Actually they
compute that if CO2 concentration increases then temperatures will rise - do you dispute this?
Old models are being borne out, predictions made years ago are close to what we see today.
"...In the global climate models (GCMs) most of the warming that has taken place since 1950 is attributed to human activity. Historically, however, there have been large climatic variations.Temperature reconstructions indicate that there is a ‘warming’ trend that seems to have been going on for as long as approximately 400 years. Prior to the last 250 years or so, such a trend could only be due to natural causes..."
"...GCMs are not sufficiently reliable to distinguish between natural and man-made causes of the temperature increase in the 20th century. Some of the predictions from GCMs are accompanied by standard errors, as in statistical analysis. But since the GCMs are deterministic models one cannot interpret these standard errors in the same way as in statistics. GCMs are typically evaluated applying the same observations used to calibrate the model parameters. In an article in Science, Voosen (2016) writes; “Indeed, whether climate scientists like to admit it or not, nearly every model has been calibrated precisely to the 20th century climate records – otherwise it would have ended up in the trash”. Unfortunately,models that match 20th century data as a result of calibration using the same 20th century data are of dubious quality for determining the causes of the 20th century temperature variability. The problem is that some of the variables representing sources of climate variability other than greenhouse gases are not properly controlled for during the calibrations. The resulting calibration of the climate sensitivity may therefore be biased. Further critical evaluations are given by several authors, such as Essex (2022)..."
"...As mentioned in the previous section climate can also change owing to internal processes within the climate system even without any variations in external forcings (chaos). In the GCMs the source of chaos is the nonlinearity of the Navier-Stokes equations. If the initial conditions are not known exactly for a dynamic model based on the Navier-Stokes relations the forecast trajectory will diverge from the actual one, and it is not necessarily the case that small perturbations have small effects. In fact, slightly different initial conditions can yield wildly different outputs..."
"...In order to assess the uncertainty due to internal variability, researchers use so-called ICE (Initial Condition Ensembles) simulations. This means that outputs of GCMs are simulated starting from slightly different initial conditions. As the climate system is chaotic, slightly different initial conditions lead to different trajectories..."
"...Subsequently, we have summarized recent work on statistical analyses on the ability ofthe GCMs to track historical temperature data. These studies have demonstrated that the timeseries of the difference between the global temperature and the corresponding hindcast from theGCMs is non-stationary. Thus, these studies raise serious doubts about whether the GCMs are able to distinguish natural variations in temperatures from variations caused by man-made emissions of CO2..."
https://www.ssb.no/en/natur-og-milj...594b9225f9d7dc458b0b70a646baec3339/DP1007.pdf
