In short, John N-G did a long post in which he argued that the remarkably severe Texas drought and hot summer are (if I can risk paraphrase) not primarily due to climate change. He is no disbeliever in AGW by any means, but he is very, very cautious when it comes to attribution of single events to it.
Tobis, on the other hand, has issues with the whole approach to attribution which can be summarised by his last sentence:
You can't apply small-signal arguments to large signals in nonlinear systems. So please stop it.And someone in comments expands on this in a way which Tobis basically agrees with:
As Jay Forrester and Ed Deming kept reminding us, people are not good at predicting the behavior of non-linear feed back systems. In particular weathermen and climate scientists study the one weather system, rather than the behavior of dynamic systems in general.This commenter goes on to point that climate models should be expected to not be good at predicting this.
In his classes, Dr. Deming made his students look at the behavior of various systems as the systems went “out of control.” It was shocking how a dynamic system could be “in control” and apparently stable, then suffer some small chaotic event, “go out of control”, and exhibit violent behavior as the system moved toward an new equilibrium. We have been adding heat to the weather system, bumped it out-of -ontrol, and we can expect weather that we have never see before as the system seeks a new equilibrium.
John Nielsen-Gammon missed the point that he has a system that is out of control and that his system is violently seeking a new equilibrium. We can expect ongoing violent behavior until the weather system comes back into control. The studies that he cites all assume that the system is "in control" and that the old rules hold. However, those old rules do not apply to the new, “out-of-control” weather system.
Tobis' point seems to me to make sense, but I guess we may have to wait for another few years of "weather weirding" to see how it pans out.
UPDATE: Nielsen-Gammon makes a further point in clarification in comments:
We're a degree F warmer because of anthropogenic greenhouse gases. The standard deviation around the best-fit curve seems to be about a degree F. So an event which would have been close to the best-fit curve is one standard deviation off it. Given the lack of rainfall, a temperature which would have been expected to be attained about 16% of the time is now expected to be attained about 50% of the time.
So, this event (i.e., this particular combination of drought and heat) has been made three times as likely by anthropogenic greenhouse gases, with lots of assumptions built in. The least of which is what global warming is doing to our local PDF of precipitation in Texas, which could go either way.