"97 Percent of Climate Scientists Surveyed..."

We've seen that phrase a lot over the past few months/years.

What does it mean and how was it established?

Well, let's go to a recent source, this paper at the peer-reviewed Environmental Research Letters.  And this is from the abstract:

We analyze the evolution of the scientific consensus on anthropogenic global warming (AGW) in the peer-reviewed scientific literature, examining 11 944 climate abstracts from 1991–2011 matching the topics 'global climate change' or 'global warming'. We find that 66.4% of abstracts expressed no position on AGW, 32.6% endorsed AGW, 0.7% rejected AGW and 0.3% were uncertain about the cause of global warming. Among abstracts expressing a position on AGW, 97.1% endorsed the consensus position that humans are causing global warming.

There's another section of the paper that I'll tackle in a little bit.  So they collect a whole buncha peer-reviewed papers (about 12,000) and THEN separate them into what looks like 4 basic categories:

• No position
• Endorsing AGW
• Rejecting AGW
• Uncertain

First, I am curious about the 66% of those papers expressing no opinion of AGW.  What does the paper say about those?

In a table labeled "Definitions of each type of research category" the category "No Position" is described as:

Social science, education, research about people's views on climate

So not climate science, but important data about the science nonetheless.  So a great deal of the papers they collected mention AGW but aren't actually climate science papers, per se.  If I am reading this correctly.

And what does "Endorsing" mean?  Here there are three different types:

• Explicit endorsement with quantification - Explicitly states that humans are the primary cause of recent global warming
• Explicit endorsement without quantification - Explicitly states humans are causing global warming or refers to anthropogenic global warming/climate change as a known fact
• Implicit endorsement - Implies humans are causing global warming. E.g., research assumes greenhouse gas emissions cause warming without explicitly stating humans are the cause

And there are three separate types of "rejection" as well

• Implicit rejection - Implies humans have had a minimal impact on global warming without saying so explicitly E.g., proposing a natural mechanism is the main cause of global warming
• Explicit rejection without quantification - Explicitly minimizes or rejects that humans are causing global warming
• Explicit rejection with quantification - Explicitly states that humans are causing less than half of global warming

So of all the 12,000 papers they found,  about a third either endorsed or rejected AGW in one way or another.  And of those 97% endorsed.

But it's one thing for the authors of this study to categorize all those papers.  How did the authors themselves categorize them?  This is the second part of the study:

We emailed 8547 authors an invitation to rate their own papers and received 1200 responses (a 14% response rate). After excluding papers that were not peer-reviewed, not climate-related or had no abstract, 2142 papers received self-ratings from 1189 authors. ... Among self-rated papers that stated a position on AGW, 97.2% endorsed the consensus. Among self-rated papers not expressing a position on AGW in the abstract, 53.8% were self-rated as endorsing the consensus. Among respondents who authored a paper expressing a view on AGW, 96.4% endorsed the consensus. [Emphasis added.]

So even the majority of those initially regarded as "no position" were held to be, by the authors of those papers themselves, as endorsing AGW.

And you can even check their work.