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The Greenhouse Effect

"Greenhouses are used to grow plants, especially in the winter. Greenhouses work by trapping heat from the sun. The glass panels of the greenhouse let in light but keep heat from escaping. This causes the greenhouse to heat up, much like the inside of a car parked in sunlight, and keeps the plants warm enough to live in the winter."

Greenhouse gases in the atmosphere behave much like the glass panes in a greenhouse. Sunlight enters the Earth's atmosphere, passing through the blanket of greenhouse gases. As it reaches the Earth's surface, land, water, and biosphere absorb the sunlight's energy. Once absorbed, this energy is sent back into the atmosphere. Some of the energy passes back into space, but much of it remains trapped in the atmosphere by the greenhouse gases, causing our world to heat up.

The greenhouse effect is the rise in temperature that the Earth experiences because certain gases in the atmosphere (water vapor, carbon dioxide, nitrous oxide,  and methane, for example) trap energy from the sun. Without these gases, heat would escape back into space and Earth's average temperature would be about 60ºF colder."
from: EPA Global Warming site -
The role of Carbon

Greenhouse gasses - the most important element in most of these gasses is CARBON

carbon dioxide - CO2 - the most important greenhouse gas, it is released to the atmosphere when solid waste, fossil fuels (oil, natural gas, and coal), and wood and wood products are burned.

carbon monoxide - CO - a toxic component of automobile exhaust.

methane - CH4 - is emitted during the production and transport of coal, natural gas, and oil. Methane emissions also result from the decomposition of organic wastes in municipal solid waste landfills, and the raising of livestock.(largely produced by cows and termites.)

Chlorofluorocarbons - CFCs - by weight, much more than potent CO at trapping heat, also destroys ozone. CFCs are byproducts of foam production, refrigeration, and air conditioning, and are generated by industrial processes (also hydrofluorocarbons (HFCs) and perfluorocarbons (PFCs) - some have an atmospheric lifetime of more than 2000 years).

water vapor - H2O - may trap heat, but it depends on where and what form.

nitrous oxide - N2O - is emitted during agricultural and industrial activities, as well as during combustion of solid waste and fossil fuels.


The Carbon Cycle:

from: EPA Global Warming site -

CO2 - The most important greenhouse gas.

Before the Industrial Revolution, human activity released very few gases into the atmosphere, but now through population growth,  fossil fuel burning, and deforestation, we are affecting the mixture of gases in the atmosphere.
Climate Change

Average global temperature has increased by almost 1ºF over the past century; scientists expect the average  global temperature to increase an additional 2 to  6ºF over the next one  hundred years. This may not  sound like much, but it could change the Earth's climate as never before. At the peak of the last ice age (18,000 years ago), the temperature was only 7ºF colder than it is today, and glaciers covered much of North America!
  • Global mean surface temperatures have increased 0.6-1.2°F since the late 19th century. 
  • The 20th century's 10 warmest years all occurred within the last 15 years. Of these, 1998 was the warmest year on  record. 
  • The snow cover  in the Northern Hemisphere and floating ice in the Arctic Ocean have decreased.
  • Globally, sea level has risen 4-10 inches over the past century. 
  • Worldwide precipitation over land has increased by about one percent. 
  • The frequency of extreme rainfall events has increased throughout much of the United States.

Here are some of the ways that scientists gather evidence about climate, both past and present:


Global Surface Air Temperature is based on surface air measurements at meteorological stations. Click for temperature maps and more detailed data. Since corresponding data are unavailable over the ocean, surface air temperature anomalies are combined with ocean temperature anomalies to obtain a 'Land-Ocean Temperature Index'. 

Common Sense Climate Index is based on quantities noticed by people such as extremely hot and cold days. Click for maps leading to climate indices of individual cities. 
from:  NASA Goddard Institute for Space Studies

Global Satellite Montage of Sea and Land Temperatures

 Prior to the mid-1800's, there are not enough instrumental measurements to determine
 global trends. Paleoclimatologists instead use proxy records, such as the Vostok temperature
 record below, to interpret the climate of the pre-historic past. Understanding past climate is the key
 to determining if the observed warming of the past century is natural, or the result of human

Ice Core sample taken from drill.
Photo by Lonnie Thompson, Byrd Polar Research Center, Ohio State University.

Scientists extrude the core from its barrel with the utmost care.
Photo by Kendrick Taylor, DRI, University of Nevada-Reno.

Temperature Anomaly, Vostok Antarctica. Change vs. today in degrees C., in thousands of years before present,
 derived from deuterium. Source: J. Jouzel, et al.

Scientists take samples from the center of the coral. Clipperton Atoll, 10°N, 109°W.
Photo by Maris Kazmers.

Tree rings in Mexican Cypress (Cupressus lusitanica).     Photo by Peter Brown.
Diagram of rings in a young conifer. From Fritts, H.C. 1976. Tree Rings and Climate. Academic Press, New     York, NY.

                 Lake Sediments Slide:

Image courtesy of Platt Bradbury, USGS, Denver, Colorado.

from: A Paleo perspective on Global Warming
People and Climate Change - Anthropogenic effects

"Once, all climate changes occurred naturally. However, during the Industrial Revolution, we began altering our climate and environment through agricultural and industrial practices.
Cars - Planes - Factories
from: EPA Global Warming site -