Especially when it comes to global climate change there is a lot of material on the web. How do you know what is reliable information? Other than extensive reading and becoming informed enough on the topic to make your own judgement, some initial guidelines are as follows:
Some select links to begin an exploration:
Climate monitoring and climate datasets - posted by the British Hadley Centre - gotta love that data.
Trend in global average surface temperature - data often shown to demonstrate the historical global temperature change, with links to data sources.
Daily Earth Temperatures from Satellites - this site allows you to explore the vertical temperature structure of the atmosphere, although it doesn't have historical data.
Global Warming - FAQs - hosted by the National Oceanic and Atmospheric Administration.
U.S. EPA site - this has some fairly in-depth info in a well organized format. Let us hope they don't remove it from the web.
Global Warming International Center - contains information on possible events tied to global climate change, and more of an advocate group for how humans might respond to associated changes.
Lindzen, R.S., MIT professor's thoughts on "Global Warming" as posted by the Cato Institute - this will introduce one to the political debate.
Coastal and Marine Ecosystems and Global Climate Change: Potential effects on U.S. Resources by Victor S. Kennedy, Robert R. Twilley, Joan A. Kleypas., James H. Cowan Jrt., and Stephen Hare - Pew Center for Global Climate Change.