From the environmental point of view there is no such thing as the perfect energy source, whether we are talking about renewable or non-renewable energy sources. However, if we are to compare the environmental effects of renewable and non-renewable energy sources then it is really quite clear that renewable energy sources such as wind and solar are far more environmentally friendly than fossil fuels like coal and oil.
Wind energy is no exception, and is considered by many environmentalists and energy experts as the environmentally friendly source of energy. Wind energy doesn't emit harmful carbon dioxide (CO2) emissions, nor does it contribute to air pollution. In fact if world would to replace fossil fuel power plants with wind farms this would be doing wonders for tackling the climate change and air pollution issue. Sadly this is not possible because of the intermittency of wind energy (wind doesn't blow all the time), and also because of the fact that wind power still lacks the required efficiency and cost-competitiveness.
As said before wind energy is by no means a perfect energy source, and can cause certain environmental issues such as noise pollution and bird deaths. Noise pollution coming from large wind turbines is said to be an issue in some parts of the world, but with the careful planning and the proper installation of wind turbines and by using the adequate technologies in form of noise reducing-modifications for the wind turbines, this issue can be properly addressed.
Large wind turbines have been held responsible for the deaths of thousands of birds. Birds can collide with the large, fast rotating blades, and this can lead to fatal consequences for bird population. Still, it has to be said how there were many studies which showed that the number of bird deaths caused by wind turbines is very low, especially if this number is to be compared with the number of bird deaths caused by other ways of generating electricity, especially of the environmental impacts of using fossil fuels. The newest wind turbines are also equipped with the radar in order to protect birds from colliding with its blades.
To conclude, using wind energy is overall very good from the environmental point of view. It is not perfect but in energy world there is no such thing as perfection, and compared to the currently dominant fossil fuels wind energy is certainly a recommended energy option that could significantly improve the current environmental state of our planet.