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years of cloud cover and temperature observationsfor the north-eastern Pacific Ocean. Their study provides the best evidenceyet that low-level cloud cover decreases as temperature increases— that the feedback mechanism is positive.Wrong type of clouds When temperatures are higher, Clement believes that water rises higher into the atmosphere to create upper-level cloudsat the expense of low-level clouds. These higher clouds, however, have a net greenhouse effect andtherefore their creation could further boost the positive feedback.The team compared their findings with feedback predictions made by 18 leading climate models. Only two models predicted a positive feedbackand oneof these — HadGEM1 from the UK’s Hadley Centre — was particularly good at reproducing the observed relationships between cloud cover, atmospheric circulation and temperature. Clement believes HadGEM1 performed well because Hadley scientists have “spent a lot of time looking at the lower kilometre of the atmosphere”. Clement told physicsworld.com that the strength of the positive feedback is in the upper range of that predicted by theIntergovernmental Panel on Climate Change(IPCC). An important consequence of this is that global warming could be worse thanmany scientistshad anticipated. Indeed, HadGEM1 predicts a 4.4° average global temperature increasewhen carbon dioxide is doubled — compared to the 3.1° median of the 18 models.Water vapor decreases cloud coverage – amplifies warmingRadford, 14 - [Tim, reporter for Climate News Network who won the Association of British Science Writers award for science writer of the year four times, Climate Central, “Study Sheds Light on Effects of Clouds on Warming”, 1/17/14, -sheds-light-on-effects-of-clouds-on-warming-16916, 7/25/16]JROLONDON – Australian and French scientists believe they have cracked one of the great puzzles of climate change and arrived at a more accurate prediction of future temperatures. The news is not good, according to Steven Sherwood of Australia’s Centre for Excellence for Climate System Science at the University of New South Wales. If carbon emissions are not reduced, then by 2100 the world will have warmed by 4°C(7.2°F). This figure does not, at first, sound
high: researchers have been warning for 20 years on the basis of computer models that under the notorious business-as-usual scenario in which everybody goes on burning coal and oil, then as carbon dioxide levels double, global temperatures could rise by between 1.5°C and 4.5°C (2.7°F and 8.1°F). Pessimists could cite one extreme, optimists the other: the range of uncertainty was a recognition that there were still some big unknowns in the machinery of climate, and one of those unknowns was the behavior of theclouds in a warmer world. More warmth means more evaporation, more vapor could mean more clouds. Low-level clouds reflect