I posed this question to my brother and father-in-law yesterday and they disagreed with the premise of the question, let alone the result. They debated the physics involved. Weather is generally a result of the sun's uneven heating of the atmosphere and the resulting convection currents, ie. wind, follows generally constant patterns across the face of the earth. A windmill, by the laws of conservation of energy, does not "create" electricity. It converts kinetic energy from moving air to motion of the windmill blades, which in turn is converted into electrical energy. Maybe a little more to it than that, but that's the gist of it. So a windmill removes energy from the atmosphere. Obviously the wind exiting the windmill can't have as much energy as the wind entering the windmill (energy was "used" to move the blades) no matter how efficient and/or aerodynamic the blades are. With each windmill then, the weather pattern is slightly affected. With enough windmills, would wind be reduced enough to affect weather? Could windmills be causing climate change? My point of posting this on here is to pose the concept, but to debate the physics since that is what I was challenged on. Is my understanding of the conservation of energy principals above correct? My in-laws said that the wind isn't affected because the blades are so aerodynamic and that wind behind a windmill actually moves faster. Thoughts?