Thing is the wind isn't constant so you still need all the unfriendly enviromental stuff sitting in standby for when there is no wind. Also the wind isn't very good at picking up up just around lunch and dinner time. Mind you Nukes arn't very good at that either hence why they are best paired with a pump storage scheme.
So by the time you have built the wind turbine which produces loads of CO2 from making the materials and the concrete etc and then built the backup generation capability your actually not really saving any CO2.