The authors sent emails to 7,555 individuals gathered from a few similar sources: those who had published papers or assessment reports that included the keywords āglobal warmingā or āglobal climate changeā during the period from 1991 to 2011, a separate database of actively publishing climate scientists, and a separate review of climate science papers from 2009 to 2011. A total of 6,550 people were successfully contacted, and 1,868 questionnaires were returned, resulting in a response rate of 29 percent.

The surveyās first question asked these scientists ā[w]hat fraction of global warming since the mid-20th century can be attributed to human induced increases in atmospheric GHG [greenhouse gas] concentrations?ā There were several possible answers, allowing respondents to choose a specific range of contribution to warming. The combined group that pegged the contribution as above 50 percent ā meaning, greenhouse gases have accounted for more than half of the observed warming ā was considered to agree with the consensus. A total of 1,231 people agreed with the consensus, or 65.9 percent of the 1,868 respondents.
But Verheggen said the authors found a consensus of between 79 percent and 97 percent. How did he arrive at that range? Two of the possible responses to the first question were āunknownā and āI donāt know,ā which the authors called āundeterminedā responses. A large number of people selected these options: 9.9 percent said āunknown,ā and 8.8 percent said, āI donāt know.ā But undetermined responses do not mean the respondents donāt believe humans are the primary driver of climate change. Pinpointing the specific
amount of human contribution is a difficult task.
The
study authors argue that these answers should not be included in the analysis of the consensus, resulting in Verheggenās range. The lowest possible value after excluding undetermined responses was 79 percent (
see table S3 of supplemental information), among 278 respondents who had published only zero to three papers on climate science. The highest possible value was 97 percent, among 142 respondents who were authors on the IPCCās scientific report published in 2007. Among all 1,868 respondents, the rate was 84 percent that agreed with the consensus.
You have to be really brain damaged not to understand all this
Severely damaged indeed........