A 2007 Harris poll found that 71 percent of Americans believed that the continued burning of fossil fuels would cause the climate to change. By 2009 the figure had dropped to 51 percent. In June 2011 the number of Americans who agreed was down to 44 percent. According to the climate and atmospheric history of the past 420,000 years on the climate change is a natural process strongly supported by human behaviour. Please see the evidence of Petit et al. (1999).
Petit, J. R., Jouzel, J., Raynaud, D., Barkov, N. I., Barnola, J.-M., Basile, I., Bender, M., et al. (1999). Climate and atmospheric history of the past 420,000 years from the Vostok ice core, Antarctica. Nature 399, 429–436. Available http://www.daycreek.com/dc/images/1999.pdf