Does global warming exist?

Hendrik Tennekes, retired Director of Research, Royal Netherlands Meteorological Institute: "The blind adherence to the harebrained idea that climate models can generate 'realistic' simulations of climate is the principal reason why I remain a climate skeptic. From my background in turbulence I look forward with grim anticipation to the day that climate models will run with a horizontal resolution of less than a kilometer. The horrible predictability problems of turbulent flows then will descend on climate science with a vengeance."
Antonino Zichichi, emeritus professor of nuclear physics at the University of Bologna and president of the World Federation of Scientists : "models used by the Intergovernmental Panel on Climate Change (IPCC) are incoherent and invalid from a scientific point of view"
Individuals in this section conclude that the observed warming is more likely attributable to natural causes than to human activities.

Khabibullo Abdusamatov, mathematician and astronomer at Pulkovskaya Observatory of the Russian Academy of Sciences: "Global warming results not from the emission of greenhouse gases into the atmosphere, but from an unusually high level of solar radiation and a lengthy - almost throughout the last century - growth in its intensity...Ascribing 'greenhouse' effect properties to the Earth's atmosphere is not scientifically substantiated...Heated greenhouse gases, which become lighter as a result of expansion, ascend to the atmosphere only to give the absorbed heat away."
Sallie Baliunas, astronomer, Harvard-Smithsonian Center for Astrophysics: "[T]he recent warming trend in the surface temperature record cannot be caused by the increase of human-made greenhouse gases in the air."
Reid Bryson, deceased, former emeritus professor of Atmospheric and Oceanic Sciences, University of Wisconsin-Madison: "It’s absurd. Of course it’s going up. It has gone up since the early 1800s, before the Industrial Revolution, because we’re coming out of the Little Ice Age, not because we’re putting more carbon dioxide into the air."
George V. Chilingar, Professor of Civil and Petroleum Engineering at the University of Southern California: "The authors identify and describe the following global forces of nature driving the Earth’s climate: (1) solar radiation ..., (2) outgassing as a major supplier of gases to the World Ocean and the atmosphere, and, possibly, (3) microbial activities ... . The writers provide quantitative estimates of the scope and extent of their corresponding effects on the Earth’s climate [and] show that the human-induced climatic changes are negligible."
Ian Clark, hydrogeologist, professor, Department of Earth Sciences, University of Ottawa: "That portion of the scientific community that attributes climate warming to CO2 relies on the hypothesis that increasing CO2, which is in fact a minor greenhouse gas, triggers a much larger water vapour response to warm the atmosphere. This mechanism has never been tested scientifically beyond the mathematical models that predict extensive warming, and are confounded by the complexity of cloud formation - which has a cooling effect. ... We know that [the sun] was responsible for climate change in the past, and so is clearly going to play the lead role in present and future climate change. And interestingly... solar activity has recently begun a downward cycle."
David Douglass, solid-state physicist, professor, Department of Physics and Astronomy, University of Rochester: "The observed pattern of warming, comparing surface and atmospheric temperature trends, does not show the characteristic fingerprint associated with greenhouse warming. The inescapable conclusion is that the human contribution is not significant and that observed increases in carbon dioxide and other greenhouse gases make only a negligible contribution to climate warming."
Don Easterbrook, emeritus professor of geology, Western Washington University: "global warming since 1900 could well have happened without any effect of CO2. If the cycles continue as in the past, the current warm cycle should end soon and global temperatures should cool slightly until about 2035"
William M. Gray, Professor Emeritus and head of The Tropical Meteorology Project, Department of Atmospheric Science, Colorado State University: "This small warming is likely a result of the natural alterations in global ocean currents which are driven by ocean salinity variations. Ocean circulation variations are as yet little understood. Human kind has little or nothing to do with the recent temperature changes. We are not that influential."[22] "I am of the opinion that [global warming] is one of the greatest hoaxes ever perpetrated on the American people." "So many people have a vested interest in this global-warming thing—all these big labs and research and stuff. The idea is to frighten the public, to get money to study it more."
William Kininmonth, meteorologist, former Australian delegate to World Meteorological Organization Commission for Climatology: "There has been a real climate change over the late nineteenth and twentieth centuries that can be attributed to natural phenomena. Natural variability of the climate system has been underestimated by IPCC and has, to now, dominated human influences."
George Kukla, retired Professor of Climatology at Columbia University and Lamont-Doherty Earth Observatory, said in an interview: "What I think is this: Man is responsible for a PART of global warming. MOST of it is still natural."
David Legates, associate professor of geography and director of the Center for Climatic Research, University of Delaware: "About half of the warming during the 20th century occurred prior to the 1940s, and natural variability accounts for all or nearly all of the warming."
Marcel Leroux, former Professor of Climatology, Université Jean Moulin: "The possible causes, then, of climate change are: well-established orbital parameters on the palaeoclimatic scale, ... solar activity, ...; volcanism ...; and far at the rear, the greenhouse effect, and in particular that caused by water vapor, the extent of its influence being unknown. These factors are working together all the time, and it seems difficult to unravel the relative importance of their respective influences upon climatic evolution. Equally, it is tendentious to highlight the anthropic factor, which is, clearly, the least credible among all those previously mentioned."
Tad Murty, oceanographer; adjunct professor, Departments of Civil Engineering and Earth Sciences, University of Ottawa: global warming "is the biggest scientific hoax being perpetrated on humanity. There is no global warming due to human anthropogenic activities. The atmosphere hasn’t changed much in 280 million years, and there have always been cycles of warming and cooling. The Cretaceous period was the warmest on earth. You could have grown tomatoes at the North Pole"
Tim Patterson, paleoclimatologist and Professor of Geology at Carleton University in Canada: "There is no meaningful correlation between CO2 levels and Earth's temperature over this [geologic] time frame. In fact, when CO2 levels were over ten times higher than they are now, about 450 million years ago, the planet was in the depths of the absolute coldest period in the last half billion years. On the basis of this evidence, how could anyone still believe that the recent relatively small increase in CO2 levels would be the major cause of the past century's modest warming?"
Ian Plimer, Professor emeritus of Mining Geology, The University of Adelaide: "We only have to have one volcano burping and we have changed the whole planetary climate... It looks as if carbon dioxide actually follows climate change rather than drives it".
Nir Shaviv, astrophysicist at the Hebrew University of Jerusalem: "[T]he truth is probably somewhere in between [the common view and that of skeptics], with natural causes probably being more important over the past century, whereas anthropogenic causes will probably be more dominant over the next century. ... [A]bout 2/3's (give or take a third or so) of the warming [over the past century] should be attributed to increased solar activity and the remaining to anthropogenic causes." His opinion is based on some proxies of solar activity over the past few centuries.
Fred Singer, Professor emeritus of Environmental Sciences at the University of Virginia: "The greenhouse effect is real. However, the effect is minute, insignificant, and very difficult to detect." “It’s not automatically true that warming is bad, I happen to believe that warming is good, and so do many economists.”
Willie Soon, astrophysicist, Harvard-Smithsonian Center for Astrophysics: "[T]here's increasingly strong evidence that previous research conclusions, including those of the United Nations and the United States government concerning 20th century warming, may have been biased by underestimation of natural climate variations. The bottom line is that if these variations are indeed proven true, then, yes, natural climate fluctuations could be a dominant factor in the recent warming. In other words, natural factors could be more important than previously assumed."
Roy Spencer, principal research scientist, University of Alabama in Huntsville: "I predict that in the coming years, there will be a growing realization among the global warming research community that most of the climate change we have observed is natural, and that mankind’s role is relatively minor"
Philip Stott, professor emeritus of biogeography at the University of London: "...the myth is starting to implode. ... Serious new research at The Max Planck Society has indicated that the sun is a far more significant factor..."
Henrik Svensmark, Danish National Space Center: "Our team ... has discovered that the relatively few cosmic rays that reach sea-level play a big part in the everyday weather. They help to make low-level clouds, which largely regulate the Earth’s surface temperature. During the 20th Century the influx of cosmic rays decreased and the resulting reduction of cloudiness allowed the world to warm up. ... most of the warming during the 20th Century can be explained by a reduction in low cloud cover."
Jan Veizer, environmental geochemist, Professor Emeritus from University of Ottawa: "At this stage, two scenarios of potential human impact on climate appear feasible: (1) the standard IPCC model ..., and (2) the alternative model that argues for celestial phenomena as the principal climate driver. ... Models and empirical observations are both indispensable tools of science, yet when discrepancies arise, observations should carry greater weight than theory. If so, the multitude of empirical observations favours celestial phenomena as the most important driver of terrestrial climate on most time scales, but time will be the final judge