The Science of Sustainability
Human Activity Impacts on Ecosystems
Threats to Ecosystems
Business and human activities can be direct threats to ecosystems. They can cause destruction, degradation, and the impairment of biodiversity and other natural resources. Ecosystem threats include
1. Climate Change
3. Habitat Destruction
5. Introduction of invasive species.
Human Activity Impacts on Ecosystems
Stressing the Ecosystem
Business and human activities can stress the ecosystem they operate in reducing its overall health and at some point the accumulation of all negative impact from human activities can exceed the ecological threshold of the planet. Driving these human activities are population, affluence, and technology.
Climate change is one of the greatest threats to sustainability. It is a controversial and contested topic. As highlighted in the previous unit, the earth’s climate does fluctuate over time due to a variety of factors. However, there is a significant body of scientific research that indicates that global temperatures are rising and that rising global temperatures are directly linked to human activities involving the emissions of greenhouse gases (GHG). 
GHG traps heat in the atmosphere allowing the planet to be a habitable place. The primary GHG of interest is carbon dioxide (CO2), which is a vital gas in our earth system and is released from various sources, including the combustion of fossil fuels. Over the last two centuries, rapid industrialization and the corresponding increased burning of fossil fuels and deforestation of large tracts of land globally has caused the concentrations of greenhouse gases to increase significantly in our atmosphere.
Some greenhouse gases, such as carbon dioxide, occur naturally and are emitted to the atmosphere through natural processes and human activities. Other greenhouse gases (e.g., fluorinated gases) are created and emitted solely through human activities. Not all greenhouse gases have the same impact.
The principal greenhouse gases that enter the atmosphere because of human activities-also called anthropogenic-are as follows:
Emitted from a variety of industrial processes and sometimes used as substitutes for ozone-depleting substances. Although fluorinated gases are typically emitted in smaller quantities, they are potent greenhouse gases sometimes referred to as high global warming potential gases (“high GWP gases”).
Emitted during agricultural and industrial activities as well as during combustion of fossil fuels and solid waste.
Emitted during the production of coal, natural gas, and oil; from livestock and other agricultural practices; and by the rotting of organic waste in municipal solid waste landfills.
Emitted through the burning of fossil fuels (oil, natural gas, and coal), solid waste, trees and wood products, and chemical processes.
Average global temperatures have increased 1.3 degrees Fahrenheit since 1850, with the trend in warming in the last fifty years being almost double that of the prior one hundred years. The twentieth century’s last two decades were the warmest in four hundred years. Current projections have global temperature further increasing by a significant two degrees to twelve degrees Fahrenheit by 2100.
Temperature increases of this magnitude will adversely affect the planet through rising sea levels, shrinking glaciers, changing of the range and distribution of plants and animals, lengthening of growing seasons, changing of weather patterns, and human health effects. People are affected by climate change through extreme periods of heat and cold, storms, climate sensitive diseases, prolonged and increased levels of smog, and economics (e.g., volatility in retail prices; resource scarcity; and changing work patterns, conditions, and incomes).
Changes in global temperature are impacting the global climate in significant ways, including the following:
1. Mountain glaciers and snow cover have declined significantly, contributing to rises in sea level. For example, Montana’s Glacier National Park now has only 27 glaciers, versus 150 in 1910. In the Northern Hemisphere, thaws also come a week earlier in spring and freezes begin a week later.
2. Sea levels will rise dramatically. Thermal expansion has already raised the oceans four to eight inches (ten to twenty centimeters). There is a possibility for a three-foot sea rise by the end of the century, which would flood many cities along the US seaboard. 
3. Average Arctic temperatures have increased at almost twice the global rate in the past one hundred years. Arctic ice is rapidly disappearing, and the region may have its first completely ice-free summer by 2040 or earlier. Polar bears and indigenous cultures are already suffering from the sea’s ice loss.
4. Increased precipitation has been observed in the eastern parts of North and South America, northern Europe, and northern and central Asia.
5. An upsurge in the amount of extreme weather events, such as wildfires, heat waves, and strong tropical storms, is also attributed in part to climate change by some experts. Examples of these types of extreme events are already occurring with greater frequency, including recent flooding in Nashville and extreme droughts in Russia.
6. Coral reefs, which are highly sensitive to small changes in water temperature, suffered the worst bleaching-or die-off in response to stress-ever recorded in 1998, with some areas seeing bleach rates of 70 percent. Experts expect these sorts of events to increase in frequency and intensity in the next fifty years as sea temperatures rise. Coral systems are rich ecosystems providing breeding grounds for sea life and are major recreational draws. The loss of these vital resources has a devastating economic impact on local economies.
Denial of Climate Change
It is important to note that there are those that deny the significance of climate change on the human condition and the impact of human and business activity on climate change. Climate change denial dismisses the scientific consensus on the extent of global warming, its significance, and its connection to human behavior.
Pollution is the contamination, harm, or disruption of the natural environment through the emissions of harmful substances. Pollution is most typically associated with anthropogenic sources but can also occur from natural activity, such as volcanic eruptions. Pollution can impact air, water, and land. Pollutants include domestic, industrial, and agricultural waste. It comes in many different forms and can be chemical substances or noise, heat, or light.
Sources of Pollution
Pollution can be either point source or nonpoint source. Point source is a specific and easily identifiable source of pollution, such as a factory or power plant. Nonpoint sources consist of many small, distributed sources of a pollutant that are difficult to individually identify and on their own may not be that harmful but in aggregate are significant sources of pollution.
Pollution is not just toxic substances; it can be pollutants that are actually part of a healthful ecosystem in the proper quantities, such as nitrogen or carbon dioxide, but that in excessive quantities alter the normal functioning of an ecosystem resulting in harm to the ecosystem. Pollution can range from highly dangerous radioactive materials to airborne dust (a substance that is typically benign) resulting from land erosion.
A classic example of nonpoint source would be soap detergents, fertilizers, and other commonly used chemicals and products from many residences and businesses that then contaminate watersheds with high levels of nitrogen. Nonpoint sources tend to be more complex to regulate for pollution emissions.
Air pollution, the contamination of the atmosphere by airborne pollutants, is most often related to combustion of fuel from either stationary or mobile sources. Stationary sources include the smoke stacks of factories, power plants, and furnaces or boilers. Mobile sources refer to motor vehicles, aircraft, and other forms of fossil-fuel-based transportation. Paints, chemicals, and aerosol sprays also can pollute the air. Natural sources of air pollution include dust, methane from livestock, volcanic activity, wildfires, and even vegetation.
Municipal Solid Waste
Municipal solid waste (MSW) is a waste product that becomes a form of pollution if not properly managed. MSW is more commonly thought of as garbage, refuse, or trash. Solid waste is not necessarily toxic but includes discarded materials that need to be properly processed and disposed. Examples of solid waste include household trash, used tires, discarded appliances, furniture, paints, and construction and demolition
Energy can be recovered from landfill sites through different forms, such as methane gas. Methane gas can be used to generate electricity or be burned as a heat source. However, the vast majority of waste is being disposed of, even though it contains resources (metals, plastics, and paper) that could be reused or recycled to reduce the demand on new resources. For example, cardboard that is recycled helps reduce the demand for trees to be cut down to make new cardboard.
Habitat destruction brought on by the activity of humans threatens resident species and ecosystems. Two examples of habitat destruction are deforestation and desertification. Deforestation occurs when a forest or stand of trees is removed, converting the land to a nonforest use. This changes the ecosystem drastically and results in a dramatic loss of biodiversity.
Deforestation can be the result of timber harvesting or of clearing land for agricultural, commercial, or residential use. The loss of biodiversity and trees alters the ecosystem and can result in aridity and erosion. It also results in climate change and extinction, and it can lead to desertification if on a significant enough scale. The social impacts can include displacement of indigenous peoples.
Desertification is the degradation of land quality and features low biodiversity, dry conditions, and poor soil quality. Deserts are formed through both natural processes and human activity. However, desertification is occurring at a greater rate than past geological time scales due to human activity. The concept of desertification became well known in the United States in the 1930s, when parts of the Great Plains in the United States turned into the “Dust Bowl” as a result of drought and poor agricultural practices.
Overexploitation is a major threat to ecosystems and therefore sustainability. It is the consumption of a natural resource at a rate greater than that natural resource can maintain itself. Overhunting of species is one of the clearest examples of overexploitation, but there are other forms. Land degradations are human-induced changes that impair the capacity of the land to sustain life. Deforestation and overgrazing exploit the land and result in the exceeding of sustainable yield.
Invasive species are brought on by transporting species either intentionally or accidentally from other areas of the world. This can be devastating to existing species as invasive species are introduced on a timescale much more quickly than typically would happen with evolution over longer time periods. This can include outcompeting native species in the ecosystem, leading to the decline or extinction of local species, and overpopulation as these invasive species may not have any predators in this new ecosystem. They also can be a major economic cost.
The zebra mussel provides an invasive species that has had significant economic impacts. The zebra mussel is native to lakes in Russia but was accidentally introduced in the United States and Canada through the ballast water of commercial ships that were transporting goods to the Great Lakes region in the 1980s. They have been spreading ever since and have recently been found in lakes in Massachusetts; they attach to recreational boats and are transported wherever the boat may go. They colonize rapidly and have covered the undersides of docks, boats, and other marine structures and can grow so thick that they block municipal water and hydroelectric pipelines. The cost of pest management for zebra mussels at power plants and other water-consuming facilities is approximately $500 million a year in the United States. 
Human population growth is a factor in human ecosystem impact. From 0 AD to the present, global population has increased from three hundred million to seven billion. While population growth was once considered to be one of the leading drivers of human impacts on ecosystems, it does not adequately explain all the impacts that come from human activities. One concept that is useful in understanding the multiple factors that interact to impact environmental quality is the IPAT equation. The equation was developed in the early 1970s by scientists John Holdren and Paul Ehrlich to explain the human factors that create environmental impact.
I = P x A x T
Impact (I) was expressed as the product of population (P), affluence (A), and technology (T). This formula doesn’t quantify actual impacts, but is meant to state relationships. Also, P, A, and T are not independent variables but are interdependent. It does not show a simple multiplicative relationship among the main factors; research has shown that a doubling of population, for example, does not necessarily lead to a doubling of impact. Affluence is related to consumption where more affluent societies are able to consume more resources than less affluent societies can. Technology is a more complex factor as it can provide the means to extract greater quantities of resources but also can be used to limit consumption of resources.
The IPAT equation does not identify sustainable limits but does assist in increasing understanding of the general factors that increase or decrease environmental impact. By highlighting the interplay among a variety of factors in creating an impact, the IPAT equation demonstrates that there are multiple ways of reducing undesirable effects.
 “IPCC Fourth Assessment Report, Working Group III, Mitigation of Climate Change,” IPCC, http://www.ipcc.ch.
 “IPCC Fourth Assessment Report, Working Group III, Mitigation of Climate Change,” IPCC, http://www.ipcc.ch.
 “Climate Change-Health and Environmental Effects,” US Environmental Protection Agency, http://www.epa.gov/climatechange/effects/index.html#ref.
 “World Needs to Axe Greenhouse Gases by 80 pct: Report,” Reuters, April 19, 2007, http://www.reuters.com/article/2007/04/19/us-globalwarming-idUSL194440620070419.
 “Warming to Cause Catastrophic Rise in Sea Level,” National Geographic, April 26, 2004, http://news.nationalgeographic.com/news/2004/04/0420_040420_earthday.html.
 “Desertification,” US Geologic Services, http://pubs.usgs.gov/gip/deserts/desertification.
 Center for Invasive Species Research at the University of California, Riverside.
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