Policy Documents

Scientific Consensus on Global Warming

Joseph Bast and James M. Taylor –
April 3, 2007

This booklet summarizes the results of international surveys of climate scientists conducted in 1996 and 2003 by two German environmental scientists, Dennis Bray and Hans von Storch. Bray is a research scientist at the GKSS Institute of Coastal Research in Geesthacht, Germany. Von Storch is a climatology professor at the University of Hamburg and director of the Institute of Coastal Research.

More than 530 climate scientists from 27 different countries provided numerical answers each time the survey was conducted. All responses were anonymous. The same questions were asked each time the survey was conducted, plus an additional 32 questions were asked in 2003. The 2003 survey was conducted online.

The surveys presented dozens of assertions regarding climate change and asked respondents to give a numerical score, on a scale of 1 to 7, indicating the extent to which the respondents agreed or disagreed with each assertion. The average responses to every question in both the 1996 and 2003 surveys are reported in the appendix of this booklet.

To make the survey results more transparent, we singled out 18 questions from the 2003 survey and present the answers here in a simplified and less academic style. For each question, we combined the percentages of those respondents who gave numeric scores of 1, 2, or 3 and called this “agree.”  We combined those who gave numeric scores of 5, 6, or 7 and called this “disagree.” Those who answered with the numeric score of 4 we called “uncertain.”

The results reveal a lack of consensus on the most important questions in the climate change debate. For example:

  • When asked, “do you agree or disagree that climate change is mostly the result of  anthropogenic (manmade) causes?” slightly more than half (55.8 percent) of climate scientists surveyed agreed, 14.2 percent were unsure, and 30 percent disagreed. Interestingly, more scientists “strongly disagree” than “strongly agree” that climate change is mostly the result of anthropogenic causes.
  • When climate scientists were asked if “climate models can accurately predict climate conditions in the future,” only a third (35.1 percent) agreed, while 18.3 percent were uncertain and nearly  half (46.6 percent) disagreed.
  • Roughly three of four climate scientists (72.7 percent) believe “the IPCC reports accurately reflect the consensus of thought within the scientific community.” However, nearly one in five (19.8 percent) disagree. Only 24.4 percent of respondents “strongly agreed” with the statement.
  • Only one-third (32.1 percent) of scientists reported having confidence in our ability to make predictions of time scales of 10 years, while more than half (53.3 percent) reported little or no confidence. When asked about time scales of 100 years, slightly more than a quarter (27.4 percent) of scientists reported being confident while 55.6 percent had little or no confidence.
  • Asked to respond to the statement, “Climate models accurately verify the climatic conditions for which they are calibrated,” barely half (46.8 percent) of scientists agreed, 17.6 percent were uncertain, and more than a third (35.6 percent) disagreed. Four times as many scientists “strongly disagreed” with the statement as “strongly agreed” with it.

Read the whole document at the link above.