PCHiway wrote:Your other post tastes of Malthus.
I'll have to do something about that. It should reek of Malthus.
In your response to my graphs you spent most space talking about policy options. I largely agree with everything you said. But I thought we were going to discuss the cause(s) of global warming, not the implications. On cause(s) it's me and Ricky against you; on implications it's you and me against Ricky (to be utterly simplistic and reduce things to the silly level of personalities).
You had previously stated, remarking upon the graph of Greenland data, "My take from this is that we're in an unusually cool time and are overdue for a return to warmer times." And it seems that was the basis of your belief that warming is indeed the current trend. I went to great effort to rebut the contention that your graph is convincing in this regard, which it seems to me is a critical issue; you completely ignored that main point of my post.
Do you still believe we are in an unusually cool period relative to the relevant trends and cycles?I had thought that most scientists placed us at a point relative to natural cycles where
cooling could be expected. That was the basis for worrying about us entering a new ice age, and indeed if you look at my fourth graph, especially the red line representing ice volume, we certainly seem to be poised at the peak of an interglacial warm period, not one of unusual coolness. But as I said, everything depends on what amount of time you look at. My understanding, however, is that at this point in earth's history the most relevant set of natural trends/cycles is those having to do with the current glacial period.
It's against
that background that the sudden (?) warming must be explained, and the simplest and most obvious explanation is AGW. But I say it's obvious in part because of the rate of increase; I said it was unprecedented, you said my graphs show it's not. Let's discuss that.
The first graph is of the last 125 years; it shows the current rise of which I speak and little else, so is of no use to us expect to note that the increase has been about .9 degrees over a century. The second graph is the one I think most useful, so I'll reproduce it here:
It covers twenty centuries, and at a scale we might make some sense of. Note that a swing of .8 degrees would cover exactly half the height of the graph. Except for the 20th, do any centuries show a swing of that magnitude? The light green line is the most erratic, but even it shows no such rise or fall in a mere century. Ergo, I submit that this past century's rise has been at a rate unprecedented for the last 20 centuries. How about before that? The next graph, which covers 100 centuries, is too large-scale for me to discern century-by-century numbers. I don't think we can draw any conclusions from it about short-term (yes, a century is "short-term" relative to a glacial cycle) rates of change. Note that the time scale along the bottom is not linear. On the far right the difference between two adjacent data points is 113 years, while in the middle the same distance seems to cover over 200 years and on the far left it's over 400 years. Judging relative slopes of lines (which seems tough to do anyway) wouldn't be enough - you'd have to compensate for the log scale used on the time axis.
So I cannot find in these graphs any evidence to contradict a claim that the last century's rise has occurred at an unprecedented rate. To the contrary, we can see that within the last 20 centuries it is anomalous. But you know what? I'm going to concede this point to you anyway. There had to have been times in the past when temps shot up. Volcanos spew various gases as well as particulates and eruptions typically cool the planet, but not always. There are such things as super-volcanoes (I'm sitting close to the rim of an old one right now!) and maybe they've caused abrupt upward as well as downward moves on a global basis. Also, the earth sometimes experiences weird events. The Mediterranean basin has dried and been filled several times, and supposedly one of those fillings took mere months to occur. Our planet's magnetic field can reverse polarity in something like weeks. So who knows?
The fast rise relative to the last twenty centuries suggests to me that something very odd is going on, and the only odd-enough phenomenon is our burning of fossil fuels. But the rate of change is not a basis for IPCC's conclusions about AGW. They see the strongest evidence as coming from this set of investigative steps:
1) reconstruct global (or at least northern hemisphere) and regional temps for the past X number of years at a fine enough scale for the purposes at hand. Also sea level, ocean currents, and a bunch of other things related to climate.
2) investigate all possible causes (forcings) of change, from solar fluctuations to orbital changes to El Nino/La Nina and so on; determine the power of each forcing and reconstruct (insofar as possible) a history of forcing events and cycles.
3) build a computer model that can use the known forcings to account for the known fluctuations in temp and other climate measurements. "Success" is when it can explain all pre-1950 fluctuations via the application of natural forcings.
4) now give the model the more recent data, as well as a module for simulating the effects of human activities on atmospheric CO2 levels. Can the model which explained everything else so nicely, explain 1950-20XX data without using the new module? No? Can it explain (simulate) the recent changes if it does employ the new module? Yes? Then man's contribution of greenhouse gases must be the cause of the recent observations.
In fact, the IPCC has only found that humans have caused most of the recent rise, not all of it. Their predictions for the future are made on that basis.
Now you may feel qualified to critique the work of umpteen researchers over umpteen years that went into the above, and do so with enough perspicuity to prove them wrong. I do not feel qualified to defend all that research. Maybe, if you raise some very specific objection or question, I can, in an hour or two, find some info that will help to clarify things, but maybe not. So truth to tell, I doubt it's worth a lot more discussion. If you are convinced humans aren't responsible for most of the recent warming, I can't convince you otherwise.
HERE is the IPCC report on the physical science basis for their recommendations. I can't be any more convincing than it is. Can you convincingly refute it?
20 Jan 2011, 2:13 am 
