At http://chiefio.wordpress.com/2015/03/27/geomagnetism-jerk-excursion-rpi-… … we have some interesting information where science is at a boundary of knowledge and is in the process of changing its mind. The settled science, it seems, has not settled too well (an it all comes in the indomitable style of EM Smith, computer whizz kid).
It involves, most importantly, RPI (= relative palaeo intensity of magnetism as found in sediments). Lows in RPI appear to coincide with the end of interglacials and interstadial stages – coinciding with the advent of cooler climate. Then, it says, there has been a geomagnetic loss over the last 2000 years – which might foreshadow the end of the current interglacial. The elephant in the cupboard is that there was a geomagnetic high 2200 years ago = 200BC. This happens to coincide with one of Mike Baillie's low growth tree ring events (see A Slice Through Time: dendrochronology and precision dating) at between 210 and 205BC. This implies the lower geomagnetic strength that has subsequently occurred could be a relic of the post-Roman cooling period and the Little Ice Age (assuming it is based on averages). We may also note the 200BC date is also not far distant from the Maccabees era and the armies that marched across the sky. This appears to refer to transient phenomena such as auroral shape shifting on the horizon – but as seen from the Levant (much further south than your normal aurorae).
Chiefio recognises this is just another 'scare the children' piece of alarmism – and it is entirely speculative to say we are approaching the end of the current interglacial. Taking an average of temperature across 2000 years is not the same as a graph that shows a consistent and gradual cooling. How does it explain the medieval warm period?
The magnetic field itself changes all the time. If the field flips and stays on the other side for a long time it is known as a geomagnetic reversal. However, over the last 50 years the magnetic north pole has shifted from somewhere near central Canada as far as Siberia. Something is going on – but what?
A jerk is a short time change in the magnetic field (see http://en.wikipedia.org/wiki/Geomagnetic_jerk) which occurs suddenly as noted by Courtillot as long ago as 1978. Jerks appear to be random events, as far as they are spread out – and have occurred in 1969, 1978, 1991, and 1999. Jerks are thought to originate in the interior of the Earth rather than from an external source such as the solar wind. However, the cause of jerks has yet to be established with any degree of confidence (and why not both interior and exterior prompt).
A geomagnetic excursion, like a reversal, is a much more significant change in the magnetic field – but unlike a reversal an excursion is also short lived with a variation in orientation of the Pole – up to 45 degrees from the previous position. Excursions last a few thousand to a few tens of thousands of years – so they are quite different in scale to jerks. They are also more difficult to locate in the geological record. One such excursion occurred around 40,000 years ago – and this was undoubtedly a global excursion. What causes excursions is also open to debate – but a few days ago we had a post on a catastrophic event around 40,000 years ago. Interestingly, it is thought an excursion might involve the mantle – but not the core (unlike a reversal). Is this spitting into the wind?
Richard A Muller says geomagnetic excursions are triggered by external events which directly disrupts the flow in the core. As 40,000 years ago has already been fingered as the date of a massive volcanic event one may wonder if these are symptoms are something greater, something cosmic rather than just external. The 40,000 year event is also associated with the onset of a period of very cold weather (a stadial) which is the whole point of the article by Chiefio – and the claim that we are approaching the end of the current interglacial period. Muller see earth processes, such as subduction and plate tectonics, as the external vector, and never mentions anything on a cosmic scale.
In association with such geomagnetic behaviour we may note that it is acknowledged greater amounts of radiation reached the surface of the Earth – leading to an increase in Beryllium 10 and an injection of C14 into the atmosphere. In other words, a C14 plateau event – as noted a few days ago in the piece on the 40,000 years ago catastrophic event. A weakening of the geomagnetic field is then supposed to have led to less resistance to the solar wind – or that is the easy option that springs to mind. The Wiki author does not envisage problems for humans and animals as a result of excursions – which is rather strange as there was a massive die-off event around 40,000 years ago. He is of course only looking at two factors, the geomagnetic event and the cooling climate that followed in its wake. Humans clearly seem to have come through the various cooling episodes and have managed to survive and proliferate. However, human numbers probably did decline – as evidenced by the disappearance and absorption of the Neanderthals. Rampino, in a GSA study (see the Chiefio in the link above) claimed changes in sea level – or what he calls a redistribution of water mass – can cause rotational instabilities that led to the magnetic excursion. What are rotational instabilities – a recognition perhaps that the axis of rotation can change? We might ask – what came first, a rearrangement of the boundaries of the oceans, or an excursion event. Something must have caused a redistribution of the water in the ocean basins (a rearrangement of the geoid for example) which in turn provoked an excursion (followed by a sudden and deep cooling event). Such a vector is not being discussed – at least, not in the open or in public view. The effects of the vector have been seen in the geological record – we might hazard a guess.
Geomagnetic reversals (http://en.wikipedia.org/wiki/Geomagnetic-reversal) differ as they can last for very long periods of time – between such events. On average, we are talking about a figure of 450,000 years between events – even though the last one has been dated 780,000 years ago. Suffice to say excursions are more numerous than reversals. However, we are then informed a brief reversal occurred as recently as 41,000 years ago, the so called Laschamp geomagnetic event. This appears to be none other than the 40,000 years ago event – distanced by an additional 1000 years in order to not mention the other in any discussion. Suddenly, the 40,000 year event is looking a whole lot more catastrophic – a reversal (though it is described as brief) as well as a sudden and drastic drop in temperature – and a massive die-off of animals and humans (and an outbreak of extraordinary volcanism).
Interestingly, the Younger Dryas event has been connected with an otherwise erratic geomagnetic anomaly, the so called Gothenberg event. It is known solely from sediments from the botanic gardens in Gothernberg, Sweden, and nowadays is disputed – as it has not been seen (or acknowledged as seen) anywhere else. It is described as the Gothenberg flip (so was it a reversal – or a wobble at the Poles?). Firestone et al, in their book, 'The Cycle of Cosmic Catastrophes', said that events with a direct cosmic association occurred at both the Younger Dryas boundary and at 40,000 years ago (or thereabouts). We also know that both events were followed by a cooling event – very cold temperatures. These can be catalogued as major events – but there are also what we might call smaller episodes of cooling that might likewise have an association with cosmic intrusions into the atmosphere, all the way down to the Little Ice Age where there is abundant documentary sources telling us of heavy meteoric activity and the appearance of comets in the sky that appear to have loomed larger than any in recent years. EM Smith, on the other hand, is currently thinking in terms of solar activity – waxing and waning. Tall Bloke has a similar fixation – and so do many others. We are currently in a low sun spot period and yet the temperatures have not plummeted. This suggests other factors should also be taken into account. However, EM Smith redeems himself as he adds, 'some of the electric universe stuff' may play a role. He has promised to keep digging away at the subject.