Cumulative environmental effects can be defined as effects on the environment which are caused by the combined results of past, current and future activities. Over time, direct and indirect human activities combine to collectively impact the environment. These effects may differ from the original, individual activities. For example, ecosystems can be damaged by the combined effects of human activities, such as air, land, and/or water pollution, improper handling of industrial waste, and other human development activities. Global warming is the cumulative effect caused by too much greenhouse gas, and it may then cause a loss in biodiversity and acid rain.
North America has contributed to creating various cumulative effects on the environment. Many states in the United States have inadequate or no formal environmental review requirements in order to assess the cumulative effects on the environment from harmful practices. The extent to which cumulative effects in each state are evaluated varies greatly. For example, some programs only require an assessment on specific natural resource issues and others require comprehensive examination of cumulative effects on the environment. Environmental assessments are a necessity to ensure the further advancement of healthy ecosystems, habitats, and wildlife.
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Contributors and types
The concept of cumulative effects is based on the fact that little things, when combined together, form a larger result. For example, "a single automobile, a small clear- cut in a forest, or a single septic tank is unlikely to have a measurable effect on air quality, runoff, or water quality, respectively. However, with increasing numbers of cars, clear-cuts, or septic tanks, the likelihood of a detectable change increases. This change results from multiple activities at different locations, this type of cumulative effect occurs either off-site or across a large area, such as an airshed".
Human disturbances in the environment create cumulative effects. The human "footprint" is a major driver of biodiversity change and cumulative effects over time, some examples are physical disturbances from activities such as energy development, cultivation, forest harvesting, and transportation infrastructure.
Oil and gas
Canada’s offshore oil and gas industry creates cumulative environmental effects, such as noise pollution, which can affect whales, and oil pollution, which if exposed to seabirds can kill them. Oil and gas activities are usually only thought to be affecting one region of an ecosystem, but it is important to realize the connective nature of populations in different regions. Oil and gas activities can even disrupt the population of a species that is in more than one region of Canada. These effects may harm migrating populations, so every aspect must be considered in the management of offshore oil and gas activities in Canada.
Air pollution
Air pollution is caused by sulfur dioxide and nitrous oxide human emissions, such as electricity generation, factories, and vehicles. "Electrical power complexes using coal are among the greatest contributors to gaseous pollutions that are responsible for acidic rain. The gases can be carried hundreds of kilometers in the atmosphere before they are converted to acids and deposited," which can then cause widespread ecological damage.
Global warming
Global warming is caused primarily by anthropogenic, human caused, CO2 emissions greenhouse gases. Other cumulative effects include ocean acidification, caused by increasing amounts of carbon dioxide in the atmosphere, resulting from human actions. Also the long-term melting of ice sheets, from global temperature increases, contributes to sea level rising.
Not recycling
If we do not recycle recyclable materials it will increase air pollution (from incineration) and water pollution (from landfilling), and increase greenhouse gas emissions caused by plastic production. These are negative contributors to cumulative environmental effects that can cause global warming.
Policies
The United States uses a cumulative impact assessment (CIA), also referred to as cumulative effects assessment (CEA), which is a process that identifies additive or interactive environmental effects occurring from human activities over time in order to then avoid cumulative environmental effects. This is an effective potential policy that can also help in productive environmental planning and management. Most development activities have individually minor impacts but collectively over time their impact on the environment is more substantial. In many countries, CIA is undertaken as part of the environmental impact assessment (EIA) process.
Landscape management, such as creating wildlife reserves will help to ensure human development can not occur there and therefore reduce cumulative effects in that area. In many cases in the United States the government will not fund these environmental assessments because it requires great funding over a long term.
Solutions
A strategic environmental assessment is necessary to generate safer policies and programs for future industrial activities, while also being aware of environmental concerns from all potential sources. The large number of resources and the many ways by which these resources can be affected make cumulative effect assessments problematic.
Two ideas for improvement on United States' environmental review programs with CIA requirements are, creating detailed guidelines to specify what to include in a CIA and implementing better coordination between the agency responsible for carrying out CIA (the permitting and/or funding agency) and other relevant state agencies. Both ideas suggest that future effort to improve CIA practices should focus on strengthening the state’s environmental review programs ability to carry out CIA implementation. Also, including detailed guidelines will support the development of a definition of CI, clarify the steps required to conduct an assessment and specify content to be included in the write-up.
Three major problems were identified by administrators of environmental review programs with CIA requirements, they are a lack of specific procedures, unavailable data, and unclear definitions of cumulative effects. These are imperative problems to solve to then be able to properly manage activities contributing to cumulative effects. There is a reluctance to start a cumulative effect analysis in some cases due to the cost of the analysis, as well as the problems of uncertainty and complexity.
In order to stabilize the global average temperature, to decrease the cumulative effects of global warming, the world would need to reduce CO2 emissions, and also methane and nitrous oxide emissions. "For CO2, anthropogenic emissions would need to be reduced by more than 80% relative to their peak level" to reduce the effect of global warming.
Impacts and significance
The lack of environmental assessments can cause harm to wildlife populations and the habitats that are dependent on ocean ecosystems (specifically in the problem with offshore oil and gas industries), especially as these effects become additive, exponentially larger, and more harmful.
Environmental planning and management need to include cumulative effects as their top priority. Our ability to assess cumulative effects is hindered by the lack of information on past management activities and the uncertainty of future events. Secondary and interacting effects make it even more complex to assess current and potential cumulative effects.
Moreover, the very definition of a "cumulative effect" and its assessment in terms of cumulative significance" can result in a paradox. Eccleston describes some of the difficulties and paradoxes, and offers tools and techniques for resolving such problems.