I. Background

A. global warming: the gradual increase in planet-wide temperatures

B. temperature of Earth depends on amount of sunlight received,

amount absorbed, amount reflected into space and the heat

retained in the atmosphere

C. greenhouse effect: keeps Earth’s temperature warm enough to

support life by trapping heat in the atmosphere

1. Caused by water vapor and carbon dioxide (“greenhouse

gases”)

2. Sunlight penetrates atmosphere to warm Earth’s surface. This

energy is absorbed by the greenhouse gases and reradiated

back to earth

D. In 1896, the Swedish chemist Arrhenius was the first to suggest that

carbon dioxide would increase greenhouse effect and lead to global

warming

II. Evidence

A. surface land and ocean temperature records show that average

global temperatures have risen by half a degree centigrade in about

a century

B. rate of temperature change significantly faster than any observed

changes in last 10,000 years

C. precipitation has increased 1% and sea-levels have risen 15-20 cm

world wide due to melting glaciers and expansion of ocean water

from warmer temperatures

III. Greenhouse Gases

A. include both natural and manmade gases:

1. CO2

2. CH4

3. H2O

4. N2O

B. natural sources:

1. CO2 - respiration, decay of plants/animals, oxidation of soil

humus, forest fires

2. CH4 - wetlands and termites

3. H2O - evaporation

4. N2O - bacterial action

C. human sources

1. CO2 - burning of fossil fuels and wood (in industry,

transportation, forest fires, burning trash)

2. CH4 - cattle farming, rice fields, land fills, coal mining, petroleum,

and natural gas production

3. H2O - product of hydrocarbon combustion

4. N2O - nitrogen fertilizers

IV. What happens

A. Earth’s natural processes are unable to absorb all the greenhouse

gases

1. CO2 entering atmosphere faster than oceans and plants can

remove it

B. the CO2 gas acts similarly to glass or plastic on a greenhouse, that

is, it acts as a one way filter

C. incoming solar radiation is of high energy (therefore short wave-

length) and is able to penetrate the atmosphere. Because the earth

absorbs some of the energy, the outgoing radiation is of lower

energy (longer wavelength), which is absorbed by water vapor,

carbon dioxide, ozone, and other greenhouse gases and then

reradiated toward the Earth

D. in other words: the greenhouse effect allows visible and uv light to

pass through the atmosphere the air and the earth but it traps the

longer wavelength infrared heat rays emitted from the warm soil

and air, thus raising the temperature

V. Industry

A. since the industrial revolution, levels of greenhouse gases have

significantly increased

GAS INCREASE ATMOSPHERIC LIFE (YEARS)

CO2 25% 50 - 200

CH4 145% 12

N2O 15% 120

VI. Effects

A. the increase in temperature and rise in sea level will impact health,

agriculture, forests, water resources, coastal areas, species and

natural areas

1. Health: life cycles of pathogens and insects such as mosquitoes

are affected by climate; greater chance of malaria, etc.

2. Agriculture: effect on crop yields and geographic distribution of

crops; some crops will thrive, others will not

3. Forests: insects and diseases may increase; increase in summer

droughts would produce more forest fires

4. Water resources: decreased water quality due to flooding; floods

more likely due to more intense rainfall; droughts more severe

due to increased evaporation and drier soil

5. Coastal areas: raise the level of seas eroding beaches,

inundating low lands, increasing coastal flooding

6. Species and natural areas: loss of cold water fish habitat, shift

in ecological areas, loss of habitats and species, desertification

VII. Particulates

A. particulates are produced by nearly all combustion and industrial

processes, heavy industry, and incinerators

B. they have the effect of cooling the earth as small scatterers of

radiation and reflectors of sunlight, thus less radiation reaches the

earth

C. help as nuclei in condensation of water vapor in the atmosphere

1. Contributes to cloudiness and precipitation, which in turn leads

to a decrease in temperature

VIII. Predictions

A. many scientists predict that unless these gases are significantly

reduced, the earth’s average temperature will rise about 1 to 3ºC by

the end of the 21st century

B. overall concentrations of greenhouse gases are likely to double pre-

industrial levels by 2060