The greenhouse effect is the rise in temperature of the Earth because certain gases in the atmosphere, such as, water vapor, carbon dioxide, nitrous oxide, and methane, trap energy from the Sun. Without these gases, heat would escape back into space and the Earth's temperature would be too cold for human life to exist. In the greenhouse effect, sunlight warms the Earth's surface and helps to regulate the temperature of the planet. The Earth in turn emits infrared radiation once heated. A great deal of the radiation is absorbed by atmospheric gases, which help to raise the average temperature of the surface. Some infrared radiation penetrates the atmosphere and leaks into space. In a state of equilibrium, the rate at which the Earth loses energy to space in this way is equal to the rate at which it absorbs energy from the Sun.
The Earth's surface temperature has risen by about 1 degree Fahrenheit in the past century, with an increase in warming during the past two decades. Many scientists say that there is evidence that most of the warming over the last 50 years is attributed to human activities.(9) They say that human activities have changed the chemical composition of the atmosphere through the buildup of greenhouse gases. These greenhouse gases consist mainly of carbon dioxide, methane, and nitrous oxide, which have heat trapping properties. Scientists have evidence that atmospheric concentrations of carbon dioxide have increased by approximately 30%, methane concentrations have more than doubled, and nitrous oxide concentrations have risen by about 15%.
This buildup of greenhouse gases is mostly caused by human activity. The rise in carbon dioxide caused by widespread combustion of fossil fuels, such as coal, oil and natural gas may have long-term effects on climatic changes. Fossil fuels burned to run cars and trucks, heat homes and businesses, and power factories are responsible for approximately 98% of U.S. carbon dioxide emissions, 24% of methane emissions, and 18% of nitrous oxide emissions. Also, increased agriculture, deforestation, landfills, industrial production, and mining have contributed a great deal of emissions. The US emits about one-fifth of total greenhouse gases. What is important is figuring out to what extent the human activities is facilitating the accumulation of green house gases The major greenhouse gases emitted by human activity remain in the atmosphere from decades to centuries. The increases in greenhouse gases have enhanced the heat-trapping capability of the earth's atmosphere.(11)
Several scientists speculate that an increase in atmospheric concentrations of other trace gases such as chlorofluorocarbons (Freons), nitrous oxide, and methane due to human activity may aggravate greenhouse conditions. They fear that significant changes in climate patterns will be seen by the turn of the century. Such global warming would cause polar ice caps and mountain glaciers to melt resulting in higher coastal waters.(12)
The Intergovernmental Panel on Climate Change (IPCC) stated that humans influence climate and that the observed warming trend is not likely to have natural origins. The
IPCC has been established by the World Meteorological Organization (WMO ) who is the United Nations system's authoritative voice on the state and behavior of the Earth's atmosphere, its interaction with the oceans, the climate it produces and the resulting distributions of water resources(13) and the United Nations Environment Programme (UNEP) who provide leadership and encourage partnership in caring for the environment by inspiring, informing, and enabling nations and peoples to improve their quality of life without compromising that of future generations.(14) The IPCC assesses scientific, technical and socio-economic information relevant for the understanding of climate change, its potential impacts and options for adaptation and mitigation.
Scientists believe levels of greenhouse gases in the atmosphere are rising, but to what extent are undetermined. They feel that increase in temperature may include natural variability. Scientists seem more comfortable about their projections on issues of global temperature and precipitation change, average sea level rise and less certain about local temperature and precipitation changes, as well as, other weather patterns.
IPCC cautions that warmer temperatures can lead to more storms, such as hurricanes. They admit that they do not have all the answers to global warming. They know that human activities causes global warming, but there is a lot of uncertainty about how much warming? How fast it will occur? To what are the potential adverse and beneficial effects? The next session will discuss Is the Greenhouse Effect Affecting Our Climate?
Is the Greenhouse Effect Affecting Our Climate?
Global surface temperatures have increased since the late 19 th century. This section will address whether global temperatures have any effects on weather pattern.
The United States National Climatic Data Center shows evidence that global mean surface temperatures have increased 0.5-1.degrees Fahrenheit since the late 19th century. The 20th century's warmest years occurred in the last 15 years of the century with 1998 being the warmest year on record. However, this does not mean that all areas have warmed up. Some areas such as southeastern U.S. have cooled over the last century. The recent warmth has been greatest over North America. Increasing concentrations of greenhouse gases are likely to speed up the rate of climate change. Scientists speculate that the average global surface temperature could rise 0.6-2.5 degrees Celsius in the next fifty years, and 1.4-5.8 degrees Celsius) in the next century, with a great deal of regional variation.(15)
An enhanced greenhouse is expected to cause cooling in higher parts of the atmosphere because of the increased blanketing effect in the lower atmosphere holds in more heat, allowing less to reach the upper atmosphere. (16)
The IPCC has concluded that greenhouse gases will continue to rise over the 21st century. This will impact the lives of mankind both positively and negatively. The more gases are emitted, the higher the tendency for earth to warm. The IPCC predicts that the greater and faster the warming, the more the adverse effects will dominate and the greater the possibility of large-scale and possibly irreversible impacts.(17)
The next section discusses the greenhouse effect on Venus to see what could happen if Earth has a run away greenhouse effect.