Biology 2014-2015

Sec. 6-4 Charting a Course for the Future
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       Two important systems in the biosphere are the main focus of researchers today: the ozone layer and the global climate system.

 

Ozone Depletion

       The ozone layer is 20 to 50 kilometers above the Earth’s surface and contains a high concentration of ozone gas.

       Molecules of ozone consist of three oxygen atoms.

       Ozone at ground level is a pollutant but the ozone layer absorbs the harmful ultraviolet radiation from the sun before it reaches Earth’s surface.

       Overexposure to UV rays not only causes sunburn but also cancer, damages eyes, and decreases an organisms’ resistance to disease.

       So, the ozone layer serves as a global sunscreen.

       In the 1970’s, scientists found a gap or “hole” in the ozone layer over Antarctica during winter.

       That ozone hole has grown larger and a similar hole has now appeared over the Arctic.

       The gases called chlorofluorocarbons, or CFCs were found to cause damage to the ozone layer.

       CFCs were used in:

       Aerosol cans

       Coolant in refrigerators, freezers, and air conditioners

       Production of plastic foams

       In, 1987, the U.S. and many nations began reducing the use of CFCs.

       Today, most uses of CFCs are banned.

       Current data predicts that the ozone holes should shrink and disappear within 50 years.

 

Global Climate Change

       Since the late 19th century, average temperatures on Earth’s surface have risen about 0.6 Celsius degrees.

       Since 1980, average temperatures have risen between 0.2 and 0.3 Celsius degrees.

       The 1990s were the warmest decade ever recorded and 1998 was the warmest year since record-keeping began.

       Global warming is the term used to describe this increase in average temperature of the biosphere.

       One sign of global warming is melting polar ice.

 

Evidence of Global Warming

       Researchers must determine whether the current warming trend is part of a larger, natural cycle of climate change, or whether it is caused by human activity.

       The most widely accepted hypothesis is the warming is related to human activities that are adding carbon dioxide and other greenhouse gases to the atmosphere.

       The burning of fossil fuels combined with the cutting and burning of forests worldwide is adding carbon dioxide faster than the carbon cycle can remove it.

       The atmosphere is now retaining more heat.

 

Possible Effects of Global Warming

       The models suggest that average global surface temperatures will increase 1 to 2 Celsius degrees by the year 2050.

       What problems might arise?

v      Sea levels may rise enough to flood some coastal areas.

v      Parts of North America may experience more droughts during the summer growing season.

       Long-term change in climate will affect ecosystems and threaten the organisms that live there.