¨ 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:
Ø Aerosol cans
Ø Coolant in refrigerators, freezers, and air conditioners
Ø 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.
