Lessons on the Lake: Natural Forces Affecting the Basin

The earth’s atmosphere is a thin blanket of gases which serves many important functions. It protects the planet from harsh ultraviolet (UV) rays from the sun, and it warms the Earth’s surface and modifies our climate. This naturally occurring phenomenon is called the greenhouse effect.

Earth’s atmosphere is made up of about 78% nitrogen, 21% oxygen, and about 1% of trace gases that absorb infrared radiation. These trace gases, which trap heat to warm the earth, are known as the greenhouse gases. The two most
important ones in producing the insulating effect of Earth’s atmosphere are carbon dioxide (CO2) and water vapor (H20), but others include methane (CH4), chlorofluorocarbons (CFC’s), nitrous oxide (N20), and ozone (03). The following chart lists the major greenhouse gases and their sources.

Greenhouse Gases	Natural Sources	HumanMade Sources
Carbon Dioxide CO2	• respiration of animals and plants • volcanic eruptions • decay of organisms	• burning of fossil fuels • clearing land for agriculture • cement manufacturing
Methane CH4	• livestock • wetlands • termites	• landfills • coal mines • rice paddies • natural gas leaks • burning of biomass
Chlorofluorocarbons CFC’s	• none	• refrigerators • auto air conditioners • solvents • insulation • aerosols
Nitrous Oxide N2O	• soil microbes’ digestion	• burning coal and wood • chemical fertilizers
Ozone O3	• lightning • pine trees	• photochemical reaction between nitrogen oxides and organic compounds
Water Vapor H2O	• evaporation • transpiration	• will increase as evaporative effect rises proportionally to increasing amounts of other greenhouse gases

Atmospheric Greenhouse Gases	Range from Dawn of Humans to 1750 A.D.	concentration in 2005 A.D.* (from 2007 IPCC SPM)	Annual Rate of Increase
Carbon Dioxide CO2	180-295 parts per million (ppm)	379 ppm	25%
Methane CH4	0.3-0.8ppm	1.7 ppm	115%
Nitrous Oxide N2O	0.27-0.29 ppm	0.32 ppm	9%
CFC-11	not invented yet	0.28 ppm (1990)	--
CFC-12	not invented yet	0.48 ppm (1990)	--

*note: table updated from the 2007 International Panel on Climate Change's Summary for Policymakers

During those same time periods, the human population of the planet increased
from 760 million people in 1750 to 5.3 billion people by 1990.

HOW DO YOU THINK THIS AFFECTED THE AMOUNTS OF GREENHOUSE GASES?

What other sources of greenhouse gases can be associated with increasing human
population growth? Refer to the chart above for help.

The amount of carbon dioxide in the atmosphere has been increasing rapidly, as has
methane, which traps heat 20-30 times more efficiently than carbon dioxide. One CFC
molecule traps 20,000 times the heat of one carbon dioxide molecule.

There is much concern about the negative effects on our climate which can be
produced by these atmospheric changes. The increase in the amount of heat trapped by
the greenhouse effect due to higher greenhouse gas concentrations will make the earth’s
climate warmer than it would otherwise be.

GLOBAL CLIMATE CHANGE

HOW DO YOU THINK THIS AFFECTED THE AMOUNTS OF GREENHOUSE GASES?

This is called global warming.

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