Hi dehammer,
I do hope we don't get bogged down in volcanos because they really are not relevant to global warming. They change climate drammatically occasionaly in geologic terms. That is, every few hundred thousand years or million years or so. We live in a period where the climate flips much shorter than that and being humans, the human scale of time is what interests us. And in a discussion about global warming in this century and the odds of particular events, it really doesn't figure large at all.
Actually the VEI index relates to the release of all material. Any VEI-8 is going to be a huge upper atmosphere releaser. And the 1815 eruption was an upper atmosphere releaser. Pyroclastic flows are most common with sudden release, not so much with smouldering cone volcanos. And even steady slow large eruptions can and do release enormous upper atmosphere clouds.
The point to the 70% in this ice age is that these are increased volcanic activities over the earth, not single eruptions. The single eruptions are well known and they do not correspond, except once, with the evidence showing the activity. So you could say that major volcanic eruptions of a single volcano almost never correspond with interglacial ending.
I agree with you entirely if you are looking at massive climate shifts in a geologic time frame. Volcanos play a big part but that is not at all relevant to a global warming argument because we are discussing a much more short term cycle or climate shift and there just is no evidence that in this ice age super volcanos had pretty much anything to do with transitions between warm and cool periods.
Worse, from the point of view of arguing that volcanos will send us back to a cold period, some very major volcanic eruptions with massive amounts of high altitude releases have many times had absolutely no long term effect to climate.
Volcanos can and will start the next ice age or deepen this one but it is likely this will happen outside human time frames. Similarly, a major meteor impact will do the same but they seem to happen with even less frequency than volcanic eruptions of major extinction level proportions.
As to plates, the Pacific really isn't getting much smaller. Yes, the Altantic has two plates that are spreading but it is the Indian that seems to be the loser, with the Australian and Indian plates both moving north. This really is not relevant to global warming at all.
Currents are not particularly "sun driven". They arise because of heat transfer from the tropics to the high latitudes. The residual heat within the oceans is actually quite large. That is why an eruption such as Tambora, which really did have a large chilling effect for well over a year, did not effect the currents, even though it occurred right in the middle of the "mini ice age". Mt St Helens, was a very high altitude eruption. The cloud had a cooling effect for around three years and it was at exactly the right latitude to effect the Atlantic currents, as was the Mexican eruption not long afterwards that was far less reported but actually had a larger climatic effect because of the gas mixture and the very high altitude release. I guess you could argue they weren't big enough but once again they had no effect other than very short term.
It actually seems that the stability of interglacial periods and glaciations is really quite robust. They seem to survive quite significant events that should flip them to the opposite. Yet when the transition actually occurs, from current knowledge it seems that the triggers really are quite minor things (either that or the trigger is some effect that leaves no evidence available for human study such as solar radiation cycles we know nothing of). That parodox makes the prediction of any transition nigh on impossible.
It was actually this very strange stability and delicacy that fascinated me when I was first exposed to the study at Uni.
There are warning signs however. It would seem that jet streams become vertically unstable before a transition. That is one explanation for wooly mammoths found chewing grass. If you are slowly freezing to death you tend to swallow what you are eating and where did the grass come from in the first place if the transition is a nice slow progression?
Parodixically, especially after all my arguments that volcanic eruptions seem to almost never cause the end of interglacial periods, volcanic activity remains a very good indicator of the end of an interglacial period. For some reason volcanic activity seems to increase in the period before or just at the transition. The increased activity does not seem to be larger than other volcanic events that did not correspond with transitions. But even so, if you were actually looking at a particular period as a candidate for a transition then increased volcanic activity would certainly strengthen the odds of a correct prediction, even if the mechanism or the reason for the correlation was not understood at all.
There are biological indicators as well. Certain animals seem to have programming built in to rapidly adjust to the coming of a new glaciation (otherwise cool temperature environment animals would have little chance surviving each of the periods - and animals such as rabbits, stoats, foxes, wolves, deer, bears, etc seem to have managed quite well despite living three quarters of the time in a frigid world and the rest in a very seasonal one). Some of these indicators are as simple as the pelts turning white and staying that way year round; others are changing in herd behaviour; others are changes in body mass and group dynamics. If you are a bee and live in the sub Arctic region, if you did not change dramatically how the hive worked that species of bee would just cease to exist as soon as a glaciation occurred, yet the bees do exist so somehow they know how to adapt. But more importantly, it would seem they have some way of sensing the change in climate as opposed to seasonal variations (which they often do not cope well at all with). All of these things have actually been studied because evidence of these changes is often readily available.
The trouble is I have not seen one single study of global warming that includes any of this. Yet, it seems that the study of things seemingly totally unrelated to the science of climate is a much better indicator of just what is likely to be happening climate wise, if you are trying to divine the near future of climate change.
If a biologist released a major study showing specific changes in certain animals that suggested they were adapting to a coming warmer period, I for one, would really start to worry that the world is going to get much hotter. However, I would worry a great deal more if the study showed adaption to a colder period.
It has always interested me that the more advanced science becomes, the more specialised the experts and the more they end up knowing about less and less. Climate is a big picture thing. What is actually needed is a few studies that are done by generalist scientists. But unfortunately they would not be believed. By the very nature of attempting to understand several subjects in some depth but not become a world expert in the field, there is always going to be someone who really is a greater expert to dispute your findings in a very narrow field. Thus, a more generalist study will be attacked by a great many scientists all seemingly with much better credentials than the authors of the studies.
Bottom line. You really are never going to find out what the world's climate is doing until it actually does it, at least not on the basis of current studies imho.
Richard
