Human Activities and their Impacts
Humans, like all species, exploit their surroundings for the resources they need to survive. Our current exploitation of the world, however, is greater than those of most species, for three main reasons. The first is our technology. Like a few other species, we use tools, but the hand-held tools that we originally used could only alter extremely local conditions. Today we are able to affect entire regions and our technology has progressed to the point where we can level mountains and control the flow of rivers, something that was simply impossible a relatively short while ago. We can now modify our world relatively easily and quickly.
The second reason, our skyrocketing population, also increases the extent to which we modify the earth. It is estimated that the world's population reached one billion (10^9) in 1804. By 1927 it was two billion, and it was three billion by 1960. It is currently six billion, and estimates for the year 2050 are for a global population of just under nine billion. With so many people, even minor activities per person will have major impacts when multiplied six billionfold.
Finally, consumption habits also have an affect; richer nations consume more resources and generate more waste than the less well-off. These three factors, acting together, are responsible for the changes that humans are bringing about on the planet. The major activities that are causing these changes are detailed below.
In the past few decades, fishing fleets have grown enormously, and the UN Food and Agriculture Organization (FAO) estimates that the more than 3.5 million fishing vessels in the world hauled in 122 million tonnes of fish in 1997, six times what it had been in 1950. Here "fish" can mean both finfish (what we usually think of as fish) and shellfish (such as crustaceans and molluscs).
Fisheries currently catch far more fish than the oceans can produce. Almost every major fishery in the world has seen its catch drop despite increasingly intense efforts, and many fisheries have collapsed entirely, the Grand Banks cod fishery being a noteworthy Canadian example. This overfishing isn't due to a lack of knowledge; as the New Scientist put it, "… for years, fisheries scientists have politely recommended to their governments that they should not let their fishing fleets catch quite so many fish next year. But every year… the answer comes back: we will let our fisherman catch far more fish than you scientists recommend." Governments are tempted to keep fishing quotas high for short-term economic and political benefits, and are willing to heavily subsidize their fishing fleets. The FAO concluded that in 1992 fisheries were subsidized $50 billion dollars, almost as much as the $70 billion dollars of fish that they pulled from the sea.
The result of this overfishing is that populations of economically important fish often become commercially extinct, reduced in numbers to the point where it is no longer viable to harvest them. If fishing is stopped at this point, the fish species can hopefully avoid becoming biologically extinct. How long it takes the fish to return to commercially viable levels depends on the life cycle of the species, but several decades seems to be the minimum.
When fish populations are drastically reduced, the ecological dynamics in the ocean change. Predators of the affected fish suffer, and other species may fill the role that the reduced species once did, making it unlikely or even impossible for that species to achieve its former numbers. If a species finds its role usurped by another species, it may be doomed to extinction even though it is no longer being actively fished.
Modern fishing techniques do more than just catch their intended species. Driftnets and longlines are notorious for killing other species, including seabirds and marine mammals. Bycatch, unwanted species that are caught along with the desired ones, makes up a quarter of the hauls that are harvested. Most individuals caught as bycatch do not survive and their bodies are thrown back into the ocean. Seabed trawling destroys the structure and devastates the communities on the seabed, many of which take a long time to recover.
Aquaculture (fish farming) has risen in popularity in the past several years as a possible answer to declining fish stocks around the world. It consists of raising fish in enclosed areas, often simply fenced-off sections of natural waterways. Unfortunately, many of the most commercially important fish species are piscivorous (i.e. they eat fish), which can mean that three to five kilograms of other fish are needed to obtain one kilogram of the desired fish. This means that fisheries will be needed to feed the fisheries.
One concern with aquaculture is the excessive fertilization (eutrophication) of the surrounding waters by feces and uneaten food. Another is the inevitable escape of the farmed animals. These escaped fish can be an invasive species, displacing native fish and altering the ecosystem. If the escaped fish are the same species as locally-occurring fish, they may interbreed with them, introducing new genetic traits that may harm the native population.
Freshwater sport fishing may also cause problems through overfishing and the introduction of commercially desirable fish to lakes and rivers that they are not native to. This has happened throughout Canada and the world. The Nile Perch is a dramatic example of the possible results: introduced to Lake Victoria in 1954 as a game fish, the population exploded in the 1980s. Other fish species in the lake were its prey; 65% of them eventually went extinct and the ecology of the lake was radically changed.
Forestry is similar to fishing, in that it is the harvesting of a natural growing resource. A major difference is that in fisheries the amount of fish caught is the number of concern, while in forestry the numbers refer to the area logged. 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 clearcutting, 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. Out of the million hectares of Canadian forests harvested in 1996, 86% were clearcut, with less than half of that being reseeded or planted with seedings. 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. Regrowth, especially from treeplanting, is typically uniform in density and type of tree, which is unnatural. This uniformity in a forest also help reduce diversity as there different environments are no longer present for different species.
In addition to the drop in diversity clearcut 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 rainflow; without them, floods are more common.
Even when strips or sections of forest are left uncut instead of clearcutting, 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.
Statistics Canada reported that 78% of Canada's population lived in urban areas in 1996. Urban areas are relatively small, with high population densities, though the spread of urban sprawl, largely through suburbs, has made them much larger in the past few decades. 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. The Mixedwood Plains ecozone includes half of Canada's population in the Quebec City-Windsor corridor. This ecozone is also extremely rich in species, though the development of the region has put such a strain on natural communities that half of Canada's endangered species are found here.
Agriculture is the major farming activity, taking up much of the land in the south of Canada. The Prairies ecozone has almost entirely been taken over by agriculture, with only 13% of the shortgrass prairie, 19% of the mixedgrass prairie, and virtually none of the tallgrass prairie community remaining. With so little remaining original land, many Prairie species are threatened. In contrast, many pest species are introduced to the region and flourish with the large expanses of a single food source.
Agriculture's scale means not only that large areas are directly affected, but that local and even regional climates can be affected. The draining of water 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.
In comparison to arable farming, livestock farming has a relatively minor impact, though intensive livestock production results in local problems, with fecal matter pollution of waterways often becoming a major issue.
As a wide term covering not only manufacturing, but also other activities such as mining, dams and power plants, industry as a whole affects huge areas of the country. Some effects, like mining, are fairly small-scale, while dams can affect enormous areas. 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 more. In older economic models pollution was an "externality," outside of the model and therefore ignored. This thinking is happily now changing.
Probably the most drastic effect is climate change, usually referred to as global warming. The greenhouse gases released by industry as well as by vehicles is changing the climate of the entire planet. Exactly what the changes will be is still unknown, but our current set of constructions and farms are not easily moved to new locations, so most any change would have deleterious effects. A larger effect than changing the weather on the entire planet is hard to imagine, but it is being done and no one knows where it will take us.