Geography and politics will combine to limit turbine placement to certain areas, and the question of diminishing returns from dense arrays will become a significant factor, Adams said. "You're not going to be able to put turbines across the entire globe." The work raises enough doubts that policymakers should be emphasizing research into other energy sources to replace fossil fuels, argues Harvard's Keith: "While they have their problems, you can clearly take nuclear and solar energy to gigantic scale." It's not the first time Keith has raised concerns over wind power. A 2008 paper published in the Journal of Atmospheric Sciences, co-written by Keith with atmospheric scientist Daniel Kirk-Davidoff of the University of Maryland, said huge wind farms could change air patterns enough that it would also affect worldwide climate. A more alarming conclusion came from a 2011 paper published by the Max Planck Institute for Biogeochemistry, a German research organization, that said that trying to get the maximum power from the Earth's winds could have the same impact on climate change as a doubling in atmospheric carbon dioxide. (The Planck paper, published in Earth System Dynamics, is another that argues that wind is a limited resource, concluding it is "considerably less than recent estimates that claim abundant wind power availability.") At the least, in the cheap ray ban next decade or so wind farms will get big enough to cause more localized climate changes, Keith said. While wind clearly raybanforsala is a better option than coal, "we ray ban sunglasses have to get past the reflexive view that all renewables are good and have negligible impacts," Keith said. No doubt, the models will be refined as research continues, said Adams. Less is understood about the Earth's winds than, say, the potential of solar power, where sunrises and sunsets are known and satellites can measure clouds, she said. There is so much unknown about wind energy and how it interacts with the atmosphere, Adams said. "There are ray ban for sale never-ending questions." This story is part of a special series that explores energy issues. For more, visit The Great Energy Challenge.