This comment was getting a bit long, so I decided to just post relevant stuff from Armstrong and Green first and then offer my own thoughts in a follow-up comment.

We surveyed scientists involved in long-term climate forecasting and policy makers. Our primary concern was to identify the most important forecasts and how those forecasts were made. In particular, we wished to know if the most widely accepted forecasts of global average temperature were based on the opinions of experts or were derived using scientific forecasting methods. Given the findings of our review of reviews of climate forecasting and the conclusion from our Google search that many scientists are unaware of evidence-based findings related to forecasting methods, we expected that the forecasts would be based on the opinions of scientists. We sent a questionnaire to experts who had expressed diverse opinions on global warming. We generated lists of experts by identifying key people and asking them to identify others. (The lists are provided in Appendix A.) Most (70%) of the 240 experts on our lists were IPCC reviewers and authors. Our questionnaire asked the experts to provide references for what they regarded as the most credible source of long-term forecasts of mean global temperatures. We strove for simplicity to minimize resistance to our request. Even busy people should have time to send a few references, especially if they believe that it is important to evaluate the quality of the forecasts that may influence major decisions. We asked: “We want to know which forecasts people regard as the most credible and how those forecasts were derived… In your opinion, which scientific article is the source of the most credible forecasts of global average temperatures over the rest of this century?” We received useful responses from 51 of the 240 experts, 42 of whom provided references to what they regarded as credible sources of long-term forecasts of mean global temperatures. Interestingly, eight respondents provided references in support of their claims that no credible forecasts exist. Of the 42 expert respondents who were associated with global warming views, 30 referred us to the IPCC’s report. A list of the papers that were suggested by respondents is provided at publicpolicyforecasting.com in the “Global Warming” section.

Unfortunately, the Forecasting Principles website seems to be a mess. Their Global Warming Audit page:

http://www.forecastingprinciples.com/index.php?option=com_content&view=article&id=78&Itemid=107

does link to a bibliography, but the link is broken (as is their global warming audit link, though the file is still on their website).

(This is another example where experts in one field ignore best practices -- of maintaining working links to their writing -- so the insularity critique applies to forecasting experts).

Continuing:

Based on the replies to our survey, it was clear that the IPCC’s Working Group 1 Report contained the forecasts that are viewed as most credible by the bulk of the climate forecasting community. These forecasts are contained in Chapter 10 of the Report and the models that are used to forecast climate are assessed in Chapter 8, “Climate Models and Their Evaluation” (Randall et al. 2007). Chapter 8 provided the most useful information on the forecasting process used by the IPCC to derive forecasts of mean global temperatures, so we audited that chapter.

We also posted calls on email lists and on the forecastingprinciples.com site asking for help from those who might have any knowledge about scientific climate forecasts. This yielded few responses, only one of which provided relevant references.

Trenberth (2007) and others have claimed that the IPCC does not provide forecasts but rather presents “scenarios” or “projections.” As best as we can tell, these terms are used by the IPCC authors to indicate that they provide “conditional forecasts.” Presumably the IPCC authors hope that readers, especially policy makers, will find at least one of their conditional forecast series plausible and will act as if it will come true if no action is taken. As it happens, the word “forecast” and its derivatives occurred 37 times, and “predict” and its derivatives occurred 90 times in the body of Chapter 8. Recall also that most of our respondents (29 of whom were IPCC authors or reviewers) nominated the IPCC report as the most credible source of forecasts (not “scenarios” or “projections”) of global average temperature. We conclude that the IPCC does provide forecasts. In order to audit the forecasting processes described in Chapter 8 of the IPCC’s report, we each read it prior to any discussion. The chapter was, in our judgment, poorly written. The writing showed little concern for the target readership. It provided extensive detail on items that are of little interest in judging the merits of the forecasting process, provided references without describing what readers might find, and imposed an incredible burden on readers by providing 788 references. In addition, the Chapter reads in places like a sales brochure. In the three-page executive summary, the terms, “new” and “improved” and related derivatives appeared 17 times. Most significantly, the chapter omitted key details on the assumptions and the forecasting process that were used. If the authors used a formal structured procedure to assess the forecasting processes, this was not evident. [...] Reliability is an issue with rating tasks. For that reason, it is desirable to use two or more raters. We sent out general calls for experts to use the Forecasting Audit Software to conduct their own audits and we also asked a few individuals to do so. At the time of writing, none have done so.