Ever since the industrial revolution, human activities have constantly changed the natural composition of Earth's atmosphere. Concentrations of trace atmospheric gases, nowadays termed "greenhouse gases," are increasing at an alarming rate. There is conclusive evidence that the consumption of fossil fuels, conversion of forests to agricultural land, and the emission of industrial chemicals are principal contributing factors to air pollution.
Global Greenhouse Gas Emissions - Sources & Activities
According to the National Academy of Sciences, Earth's surface temperature has risen by about one degree Fahrenheit (33.8°C) in the past century, with accelerated warming occurring in the past three decades. According to statistical review of the atmospheric and climatic records, there is substantial evidence that global warming over the past 50 years is directly attributable to human activities.
Under normal atmospheric conditions, energy from the sun controls Earth's weather and climate patterns. Heating of Earth's surface resulting from the sun radiates energy back into space. Atmospheric greenhouse gases, including carbon dioxide (CO^2), methane (CH^4), nitrous oxide (N^2O), tropospheric ozone (03), and water vapour (H^2O) trap some of this outgoing energy, retaining it in the form of heat, somewhat like a glass dome. This is referred to as the greenhouse effect.
Without the greenhouse effect, surface temperatures on Earth would be roughly 30°C [54 degrees Fahrenheit (OF)] colder than they are today—too cold to support life. Reducing greenhouse gas emissions depends on reducing the amount of fossil fuel-fired energy that we produce and consume.
Fossil fuels include coal, petroleum, and natural gas, all of which are used to fuel electric power generation and transportation. Substantial increases in the use of nonrenewable fuels are a principal factor in the rapid increase in global greenhouse gas emissions. The use of renewable fuels can be extended to power industrial, commercial, residential, and transportation applications to substantially reduce air pollution.
Location of the World's Main Fossil Fuel Reserves (Gigatonnes of oil equivalent)
Examples of zero-emission, renewable fuels include solar, wind, geothermal, and renewably powered fuel cells. These fuel types, in combination with advances in energy-efficient equipment design and sophisticated energy management techniques, can reduce the risk of climate change and the resulting harmful effects on the ecology. Keep in mind that natural greenhouse gases are a necessary part of sustaining life on Earth. It is the anthropogenic or human-caused increase in greenhouse gases that is of concern to the international scientific community and governments around the world.
Since the beginning of the modern industrial revolution, atmospheric concentrations of carbon dioxide have increased by nearly 30 percent, methane concentrations have more than doubled, and nitrous oxide concentrations have also risen by about 15 percent. These increases in greenhouse gas emissions have enhanced the heat-trapping capability of Earth's atmosphere.
Fossil fuels burned to operate electric power plants, run cars and trucks, and heat homes and businesses are responsible for about 98 percent of U.S. carbon dioxide emissions, 24 % of U.S. methane emissions and 18% of U.S. nitrous oxide emissions. Increased deforestation, landfills, large agricultural production, industrial production, and mining also contribute a significant share of emissions. In 2000, the United States produced about 25 percent of total global greenhouse gas emissions, the largest contributing country in the world.
Estimating future emissions depends on demographics, economics, technological policies, and institutional developments. Several emissions scenarios have been developed based on differing projections of these underlying factors. It is estimated that by the year 2100, in the absence of emission-control policies, carbon dioxide concentrations will be about 30 to 150 percent higher than today's levels.
Increasing concentrations of greenhouse gases are expected to accelerate global climate change. Scientists expect that the average global surface temperatures could rise an additional 1°F to 4.5°F within the next 50 years and 2.2°F to 10°F over the next century, with significant regional variation. Records show that the 10 warmest years of the twentieth century all occurred in the last 15 years of that century. The expected impacts of this weather warming trend include the following:
Electric energy: Increased summer heat is likely to cause an increase in the demand for electricity due to an increased reliance on air conditioning. Reduced snowpack is likely to decrease the availability of hydroelectric supplies.
Regional air quality and human health: Higher temperatures may worsen existing air quality problems, particularly if there is a greater reliance on fossil fuel generated electricity. Higher heat would also increase health risks for some segments of the population.
Rising ocean levels: Thermal expansion of the ocean and glacial melting are likely to cause a 0.5 to 1.5 m (2 to 4 ft) rise in ocean levels by 2100.
Natural habitat: Rising ocean levels and reduced summer river flow are likely to reduce coastal and wetland habitats. These changes could also adversely affect spawning fish populations. A general increase in temperatures and accompanying increases in summer dryness could also adversely affect wild land plant and animal species.
Forestry: An increase in summer heat and dryness is likely to result in forest fires, an increase in insect populations, and disease.
Agriculture: The agricultural industry will be adversely affected by lower water
Water resources: A warming-induced decrease in mountain snowpack storage will increase winter stream flows (and flooding) and decrease summer flows. This along with an increased evaporate transpiration rate is likely to cause a decrease in water deliveries.
Scientists calculate that without considering feedback mechanisms a doubling of carbon dioxide would lead to a global temperature increase of 1.2°C (2.2°F). But, the net effect of positive and negative feedback patterns would cause substantially more warming than would the change in greenhouse gases alone.
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