Cities produce large amounts of pollution, which can be problem to those living downwind and downstream and also influence local climates. Because cities began in areas with good farmland, their growth ends up paving over the former farms.
The inevitable network of roads, railways and satellite communities end up fragmenting natural habitats and putting pressure on the species in the area.
Urbanization is a need that humans have in terms of providing housing for an increasing world population. Yet, planning must take into account issues such as fragmentation or disruption of habitats.
We also have to take into consideration how our garbage and other waste may disrupt the habitat of others. Perhaps considerations must be taken for long-term impact as opposed to only short-term consequences.
Dams disrupt water flow downriver while flooding large areas upriver. This flooding often releases mercury from decaying plants into the water.
Pollution is produced from many activities and comes in many forms: heat pollution (such as warm water used for industrial processes and then released back into natural waterways), chemical pollution of water and soil, atmospheric pollution that causes acid rain, and many more.
The burning of coal, oil, and natural gas, as well as deforestation and various agricultural and industrial practices, are altering the composition of the atmosphere and contributing to climatic change.
These human activities have led to increased atmospheric concentrations of a number of greenhouse gases, including carbon dioxide, methane, nitrous oxide, chlorofluorocarbons, and ozone in the lower part of the atmosphere.
Carbon dioxide is produced when coal, oil, and natural gas (fossil fuels) are burned to produce energy used for transportation, manufacturing, heating, cooling, electricity generation, and other applications. The use of fossil fuel currently accounts for 80 to 85% of the carbon dioxide being added to the atmosphere.
Land use changes, e.g., clearing land for logging, ranching, and agriculture, also lead to carbon dioxide emissions. Vegetation contains carbon that is released as carbon dioxide when the vegetation decays or burns. Normally, lost vegetation would be replaced by re- growth with little or no net emission of carbon dioxide.
Human activities, such as the burning of fossil fuels and changes in land use, have increased the abundance of small particles in the atmosphere. These particles can change the amount of energy that is absorbed and reflected by the atmosphere. They are also believed to modify the properties of clouds, changing the amount of energy that they absorb and reflect.
Methane (natural gas) is the second most important of the greenhouse gases resulting from human activities. It is produced by rice cultivation, cattle and sheep ranching, and by decaying material in landfills. Methane is also emitted during coal mining and oil drilling, and by leaky gas pipelines. Nitrous oxide is produced by various agricultural and industrial practices.
Chlorofluorocarbons (CFCs) have been used in refrigeration, air conditioning, and as solvents. Other fluorocarbons that are also greenhouse gases are being used as substitutes for CFCs in some applications, for example, in refrigeration and air conditioning.
Ozone in the troposphere, that is, in the lower part of the atmosphere, is another important greenhouse gas resulting from industrial activities. It is created naturally and also by reactions
in the atmosphere involving gases resulting from human activities, including nitrogen oxides from motor vehicles and power plants.
Earth’s climate and biodiversity aren’t the only things being dramatically affected by humans. Global soil change due to human activities is a major component. But global soil change is also occurring in more remote areas due to the spread of contaminants and alterations in climate. Worldwide, soils are being transformed by human activities in ways that we poorly understand, with possibly dire implications.
As the amount of depleted and damaged soils increases, global cycles of water, carbon, nitrogen, and other materials are also being affected.
Crop residue is taken away for competing uses, animal dung is used as cooking fuel rather than as soil amendment, topsoil is used for brick making, and nutrients are harvested and not replaced.
Such local impacts are causing global problems. Soil degradation plays much a larger role in climate change.
The draining of water for agriculture from rivers and watersheds for irrigation leads to drier natural habitats. Those rivers that receive runoff from farmland are often poisoned by excessive nutrients and pesticides.
Agriculture also leads to soil erosion, both through rainfall and wind. This soil can damage the aquatic ecosystems it ends up in, and the loss of nutrients can result in productive farmland becoming barren.
As population is increasing we need more land area for settlement and shelter that causes removal of forest area. Forestry is the removal of individuals but also the destruction of habitat which the trees create.
The most common method of harvesting in forestry is clear cutting, in which entire stands of trees are cut down at the same time. This is much more destructive than the selective cuttings that can be employed instead.
Biological diversity obviously drops instantly when everything is cut, and it takes decades for a new forest to grow back to the same size and density as the previous forest had. Even when the trees are the same size as those that were originally cut, the forest that has grown will have lower biodiversity than the original forest; the older the original forest, the more the new forest will be lacking.
Re-growth, especially from tree planting, is typically uniform in density and type of tree, which is unnatural. This uniformity in a forest also helps reduce diversity as their different environments are no longer present for different species.
In addition to the drop in diversity clear-cut regions have much of their nutrient-rich topsoil swept away by rain and wind, and the nutrients often end up in rivers, overloading the river with nutrients in a process called eutrophication. Forests also act to absorb rain- flow; without them, floods are more common.
Even when strips or sections of forest are left uncut instead of clear-cutting, the results are far from ideal. The edges of the uncut fragments of forest suffer from wind and the area becomes drier. While this happens in normal forests as well, it only happens to the edges of the forest. The fragments left after logging are largely edge, and much of the total forest left begins to dry out.
Species that need large areas, including large mammals such as bears, cannot live in the small fragments. Roads, including forestry roads, have much the same effect, effectively cutting the forest into fragments for them.