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Global climate models are accurate enough to be relied upon

Thanks Pro for concise and focused argument. General limitations of Climate modelling In perfect scenario, we would have simple deterministic mathematical model to simulate deterministic phenomena on which we can run multiple experiments with controlled conditions in order to validate the model. While for example engineering simulations can comply with such scenario to some extent, complex phenomena in economic, social or climate sciences are another story. We don't have enough beforehand knowledge about every important climate feedback so we in fact estimate such feedback's with the model itself based on its output compared to measurements. But unless we know all other forcing that can influence output in similar way, we won't get good estimate of the parameter we look for. For example Koutsoyiannis[1] or Tennekes[2] (extending on Poper and Lorenz) challenge the notion that complex models could ever be reliable according to their nature. "Theories that are complex may become untestable, even if they happen to be true."[2] etc. If we look at QT's definition of GCM, it is clear that to fulfill their purpose, those models must have the structure of forcings and feedbacks right. We won't get reliable "scenario predictions", no matter how lucky we are in predicting aggregated mean temperature if the true causes are different then we thought. What is the reliability of current GCMs in scientists eyes? "We compare the output of various climate models to temperature and precipitation observations at 55 points around the globe... Besides confirming the findings of a previous assessment study that model projections at point scale are poor, results show that the spatially integrated projections are also poor."[1] "We examine tropospheric temperature trends of 67 runs from 22 ‘Climate of the 20th Century' model simulations and try to reconcile them with the best available updated observations (in the tropics during the satellite era). Model results and observed temperature trends are in disagreement in most of the tropical troposphere, being separated by more than twice the uncertainty of the model mean."[3] "These weaknesses combine to make GCM-based predictions too uncertain to be used as the bases for public policy responses related to future climate changes." [4] "So there has been a large activity to bring models and observations into agreement, strangely only by adjusting the measurements instead of adjusting the models. "[5] Even Kevin Trenberth (from the Mann et al. group) now acknowledges many of the GCM's troubles in his paper "More knowledge, less certainty"[6] publicly. "The scientific literature is filled with studies documenting the inability of even the most advanced GCMs to accurately model radiation, clouds, and precipitation."[7] For those interested, NIPCC report [7] and their topical updates [8] provide comprehensive information about studies dealing with GCM reliability. Refutation As you put it, Hansen's predictions look totally perfect and within 100th of degree of Celsius. Lets examine the claim. "Dr. Jim's 1988 projections weren't looking so good, so he dropped an apple in the middle of his oranges. The red line is land only temperatures, but his projections were for global temperatures."[9] Let us also compare it with satellite [10] and other [11] data. Now suppose I made highly oscillating prediction. At some points in time, my prediction would be always spot on as it would cross the real data. Look back at the figures. Where is this precision from 2006 until now, or in early nineties? Also note that curve C assumes "emissions drastically reduced" in 1990 [10,11]. I therefore call this conduct a fallacy of cherry-picking. On top of that, Hansen is known for not so transparent temperature data manipulation.[12,13] Dessler's assumptions are refuted by Spencer's satellite observations [14], supporting rather Lindzen's hypothesis:"Our measured sensitivity of total (SW + LW) cloud radiative forcing to tropospheric temperature is -6.1 W *m^-2 K^-1... This decrease in ice cloud coverage is nominally supportive of Lindzen's 'infrared iris' hypothesis." "This is exactly opposite of the way all climate models behave," as Spencer put it in his own words in [15]. (technical note: Don't take the whole video as extension of my argument. Its used only as source of the quote in 6:19 and for information purpose as I acknowledge I must make my argument myself on this page within its limitations.) Now lets see the warming troposphere, because it was predicted it would be significantly warmed by CO2 forcing. See figures 3.4.1 and 3.4.2 for PCM model prediction and 3.4.3 for radiosondes. Updated study [17], taking in account errors stated by Pro, supports overall warming trend in troposphere of +0.052 ± 0.07 K per decade (while RSS temperature is somewhat higher then other methods, but much less then models). That is in good agreement what the figure 3.4.3, but in complete disagreement with figure 3.4.2 (also note the scales). The problem is not whether the troposphere warmed, but how much it warmed (1.2 °C at hotspot vs 0-0.3°C) and how different layers warmed relative to each other. The model predicted much stronger warming in troposphere then on surface, but that is not true. It means that model is wrong about GHG forcing or feedbacks in troposphere. Conclusion Models may be useful in furthering our knowledge of the problem, mostly by showing us what our assumptions really mean. If we are humble enough and learn from comparing our assumptions to measurements, we can learn from our mistakes. But the climate models fail if used as defined by Pro. [1] http://www.tandfonline.com... [2] http://ff.org... [3] http://www.pas.rochester.edu... [4] http://www.ncpa.org... [5] http://hockeyschtick.blogspot.com... [6] http://www.nature.com... [7] http://www.nipccreport.org... [8] http://www.nipccreport.org... [9] http://sppiblog.org... [10] http://www.climate-skeptic.com... [11] http://rankexploits.com... [12] http://stevengoddard.wordpress.com... [13] http://www.omsj.org... [14] http://www.drroyspencer.com... [15] Video: "Why the IPCC Models...." http://www.youtube.com... [16] http://www.nipccreport.org..., pages 106-108 [17] https://www.cfa.harvard.edu...