According to an April 30, 2012 "New York Times" article, "Dr. Lindzen accepts the elementary tenets of climate science. He agrees that carbon dioxide is a greenhouse gas, calling people who dispute that point "nutty." He agrees that the level of it is rising because of human activity and that this should warm the climate." He also believes that decreasing tropical cirrus clouds in a warmer world will allow more longwave radiation to escape the atmosphere, counteracting the warming. Lindzen first published this "iris" theory in 2001, and offered more support in a 2009 paper.