which human development occurs.[1]
The emergence of cumulative effects in environmental regulations began in the 1970s and has since been increasingly seen as a consideration in environmental impact assessments and land management.[2] However, despite its growing relevance, there are no generally accepted methodologies for cumulative effects assessments and there remains debate surrounding the issue.[3]
Many human activities result in direct and indirect impacts that collectively impact the environment. The impacts of activities in combination with natural processes can result in cascading responses in ecosystems that can become unpredictable. Some activities known to have significant impacts on the environment and contribute highly to cumulative effects are marine resource development, energy production and consumption, and land use changes. The cumulative environmental effects of human activities ultimately intensify global warming and climate change.[4]