Global Climate?

Lumo has some comments that illuminate his point of view of climate change.

There is no "global climate". When people talk about "global climate change", it is the whole "climate change" that is supposed to be supplemented by the adjective "global": we are surely not talking about the changes of the "global climate" because the latter doesn't exist. . .

As the logicians have noted, once you make one false assumption, you can proceed to deduce anything whatsoever. It's true, of course, that climate was originally a local concept. Different regions of the planet have different climates, so going to the idea of a global climate is a generalization, slightly remniscent of the generalization of the concept of kinetic energy to other forms of energy.

Global climate only makes sense if global climate trends and events exist. Fortunately, the evidence is uniquivocal on this account, even if the causes are less certain. There is ample geological evidence that climate can change on a global scale - ice ages, dramatic warming events, and associated mass extinctions. More recent global climate perturbations from volcanos have also been documented.

He continues, a bit later:

. . .
Even if you don't understand these words about the Hurst exponents, you should understand that the predictions of the climate models for any particular region in the world will be essentially uncorrelated with reality because the reality is dominated by effects that are not properly simulated by the models. Because every single person lives in a particular region of the world and every region of the world is more or less incorrectly predicted by the models, I think it means that no rationally thinking person should pay serious attention to the predictions of these models.
. . .

Observational and historic evidence clearly indicates the existence of global climatic events, but the case from theory is even more clearcut. We know that CO2 is fairly well mixed in the atmosphere, and that it has a long residence time. Thus, the forcing function is global rather than local. Moreover, we know that lateral transport of energy in the atmosphere is a big driver of local energy balances. Weather in the arctic affects the whole Northern Hemisphere, and on a longer time scale, the whole planet.

. . . When you average the known data over these very long scales, you are exactly at the moment when you lose all nontrivial climate information that could have been used to validate the model. It is exactly the moment when you are supposed to start to believe the models.

Similarly, if a theory highly incorrectly predicts the global climate trends for 10 or 20 years, which we already know to be the case from observations, it seems unreasonable to expect that the theory will be very accurate for 30-year, 50-year, or 100-year predictions. . .

If what Lumo's asserted in the last paragraph were true, then we would indeed have reason to doubt the models. It is not, however. The time and space averaged large scale features of climate change are actually in fairly good agreement with predictions, with the obvious and important proviso that the models are not yet good enough to predict small scale space and time fluctuations.

This year has been cooler than many past years, for example, even it is warmer than every single year before 1989. This sort of fluctuation is expected. If no year hotter than 2005 were to appear in the next ten, however, there would be ample reason to suspect that some crucial piece of the environment was being badly modeled. The models are known to be imperfect - that point is not in question. The evidence suggests, however, that they are broadly correct.