Les climatosceptiques adorent les nouilles, ils ne se lassent jamais de montrer ce joli dessin destiné à "prouver" que les modèles sont faux et donc totalement inutiles:
|source : https://wattsupwiththat.com/2015/05/29/claim-data-does-not-prove-that-climate-models-are-wrong/|
- les données sont improprement alignées pour exagérer visuellement la différence
- pas de marge d'incertitude montrée
- fait la moyenne de l'ensemble des données, cachant le fait qu'elles ne sont pas en parfait accord (i.e. compare des carottes avec des navets)
- n'inclut pas les travaux d'autres groupes qui estiment un réchauffement plus important
- nous ne vivons pas à l'altitude du mont Everest ou dans des avions!
Sur SkepticalScience on trouve des explications claires sur ce qu'est un modèle climatique et sur ce qu'il n'est pas (ou ne fait pas)
- Climate models are mathematical representations of the interactions between the atmosphere, oceans, land surface, ice – and the sun. This is clearly a very complex task, so models are built to estimate trends rather than events.
- For example, a climate model can tell you it will be cold in winter, but it can’t tell you what the temperature will be on a specific day – that’s weather forecasting.
- Climate trends are weather, averaged out over time - usually 30 years. Trends are important because they eliminate - or "smooth out" - single events that may be extreme, but quite rare.
- Climate models have to be tested to find out if they work. We can’t wait for 30 years to see if a model is any good or not; models are tested against the past, against what we know happened. If a model can correctly predict trends from a starting point somewhere in the past, we could expect it to predict with reasonable certainty what might happen in the future.
- Testing models against the existing instrumental record suggested CO2 must cause global warming, because the models could not simulate what had already happened unless the extra CO2 was added to the model.
- All other known forcings are adequate in explaining temperature variations prior to the rise in temperature over the last thirty years, while none of them are capable of explaining the rise in the past thirty years. CO2 does explain that rise, and explains it completely without any need for additional, as yet unknown forcings.
- Where models have been running for sufficient time, they have also been proved to make accurate predictions. For example, the eruption of Mt. Pinatubo allowed modellers to test the accuracy of models by feeding in the data about the eruption. The models successfully predicted the climatic response after the eruption. Models also correctly predicted other effects subsequently confirmed by observation, including greater warming in the Arctic and over land, greater warming at night, and stratospheric cooling.
- The climate models, far from being melodramatic, may be conservative in the predictions they produce. For example, here’s a graph of sea level rise:
Observed sea level rise since 1970 from tide gauge data (red) and satellite measurements (blue) compared to model projections for 1990-2010 from the IPCC Third Assessment Report (grey band). Sea level rises mainly as a result of melting land ice and thermal expansion of ocean water as temperatures rise. Observed sea level is tracking at the upper range of the IPCC projections. (Source: The Copenhagen Diagnosis, 2009)
Et qu'en est-il pour l'extension de la banquise arctique?
|Comparison of observed September minimum Arctic sea ice extent through 2008 (red line) with IPCC AR4 model projections. The solid black line shows the mean of the 13 models, and dashed black lines show the range of the model results. Arctic sea ice is melting much faster than predicted by climate models. (Source: Copenhagen Diagnosis, 2009)|
Un papier récent de Mann et Rahmstorf (plus 3 autres scientifiques) publié en janvier 2016 nous dit ceci:
- 2014 was nominally the warmest year on record for both the globe and northern hemisphere based on historical records spanning the past one and a half centuries1,2. It was the latest in a recent run of record temperatures spanning the past decade and a half. Press accounts reported odds as low as one-in-650 million that the observed run of global temperature records would be expected to occur in the absence of human-caused global warming. Press reports notwithstanding, the question of how likely observed temperature records may have have been both with and without human influence is interesting in its own right. Here we attempt to address that question using a semi-empirical approach that combines the latest (CMIP53) climate model simulations with observations of global and hemispheric mean temperature. We find that individual record years and the observed runs of record-setting temperatures were extremely unlikely to have occurred in the absence of human-caused climate change, though not nearly as unlikely as press reports have suggested. These same record temperatures were, by contrast, quite likely to have occurred in the presence of anthropogenic climate forcing.
bleu les effets de la seule variabilité naturelle du climat et en rouge les données brutes (i.e. non ajustées) des températures observées, par contre je ne comprends pas ce que signifie la courbe grisée (surrogate signifie substitut ou de remplacement et ARMA semble être l'acronyme de autoregressive moving average, tout ça c'est trop pour mes faibles connaissances scientifiques...), mais je fais confiance à mes fidèles lecteurs (pas ceux venant de Skyfall évidemment) pour éclairer ma lanterne.