CO2 is well known to be an effective greenhouse gas. If you are getting information from andre on this issue, I assure you that you are being misled. You might want to check out some work by Dana Royer on CO2's effect on past climates. Impacts depend on how much warming. 1 or 2 degrees probably won't be bad, but we're introducing a climate shift an order of magnitude greater than the noise of natural variability, and at a very fast rate. Ice is not doing well, ecosystems will not adjust to rapid 3 C warming, and poor countries and those that live off of glaciers may not do well under business-as-usual. There is a lot of mention on impacts in the literature, including IPCC AR4 WG2.