This article says that according to a study, wind farms may not affect air pollution negatively (i.e. decrease greenhouse gas emissions to the atmosphere). I at first found the idea incredible because the mere fact of supplanting coal-based energy with wind energy (completely renewable and clean) means that the supposed pollution had been reduced upon use of wind energy. But this study says otherwise. In fact it says:

"...Building thousands of wind turbines would probably not reduce the pollutants that cause smog and acid rain, but it would slow the growth in emissions of heat-trapping gases..."

I think that wind power does contribute very little to climate change mitigation, since its still a very small contributor to the total energy output of the planet, but its still a contribution. Whatever magnitude that contribution is, its still significant.