Science as Inquiry
Earth and Space Science
Science in Personal and Social Perspectives
What a race! Tuesday, November 7, 2000 the United States voted for a new President, and after more than a month of pregnant chads and butterfly ballots George W. Bush was announced the winner. Even though most students were not old enough to vote, they were probably aware that one of the big campaign issues was the environment. And within that broad subject, the topic of global warming was hot. Scientific evidence has revealed that a warming trend occurred in the last century - on that there is consensus. The debate was about whether or not this is a natural cycle and how to respond to the evidence. The scientific uncertainty surrounding global warming makes it particularly difficult for public policy makers, who must decide whether or not to implement costly greenhouse gas reduction policies. The views of our two major candidates varied widely on climate change and the Kyoto Protocol, an international treaty to reduce greenhouse gas emissions. Let's investigate the topic further and examine some data so that you can cast your vote on this issue.
Global warming refers to an expected rise in global average temperature due to the continued emission of greenhouse gases produced by industry and agriculture. Greenhouse gases are so named because they trap heat in the atmosphere by allowing sunlight through but preventing some heat from escaping into space, thus acting like the glass in a greenhouse. The majority of this greenhouse effect is natural, keeping the Earth's average temperature at a pleasant 60° F (15° C), as opposed to the frigid 0° F (-18° C) we would experience otherwise. However, the atmospheric concentrations of several greenhouse gases have been rising as a result of human activity. Levels of carbon dioxide, which is released primarily by the burning of fossil fuels such as coal, oil and natural gas, have increased by nearly 30% since pre-industrial times. Levels of methaneemitted during the production and transport of coal, natural gas and oil, and released from the decomposition of organic wastes in municipal solid waste landfills and the raising of livestockhave more than doubled, and levels of nitrous oxideemitted during agricultural and industrial activities, as well as during combustion of solid waste and fossil fuelsare increasing, too.
Higher average global temperatures are expected to cause changes in precipitation frequency and intensity patterns, changes in soil moisture, and a rise of global sea level. Sea level would rise as a result of warmer air temperatures because ocean waters expand when heated, and many mountain glaciers would melt. Significant sea level rise may eliminate beaches and plague coastal towns and cities with flooding. Certain islands and low-lying countries such as Bangladesh are at particular risk. In addition to the loss of property and historically and culturally significant landmarks caused by flooding, mosquito-borne illnesses and other diseases may increase in incidence. Coastal marine ecosystems may be severely affected by a combination of sea level rise and warmer temperatures. The potential impacts of global warming are numerous.
It has recently been discovered that the polar ice caps have been thinning and shrinking, and many scientists believe that the chances of the ice shrinkage being due to natural cycles are slim. If Arctic ice continues to melt at its present rate, in a few decades it could be nonexistent during summer months. The Arctic would become a huge heat collector, absorbing 80% of the sunlight that reaches it, rather than reflecting it back into space as it does now. Major ocean currents that exchange energy from the tropics to the poles would be altered, as would world weather patterns.
In the past 100 years, Earth's average temperature has increased by 1° Farenheit. When deciding what to wear in the morning, this seems trivial; however, consider the fact that during the last Ice Age, the planet was only 9° F cooler than it is now. It doesn't take much to seriously affect climate patterns and ecosystems. If greenhouse gas emissions continue to rise, projections for temperature increases in the next century range from 1.8° F to 6.3° F (assessments by the U.S. National Academy of Sciences and the United Nations' Intergovernmental Panel on Climate Change (IPCC)). During that same period, sea level is projected to rise six inches to as much as three feet. If future climate change occurs at this magnitude, 21st century Earth would experience the fastest warming in the history of civilization and the warmest temperature since the evolution of modern humans. What does this mean for our existence? We cannot possibly know. We are conducting an experiment in real time.
Some scientists believe that too much "gloom and doom" is being predicted, and that the potential impacts of global warming could be negligible or even positive. They say that correlations of temperature and greenhouse gas concentrations indicate that the greenhouse effect has had little, if any, effect on global climate change. In the May 1992 report of the George C. Marshall Institute, scientists stated that the greenhouse warming produced from a doubling of CO2 in the next century will be "less than 1° C, and may be as small as 0.5° C." The report contends that differing levels of solar activity provide a much more likely explanation for increases in average global temperature.
The longest continuous record of atmospheric carbon dioxide measurements in the world dates back to 1958 and comes from a site in Mauna Loa, Hawaii. This site is considered one of the most favorable locations for measuring undisturbed air because possible local influences of vegetation or human activities on atmospheric CO2 concentrations are minimal, and any influences from volcanic vents may be excluded from the records. Because of the favorable site location, continuous monitoring, and careful selection and scrutiny of the data, the Mauna Loa record is considered to be a precise record and a reliable indicator of the regional trend in the concentrations of atmospheric CO2 in the middle layers of the troposphere.
In the TOPEX/Poseidon activity Analyzing Greenhouse Gases and Global Temperature Data Over Time, you will graph the Mauna Loa data as well as three other data sets representing other greenhouse gases (methane, chlorofluorocarbon (CFC), and nitrous oxide). You will look for trends in the data and project the curves for another 50 years. (To find this activity in the list, scroll down to the section called Process & Change. This list of classroom activities is found on the Topex/Poseidon site, and there are many interesting ones for you to use.) You may also want to try the Ocean Seasons Activity in the same section, in which you will examine seasonal variations in sea level and discuss how such data can help scientists to better understand patterns and changes in global climate. After completing your projections for the next 50 years, you can compare your 1989-1999 CO2 values with the actual data from the Mauna Loa record (click on Digital Data).
Various ideas exist for dealing with the pollution which may be causing climate change. Many of us could take steps in our daily lives to reduce our consumption of energy. There are also good reasons for switching to renewable energy sources. These energy sources are rapidly replaced, unlike fossil fuels, and are generally less polluting. Examples of renewable energy sources are solar power, wind power, hydropower, geothermal energy, and biomass energy.
For more activities and resources, check out the Bridge's Climate & Atmosphere page, as well as the following sites:
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