Here are some points to help you. But you might read back through the Q & A's here to get an idea of how your opponents will argue and how you might respond.
National Oceanic and Atmospheric Administration FAQ's
http://lwf.ncdc.noaa.gov/oa/climate/globalwarming.html
Scientific American
http://www.sciam.com/article.cfm?id=special-report-climate-change
http://www.sciam.com/article.cfm?id=clash-climate-change-coverage
Current information on Arctic Sea ice.
http://www.nsidc.org/arcticseaicenews/faq.html
IPCC Fourth Assessment Report
http://www.ipcc.ch/ipccreports/ar4-wg2.htm
http://www.ipcc.ch/ipccreports/ar4-wg3.htm
Pew Center, The Causes of Global Climate Change.
http://www.pewclimate.org/global-warming-basics/science-brief-092006
Union of Concerned Scientists
http://www.ucsusa.org/global_warming/science/Fingerprints.html
Nation Resources Defense Council Annotated Bibliography
http://www.nrdc.org/globalwarming/fgwscience.asp
2007 Arctic Sea ice
http://www.washingtonpost.com/wp-dyn/content/article/2007/09/06/AR2007090602499.html
Finally, look at the video on melting glaciers in Glacier National Park on ABC news tonight.
http://abcnews.go.com/search?searchtext=glacier%20national%20park&type=