Fifty-two percent of Americans think most climate scientists agree that the Earth has been warming in recent years, and 47% think climate scientists agree (i.e., that there is a scientific consensus) that human activities are a major cause of that warming, according to recent polling (see http://www.pollingreport.com/enviro.htm). However, attempts to quantify the scientific consensus on anthropogenic warming have met with criticism. For instance, Oreskes  reviewed 928 abstracts from peer-reviewed research papers and found that more than 75% either explicitly or implicitly accepted the consensus view that Earth's climate is being affected by human activities. Yet Oreskes's approach has been criticized for overstating the level of consensus acceptance within the examined abstracts [Peiser, 2005] and for not capturing the full diversity of scientific opinion [Pielke, 2005]. A review of previous attempts at quantifying the consensus and criticisms is provided by Kendall Zimmerman . The objective of our study presented here is to assess the scientific consensus on climate change through an unbiased survey of a large and broad group of Earth scientists.