Last updated on: 1/29/2009 6:11:00 AM PST
What Are Greenhouse Gases?
General Reference (not clearly pro or con)
Windows to the Universe, a project undertaken by the University of Colorado at Boulder (UCB) and University Corporation for Atmospheric Research (UCAR), in a section of the UCAR website titled "The Greenhouse Effect & Greenhouse Gases" (accessed Dec. 3, 2008), wrote the following:
Source: The COMET Program, www.comet.ucar.edu (accessed Dec. 3, 2008)
Dec. 3, 2008 - Windows to the Universe
The US Environmental Protection Agency (EPA), in a section of its website, www.epa.gov, titled "Climate Change - Greenhouse Gas Emissions" (accessed Dec. 3, 2008), wrote the following:
"Gases that trap heat in the atmosphere are often called greenhouse gases. This section of the EPA Climate Change Site provides information and data on emissions of greenhouse gases to Earth's atmosphere, and also the removal of greenhouse gases from the atmosphere.
Some greenhouse gases such as carbon dioxide occur naturally and are emitted to the atmosphere through natural processes and human activities. Other greenhouse gases (e.g., fluorinated gases) are created and emitted solely through human activities. The principal greenhouse gases that enter the atmosphere because of human activities are:
Dec. 3, 2008 - Environmental Protection Agency (EPA)
The Energy Information Administration (EIA), a statistical agency of the US Department of Energy, in a brochure available on its website, www.eia.gov, titled "Greenhouse Gases, Climate Change, and Energy" (accessed Dec. 3, 2008), wrote the following:
"Many chemical compounds found in the Earth's atmosphere act as 'greenhouse gases.' These gases allow sunlight to enter the atmosphere freely. When sunlight strikes the Earth's surface, some of it is re-radiated back towards space as infrared radiation (heat). Greenhouse gases absorb this infrared radiation and trap the heat in the atmosphere. Many gases exhibit these 'greenhouse' properties. Some of them occur in nature (water vapor, carbon dioxide, methane, and nitrous oxide), while others are exclusively human made (certain industrial gases). Over time, if atmospheric concentrations of greenhouse gases remain relatively stable, the amount of energy sent from the sun to the Earth's surface should be about the same as the amount of energy radiated back into space, leaving the temperature of the Earth's surface roughly constant...In computer-based models, rising concentrations of greenhouse gases produce an increase in the average surface temperature of the Earth over time. Rising temperatures may, in turn, produce changes in precipitation patterns, storm severity, and sea level commonly referred to as 'climate change.'
Assessments by the Intergovernmental Panel on Climate Change (IPCC) suggest that the Earth's climate has warmed between 0.6 and 0.9 degrees Celsius over the past century and that human activity affecting the atmosphere is 'very likely' an important driving factor. The IPCC's Fourth Assessment Report (Summary for Policymakers) states, 'Most of the observed increase in globally averaged temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations.' It goes on to state, 'The observed widespread warming of the atmosphere and ocean, together with ice mass loss, support the conclusion that it is extremely unlikely that global climate change of the past 50 years can be explained without external forcing, and very likely that it is not due to known natural causes alone.'"
Dec. 3, 2008 - Energy Information Administration (EIA)