No Reduction in CO2 Emmissions
Wind turbines do not generate CO2 (carbon dioxide) emissions. However, this is not the whole story. Wind-generated electricity is weather dependant, so it is intermittent and unpredictable. Therefore, when electricity from wind turbines is brought into the grid system, it requires continuous spinning reserve as backup, ready to take over when the wind does not blow or blows too hard. This backup is usually provided by fossil fuel plants, which do generate CO2 emissions. To compound the problem, when operating in this spinning reserve mode, these fossil fuel plants generate more CO2 per kWh than if operating normally. So the spinning reserve is burning fossil fuels and generating higher than normal CO2 emissions even when not producing electricity.
There are further CO2 emissions associated with the manufacturing of wind turbines, the transport of component parts, and the construction of the wind farm site with its access roads, grid connections, substations, etc.
Each turbine foundation requires between 500 and 1,000 tonnes of concrete and aggregate; concrete manufacture is one of the largest sources (about 7%) of man-made CO2 emissions. 
Some wind farm sites require tree clearance and/or peat removal. This not only removes a valuable carbon sink, it also adds to the CO2 emissions problem.
Below are some links to further information on the subject of wind turbines and CO2 emissions.
Wind power: inordinately expensive and ineffective at cutting CO2 emissions
Wind farms will create more carbon dioxide, say scientists
Wind farms generate enough power for a few cups of tea
Wind Energy: Facts and Fiction