"Forecasting is difficult: particularly about the future” This piece of wisdom is attributed to Yogi Bear. But it does not apply to the Intergovernmental Panel on Climate Change, since they do not make “forecasts” at all, only “projections”. As they make clear, “projections” are dependent on the correctness of the assumptions made by the computer models and the futures scenarios from which they are made.
This has not always been so. In the first IPCC Report (1990). on the first page of the “Executive Summary” there was nearly a whole page headed “ Based on current model results, we predict” with no less than ten actual “predictions”.They used the phrase “models predict” several times throughout, but they did, at least admit that there were “uncertainties”.
Chapter 4 was entitled “Validation of Climate Models”. Paragraph 4,12 “Methods and Problems of Model Validation” showed that such validation is quite a problem, and it seemed to show that, so far, no model has been truly validated. Chapter 8 “Detection of the Greenhouse Effect in the Observations” had the answer when it said (paragraph 8.4) “the fact that we have not yet detected the enhanced greenhouse effect leads to the question: when is this likely to occur”