Do they quote wikipedia or skepticalscience? No, they read the papers.
The first one was by Doran and Zimmermann in 2009: http://tigger.uic.edu/~pdoran/012009_Dor...
They sent questionnaires out to 10,257 "Earth scientists". They got replies from 3,146. Strangely, they used the replies from only the 79 scientists who were deemed to be suitably qualified. Of those, two of the "suitably qualified" scientists did not agree that the earth had warmed from pre-1800 levels. So they ignored the answer from those two (who wouldn't?) for the second question which was: "Do you think human activity is a significant contributing factor in changing mean global temperatures?"
There was apparently, and not surprisingly, much concern over the definition of "significant" (not over 50% note - just "significant". Of the remaining 77, 75 replied yes (97.4% i.e (75/77)*100 and not (75/3146)*100).
The next paper by Anderegg et al in 2010 is harder to debunk. They did not survey anybody. They sat in front of Google Scholar or similar and counted up papers and split scientists up into groups depending on whether they had signed petitions against AGW. The contents of the papers were not addressed as far as I can remember. They just counted them. As the AGW position generates funding there are more papers supporting AGW. They compared the top few from a small list with the top few of a large list, crunched the numbers and published another 97% figure.
(Why is the "big list" "small list" comparison significant? Example: Compare the heights of the tallest 700 people in the Vatican with the tallest 700 people in the USA. Conclusion: People in the Vatican are all midgets!)
The most recent attempt by Cook et al in 2013 decided how they were going to publish the results before starting the survey. In their paper http://iopscience.iop.org/1748-9326/8/2/... they do not go into detail about their collected data. Basically, they read through over 12,000 abstracts and assigned categories. They fail to describe how only about 0.5% (or 0.3% if you closely examine the data) claimed that man was mainly responsible. However, by manipulating the categories they still managed to get a 97% figure and not a 99.5% figure against! Science at its best.
This is a summary but reading the papers yourself is educational not least because it will let you in to the standards to which these people work.
http://www.friendsofscience.org/assets/d...
EDIT: Oreskes (2004) claimed only 75%. Her survey was NOT one of the 97% ones. She relied on looking at papers, it was not a survey of scientists, Peiser tried to replicate her work in 2005 and found only 1.2% explicitly supported the view that man was mainly responsible.
Edit2: All you thumbs-downers. Look in the mirror and ask yourself who is denying what exactly.
The number you refer to is one based on a review of papers in scientific journals, the fact is few deniers theories can make it past even basic review. Given that in the science field concerned the main forum for checking what the next scientist is doing is the peer reviewed journals, 97% is probably a conservative figure.
Deniers have tried to counter this with messes like the OISM petition which claims to have 31,000 scientists as signatories, yet it was a list riddled with obvious fake names, and the rather obvious question, where are all these scientists, as the claim is now almost a decade old yet in the interim there have been numerous annual meetings on climate (and similar fields) that attract 10's of thousands of scientists, like the annual AGU meeting which can have up to 18,000 scientists, but in almost a decade not a peep out of these claimed 31,000. Although of late I note deniers have stopped talking about the OISM petition so I think even they are starting to get embarrassed by these long periods when these claimed scientists seem to vanished completely.
Other attempts deniers have tried to make along these lines is to try and claim the lead groups of various scientific bodies are forcing their members to comply with the public stances of the organisations. As I recall (I think it was the Royal society) was claimed to have ignored a letter from a group of it's members saying they didn't support the Royal Society pro- AGW stance, yet as it turned out the letter had less than 10 signatories in an organisation that has 1350 members. As I recall 9 where in the petition, 13 would be 1% of the membership, you do the math, I guess deniers think this is impressive evidence when it is in fact deniers making fools of themselves, yet again.
Most of these other organisations change leadership regularly, if any member really felt they where not being listened to, they could easily stand themselves and if there where as many disaffected scientists as deniers claim they would easily win, yet again in 5 or 6 changes of leadership in half a dozen different organisations over almost a decade nothing, not a peep from any scientists claiming to not think AGW was happening. Then you have the scientists denier actually use as reference on their blogs etc, it is hard not to notice the same short list of names repeat Soon, Lindzen, Spencer and perhaps a dozen more and these same names go back also about a decade and while deniers try to pin this all on just Mann and Hansen it is equally hard not to notice that there is an every changing list of names associated with new papers coming out all the time on AGW. While deniers continue to try and attack just Mann and Hansen, Hansen has in fact retired from NASA almost a year ago.
The public positions of groups like AGU, the Royal Society or the Geology Society of America are a matter of public record and give a quite clear view of their members views, of course ask any denier to post the views of any of the many scientific bodies that support their claims and you will get utter silence, for the simple reason there are none.
Edit: Of course you also have those like Barry UK who try to use Galileo as a comparison, which is bit of history confusion, as he was using science to try and confront denial (the Church) he was not alone as a number of others, of the few real scientists of the time also thought as he did and had the evidence to prove it, Copernicus pre-dates Galileo by 100 years and he put forward the theory that Galileo later supported, but Copernicus lived in an even harsher period where people where still routinely burned for talking this sort of science. Giordano Bruno a contemporary of Galileo was actually burned at the stake for going even further in these theories than Copernicus had. But in their day, the deniers could have you put to death, nowadays they can only rant in blogs.
Other lead scientists of the the time also supported the Copernican theory, Kepler took the theory even further all these men are remembered as the fathers of modern astronomy.
Edit 2: Then we have James answer: according to him it is "fraudulent claim" from Skeptical science, but James seems to not mention that the number 97% used by skeptical science was in fact based on a peer review work by Naomi Oreskes 2004
http://www.sciencemag.org/content/306/57...
So not actually a fraudulent claim at all or by just skeptical science.
Deniers fantasies are built on a long history of this sort of leaving out of vital info.
Listen to the three percent, what do they say? These brave fellows are risking all by disagreeing with such a concensus. Galilio was placed in the same position for uttering a similar heresy
"Ninety-seven percent of climate scientists agree that climate-warming trends over the past century are very likely due to human activities (1), and most of the leading scientific organizations worldwide have issued public statements endorsing this position. The following is a partial list of these organizations, along with links to their published statements and a selection of related resources..."
http://climate.nasa.gov/scientific-conse...
See also: https://www.skepticalscience.com/global-...
http://climate.nasa.gov/scientific-conse...
That was a fraudulent claim purported by a blog deceivingly called "Skeptical Science."
http://www.forbes.com/sites/jamestaylor/...
Leftists always must resort to misleading and distorting information. The truth hurts their causes.
http://answers.yahoo.com/question/index?...
http://en.wikipedia.org/wiki/Scientific_...
How do they know that 97% of scientists 'believe' in man caused global warming that threatens to destroy us if we don't act?
I need to know this for school.
I'm guessing it was a world wide poll that all scientist got or something?
