Today\'s mega forest fires in the U.S. Southwest are truly unusual compared to the long-term record and may be the result of human activity, researchers say. A study that examined hundreds of years of ancient tree ring and fire data from two distinct climate periods suggests today\'s dry, hot climate is not the lone cause of the megafires that routinely destroy millions of acres of forest, researchers from Southern Methodist University reported Tuesday. Human activity over the last century in terms of dealing with fires is at least partly to blame for today\'s megafires, they said. \"The United States would not be experiencing massive large-canopy-killing crown fires today if human activities had not begun to suppress the low-severity surface fires that were so common more than a century ago,\" said Christopher I. Roos, a professor in the SMU Department of Anthropology. Today\'s extreme droughts caused by climate change probably would not cause megafires if not for a century of livestock grazing and firefighting, researchers said, which have combined to create more dense forests with accumulated logs and other fuels. \"If anything, what climate change reminds us is that it\'s pretty urgent that we deal with the structural problems in the forests. The forests may be equipped to handle the climate change, but not in the condition that they\'re currently in,\" Roos said. \"They haven\'t been in that condition before.\"