On the credibility of climate predictions

Abstract

Geographically distributed predictions of future climate, obtained through climate models, are widely used in hydrology and many other disciplines, typically without assessing their reliability. Here we compare the output of various models to temperature and precipitation observations from eight stations with long (over 100 years) records from around the globe. The results show that models perform poorly, even at a climatic (30-year) scale. Thus local model projections cannot be credible, whereas a common argument that models can perform better at larger spatial scales is unsupported.Key words climate models; general circulation models; falsifiability; climate change; Hurst-Kolmogorov climate De la crédibilité des prévisions climatiquesRésumé Des prévisions distribuées dans l'espace du climat futur, obtenues à l'aide de modèles climatiques, sont largement utilisées en hydrologie et dans de nombreuses autres disciplines, en général sans évaluation de leur confiance. Nous comparons ici les sorties de plusieurs modèles aux observations de température et de précipitation de huit stations réparties sur la planète qui disposent de longues chroniques (plus de 100 ans). Les résultats montrent que les modèles ont de faibles performances, y compris à une échelle climatique (30 ans). Les projections locales des modélisations ne peuvent donc pas être crédibles, alors que l'argument courant selon lequel les modèles ont de meilleures performances à des échelles spatiales plus larges n'est pas vérifié.

Comparison of Water Flows in Four European Lagoon Catchments under a Set of Future Climate Scenarios

“…It is common knowledge that even multi-model climate change impact assessments come with some uncertainty [6,63], which should be kept in mind when the results are analysed and interpreted. The uncertainties are mainly related to (A) the ability of climate and eco-hydrological models to represent the interrelated processes in the atmosphere and in a landscape (so-called structural and parametrization uncertainties); (B) the reliability of climate scenarios applied for the impact assessment; and (C) data availability and quality for (eco-)hydrological model setup and calibration.…”

Validation and forecasting accuracy in models of climate change

“…Reliable prediction intervals are also needed. In addition, localised forecasts derived from the AOGCMs need to be subjected to the same tests, since policies will typically be implemented locally (see for example Anagnostopoulos, Mamassis, 2010, andChristofides, 2008; and our discussion of the same issue in Section 3.3 of this paper).…”

“…In terms of forecast validation, they also provide a further testbed for understanding the strengths and deficiencies of the GCMs. Anagnostopoulos et al (2010) and Koutsoyiannis et al (2008) have explored this issue by evaluating various GCMs which were used in both the third and fourth IPCC assessment reports. In brief, Koutsoyiannis et al measured the rainfall and temperature at 8 locations around the world.…”

Climate, hydrology and freshwater: towards an interactive incorporation of hydrological experience into climate research

“…GCMs reported by IPCC) were not subject to such validation (the term "validation" does not appear in IPCC AR4) and, therefore, the reliability of the outputs of these models, that have been used to assess the impacts on water resources, is not tested. Recent independent studies on the validation of IPCC models (Douglass et al, 2008;Frank, 2008;Koutsoyiannis et al, 2008a) indicate a rather poor performance, especially on long-term (climatic) scales. Solely using different unvalidated models to produce ensembles of climate predictions (or projections, in IPCC's vocabulary), as is current practice in IPCC reports, does not provide a scientific basis for uncertainty estimation.…”