Well, part of the problem is that the whole postulation of Global Warming (oh wait, it's merely Climate Change now, isn't it?) is such a hash of assumptions and begged questions. If an argument has 100 failed component parts, where do you begin in listing who's "opposed" to it?
That said here's a partial list of climate-specific scientists who have publicly critiqued one or more aspects of the general premise "The globe is generally warming and humans are a significant cause."
Richard Lindzen, Alfred P. Sloan Professor of Atmospheric Science at the Massachusetts Institute of Technology and member of the National Academy of Sciences
Garth Paltridge, Visiting Fellow ANU and retired Chief Research Scientist, CSIRO Division of Atmospheric Research and retired Director of the Institute of the Antarctic Cooperative Research Centre.
Hendrik Tennekes, retired Director of Research, Royal Netherlands Meteorological Institute:
Antonino Zichichi, emeritus professor of nuclear physics at the University of Bologna and president of the World Federation of Scientists
Chris de Freitas, Associate Professor, School of Geography, Geology and Environmental Science, University of Auckland
William M. Gray, Professor Emeritus and head of The Tropical Meteorology Project, Department of Atmospheric Science, Colorado State University
William Kininmonth, meteorologist, former Australian delegate to World Meteorological Organization Commission for Climatology
David Legates, associate professor of geography and director of the Center for Climatic Research, University of Delaware
Tad Murty, oceanographer; adjunct professor, Departments of Civil Engineering and Earth Sciences, University of Ottawa
Fred Singer, Professor emeritus of Environmental Sciences at the University of Virginia
Jan Veizer, environmental geochemist, Professor Emeritus from University of Ottawa
Tim Patterson, paleoclimatologist and Professor of Geology at Carleton University in Canada
Syun-Ichi Akasofu, retired professor of geophysics and Founding Director of the International Arctic Research Center of the University of Alaska Fairbanks
John Christy, professor of atmospheric science and director of the Earth System Science Center at the University of Alabama in Huntsville, contributor to several IPCC reports
Craig D. Idso, faculty researcher, Office of Climatology, Arizona State University and founder of the Center for the Study of Carbon Dioxide and Global Change
Patrick Michaels, Senior Fellow at the Cato Institute and retired research professor of environmental science at the University of Virginia
August H. "Augie" Auer Jr. New Zealand MetService Meteorologist, past professor of atmospheric science at the University of Wyoming
Reid Bryson, Emeritus Professor of Atmospheric and Oceanic Sciences, University of Wisconsin-Madison
Marcel Leroux Professor of Climatology, UniversitÃ© Jean Moulin
Frederick Seitz, solid-state physicist, former president of the National Academy of Sciences
Does that list seem trivial to you?