In what sense is human civilization a global geosystem? Human society has harnessed the means of energy production on a global scale and now competes with the plate tectonic and climate systems in modifying Earth’s surface environment. Most of the energy used by human civilization today comes from carbon-based fuels. The rise of this carbon economy has altered the natural carbon cycle by creating a huge new flux of carbon from the lithosphere to the atmosphere. If that flow continues unabated, CO2 concentrations in the atmosphere will double by the mid-twenty-first century.
How do we categorize our natural resources? Natural resources can be classified as renewable or nonrenewable, depending on whether they are replenished by geologic processes at rates comparable to the rates at which we are consuming them. Reserves are the known supplies of natural resources that can be exploited economically under current conditions.
What is the origin of oil and natural gas? Oil and natural gas form from organic matter deposited in oxygen-poor sedimentary basins, typically on continental margins. These organic materials are buried as the sedimentary layers grow in thickness. Under elevated temperatures and pressures, the buried organic matter is transformed into liquid and gaseous hydrocarbons. Oil and gas accumulate where geologic structures called oil traps create impermeable barriers to their upward migration.
Why is there concern about the world’s oil supply? Oil is a nonrenewable resource: at current rates of use, it is being depleted far faster than geologic processes can replenish it. Therefore, as oil is withdrawn from the hydrocarbon reservoirs of the world, its availability will diminish and its price will rise. The key issue is not when oil will run out, but when global oil production will reach Hubbert’s peak—when it will stop rising and begin to decline. The current data supports the oil optimists, who argue that oil resources will meet demand for decades to come.
What is the origin of coal, and what are the consequences of burning it? Coal is formed by the burial, compression, and diagenesis of wetland vegetation. There are huge resources of coal in sedimentary rocks. Coal combustion is a major source of atmospheric CO2 as well as sulfur-containing gases that contribute to acid rain. Furthermore, coal mining and toxic substances produced by coal burning present risks to human life and to the environment. Because of its abundance and low cost, however, the use of coal is likely to increase on a global scale.
What are the prospects for alternative energy sources? Alternative energy sources include nuclear power, biofuels, and solar, hydroelectric, wind, and geothermal energy. Taken together, these energy sources currently supply only a small percentage of world energy demand. Nuclear energy produced by the fission of uranium, the world’s most abundant minable energy resource, could be a major energy source, but only if the public can be assured of its safety and security. With advances in technology and reductions in cost, renewable sources such as solar energy, wind energy, and biomass could become major contributors in the twenty-first century.
How much global warming will there be in the twenty-first century, and what will be its consequences? Atmospheric concentrations of greenhouse gases will continue to rise throughout the twenty-first century, primarily because of fossil-fuel combustion and other human activities. The magnitude of the increase will depend on whether human society takes active steps to limit its greenhouse gas emissions. Projections of climate warming during the twenty-first century are highly uncertain, but the range of likely warming is 0.58C to 5.58C. This warming will disrupt ecosystems and increase the rate of species extinctions. The oceans will warm and expand, raising sea level as much as a meter. The Arctic ice cap will continue to shrink rapidly, and much of the Arctic Ocean is expected to become ice-free.
What other types of anthropogenic global change are degrading our environment? Ocean acidification is decreasing the ability of shellfish and corals to calcify their shells and skeletons and may adversely affect many other types of marine organisms, disrupting marine ecosystems. The biodiversity of ecosystems on land is declining through loss of habitat as well as the effects of global warming. The current rapid rate of species extinction may eventually lead to a decline in biodiversity equal to major mass extinctions of the past.
How might we stabilize carbon emissions at their current levels? If human civilization continues to rely on fossil fuels, anthropogenic carbon emissions will increase by at least 7 Gt per year during the next 50 years. This problem could be addressed by implementing seven stabilization wedges, each of them a strategy for reducing the projected growth of carbon emissions by 1 Gt per year.
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