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Humans as a Geological Force Study Guide (page 2)

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Updated on Sep 26, 2011

Toward a Sustainable Future

Humans are altering the biosphere in ways that will change it for very long periods of time. That's simply what we do. Here we will look at some of the global changes in land use. Then we will focus on several fluxes made by humans that exceed those of nature. Finally, we will note the concept of sustainability, which deals with the question of how we will continue to provide life support for what soon will be 7 billion people without further stressing the systems that nature provides.

As of 2005, the human population was about 6.4 billion people. It is growing at approximately 80 million people per year. Population is rising, but, as they say, land is one thing that doesn't increase. The global land area is 140 million square kilometers. The common land unit in the metric system is the hectare, which is a square 100 meters on a side. How many square meters in a hectare? You will be asked this in a practice question.

Using the conversion for the number of square meters in a hectare and the fact that one million square meters are in a square kilometer, we can calculate the global land area to be 14 billion hectares. That means there are about 2.2 hectares per person. If you are more familiar with the unit of acres, this figure is about 5.4 acres per person (1 hectare = 2.47 acres).

How much of this do humans currently use? How much could they use? First of all, 31% of the world's land (4.4 billion hectares) is unusable, because it is rock, ice, tundra, or desert. That leaves 9.6 billion hectares for potential use.

The major human land use is for agricultural production, which currently uses 4.7 billion hectares. So agriculture (pastureland and cropland) takes 34% of the world's land (4.7/10.4). Of that, 70% is permanent pasture and 30% is cropland.

Globally, only about 1% to 2% of land (approximately 140-280 million hectares) is considered urbanized. In some local areas, obviously, the urbanized land approaches 100% of land use.

Therefore, summing the unusable land, the agricultural land, and the urbanized land, and then subtracting that from the total land area, we arrive at the figure of 4.8 billion hectares that potentially remain. This is about 33% to 34% of the total land, or about as much as we currently use for all agriculture already. Here is the calculation: 100% - 31% - 34% - (1% or 2%) = 33% to 34%. However, much of the prime land for agriculture has already been used, so what remains is not as high in quality. This is the big picture of global land use.

Obviously, humans have made a big impact on the world's land. There is still more land that could be converted to exclusively human use, and that process is going on yearly. The conversion that is of most concern is the deforestation of tropical rainforests. However, in certain areas of the developed nations, forests are actually regrowing. An example in the United States is in the New England states. These were once nearly all converted into farms. But as the farms became less economical, when farms in the Midwest and California could produce food more cheaply, the farms in New England lost much of their value, and forests were allowed to regrow.

The appropriation of land by humans implies that humans are creating fluxes of matter for their own use. For example, when land is used for agriculture, humans take the organic carbon products of photo synthesis for food. But to produce this food, humans apply fertilizers such as phosphorus and nitrogen to boost the productivity of the agricultural soils. Plowing the soil also allows erosion to proceed at a rate that is faster than what would be the normal rate for nature.

Nature has balanced cycles. Erosion of the continents and the deposition of continental minerals into the ocean are, over the long term, balanced by the uplifting of the continents into mountains from the forces of plate tectonics. The nutrients of phosphorus and nitrogen—required by all life—cycle around and around. These nutrients are incorporated into plants on land and algae in the ocean by the process of photosynthesis. The plants and algae can be eaten, or they die. Eventually, many of the nutrients are recycled back to the soil (on land) or into the deep ocean water, primarily by bacteria. Some of the nutrients leak out and are buried in sediments. These nutrients are replaced over the long term by new nutrients put into the biosphere from the weathering of rocks and the eruption of volcanoes.

How do the fluxes caused by humans compare to the equivalent fluxes in nature? Looking at some numbers instructs us about the power of humans as a new kind of geological force on the planet.

One component or process in the cycle of nitrogen is the conversion of nitrogen gas in the air into forms such as ammonium and nitrate ions. The ammonium and nitrate ions—unlike the air's nitrogen gas—are what plants and algae need for their bodies to grow. The conversion process is called nitrogen fixation, and it is accomplished by special kinds of bacteria that are called nitrogen fixers.

The natural biological flux of nitrogen fixation, performed by the world's nitrogen-fixing bacteria in the soils and in the ocean, is about 130 million tons per year. (All tons are given in the international unit of metric tons, or 1,000 kilograms, approximately 2,200 pounds or 1.1 U.S. ton.)

Humans also create a flux of nitrogen fixation. Some happens inadvertently, as noted previously, in the creation of nitrogen oxides by fossil fuel combustion. Humans also create conditions for extra nitrogen fixation during rice cultivation. And, importantly, humans take atmospheric nitrogen and use high temperature and high-pressure industrial processes to manufacture fertilizer for the large-scale agriculture that humans think needs a boost in productivity. All these forms of human nitrogen fixation add up to 140 million tons per year, more than the global flux of nitrogen fixation by the world's nitrogen-fixing bacteria.

Phosphorus is also required by all organisms. And many agricultural soils are deficient in phosphorus. Therefore, applying phosphorus as fertilizer increases the productivity of many soils.

The natural release of phosphorus into the cycles of the biosphere from the chemical weathering of rocks and minerals is about 3 million tons per year. In contrast, humans mine phosphorus and thereby bring this new phosphorus into the cycles of the biosphere. The flux from mining activities, primarily aimed at fertilizer production, is about 12 million tons per year, or 4 times the flux of phosphorus in nature.

One major environmental concern coming from the increases in the fluxes of nitrogen and phosphorus caused by humans is the fact that these nutrients can runoff from farmlands after rains and go directly into lakes and coastal regions. Though this might seem like a good thing—to fertilize the lakes and coasts for "free" from farm runoff—it is actually bad. The extra nutrients create a condition called eutrophication. During eutrophication, algae go wild with growth. But then the algae die and fall to the bottom, where bacteria consume the bodies of the algae along with oxygen in the water. The water becomes depleted of oxygen, and fish and other creatures such as mussels and oysters die. For instance, there is currently a massive low oxygen zone in the Gulf of Mexico, around the entry of the Mississippi River into the Gulf. The low-oxygen zone has been created by the runoff of fertilizer from the Midwestern farms.

Finally, we look at sediment loads (suspended solids) in the world's rivers. The global sediment load carried by the world's rivers prior to human impact is about 10 billion tons per year (just under two tons per person). With the influence of humans, that number has tripled. In other words, human activity causes about 20 billion tons per year of sediment in the world's rivers that goes into the ocean. Humans are clearly a major geological force!

There is a new science on the horizon that can help us. It is called the science of sustainability. The science of sustainability deals with ensuring the sustained connection between humans and Earth. As we have seen, human needs are often fulfilled by compromising the environment. We drain aquifers, convert forests and prairies into farms, use water and land as waste dumps, fish without adequate limits, even change the radiation balance of the atmosphere. How can we harmonize the arrow of human progress with the cyclic, restorative processes of nature? This problem looms before us significantly. Its solution has been taken to constitute the new branch of knowledge called sustainability science.

Practice problems of this concept can be found at: Humans as a Geological Force Practice Questions

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