I would like present some composite graphic for some period of time.
I got this graphics from two different sources and considering they were closely related I put them close together. I got a list of volcanoes and put a red circle to see if it could be seen any correlation.
It is worth of notice to see Milankovitch curves of insolation present a poor correlation with the temperatures in this graphic 1.
A mystery to solve is why the dust we see in the graphic, suddenly settled as much as to permit sunlight to heat the dirt snow and ice, so much and so long as to rise the temperature. For if the start of a dusty period could be explained by the explosion of a great volcano, plus the dust caused by the extended deserts, this state could remain this way forever. But in the graphic we see it suddenly falls down.
We need of some special phenomenon that could explain the sudden fall of the dust. And this explanation could be the rains. But how could had been enough rains to settle down the dust? The cold caused by the shade of the dust is a serious antagonist of the rains. I am theorizing the possibility of some abnormal increase of sun’s radiation lasting some centuries or more. The increase in radiation could heat the surface of the oceans and start a period of rains. Those rains could bring down the dust in the atmosphere.
I am thinking of an increase of radiation, much higher than the one postulated by Milankovitch curves. I mean, the differences in radiation explained by the Milankovitch curves are too small to change the situation caused by supervolcano Toba, by example that lasted 1,500 or 1,700 years.
So, I had read about some cycles of some frequency or other. Counting the sudden spurts of temperature, or more modest bumps up, on the graphic for some 60,000 years, I can guess there is a cycle of 1,250 years. I used this period, for it is the easier to see or to count.
But in some graphic of high resolution, like this one, we can have another idea.
It is easier to calculate the cycles length of cold and warm and how long it takes for a sudden rise in temperature to surge up. Just counting the peaks we can see almost 10 in this graphic. So, 20,000/9=2,222 years. It is evident that the cycles are not regularly spaced for can be as short as 1,500 years and as long as 2,500. The graphic suggest a sudden spurt of solar radiation lasting a few centuries can produce a sudden jump in temperature. How? The oceans warmed up and they began to produce some rains and clear the air of dust. With the dust out most of the sunlight is able to reach the surface of the earth. Then it melts the thin layer of dirty snow and ice covering latitudes between 45 and 55 degrees of latitude. After reaching some maximum heat the system looks like normalized, but it is not so normal. For the radiation of the sun radiation had come down again to normal values. What does mean? It start to snow again on higher latitudes. With each year, the snow covered land increases and also increases the albedo of the planet. Then it slowly comes back to the colder temperatures, as more and more surface is covered with snow. As the surface covered with snow grows up the temperature of the planet comes down again in 1,500 or 2,000 years.
Perhaps we can consider the case of the most recent past; some 10,000 years since the last Ice Age finished. Here we have a copy of the graph GISP2
If I were to count cycles here, I will have a problem. But if we take this counting a little elastic, I can count 9 cycles, or perhaps 6, not taking the peak of the present time. So, 11,000/9=1,222 years or 11,000/6=1,833 years. The jump in temperature from the year 11,000 BP and the year 10,000 profited of the ice and snow being too dark for the dust accumulated during the Younger Dryass. It can be postulated that Emmons Lake in Alaska and some unidentified source of sulfur in the ice cores of Greenland, 11,258 years ago could had caused an increase in dust. In any case, if we choose to consider longer cycles, like 1,833 years, we can can imagine as well, some of the longer peaks were divided in two by a few powerful volcanoes. By example between 5,000 and 6,000 years ago, the Pinatubo exploded and also Pago and Taal in Philippines. Or the same for the period between 6,500 and 8,000, four powerful volcanoes broke in two the imaginary peak.
The cycles are not so precise, as you can see in the graphic. I need to revise the marks of those volcanoes in the graphic, to see I only used the most powerful of them; VEI 6 or 7. I made the annotations of these volcanoes in this graphic some years ago. I have to look for new lists of volcanoes to see if any is more complete.
The importance of the volcanoes can be variable, depending on the power of each one, or the coincidence of several of them in a short span of time. Other question is what sort of volcano it is. If it is a shield volcano like Hawaiian ones, or stratovolcanoes or other. It depends on the viscosity of the lavas to determine the power of some explosions.
In graphic 1 I had been measuring how long lasted the cold caused of volcano Toba 2.
I measured some 1,700 years of cold after the explosion, measuring the gap for dust and heat. Of course humans could had survive in some privileged sites of the planet after a Toba 2 like explosion. Some place near the equator and some place out of reach of the explosion. But what happened with the cold? After some 1,700 years the temperature rose in Greenland, as GISP2 show, you can watch the see-saw of rising and falling of temperatures, also called as Dansgaard-Oeschger cycles during the last 100,000 years. (Graphic 2). So, according to this graphic, the periods of cold lasted about like a 1,000 years or more. The mystery is to understand why the dust settled down so the sunshine could heat the earth surface to melt the dirt snow and ice, (see graphic 1).
In graphic 1, the green line represents the dust measured in the ice cores. The line of dust (green) is inverted respect to the line (red) of temperature.
Someone commented dismissing the importance of Toba explosion, and it is common sense that for some volcanoes are are not necessarily catastrophic. But I read some paper commenting that even in East Africa and Arabia peninsula also fell some tephra from Toba. But most of the tephra fell in the opposite direction, towards north-east if I remember correctly. It covered in ash most of India with a meter layer. Then, it is evident that humans survived ice age, but the question is where, how, and in which latitude they survived.
For some range of cold in high latitudes, grass can survive and perhaps thrive. Then some giant herbivores can eat this grass, and some humans could hunt them. We can consider if the great mammoths were living permanently in Siberia in high latitudes during the cold periods of the last ice age, or only on the hotter periods. Perhaps they migrated to the south during the colder periods, or just the opposite; they migrated from south to north as temperatures were rising.
I imagine a situation in which we would speak of a relative extinction, and extinction for some places, some latitudes, and some desert areas. The graphic 2 shows some peaks of higher temperature lasting only 1,000 years. Then, I imagine the possibility of humans living out of shellfish and some fishes when the cold was extreme. Most of the Neanderthals went extinct after 40,000 years ago in Eurasia. This coincide with a couple of volcanoes of great power, Uzon Geizernaya (Kamchatka) and Phlegreant Fields (south Italy). The case of Uzon Geizernaya volcano (Kamchatka) was special, for it expelled out 1,700 Km^3 of tephra; this is about 60% of the last Toba eruption. See graphic 1. The case for the Phlegreant volcano’s power was recently estimated much higher than previously thought for white tephra fell so far off as Georgia, on the easter coast of the Black sea. It showed a meter of thickness of white tephra. Some consider it could had reached as far off as the south of Urals.
The question is, how humans survived to those extremes of cold? Simply dying on the worse places, and merely surviving in the best places. There is some papers about
I recalled to have read an article that told these people lived there 75,000 years ago, and they had been living in a cavern near the sea. I recalled they had left a huge mountain of shells, refuse of what they were eating, shellfish and some fishes. So they were thriving because the sea was providing them with food in times of extreme cold. According with the prosy temperatures of GISP2 in Greenland, the extreme cold after the Toba eruption lasted some 1,500 years or more.
And with extreme cold, the deserts grow a lot in extension while the forest in the equatorial belt were shrinking by the scarcity of rains.
While Neanderthals were considered extinct after 40,000 years ago, they really survived till some 35,000 BP in some caves of Gibraltar. They were probably surviving on shellfish and fishes as well as the people living in South Africa. Then, why the Neanderthals of Gibraltar become extinct? I suppose they were the only Neanderthals surviving in Europe, and they could had died after a red tide had poisoned them. This is the risk we incur when eating exclusively shellfish and fish. A red tide can kill us.