This is found under the
What's Known for Certain section of the US Environmental Protection Agency.
Scientists know for certain that human activities are changing the composition of Earth's atmosphere. Increasing levels of greenhouse gases, like carbon dioxide (CO2 ), in the atmosphere since pre-industrial times have been well documented. There is no doubt this atmospheric buildup of carbon dioxide and other greenhouse gases is largely the result of human activities.
It's well accepted by scientists that greenhouse gases trap heat in the Earth's atmosphere and tend to warm the planet. By increasing the levels of greenhouse gases in the atmosphere, human activities are strengthening Earth's natural greenhouse effect. The key greenhouse gases emitted by human activities remain in the atmosphere for periods ranging from decades to centuries.
A warming trend of about 1°F has been recorded since the late 19th century. Warming has occurred in both the northern and southern hemispheres, and over the oceans. Confirmation of 20th-century global warming is further substantiated by melting glaciers, decreased snow cover in the northern hemisphere and even warming below ground.
This guy from NASA also seems to think that Greenhouse Gasses/Carbon Dioxide might have a little role to play;
Lead scientist James Hansen, a prominent NASA climatologist, described the findings on the planet's out-of-balance energy exchange as a "smoking gun" that should dispel doubts about forecasts of climate change. A European climate expert called it a valuable contribution to climate research.
Hansen's team, reporting Thursday in the journal Science, said they also determined that global temperatures will rise one degree Fahrenheit (.555 degree Celsius) this century even if greenhouse gases are capped tomorrow.
If carbon dioxide and other heat-trapping emissions continue to grow instead, as expected, things could spin "out of our control," especially as ocean levels rise from melting Greenland and Antarctic ice sheets, the researchers said. International experts predict a 10-degree leap in Fahrenheit readings (5.55 C) in such a worst-case scenario.
http://story.news.yahoo.com/s/cpress/20050.../global_warming
As you can see, there are two schools of thought on the issue, and while each comes out every day with 'definitive' evidence supporting their claims, its still completely up in the air.
It depresses me to watch the Kyoto Protocol die and people dance on its ashes, while providing no alternative solutions. Talk about speeding out of control, we're screwed w/ that kind of attitude. At least do _something_.