Let’s see now . . . We seem to have gone past the 350 comments mark. What (if anything) have we learned so far ?
We can clearly see that this is a free-for-all open ended blog-talk ranging from comments of the lowest common denominator to the more sublime. The quality of the discussion can only as good as what the participants can muster. The patient, polite, knowledgeable, and informative comments from Fred Moolten are clearly being missed. As a medical doctor, Fred also showed that one did not need to be a professional climatologist to understand the basic concepts of climate and climate change.
From the first 100 or so comments, it is apparent that the dominant theme of the comments is the remarkable lack of understanding displayed by most of the commentators (including their remarkable lack of understanding that there was a lack of understanding) of how the climate system works, or even the basic concepts of physics that are needed to understand climate and the world we line in.
From these comments, I am not convinced that the commentators even have a sufficiently clear understanding of the basic concept that energy must be conserved. They appear to have no clear idea of what a climate model really is, how it works, or what it does. Nor do they understand radiative transfer or the greenhouse effect. Without a clear understanding of the greenhouse effect, there is no real hope of ever understanding the nature of the global warming problem.
Also, from reading some these comments, it is obvious that there was a language communications problem. The term “unforced natural variability” is a technical term that has a specific meaning to those study climate science. In a climate model that is simulating real-world climate, there is “forcing” going on all the time, at every grid-box, vertical layer, and moment in time. Basically, nothing moves unless it is being forced. The Earth is rotating; solar illumination is changing constantly. Water evaporates, clouds form, precipitation happens. So what does “unforced” mean?
“Unforced” in the climate modeling context means that there are no “external” radiative forcing changes (e.g., changes in greenhouse gases, or changes in solar luminosity) being applied over and above all the activity that is ongoing in simulating the normal day-to-day local weather variations. A good example of natural variability is the annual temperature plot by the NY Times where the local day-to-day temperatures are plotted as a function of time of year. There is the heavy (centered) line defining the daily climate-mean temperature with the daily record high and record low temperatures defining the envelope. The day-to-day temperatures vary stochastically within this envelope (unless a new high or low record temperature is set), never repeating their previous pattern of variability.
A climate model would be expected to reproduce a similar-looking day-to-day temperature plot that varies within the climatological envelope with the warmer temperatures during the summer and colder temperatures during the winter. The day-to-day temperature variations constitute the stochastic “natural variability”, that is unpredictable, but that statistically, the temperature can be predicted to be within the climatological envelope, changing from summer to winter in response to the change in the seasonal solar forcing.
This is a fairly good example illustrating how climatic temperature change can be considered as being composed of a stochastic “natural variability” component (day-to-day temperature) with very large predictive uncertainty, and the far more deterministic component (season-mean temperature in response to the seasonal change in solar radiation).
A similar perspective applies to the global temperature, and to the inter-annual changes in global temperature that result from changes in ocean circulation (e.g., El Nino, La Nina, PDO). These temperature changes don’t have an external forcing driving them, so these temperature changes are part of the “unforced natural variability”, and hence not very predictable, except in a statistical sense. Meanwhile, global temperature change in response to the radiative forcing exerted by greenhouse gas increases is similar in nature to the seasonally driven temperature change, and thus very predictable.
