Hi dehammer and anyone else interested,
This is LONG. Most won?t be interested unless you are interested in what Volcanos can do to climate but it certainly is relevant to global climate discussions so here goes.
Dehammer, I?m responding in turn even if the items are not really relevant to global warming.
1. Super continent. Yes, there were super continents from time to time (Columbia maybe 1.5 billion BC: Rodinia about 750 m BC; Pangea 300 m BC; etc). The major continents were connected but still separate plates. Even in geological terms the last one was a very long time ago. Since then there have been many different patterns of continents.
2. Pacific Ocean. This is not a remnant of the single ocean because there have been several intermediate steps to its formation.
3. Ice Caps and Average Temperatures. There weren?t any thermometers around 2 million years ago however I do not believe that there is evidence to suggest a period in earth's history during the time of land animals that was 15 or even 7 degrees warmer for the global average. The upper end is more than double the current average temperature. The best estimates based on ice cores that go back around 800,000 years in the Antarctic (tending to indicate that the Antarctic has had an ice cap for at least 800,000 years continuously but the Antarctic actually started to form an ice cap around 40 million years ago and has had one pretty much throughout that period) is that the maximum fluctuation is around three degrees. After that world temperatures have to be guessed at through sediment cores and it is much easier to dispute the figures. The difference between the last glaciation and the peak of this interglacial period is said to be only 2 degrees.
4. Volcanos. This is very relevant to global warming. Around 70% of the interglacial periods in this ice age ended in the same period as heightened volcanic activity. With the exception of a couple of specific eruptions, it is quite possible that some of these volcanic activities cannot be easily traced to a specific volcano or group of volcanos or even region. The evidence of volcanic eruptions is in the ash left behind (the Antarctic ice cores are good for this). These thin layers of ash can be found in many places around the world for the 70% of the end of interglacial periods.
I think you are confusing the massive eruptions of volcanos that occur far less frequently than the periods were are discussing. Vulcanologists use a scale to describe these ?super volcanos?. The ones that change world climate are called VEI-8 volcanic events. The last one was 75,000 years ago in Sumatra. Depending on which expert you talk to, this caused from a low of 60% of the world?s humans to die, all the way to all but 2,000 surviving in one small part of Africa (this estimate is from DNA studies). Now that is really frightening. A few hundred breeding humans were all that stood in the way to our not having this global warming argument at all (and they were black if you are a white supremisct and think you are somehow superior).
There have been VEI-6 or 7s more recently but they do not correspond with interglacial transitions. Once again, this is not particularly my field of expertise but I did have to study eruptions around the time of interglacial/glaciation transitions because the cause and effects were and still is what interests me. In this interglacial period there has been a VEI-7. This was 6,300 years ago in Japan. It was fairly sizeable, spewing out a little less than 200 cubic kilometres of gunk. Interglacial periods have ended with volcanic activities around the same time of considerably less than this (and still get counted in the 70%). Once again, there is a problem with the bald statistic. You need to know at what altitude various percentages of the stuff actually made it to. But that is a pretty good argument that a super volcanic eruption does not necessarily result in the end of an interglacial period. Surprisingly, more than once massive eruptions have occurred around the time of a transition to an interglacial period.
Since it is the particulates that volcanos spew out that cause global cooling events, even if only for very short periods, if there is no evidence of ash at the interglacial boundary then you can be pretty sure there was no unusual volcanic activity. And I do believe that the sites of the massive eruptions are known to those that study such things, at least the last few millions years of them are.
A Caldera volcano actually doesn't necessarily change climate all that much. All a caldera is is a volcano which has blown its top, forming a depression, often becoming a lake. The eruption can cause enormous damage without changing the world's climate. Tambora went up in 1815 (a VEI-6 although it is also referred to as a VEI-7) yet it did not have any long term effect on climate, despite 1816 being known as the year without a summer (and that is throughout the world not just in the Asia/Oceanic region). Tambora is in Indonesia. The pyroclastic flows etc killed around 100,000 people and the whole world knew of the event. It was actually four times the size of Krakatoa, although Krakatoa is often remembered because it was the first world event that ?modern? communications was able to transmit around the world.
I think you are confusing major volcanic eruptions with periods of intense volcanic activities, where several volcanos become active for significant periods or the really enormous eruptions which occur much more rarely. There are several volcanos around the world that are worrying to vulcanologists. Vesuvius is one that is showing signs of being a disaster in the short term. That one volcano is capable of killing around half a million Italians without having much effect on climate at all. There is a volcano in the Canary Island that could let go at any minute, killing pretty much everyone on the US Eastern Seaboard, as well as a few French, a great many Africans but if it does happen, the effect on climate will be tiny because it will not involve prolonged high altitude particulate dispersion. There is a big difference between volcanic eruptions that are disasters and an eruption that basically blocks out the sun. And the size of the eruption or even what is chucked out of the volcano is not particularly important. What is important is how the stuff is chucked out. Spread as pyroclastic flows and you get little change. Chuck it straight up and particles will darken the world as they go around the earth for many years. Climate changing eruptions do happen and they certainly could happen tomorrow but they don't seem to be the major cause of transitions to glaciations. I don't know why. It does seem logical but the evidence does not bear it out.
As you indicated, transitions to glaciations are more often than not accompanied by periods of heightened volcanic activity but there is a chicken/egg problem with this that has not really been answered.
5. Ocean Currents. Now I might disagree with the methodology of many global warming studies and am happy to argue about whether there is any global warming, man made or not, other than a 30 year period that is clearly able to be accurately determined because of satellites, permanent buoys etc. However, I think you will find that pretty much any climatologist that has anything to do with global climate change will disagree with your statement concerning currents. Ocean currents are a real biggy in just what climate the world has. Shut down the Atlantic tractor type current today and within six weeks you will be extremely cold if you live in the US, Britain or Western Europe. You will be dead within two or three years.
El Nino turns up and Australia goes into drought. Al Nina turns up and Chile goes into drought. Now you could argue these are not exactly currents but they are heat exchange mechanisms by movement of energy within oceans.
Change a few factors such as salinity especially for the Atlantic currents by a fairly small amount and the world becomes a very different place.
There is actually a theory that the flip to glaciations could actually occur for no better reason than calving of ice sheets in the Antarctic happens to slice off too big a chunk. This theory does not argue that warming triggers the massive calving, only that calving occasionally (every several thousand years) manages to slice off a massive (we are talking something the size approaching that of Texas). It could be that the ice has built up to the extent that the piece that eventually breaks off is huge or it could be that there is a warming fluctuation. The theory suggests it can be pretty much arbitrary reasons unconnected to the actual world average temperature at the time.
My point has always been that the world is an extremely complicated place. So complicated that any attempt to model world climate is not even remotely possible with current knowledge. A vulcanologist cannot tell you the mechanisms for periods of heightened activities. A meteorologist cannot tell you where a hurricane will be two days into the future or where a tornado will touch down. A palaeobiologist cannot tell you with any certainty why pretty much all creatures that have gone extinct actually did so. They are still arguing about why dinosaurs went extinct and this was one of THE major events in this planet's history. The complexities that govern the earth to the extent that it remains inhabitable by vertebrate creatures are staggeringly immense.
Richard
