Credited to Radagast the Brown — the eccentric wizard portrayed by Sylvester McCoy in Jackson's recent films — it describes how a climate model simulation was run based upon the weather and topography described throughout Tolkien's works. That was then compared to a prehistoric version of Earth, as well as a simulation based on our current era, dubbed "Modern Earth." Among the discoveries were that The Shire so fancied by Frodo Baggins has an annual climate very similar to parts of New Zealand (not a complete surprise), and that the ships setting sail for the Undying Lands depart from Grey Havens because there are actually strong winds present in that region. As for Mordor, the study concluded that its environment would have been inhospitable to life even without the intervention of Sauron, and most resembled the climates found in western Texas or Los Angeles. You can find the full report here, and don't worry if the Common Speech isn't your native tongue; it's available in translations for elves and dwarves as well.