First, according to the holy writ from the sainted Al Gore, temperatures continue to climb, with no end in sight unless we “Do Something!” But there's a problem with the claim.
It's wrong.
If one uses the year 1998 as a reference point, global temperatures since then have fallen. If 2002 is used as the reference, then temperatures have plateaued, staying steady for the past 5 years. If atmospheric carbon dioxide is steadily rising and carbon dioxide causes global warming, shouldn't the temperatures have continued climbing?
More than one anthropogenic global warming theorist has proclaimed that carbon dioxide levels would soon reach a tipping point that would throw the Earth's climate into a runaway thermal meltdown. The problem with this theory is that it is based upon the false assumption the climate is controlled by a positive feedback mechanism, where a small change triggers a big reaction. But if that were so, none of us would be here because our climate would be more like that of Venus. The fact we are here shoots holes in that theory. The carbon dioxide level in Earth's atmosphere has been many times higher than it is now, but it didn't trigger the kind of catastrophe predicted by the AGW theory. Instead, it appears the climate is moderated by a negative feedback mechanism, where any change is minimalized by that feedback.
In a debate between two commenters to the post linked just above, we get a tutorial from one of them on how feedback works, particularly in regards to Earth's climate. The first, a dyed-in-the-wool AGW believer using the moniker The Scientist, tries to come across as an authority on the aforementioned feedback, sounding smug and condescending at the same time.
...just like the author of this blog, you don't understand what positive feedback actually means. If anyone's a complete idiot in their understanding of this, it's you.
...your simple estimate would be wrong because that's not how you calculate climate sensitivity. And you don't believe that water has a high heat capacity? Oh dear. Tell me, generally speaking, which places have more extreme climates? Those near oceans, or those far from oceans?
A number of others replied to The Scientist's comments, getting to the point that one could see he/she was fighting a battle of wits while unarmed. One reply in particular shredded The Scientist's pronouncements, showing it was he/she with little understanding, if any, about climatic feedback mechanisms. It is quoted in its entirety below.
If you choose not to explain, people will assume that you don't really know. And in any case, will not be persuaded. The concepts are not at all hard to understand. Why not simply help people out and explain them?
When people talk about positive feedbacks, what they're actually talking about are positive perturbations on an overall negative feedback. The hotter things get, the faster heat is convected or radiated away, which is a massive negative feedback. Water vapour may make that slightly less negative, and as such is a positive feedback contribution, but the overall feedback is still negative. When you're talking about the effect of changes in temperature and changes in water vapour, the bulk of the feedback drops out, and the feedback on the changes could indeed then be considered positive, but its a rather specialised usage of the term. It's because of the dreadful way they're explained by climatologists that people get confused.
It is true that positive feedback with a feedback coefficient below unity doesn't give a runaway effect. It magnifies changes by a factor of 1/(1-f). But given the wide range of changes of forcings over the past few billion years, the climate would have been a lot more unstable than it has been if f were above 0.6 as proposed. And if there were any "tipping points" as some supposedly reputable scientists have claimed, we would have hit them. That's a valid argument against a slightly different argument to the one you made.
Your examples regarding the thermal capacity of the oceans are a bit misleading. Oceans warm and cool more slowly than the land because they are transparent, not because water has a greater thermal capacity. Nevertheless, ocean surface waters can change temperature by many degrees in a matter of weeks. Adjusting a fraction of a degree, such as that proposed as being caused by AGW, would be far faster.
Where it gets complicated is when you get to the role of the deep ocean, and overturn. In fact the ocean has many different thermal capacities, when considered on many different timescales. The surface waters mix only slowly with the deeper water, on a timescale of hundreds to thousands of years. It is extremely nonlinear that way. Temperatures that when averaged over long periods are above or below normal can give net transfers of heat to or from deeper layers, and in return cool or warm the surface slightly, that could in principle give such an effect. The longer the delay involved, the slower the process and the less heat will be transferred in any given time, so it can only explain so much.
However, such effects ought to show up as long-term average temperature changes in the sub-surface ocean. Measurements are highly uncertain and subject to large errors - we don't really know much about conditions below the surface except for a few samples at isolated spots - but observations by Levitus et al. have gone looking for these changes and failed to find them. I don't regard the science here as conclusive yet.
There is also, as alluded to above, the impulse response function measured from volcanic eruptions that suggest the time constant is very short. And the calculation by Schwartz of the time constant from the autocorrelation function of temperatures suggests the global climate has about a five year delay on the decadal timescale at which AGW should show up.
There are many ways to estimate climate sensitivity, and dreamin gave a simplified version of one of them. I assume it was based on Idso's paper on natural climate experiments - if so, I suggest you comment on Idso's arguments in detail rather than dismissing it with a vague "that's not how you calculate it."
So you can see from that that the explanations aren't quite as simple as you made out, and that patronising comments about people being "beyond help" are somewhat uncalled for.
If you know this, then the best thing you can do is to take the time to explain it, without being snide about it. It helps, even if only to the extent that we don't use that particular argument again. If you didn't know it, and yet are still pretending that one would have to be a fool not to, then consider yourself 'caught out'. I assure you, seeing that sort of thing helps the skeptic case enormously. :-)
What's puzzling is that robot probes used to measure ocean temperatures at various depths (down to the ocean floor in some cases) have been showing no change in ocean temperatures anywhere. If the AGW climate models are correct, there should be some changes below the surface, but they're nowhere to be found.
Of course I'm leaning heavily towards the heliogenic model of climate change. If it holds up we might be in for a lengthy period of colder weather, perhaps another Little Ice Age. Should that happen I'll be one of those working towards anthropogenic global warming.
NOTE: As an aside, my one big question for the AGW folks: “What makes you think a warmer climate will automatically be a bad thing?” So far they've shown no evidence that this will be the case. If past history is any indication (think the Medieval Warm Period or Roman Warm Period) the climate will be better.
Just something to think about.
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