NOAA Global Warming FAQ
"What is the greenhouse effect, and is it affecting our climate?"
U.S. Environmental Protection Agency Climate Change
EPA's Climate Change Site offers comprehensive information on the issue of climate change in a way that is accessible and meaningful to all parts of society communities, individuals, business, states and localities, and governments.
The Pew Center on Global Climate Change
Supports a cooperative approach and brings critical scientific, economic and technological expertise to the global debate on climate change.
World Data Centre for Greenhouse Gases
"...data for greenhouse (CO2, CH4, CFCs, N2O, etc.)", from the UN World Meteorological Organization.