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Mass Extinction And Climate Change

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Mass extinction underway due to climate change and habitat loss

Climate Change

Scientific Issues

The greenhouse theory of climate change postulates that Earth's average temperature will rise over time due to the increased concentrations of certain gases within the atmosphere. Earth derives its energy from the sun, but much of the sun's radiation bounces back after reaching Earth. Some of this "bounced" radiation strikes molecules of carbon dioxide, water vapor, and other gases within the atmosphere, which results in the retention of some of this energy within the atmosphere. Without this effect, life on Earth would not be possible, since the planet would be too cold to support life.

Fossil records indicate that variances in temperature correspond significantly with the presence of greenhouse gases. Although the cause and effect cycle of the past is not completely understood, there is some indication that the gases act as a feedback mechanism, exacerbating other climatic changes.

Atmospheric concentrations of green house gases have risen significantly since the pre-industrial period, primarily due to the use of fossil fuels, destruction of forests, and agricultural practices. Climate scientists have prepared models predicting temperature change based upon different levels of fossil fuel consumption.

The model for the "high" scenario presented in this graph assumes that consumption of fossil fuels continues until cheap new technologies are developed to replace these energy sources. Under this scenario, atmospheric carbon dioxide concentrations would peak at about 1200 ppm, more than four times the pre-industrial levels. The global average temperature would rise 10 degrees.

In the medium scenario, no significant action is taken to replace fossil fuels until 2100. Carbon dioxide concentrations would rise to 850 ppm, and average temperatures could reach six degrees above the current mean.

The low scenario assumes significant action immediately. Even under this scenario, carbon dioxide concentrations will rise slightly, and temperature will increase about three degrees. This lingering effect is due to the fact that greenhouse gases have long life cycles within the atmosphere, enduring for decades or centuries until they pass into sinks in the ocean or forests.

These increases are in addition to the 0.6-1.2 degree increase that has already occurred since 1860, when good temperature records began. There is now a virtual consensus that this increase is due to the rise in greenhouse gas concentrations in the lower atmosphere. Since 1860, carbon dioxide concentrations have increased 30%, methane concentrations have increased 15%, and nitrous oxide levels have doubled. The result of these changes has been a rise in sea level of 4-10 inches, and an increase in annual rainfall. Many scientists believe that the greater number of severe weather events (El Nino/La Nina, Class 4 & 5 hurricanes, and typhoons) experienced during the 1990s are a direct result of the decade's high temperatures occurring due to green house gases.

These projected temperature levels do not correspond to conditions in Earth's recent past. The only era that appears to resemble the levels of global warming currently occurring is the cusp of the Cretaceous and Eocene era, also known as the Late Paleocene Thermal Maximum. This period was characterized by a global warming trend that began approximately 60 million years ago, when temperatures increased so substantially that the oceans ceased to turnover the deep, cold water efficiently, which is essential to marine ecosystems, and to the atmospheric cycle. This breakdown caused a huge mass extinction in sea life, and may have resulted in a large input of methane from the oceans to the atmosphere, which caused the terrestrial warming. Terrestrial conditions were substantially different during that time period. Sea levels were very high, because the poles retained very little of their ice caps. Antartica may have been covered with forest.

These were the conditions that eventually gave rise to the Age of Mammals, causing an increase in evolution, as well as large extinctions. Although humans could certainly survive in these temperatures, life would be much less pleasant. Looking at the current estimates for global warming, scientists predict a great increase in tropic diseases throughout the world, with outbreaks of malaria, hanta virus, encephalitis, and even dengue fever occurring frequently in the United States.

Responses to the Threats of Climate Change

The international community began to recognize the potential impacts of climate change more than two decades ago, and established the World Meteorological Organization (WMO), which convened an international climate conference and established a monitoring and study organization. In 1988, the Intergovernmental Panel on Climate Change was established.

The IPCC three separate working groups. One group focuses on scientific issues related to the climate system. The second looks at the impacts of climate change on the planet and its ecosystems. The third considers the economic and social dimensions. The three working groups have prepared two comprehensive assessment reports on climate change, in 1990 and in 1995. The IPCC has agreed to publish new assessments approximately every five years; therefore, the Third Assessment Report in scheduled for publication in late 2000/early 2001.

The 1995 report - the Second Assessment - provided more up-to-date information on the increase in greenhouse gases and their impacts. Some important observations in the report are 1) if carbon emissions remain relatively stable, atmospheric carbon dioxide concentrations will approach twice that of pre-industrial levels by 2100; 2) stabilization of carbon dioxide concentrations (at a much higher level than current amounts) can be achieved only in carbon dioxide emissions drop to 1990 levels; 3) cumulative levels depend heavily upon early emissions, so greater reductions will be required in future years if smaller efforts are made now; 4) stabilization at current levels would require an 8% reduction in emissions from the 1990 levels; 5) thermal inertia of oceans will cause temperatures to continue to increase after 2100, even if gas concentrations are stabilized.

The report attempts to describe the impacts on general types of biospheres, and to project impacts on agriculture, human settlements, and health. The scientific



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