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How accurate & reliable are model projections?

See also here and here, regarding the models' false forecast of a tropical tropospheric hot spot.
This hotspot has to be present if the greenhouse effect ascribed by IPCC to CO2 is actually at work.
Therefore, its absence is direct disproof of the IPCC CO2 greenhouse gas effect.

Chapter section & page no. IPCC Quotation - WUWT article Adam Gallon's take-home message

p 462

“Current spatial coverage, temporal resolution and age control of available Holocene proxy data limit the ability to determine if there were multi-decadal periods of global warmth comparable to the last half of the 20th century.” “We don’t know if the changes seen over the past decades are anything out of the ordinary as far as climate goes”


p 483

“Knowledge of climate variability over the last 1 to 2 kyr in the SH and tropics is severely limited by the lack of paleoclimatic records. In the NH, the situation is better, but there are important limitations due to a lack of tropical records and ocean records. Differing amplitudes and variability observed in available millennial-length NH temperature reconstructions, and the extent to which these differences relate to choice of proxy data and statistical calibration methods, need to be reconciled. Similarly, the understanding of how climatic extremes (i.e., in temperature and hydro-climatic variables) varied in the past is incomplete. Lastly, this assessment would be improved with extensive networks of proxy data that run up to the present day. This would help measure how the proxies responded to the rapid global warming observed in the last 20 years, and it would also improve the ability to investigate the extent to which other, non-temperature, environmental changes may have biased the climate response of proxies in recent decades.” ”Ditto and we can’t even decide which, if any, set of treemometers, shellfish, layers of mud or offerings to the gods are the ones we should be using, nor can we agree how we should be analysing them, even if they are the right ones to use”

8 Exec. Summ.

p 591

“The possibility that metrics based on observations might be used to constrain model projections of climate change has been explored for the first time, through the analysis of ensembles of model simulations. Nevertheless, a proven set of model metrics that might be used to narrow the range of plausible climate projections has yet to be developed.” “Actually, we’ve been winging it ever since this circus started and we’ve still not even decided if we’re on the right track”

8 Exec. Summ.

p 593

“Recent studies reaffirm that the spread of climate sensitivity estimates among models arises primarily from inter-model differences in cloud feedbacks. The shortwave impact of changes in boundary-layer clouds, and to a lesser extent mid-level clouds, constitutes the largest contributor to inter-model differences in global cloud feedbacks. The relatively poor simulation of these clouds in the present climate is a reason for some concern. The response to global warming of deep convective clouds is also a substantial source of uncertainty in projections since current models predict different responses of these clouds. Observationally based evaluation of cloud feedbacks indicates that climate models exhibit different strengths and weaknesses, and it is not yet possible to determine which estimates of the climate change cloud feedbacks are the most reliable.” “We’re using a whole load of assumptions that we’ve really not got a shred of experimental data to support and we can’t even agree about what we should be measuring”

p 594

“What does the accuracy of a climate model’s simulation of past or contemporary climate say about the accuracy of its projections of climate change” This question is just beginning to be addressed, exploiting the newly available ensembles of models.” “We’ve been winging it and we’re still flapping like mad and getting nowhere fast”

p 595

“The above studies show promise that quantitative metrics for the likelihood of model projections may be developed, but because the development of robust metrics is still at an early stage, the model evaluations presented in this chapter are based primarily on experience and physical reasoning, as has been the norm in the past.” “We’re still flapping our arms, we reckon we’ll fly because we’re doing basically what birds do and they fly”


p 608

“Consequently, for models to predict future climatic conditions reliably, they must simulate the current climatic state with some as yet unknown degree of fidelity.” “Anyone know what’s the best bird suit to wear whilst we flap?”

p 638

“Although the errors in the simulation of the different cloud types may eventually compensate and lead to a prediction of the mean CRF in agreement with observations (see Section 8.3), they cast doubts on the reliability of the model cloud feedbacks.” “Apparently, if we get enough monkeys typing, we’ll be able to produce the complete works of Shakespear!”

p 638

“Modelling assumptions controlling the cloud water phase (liquid, ice or mixed) are known to be critical for the prediction of climate sensitivity. However, the evaluation of these assumptions is just beginning (Doutraix-Boucher and Quaas, 2004; Naud et al., 2006)." "We’ve made a load of guesses, now we’ll start thinking about checking if they’re right.”


p 640

“A number of diagnostic tests have been proposed since the TAR (see Section 8.6.3), but few of them have been applied to a majority of the models currently in use. Moreover, it is not yet clear which tests are critical for constraining future projections. Consequently, a set of model metrics that might be used to narrow the range of plausible climate change feedbacks and climate sensitivity has yet to be developed.” “However, we really don’t know how to check if our guesses are the ones we should have been using for the past, oooh, 30 years?”

9 Exec Summ

p 665

“Difficulties remain in attributing temperature changes on smaller than continental scales and over time scales of less than 50 years. Attribution at these scales, with limited exceptions, has not yet been established.” “how warm is it anyway?”


p 754

“Since the ensemble is strictly an ‘ensemble of opportunity’, without sampling protocol, the spread of models does not necessarily span the full possible range of uncertainty, and a statistical interpretation of the model spread is therefore problematic.” “Quick, we really don’t know what we’re on about, write some management speak, pass me a copy of “The Dilbert Principle”!”

p 805

“The AOGCMs featured in Section 10.5.2 are built by selecting components from a pool of alternative parameterizations, each based on a given set of physical assumptions and including a number of uncertain parameters.” “Who’s for a quick game or three of Blackjack?"






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