Throughout Earth's geological history, the climate has oscillated between two primary states, which many call "greenhouses" and "icehouses." Both states of climate last for millions of years and are not to be confused with the glacial periods and interglacials, which occur as alternate phases of ice ages. The average temperature in the "greenhouse" and "ice house" periods has been 25℃ and 5℃.
There are five known "icehouse" periods in Earth's climate history, namely the Huron Ice Age, the Cryogenian Ice Age, the Andean-Saharan Ice Age, the Karoo Ice Age, and the Pleistocene Ice Age, the last of which has not concluded yet.
"Ice house" periods last millions of years. For example, the Cryogen Ice Ages lasted 85 million years, the Andean Saharan 30 million years and the Karoo Ice Age 100 million years. The Earth's current Pleistocene Ice Age has so far only lasted a few million years, and it probably has many millions of years left in its lifetime
As mentioned, ice ages are characterized by alternating phases, which are the real glacial periods, and interglacials, the latter of which has temperatures that are favorable for humans. Interglacials have a characteristic lifespan of just over 10,000 years, although some have lasted longer.
All human civilizations are now taking place in such an interglacial period that we call the Holocene, which has already lasted 11,000 years. It will most certainly end in a few thousand years, and the ice and cold will return. It is of considerable interest to predict more accurately, when that will happen.
1. Ice Age
This article is about the Pleistocene geological period, which is part of the Quaternary era. The Pleistocene is an ice age period, which is characterized by the climate alternating between actual ice ages and shorter and milder interglacials. We still live in the Quaternary, as the period has not concluded.
The Pleistocene is the earliest and largest part of the Quaternary, and it is the subject of this article.
Timeline of Earth's geological periods. Time progresses from right to left. The glowing inferno just after Earth was formed is called Hadal. Water vapor condensed in the Archean, and an atmosphere of nitrogen and methane arose along with the first rocks that we know of. In the Proterozoic, cyanobacteria produced oxygen, which oxidized iron and methane, at the end of that period life appeared on the sea floor. The entire period prior to the Phanerozoic is often called the Precambrian, as it was previously believed that life arose in the Cambrian with the appearance of trilobites.
The Phanerozoic refers to the era in which visible tangible life has existed. It is divided into the Paleozoic, Mesozoic and Cenozoic periods, which are popularly called the ancient, medieval and modern times of the Earth.
The Paleozoic is the period of early life; The Mesozoic is the age of dinosaurs and the Cenozoic is the age of mammals.
The Cenozoic is further divided into the Paleogene, Neogene and Quaternary, the last of which is not completed and thus represents the present.
Originally, the Cenozoic simply consisted of Tertiary and Quaternary, where Tertiary means the third (time) and represents the period of mammals without humans, and Quaternary means the fourth (time) where not only mammals existed, but also humans. However, in 1968 the International Stratigraphic Commission divided the Tertiary into Paleogene and Neogene, thus reducing the name Tertiary to a popular and literary term.
Quaternary is divided into Pleistocene and Holocene. The Pleistocene is what we generally refer to as the Ice Age, when North America and Northern Europe were covered by kilometer-thick glaciers, very similar to those we still have in Greenland and Antarctica. Holocene is the present.
For reasons that are not fully understood, the pleistocene glaciers partially melt away every 100,000 years, giving way to milder periods that we call interglacials, of which we have already had at least 10. They usually last a good 10-12,000 years.
For the last 11.000 we have lived in such an interglacial period, which we call the Holocene. Climatically and geologically, it is nothing special, we have already had many of these interglacials. The Holocene will probably also end in a few thousand years, and the cold will come again.
That is why the International Stratigraphic Commission tried, also in 1969, to have the Holocene incorporated into the Pleistocene, where it rightly belongs climatically and geologically, since it is simply a natural part of the coming and going of glaciations in the Pleistocene. But their proposal was rejected by the assembly.
The point is that the Holocene is historically and culturally something very special. All of known world history has unfolded in the Holocene, from the first reindeer hunters, through the Egyptian and Babylonian civilizations, the Greek city-states, the Roman Empire, the Germanic migrations, the Renaissance, the great discoveries, the industrial revolution, the two catastrophic world wars and the first manned lunar voyages. Therefore, we cannot bring ourselves to reduce the Holocene to an ordinary interglacial. Own work.
The Pleistocene is the period in Earth's history that we commonly call the ice age, because throughout a large part of the period, the northern and southern regions of the Earth were covered by kilometer-thick glaciers. At the same time, it is important to make it clear that the Pleistocene was a series of actual ice ages, separated by relatively short interglacial periods. The period started 2.6 million years ago and lasted until the end of the Weichel Ice Age just over 11,711 years ago.
Timeline of Earth's past and present ice ages. On this timeline, time progresses from left to right. The known ice ages in Earth's climate history are the Huronian and the Cryogenian, which are the Stuartian, Marinoan and Gaskier ice ages. In the Phanerozoic, which is the period, when there was life on Earth, the Andean-Saharan Ice Age occurred first and later the Karoo Ice Age; the Pleistocene ice age period is called "current". Photo William M. Connolley Wikipedia.
Several times earlier in Earth's history, huge glaciers have covered large parts of the northern and southern continents.
Already at the beginning of the Proterozoic, the Huron Ice Age occurred, where at least three ice ages succeeded each other over the course of most of a billion years.
The period, the Cryogenic Ice Ages, occurred at the end of the Proterozoic and lasted just under a hundred million years. They are believed to have been colder than the Huronian Ice Age. One of the Cryogenian ice ages was the Stuartian, which lasted 57 million years. Another was the Marinoan Ice Age (which is also called the Varanger ice age after the Norwegian peninsula where it was first detected), which lasted 22 million years. Some researchers believe that the Earth was at times a "Snowball", i.e. covered in ice and snow from north to south, although there is debate as to whether there was a small band of free water at the equator. Another Cryogen Ice Age was the Gaskier Ice Age, which lasted only 340,000 years.
The Andean-Saharan Ice Age (also called the Hirnantian Ice Age) occurred at the transition between the Ordovician and Silurian periods and lasted 30 million years. The Karoo ice age at the transition between Carboniferous and Permian lasted 100 million years.
No one knows how long the current Pleistocene Ice Age will last, but by all accounts it is geologically just beginning and will probably last for millions of years to come.
The Pleistocene Ice Ages are a natural continuation of the cooling of the Earth that has taken place throughout the Cenozoic. Time progresses from left to right. The horizontal axis is millions of years before present and the vertical axis is the temperature of the deep sea from the frequency of the oxygen isotope O 16. Graph James Hansen, Makiko Sato, Gary Russell and Pushker Kharecha Wikipedia.
The cold climate in the Pleistocene is a natural continuation of the last 55 million years of falling temperatures.
Two conditions in particular were decisive for the formation of the large glaciers.
One was that the temperature dropped so much that the snow did not melt in the summer and thus could accumulate year after year.
The second was that the Earth's continents were positioned in such a way that warm ocean currents flowed to the north, giving off their heat and moisture as precipitation in the form of snow.
The entire Quaternary period is often referred to as an ice age, because two large permanent glaciers continuously existed, namely in Antarctica and Greenland. During the coldest periods of the Pleistocene, also called ice ages, huge glaciers existed in Europe, North America and Patagonia in the southern hemisphere. The shorter and warmer intervals between the recurring Pleistocene ice glaciations are called interglacials.
During long periods, 30% of the Earth's land mass was thus covered by blinding white ice and snow, and thereby the Earth's albedo increased dramatically, and a very large part of the solar radiation was reflected back into space, which further enhanced the cooling.
At geological congresses, it has been agreed that the last Pleistocene ice age, the Weichel Ice Age, ended 11,711 years ago, and we have defined that the present is a completely new period called the Holocene. However, we cannot define and decide apart from the fact that the current Holocene warm period is an interglacial, of which there have already been many. With great probability, the ice will return to the northern and southern parts of the World's continents; we just don't know when.
2. The pleistocene glaciations
The glaciers came and went during the Pleistocene. The period was really a series of glaciations interrupted by brief periods of warmth. There were at least 10 cycles of such thrusts and retreats of the ice masses. During the glaciations, the global average annual temperature was 5-10℃ colder than today. A large part of the world's water was locked up in giant ice sheets for long periods. The water level in the World Ocean became very low, and dust storms ravaged the continents.
The graph shows the temperature in the Quaternary as a function of time, progressing from right to left, from past to present. The Quaternary period is divided into the Pleistocene, which is by far the largest part of the Quaternary, and the Holocene, which is the present since the end of the last glaciation.
The Pleistocene lasted 2,576 thousand years, namely from 2,588,000 to 11,711 years before the present, when the Weichel Glaciation ended.
The curve is produced by manipulating the graph from
Wikipedia
The scale on the left is the result of analysis of ice core drilling at the Russian Vostok station in Antarctica and shows the temperature on the surface of the ice as a deviation from the present temperature (0), and the scale on the right shows the isotopic ratios that have come from the analysis of sediments on the seabed, as the amount of the heavy oxygen isotope oxygen-18 indicates the temperature when the bottom layer was formed.
Note the increasingly pronounced temperature fluctuations between actual glaciations and interglacials. Note also that the temperature is generally decreasing from the Tertiary down towards the present. In the first one and a half million years, an actual glaciation lasted about 41,000 years, while in the last 800,000 years, the actual glaciations have lasted about 100,000 years each.
The dotted line at the temperature 4℃ below today represents the approximate temperature when the Weichel Ice Age ended 11,711 years ago. Dragons flight (Robert A. Rohde) Wikipedia.
It has been defined that the Weichel glaciation ended a good 11,711 years ago, when the temperature on the surface of the ice sheet was around 4℃ lower than today. If we draw a horizontal line through the Pleistocene temperature graph at 4℃ lower than today's temperature, we will very roughly be able to distinguish actual ice age from non-ice ages according to the same definition (see graph above).
Water level in the World Ocean over 800,000 years according to various researchers. Murray-Wallace and Prazzoli have made some point-by-point assessments, while the other researchers have drawn up more or less comprehensive curves. The assessments differ from each other, but the trend is more or less the same. During interglacial periods it is warm and some of the ice at the poles melts, thereby raising the sea level. During the glaciations, large amounts of the globe's water are bound as ice sheets at the poles, and the sea level drops again. The difference between interglacials and glaciatio ages is well over 100 metres. Graf M. Siddall, J. Chappell and E.K. Potter "Eustatic Sea Level During Past Interglacials".
It is thereby seen that the temperature in the first one and a half million years of the Pleistocene was lower than today's, but most of the time higher than 4℃ below present temperature. Apart from some cold periods of relatively short duration, the entire early period cannot therefore be described as an actual ice age climate based on our simple definition.
Reconstructed North European landscape from the last part of the early Pleistocene - Cold and harsh, but for long periods without ice. It is assumed that the glaciers reached southern Scandinavia and northern Europe only around 800,000 years before the present. Photo unknown origin.
One must assume that the climate in Northern Europe at the beginning of the Pleistocene has for long periods been similar to the climate in the first 1-2 thousand years of the Hunters Stoneage, when the temperature was at the same level. The landscape was then characterized by an open and bright birch forest, interspersed with trees such as aspen, willow, rowan and pine. The animal life may have been something with bison, wild horse and elk. These are mere conjectures; we will never have any definite knowledge as all traces have been erased by later huge glaciers.
At the beginning of the Pleistocene it was cold, but not extremely cold. Relatively small glaciers appeared at regular intervals, which may have been confined to northern Scandinavia, the Norwegian mountains, northern Canada, and probably some arctic islands. The cycle time between warm periods was 41,000 years. The temperature difference between cold and warm periods was about 4℃ or less.
The graph shows variations in the frequency of oxygen isotopes between glaciations and interglacials during the middle and late Pleistocene. It is drawn up based on analysis of oxygen isotopes in sediments on the seabed.
MIS stands for Marine Isotope Stages in the Pleistocene. Even numbers stand for cold periods, i.e. glaciations, and odd numbers stand for warm periods, including interglacials
Oxygen has two naturally occurring isotopes, namely O-16 and O-18.
O-16 makes up 99.762% and has 8 protons and 8 neutrons, for a total of 16. O-18 makes up 0.2% and has 8 protons and 10 neutrons, for a total of 18.
When water evaporates, water molecules containing the light isotope will evaporate faster than water molecules containing the heavy isotope. Building ice sheets on the continents requires the evaporation of a lot of water from the ocean, which then accumulates as ice on land. The ice will be enriched with the light isotope, while the remaining water will be enriched with the heavy isotope. The O-18/O-16 ratio in seawater must therefore have been higher in glaciation periods than in interglacials.
The isotope ratio in organisms with shells (e.g. clams) reflects the isotope ratio in the water when they lived. When they died, they sank to the bottom and became sediments on the sea floor.
In drill cores from the seabed, you can find the preserved shells, measure the isotopic ratio and thereby get an indication of the extent of ice on land when the organisms lived. Graf Michael Houmark Nielsen, Institute of Geology. Clean drawing Annabeth Andersen Geus.
It can also be seen that during the later part of the early Pleistocene, that is between 1.8 and 0.8 million years before the present, it became somewhat colder, and the temperature variations between cold and warm periods became greater. More than half of the time the temperature was below 4℃ lower than the present and thus, according to our definition, an actual ice age climate. During the Ice Age periods, the glacier margin in Europe may have stood along the Norwegian coast and the Swedish lakes. The cycle time between cold and warm periods was still about 41,000 years.
The maximum extent of the Elster, Saale and Weichel glaciations in Europe. Photo Wikimedia Commons.
The landscape of northern Europe may have been tundra, as it is known today from northern Russia. But as I said, we have no certain knowledge, as kilometer-thick glaciers have since erased all traces.
But 800,000 years ago it became serious. The cycle time between cold and warm periods changed to 100,000 years, and the temperature difference between glaciations and interglacials grew to about 9℃ measured on the surface of the ice. At the equator the difference was not so dramatic. Kilometer-thick glaciers stretched far down into Europe and America, all the way down to the 40th parallel. Throughout much of the last 800,000 years, North America, southern Scandinavia and northern Germany were covered by ice sheets. The northern European ice sheet is called the Fenno-Scandinavian ice sheet and the North American one is called the Laurentide ice sheet. Only during the short interglacials was the area free of ice.
In the southern hemisphere there were glaciers in Argentina, New Zealand, Tasmania and in Antarctica not to be forgotten, and a short-lived small glacier in the mountains of southern Australia.
Most believe that it was not until the period known as the Cromer Complex that the glaciers of the ice age reached southern Scandinavia.
In North America, the glaciers of the Weichel Ice Age covered a much larger area than in Northern Europe. The Laurentide glacier was more than four times the size of the Fenno-Scandinavian ice sheet. In North America, the Weichel is called the Wisconsin. Photo Idaho Museum of Natural History - Svendsen 2004.
The various glacial advances and the associated interglacial periods are named differently in North America, Scandinavia and the Alpine countries, and there also seems to be disagreement about the sequence and duration of the glacial advances. Here we will stick to designations used by the Geological Institute in Copenhagen.
At the maximum extent of the glaciers, they bound large amounts of the globe's water as ice sheets, and therefore the water level in the seas fell up to 120 meters below today's level.
Traditionally, the last 800,000 years of the Pleistocene are divided into the Cromer, Elster, Saale and Weichel ice age periods.
Cromer is named after a town in Norfolk, England. Cromer was originally thought to be an interglacial, but later research has shown that the period contained 6 glacial advances and as many interglacials, depending on how they are defined. How far the Cromer Ice Age glaciers advanced is not known in detail. But at least one of Cromer's ice ages reached the Don River in southern Russia (MIS 16).
The spread of the Weichel Ice Age at the Last Glacial Maximum (LGM) 18-20,000 years ago - The ice mainly covered the British Isles, Scandinavia and the Baltics as well as the Barents Sea, whereas northern Russia was free of ice. Photo Jan Mangerud Wikimedia Commons.
Elster was a very harsh ice age period. It is named after the town of Elster in Sachen Anhalt in Germany. It lasted perhaps from 480,000 to 400,000 years before the present. In Europe, the ice reached London and Slovakia. In North America, the ice reached all the way down to the American state of Kansas.
The Saale Ice Age began about 380,000 years ago and ended 130,000 years ago. It is named after the river Saale, which is a tributary of the Elbe. Previously it was assumed that the Saale was one single ice age, but later research has shown that the period contained at least 3 glaciations and a corresponding number of interglacials. The Saale ice covered the entire Baltic Sea area, northern Germany and the northern part of the British Isles. In Russia, the ice reached all the way to the river Volga and the Ural Mountains.
The Weichel was the last glaciation, beginning 117,000 years ago and ending 11,711 before present. It is named after the river Weichel in Poland. In the early Weichsel, the ice was limited to the Scandinavian mountains and large parts of southern Scandinavia, and northern Europe lay like tundra with a sparse vegetation of hardy herbs and low shrubs of dwarf birch and willow. Mammoth, woolly rhinoceros, bison, reindeer and musk oxen lived on the tundra.
LGM - Last Glacial Maximum, Older Dryas, Bølling Allerød warm period, Younger Dryas cold period and Holocene. The vertical axis shows average temperature on the surface of the ice and the horizontal axis represents time in thousand years. Time progresses from right to left. Graph of unknown origin.
During its maximum 18-20,000, perhaps 21,000 years ago, the Weichel ice mainly covered the British Isles, Scandinavia and the Baltics as well as the Barents Sea, whereas northern Russia was left free. The precipitation which supplied material to the glaciers in the form of snow came from the North Atlantic and the Gulf Stream, and the moisture was carried overland by the westerly winds. The ice sheet reached a height of 2-3 kilometers in some places and it is easy to imagine that when the westerly wind was forced up over these "mountains" it would deliver its snow there and not much precipitation would be left to the north Russia.
Evidence of human activity has been found in the arctic part of Russia, dated to be 30,000-40,000 years old; they probably descend from Neanderthals. This indicates that there could not have been ice sheets at this time, nor has there been since.
3. The climate in the ice-free part of the world
Landscape in the Pleistocene Park in Eastern Siberia. The landscapes of northern Russia and Siberia must have looked like this. Photo Boards
The temperature during the Ice Age compared to today varied greatly between different places on Earth. In the higher latitudes the temperature difference was far more dramatic than in areas closer to the equator. The cooling was more intense in the center of the continents than it was in coastal areas. For example, analyzes of cores from drilling on the central Greenland ice sheet show that the temperature during the "Last Glacial Maximum" here could be 23℃ lower than it is today, while the temperature in the tropics around the equator only fell by about 5℃ at the same time.
Pleistocene Park is a nature reserve on the Kolyma River in northern Siberia, where Sergei Zimov and his colleagues seek to recreate the ecological system on the Pleistocene steppe - including wildlife in the form of reindeer, moose, wild horses, musk oxen, chipmunks, wolves, bears and many other.
It is known that in the early part of the Weichel Ice Age, no dramatic climate change took place in the area south of the Alps. A pollen collection in Southern Italy at a place called Lago Grande di Monticchio indicates that in the first half of the Weichel glaciation from 117,000 to 75,000 years before present, one could hardly have felt the new ice age there, if there were people. Here the climate remained relatively warm until Weichel finally showed his teeth with his "Last Glacial Maximum". Only a very cold period 85,000 BC of a few hundred years was able to leave its mark on the Mediterranean environment.
Climatic belts on mountain slopes in the Pleistocene compared with the present. It was generally colder during most of the Pleistocene, and therefore all climate belts had shifted downwards compared to the present. Photo unknown origin.
The Pleistocene was mainly a cold period, which is reflected in that
all climate zones were shifted towards the equator compared to today. Especially during the Last Glacial Maximum, tundra and mammoth steppe stretched all the way down to the Alps, and the Mediterranean Sea was surrounded by a sparse growth of pine trees.
Climate zones on mountain slopes were lower than today. In some places, the snow line could be almost 900 meters lower than it is today. In Africa, the now receding glaciers on Mount Kenya, Kilimanjaro and on the Ruwenzori Mountains between Uganda and the Congo were larger. There were also glaciers in the mountains of Ethiopia and to the west in the Atlas Mountains.
From the early Weichsel, two milder periods are known, called Brørup and Odderade, each of which lasted just under 10,000 years. They culminated just less than 60,000 and 80,000 years ago. The Scandinavian Ice Shield melted much, the ice edge retreated, and the sea level rose correspondingly to 25-50 meters below today's level. Plant growth in Northern Europe and Denmark was characterized by open birch forest mixed with pine. Spruce immigrated at the end of the mild periods.
Differences in sea water temperatures between the "Last glacial maximum" and the present in the North Atlantic in August and February differences. Photo CLIMAP 1976.
World sea surface temperatures averaged 4-5℃ lower than today, and the deep sea temperature was 1-2℃ lower than today's 2℃. In parts of the North Atlantic the surface temperature was 10℃ lower than today. There is some disagreement about Pleistocene sea temperatures in tropical waters. Some believe that they were the same as today, while others believe that they were around 2-3℃ lower.
Many researchers believe that the overall climate of the Pleistocene in the Pacific can be characterized as a continuous El Nino.
The sun's heat is strongest around the equator. This leads to rising air and a constant low pressure around the equator. The trade wind is a wind that blows from the tropic towards the equator and seeks to fill this low pressure. There are trade winds both north and south of the equator. Due to the Earth's rotation, the trade winds are deflected to a northeasterly wind in the northern hemisphere and a southeasterly wind in the southern hemisphere.
The sun heats the area at the Equator. The warm air rises into the air, thereby creating a low pressure. Trade winds blow from the area between the tropics towards the equator and seek to fill the low pressure. The winds are deflected to the west by the Coriolis force, as the air comes from an area of lower rotational speed and blows towards an area of higher rotational speed. Photo RA Online Climate and Vegetation.
When it is not an El Nino year, the trade winds in the Pacific thus blow from east to west and thereby "push" warm surface water over to Indonesia. At the same time, nutrient-rich cold bottom water rises off the west coast of America. The high sea temperatures cause large amounts of precipitation in the Indonesian area, and the correspondingly lower sea temperatures on the West Coast of America cause a drier climate.
An El Nino occurs when the trade winds weaken. Thereby the difference in water temperature between the sea off Indonesia and the sea off America is equalised. Indonesia therefore does not get the usual amounts of rain, and America gets more cloudbursts than usual, less rising cold bottom water and thus poorer fishing.
It is thus the Sun's heat at the equator that drives the trade winds and thus the current usual climate in the Pacific Ocean. It is easy to imagine that in a cold period, such as the Pleistocene, the Sun would not warm as much at the equator as it does today, and therefore the trade winds would not be as strong, which could lead to permanent El Nino.
Australia in the Pleistocene. Due to the low water level in the World Ocean, both New Guinea and Tasmania were landlocked with Australia itself. Photo Digital Classroom.
In Australia, in some periods more rainfall occurred in the inland areas than today, in other periods the continent was mainly desert. Lake Eyre covered in wet periods 100,000 km2 and was surrounded by many smaller lakes. Scattered across the continent were areas of rainforest. It is believed that Aboriginal immigration coincided with a wet period between 60,000 and 40,000 years ago.
Before the last Ice Age maximum, North Africa was for some periods greener than today, and the country was home to many species, including many ostriches (Uriarte). The deep parched canyons, now called wadis, had permanent streams. The prehistoric Niger flowed to the north and had an outlet in the Mediterranean.
A large part of present-day Israel and Jordan was covered by a large lake, 250 km. long and 50 km. wide. Today it has shrunken into the Dead Sea.
The humid climate throughout much of the first part of the Pleistocene created many freshwater and brackish water lakes in depressions in present-day Syria, Iraq, Saudi Arabia, Iran, Afghanistan and elsewhere in the now arid Middle East.
In the "Great Basin" of North America, which includes depressions in the desert states of Nevada, Utah, Oregon, California and New Mexico, there were at least 68 large and small lakes during the Weichel Ice Age. Today, only the Great Salt Lake and Pyramid Lake remain, and the former lakes have turned into desert. Some experts believe that they have dried up and regenerated at least 28 times over the past 3 million years.
In the Pleistocene, Lake Bonneville, Lake Lahontan and many other lakes existed in the present desert states of southwestern North America. Photo Washington.edu Natalie Baker.
In Asia, the summer monsoon was weaker than today, but evidence has been found that there were large lakes in the interior of the continent during part of the last ice age. The now-disappeared salt lake, Lop Nor, in the Taklamakan desert, for example, was a large lake at least during part of the Pleistocene.
The jungle in the Amazomas area today gets its rain from the trade winds, which blow moisture into the country from the South Atlantic. But for long periods in the Pleistocene, ocean temperatures were lower than today, and consequently the trade winds were correspondingly weaker, carrying less moisture with them. Much of the area which today is covered by the Amazomas jungle was therefore then open grass steppe.
In Central America and in the coastal regions of Colombia, the tropical rainforests remained essentially intact throughout the Pleistocene - probably due to the very high rainfall in these areas.
In tropical Africa, the temperature throughout most of the Pleistocene was barely 5℃ lower than now. Where today we find the tropical forests of the Congo and along the Gulf of Guinea, was then open savannah. Only along rivers and in particularly humid coastal areas were there narrow strips of tropical jungle.
Landscape forms on the Peruvian-Bolivian plateau, which is called the Altiplano, show that in periods before 28,000 and after about 12,500 until 11,000 years before the present, the lakes covered areas that were about four to six times the size of today. On this basis, it can be concluded that the rainfall in these periods must have been around 50 to 75% greater than today.
4. During the last ice age maximum, the world became cold and dusty
Landscape types and sea temperatures in Europe during the Weichel Ice Age Maximum. In present-day France, Germany and Poland there was predominantly tundra. In Russia and Ukraine lay the mammoth steppe. Only along the Mediterranean and the Black Sea did some pine forest grow. Photo unknown origin.
The Weichel Ice Age started its final spurt about 30,000 years ago. The period between 23,000 and 19,000 years before the present is called the "Last Glacial Maximum" (LGM). It is estimated that about 30% of the Earth's land mass was covered by ice. The glaciers could be between 1.5 and 3.0 kilometers thick at the highest points, and thereby they tied up a very large part of the globe's water, so that the water level in the World Ocean fell to 120 meters below today's level, some say 140 meters.
In most places the climate became cool and dry. Many deserts emerged and others expanded. The Sahara became an actual desert, which spread to the south and north.
During the last ice age maximum, the British Isles, the entire Baltic area, Scandinavia, except West Jutland, were covered by ice sheets. Southern and Eastern Europe lay as icy tundra dotted with mammoths and woolly rhinoceroses. Present-day northern Russia and Ukraine consisted of steppe and prairie. Only in a few narrow strips along the Mediterranean and the Black Sea did so-called boreal forest grow, which is a cool, light and open pine forest mixed with birch and rowan and other shrubs and trees.
Landscape types and sea temperatures in North America during the Weichel Ice Age Maximum. Note that the American tundra belt was not nearly as wide as the European one. South of the tundra belt, the vegetation was different depending on the height above sea level, mostly different open pine forest. Only along the Mexican Gulf was real deciduous forest. In the present southwestern desert states lay large lakes. Photo unknown origin.
In most places it was very dry. Dust storms must have been much more common during the cold periods of the Pleistocene than they are now. The cold and thus dry winds that blew down from the glaciers eroded tundra areas and transported fine-grained material, called loess, to more humid, vegetated areas, where it was trapped and deposited. The thickness of the loess layer varies greatly and is in some places over 100 m. Loess from the then Arctic regions was deposited in Central Europe, where it formed the so-called loess belt, which stretches from southern Belgium to the east. In Ukraine, South Russia, North China and the USA there are also large areas of loess.
Thick layers of loess in North China, perhaps in the northern parts of the provinces of Gansu, Shaanxi or Shanxi. Photo Tansuo Cultural Travel Solution.
Loess soils are some of the world's most fertile arable soils, because loess is very nutrient-rich and has great water-holding capacity. At the same time, it is easy to process, but sensitive to erosion.
A zone of permafrost extended south from the edge of the ice sheet. In North America, the permafrost zone was about a hundred kilometers, and in Eurasia it was several hundred kilometers. The annual average temperature at the edge of the ice sheet was minus 6℃, and at the edge of the permafrost belt it was 0℃. This must be compared with Denmark's current annual average temperature, which today is 8℃, and the entire Earth's annual average temperature, which today is 14℃.
The Ukok Plateau in eastern Siberia is one of the last remnants of the mammoth steppe. Steppe tundra or mammoth steppe was widespread in the Pleistocene in the middle latitudes of North America and Eurasia. It is a very cold and dry vegetation type consisting of mainly treeless open herbaceous vegetation with scattered low shrubs and occasional stunted trees in slightly sheltered locations. Photo Kobsev Russian Wikipedia.
Asia was also very cold during the Weichel Ice Age maximum, but the continent was not covered by glaciers in the main to the same extent as Europe and North America, probably due to the low rainfall in the cold northern regions.
As is still the case today, the Pamir, Tien Shan, Himalayas and other high mountain ranges around the Tibetan Plateau were covered by glaciers. Experts discuss whether there may have been ice sheets on the Tibetan Plateau itself or perhaps parts of it.
North of the Tibetan Plateau, in present-day Siberia and Mongolia, lay the vast mammoth steppe. It was freezing cold, but also dry. The permafrost area stretched all the way down to present-day Beijing.
The water level in the World Ocean from the Weichel Ice Age maximum to the present. Photo Global Warming Art Wikipedia.
It is believed that the climate in Asia was conditioned by two things in particular, namely that the Pacific Ocean and especially the Indian Ocean were warmer than the Atlantic Ocean, and that the Asian mountain ranges stretch in an east-west direction, in contrast to, for example, the American mountain ranges, which typically stretch in the north-south direction.
The high east-west running mountain ranges forced the summer monsoon to release its moisture on the mountain slopes as rain or snow. The proximity of the relatively warm oceans meant that the snow melted during the summer and the water was carried back to the ocean by the rivers. Little moisture escaped over the Pamir and Himalaya mountains, but still sufficient to form the local glaciers of the central Asian mountains.
The land connection between Asia and America during the Ice Age Maximum is called Beringia. The low water level of the World Ocean during the Ice Age Maximum allowed early humans to migrate from Eurasia to the Americas. Photo Pinpage
During the Last Glacial Maximum, the Pacific Ocean was reportedly warmer than the Atlantic Ocean, and the Indian Ocean was warmer than the Pacific Ocean. This is because the Atlantic Ocean had a direct connection with the Arctic Ocean through the waters around Iceland and Greenland, while the Pacific Ocean did not have a corresponding connection with the Arctic Ocean through the Bering Strait, as the fall in the level of the World Ocean had made Asia and America landlocked.
The Indian Ocean extends quite far under the tropical sun and apparently receives more solar heat per unit area on average than both the Pacific and Atlantic oceans. But the exchange of heat between the Indian Ocean and the Pacific Ocean was, due to the low surface level of the World Ocean, obstructed by Sundaland, which made the Indonesian islands landlocked with Eurasia.
The monsoon is a steady wind that blows from sea to land or from land to sea due to temperature differences between land and sea.
Indonesia during the last ice age maximum. Most Indonesian islands were landlocked with Eurasia. The country has been named Sundaland. Photo Maritime Mysteries.
In summer, the sun heats both land and sea, but the temperature on land rises faster than the temperature above the sea. Rocks and soil have a poor thermal conductivity and a small heat capacity, and therefore the temperature on land rises quickly. Water and sea, on the other hand, can absorb far more heat from the same solar radiation, as water has a good thermal conductivity and a high thermal density, and in addition, the heat is quickly distributed by waves and currents in the sea.
When land masses are heated in the summer, the warm air will rise and a low pressure will appear. The warm moist air over the sea will flow in to seek to fill this low pressure and this wind is the monsoon. In winter, the sea is warmer than the land, and the monsoon then blows from the land and beyond the sea.
The larger the landmass that borders the larger sea, the more pronounced the monsoon winds will be. In principle, there can be monsoon winds all over the Earth, but the East Asian monsoon is the best known, because a very large continent borders a very large and warm sea.
Summer monsoon in Southeast Asia. Photo unknown origin.
Also in the Pleistocene, the summer monsoon blew warm and moist air towards the Southeast Asian coast. As the air was forced upward by mountain sides, it poured out its moisture in the form of abundant rain and snow. However, it was so hot in southern Asia on the coasts of the Indian Ocean and the Yellow Sea that the snow melted again during the summer and the melt water was carried back to the sea by the many rivers. Only very little of the moisture managed to escape over the mountains and become glaciers on the high mountains of Central Asia.
South Annapurna Glacier in Nepal. Photo taken from Annapurna Monastery by KarimRi English Wikipedia.
Pollen analyzes from many places in Australia show that during the LGM the climate was extremely dry. The desert extended as far south as northern Tasmania, and a large area with less than 2 percent vegetation cover covered all of South Australia. Forest was largely confined to small protected areas on the east coast and extreme south-west of Western Australia.
Landforms on the Peruvian-Bolivian Altiplano plateau indicate that in periods before 28,000 BC the lakes were about four to six times as large as today. From this it can be concluded that the rainfall in these periods must have been around 50 to 75% greater than today. During the LGM itself, the plain may have been dry and dusty, like so many other parts of the world.
5. Temperature and CO2
Variations in temperature and atmospheric CO2 concentration over the past 400,000 years from analyzes of drill cores carried out at the Russian Vostock Station in Antarctica. The temperature is in degrees Celsius as a deviation from present-day temperature, and the CO2 concentration is in parts by volume per million in absolute numbers. Time progresses from left to right. It can be seen that the CO2 curve is a few hundred years behind. First the temperature rises and then the CO2 content in the atmosphere rises. Photo Research Gate uploaded by J. Marvin Herndon.
Thanks to analyzes of air bubbles found in drill cores from Greenland and Antarctica, we know that the concentration in the atmosphere of greenhouse gases such as CO2 and methane has varied throughout the most recent part of the Pleistocene. There is a striking correlation between CO2 and temperature. When it was cold, the CO2 content in the atmosphere was quite low, and at higher temperatures the CO2 content was also high.
There is actually a very fine correlation between CO2 and temperature, which was a main message in Al Gore's 2006 film "An Inconvenient Truth". Gore believed that it was self-evident that the varying content of the greenhouse gas CO2 in the atmosphere was the cause and the temperature variation was the effect.
Al Gore in the movie "An Inconvenient Truth". Photo New Tork Times.
"An Inconvenient Truth" won an Oscar in 2007 for best documentary. In 2007, Al Gore, together with the UN Climate Panel, was awarded the Nobel Peace Prize for their work in raising awareness about the emission of CO2 and the resulting man-made climate change.
The good correlation between CO2 and temperature became an important argument for the campaign against what is called man-made climate change. It was believed, and it is still believed, that when the CO2 concentration in the atmosphere could thus cause glaciations to come and go, then an increase in the CO2 content, created by modern industrial society, would cause an uncontrolled and catastrophic increase in temperature, the so-called AGW "Anthropogenic Global Warming" (Anthropogenic means man-made).
However, at this time analysis of ice cores was still in its infancy. Since then, more sophisticated methods of analysis have shown that CO2 and temperature do not correlate completely throughout the last 800,000 years of the Pleistocene. It has been shown that the CO2 graph was slightly behind each time. The CO2 content of the atmosphere always had a maximum 200 to 800 years after the temperature maximum. In other words, there is much to suggest that the temperature was the cause and the CO2 content of the atmosphere was the effect, which is the complete opposite of what AGW supporters claim.
An interglacial between two Saale ice ages 237,500 years ago. It is clear that the CO2 maximum is 800 years after the temperature maximum. From the BBC broadcast "The Great Global Warming Swindle".
We must assume that during cold periods large amounts of CO2 were dissolved in the oceans. When the temperature rose, the world's oceans could no longer hold as much CO2, and the excess was eventually released into the atmosphere. The world's oceans constitute an enormously large volume of water, and all processes therefore take a long time. It is not unreasonable to assume that it takes hundreds of years for the ocean to adjust the amount of dissolved CO2 to a new temperature.
The world's oceans can dissolve very large volumes of CO2. As we know from cola and soft drinks, large amounts of CO2 can dissolve in water. One liter of cola contains more than two liters of CO2 at normal pressure and temperature. If we heat the cola, CO2 will escape as bubbles because CO2 cannot dissolve as much in hot water as in cold water.
6. Milankovitch's astronomical climate theory
The Serbian engineer Milutin Milankovitch developed a theory during the First World War that the ebb and flow of ice ages is due to small, cyclical variations in the Earth's orbit around the Sun. The theory has today gained wide recognition because it fits so well with the temperature variations found throughout Earth's history.
The three Milankovitch parameters, which are the precession, the axis tilt and the eccentricity. Photo Universe Today.
The Milankovitch theory is based on three basic cycles in the Earth's motion around the Sun. They are the eccentricity, axis inclination and precession. These parameters are created by gravitational forces from the Sun, Moon, Jupiter, Venus and the other planets. Photo Universe Today
The precession is the shortest Milankovitch cycle. Consider a spinning top that is coming to a standstill. For a few seconds before it topples, it will wobble and the upper end of its axis of rotation will begin to describe a circle. It is called axial precession. While a spinning top precesses all the way around in less than a second, larger tops will precess more slowly. The Earth is a very large spinning top, it precesses one cirkel every 25,772 years. The precession was mentioned as early as 120 BC. by the Greek astronomer Hipparchus, who found a discrepancy between his own observations and earlier Babylonian records from 4,000 BC. In 12,000 years from now, due to the precession, the Earth's axis will point to the star Vega instead of Polaris, and the Northern Hemisphere will experience summer in December and winter in June.
The precession. Photo mungfali
The axis tilt is another Milankovitch parameter. We know that the Earth rotates around its own axis, which is why we have night and day. The axis is not vertical to the plane of the earth's orbit; today it inclines 23.5 grader vertically from the plane of the earth's orbit, which is the cvause of the seasons. But this angle varies between 22.1 and 24.5 grader over a period of approximately 41,000 years. It will thus take 41,000 years for the axis to move from minimum to maximum position and back again. The greater the angle, the more pronounced the seasons will be. With a large axis tilt, the Earth will experience hot summers and cold winters, and with a smaller axis tilt, the winters will be not so cold and the summers not so hot.
The third Milankovitch parameter is the eccentricity of the Earth's orbit. The Earth's orbit around the Sun is roughly circular, but it does not form a perfect circle, but rather an ellipse with the Sun at one focal point.
Eccentricity is given as a number between 0 and 1. For a perfectly circular orbit, the eccentricity is 0. The eccentricity of the Earth's orbit ellipse fluctuates between nearly 0 and 0.06 and back again over a period of an average of 100,000 years. At the same time, the entire ellipse revolves around the Sun. Today, the eccentricity of Earth's orbit is about 0.017; which is very close to a circle.
The axis inclination. Photo mungfali
Between 120,000 and 90,000 years ago, the eccentricity was about 0.04, and the difference in the incoming solar power was about 14-17% between Earth at maximum and minimum distance from the Sun, respectively. Nowadays, the difference is approx. around 7%.
But there is another factor that must be taken into account. Namely this, that when the Earth in its elliptical orbit is near the Sun, it will move faster than it does when it is farthest from the Sun. Thus, the incoming solar energy per unit of time will indeed be high at the focal point near the Sun, but due to the increased speed of the Earth, it will not stay there for such a long time; therefore, the difference in the total received solar energy between maximum and minimum distance from the Sun in a maximum elliptical orbit is significantly smaller than the 7%, namely only approx. 0.3%. The Earth's increased speed near the Sun is described by Kepler's 2nd law of planetary motion, namely that the radius vector (the line between the Sun and the Earth) covers equal areas in equal periods of time.
The eccentricity of the Earth's orbit. The shape of the Earth's orbit oscillates between nearly circular and somewhat eccentric and back again over a period of about 100,000 years. Photo apollo.edu.
It is clear that the Milankovitch theory applies. At the beginning of the Pleistocene, a glaciation cycle lasted 42,000 years, which is very close to the axis tilt cycle of 41,000 years. Only 800,000 years ago began a series of ice ages with periods of 100,000 years, which is the cycle time of the eccentricity.
The eccentricity is the only one of the three Milankovitch parameters that makes any difference in the total amount of solar energy the Earth receives because the distance to the Sun varies. Seen from the Sun, the Earth is a disk with a diameter of about 12,760 km, and no matter in which direction and how much its axis of rotation tilts, this disk will receive the same amount of solar energy when the distance from the Sun is the same. If the northern hemisphere receives less solar energy, the southern hemisphere will receive something almost correspondingly more.
But the Milankovitch theory does not deal with the total amount of solar energy that the Earth receives. What matters is the incoming solar energy at the critical time at the critical location, and that is the month of June at 65 degrees northern latitude.
The critical area around 65 degrees northern latitude is to a very large extent covered by land masses on which ice can build up. Photo NASA Terra satellite Meow Wikipedia.
Milankovitch believed that the northern hemisphere is climatically controlling compared to the southern because the northern is dominated by large land masses on which ice sheets can build up; while the southern hemisphere is dominated by sea. The solar heat in the month of June is critical, because the summer sun must be sufficient to melt the winter ice and snow, otherwise it will accumulate year after year and form ice sheets.
A Scandinavian landscape covered in snow and ice will reflect a very large part of the solar radiation back into space. Photo NASA's Terra satellite NASA visible Earth.
A belt around the Earth along the 65th parallel just south of permanent sea ice is the critical place, because if ice sheets are allowed to spread to this area, it will trigger some feedback mechanisms that will further contribute to the cooling of the Earth.
Ice and snow are blindingly white, and sunlight hitting its surface will be largely reflected back into space. New snow has an albedo of 0.8-0.95, sandy soil 0.25-0.45, and a water surface has 0.05-0.08. This means that most of the sun's rays that hit snow will be reflected back into space, while sun's rays that hit earth or water will largely heat these bodies and only a smaller part of the heat will be reflected back into space.
An increased area of ice and snow will thus contribute to cooling the Earth further, which can lead to even more ice and snow and so on. Water vapor is the most important greenhouse gas in the atmosphere. When the globe's temperature drops, the atmosphere can no longer contain as much water vapor, which causes a loss of the greenhouse effect and thereby further temperature drops, which causes even more loss of water vapor in the atmosphere - and so on.
This figure illustrates the calculated variations in the three Milankovitch parameters over the last 800,000 years. Time progresses from the bottom towards the top. The parameters are the eccentricity of the Earth's orbit (blue), the axis inclination (red) and the precession (green). The combined signal is the insolation, which can be calculated theoretically for the past and future in received energy per unit area, since the movements of the Earth and the planets around the Sun are very predictable. The black graph is the sum of insolation contributions from the first three. The violet graph on the right is the temperature ratio over the same period based on analysis of oxygen isotopes in shellfish in layers on the bottom of the World Ocean. Hot is to the right and cold is to the left.
It is seen that there is an almost perfect correlation between "Combined signal" and "Average of marine oxygen isotope ratio", which is considered as conclusive evidence for the correctness of the Milankovitch theory. Graph "The Milankovitch theory - the astronomical explanation of the ice ages" by geologist Klaus Petersen in Geologisk Nyt.
The incoming solar energy is often called insolation, and it can be stated in, for example, watts/m2. The curves describe the insolation at 65 degrees north latitude, which passes through Iceland, northern Scandinavia and Russia, Siberia, Alaska and northern Canada.
According to some calculations of the Milankovitch parameter (see above), the future of mankind looks fairly happy, at least as far as the climate is concerned. Astronomical calculations show that insolation at 65 degrees north latitude will increase gradually over the next 25,000 years. The upcoming eccentricity the next approx. 100,000 years will not have much effect. Changes in Northern Hemisphere summer insolation will be dominated by changes in axis tilt.
The Milankovitch theory states that interglacials will be terminated by a particularly deep insolation minimum; but for the next 50,000 years, no decrease in solar radiation is expected at 65 degrees north latitude, which could give rise to a new ice age. If we dare, we can believe that the regular alternation between ice ages and brief interglacials, which has prevailed for several million years, should so conveniently be paused.
The calculated theoretical insolation, i.e. solar radiation at 65 degrees north latitude in June through past and future from Wikipedia Time progresses from left to right. The time is in "kilo years", so three zeros must be added. 0 represents the present. The red curve represents insolation calculated according to all three Milankovitch parameters. The green is the contribution from the axis inclination alone.
As one can see, big changes do not seem to come for the next fifty thousand years, and after that it may even become warmer, if we are to believe the Milankovitch theory and this calculation of the insolation. Graph Incredio Wikipedia.
There are some who expect it to be a little cooler. An often cited 1980 report by Imbrie and Imbrie predicted that the long-term cooling trend that began in the Paleolithic about 6,000 years ago will continue for the next 23,000 years. However, a recent report by Berger and Loutre suggests that the current relatively warm climate may last another 50,000 years.
One can object that the Milankovitch theory does not explain why it has become so cold in the first place. It does not explain why the Earth's temperature fell from the Jurassic and Cretaceous period's approx. 20℃ to today's 14℃ in our current interglacial and the 5℃ in the actual glaciations. In the Jurassic and Cretaceous, the Earth's orbit was probably also eccentric, and the Earth's axis of rotation probably exhibited both precession and axis tilt, yet there were no ice ages for more than 200 million years. There seems to be one or more completely superior parameters, which control the Earth's temperature and climate, and the Milankovitch theory simply superimposes the dominant parameters.
The Milankovitch theory does not explain why Earth's temperature fell steadily throughout the Cenozoic's 65 million years. Photo unknown origin.
If we ignore the eccentricity, the theory predicts that when it is cold in the Northern Hemisphere, it should be correspondingly warm in the Southern Hemisphere and vice versa. In any case, the cold should occur first in the northern hemisphere. However, all studies show that the development of glaciers in the northern and southern hemispheres respectively has been synchronous; when there was an ice age in the northern hemisphere, there was also an ice age in the southern hemisphere. There are also no indications that the ice ages started in the northern hemisphere and then spread to the southern.
About 800,000 years ago, a shift in the dominant period length for ice age cycles occurred from 41,000 years to 100,000 years. Milankovitch's theory offers no explanation for this because there were no significant changes in Earth's orbital parameters at this time. Also, the 100,000 year periods do not correlate as well with the mathematical predictions of solar irradiance as the earlier 41,000 year periods do.
7. The interglacials and other warm periods
The climate in the Pleistocene was characterized by a series of glaciations, when glaciers penetrated far into Europe and North America. In the first million and a half years, an ice age cycle lasted about 41,000 years, while in the last 800,000 years the cycles lasted about 100,000 years. The actual ice ages were separated by relatively short warm periods called interglacials, so that an actual ice age typically lasted 90,000 years and the following interglacial 10,000 years. However, the climate and duration of the interglacials varied greatly, some were warmer than today and others were colder, some lasted barely ten thousand years, and others spanned nearly 25,000 years.
MIS - Marine Isotope Stages in the Pleistocene. Even numbers stand for cold periods, i.e. glaciations, and odd numbers stand for warm periods, including interglacials. Photo Geological Institute.
Nowadays we live in such an interglacial period, which is called the Holocene. Scandinavia is an area that can be expected to be covered by ice sheets during a future glaciation, like the country has been many times before over the past 800,000 years.
Therefore, we must have a very great interest in finding out how the climate will develop throughout the rest of our interglacial period, and when it will end.
MIS stands for "Marine Isotope Stage" and refers to periods defined and described on the basis of isotopic analyzes of drill cores from the seabed.
The MIS periods are numbered, so that even numbers are cold periods, i.e. glaciations, while odd numbers are warm periods, i.e. interglacials. Here we will only deal with odd numbers.
Exactly when an glaciation ends and an interglacial begins and vice versa must depend a lot on definitions, as temperature changes often happen gradually. There is no absolute truth. For example, if you define the start of the Holocene after the Younger Dryas, then the duration will be 11,700 years until the present. But if you define the start at the beginning of the Bølling-Allerød warm period, our interglacial period will have lasted around 14,800 years until the present.
The basic data of the MISs below are mainly taken from Wikipedia which in turn has taken them from various international databases.
Scientists distinguish interglacials, with temperatures close to today's, from other warm periods with less high temperatures, which are called interstadials. There are 103 MIS periods in the Pleistocene. Many MIS numbers have been expanded by addition of letters; for example, MIS 5, which is the Eemian interglacial, has been expanded to MIS 5a, MIS 5b, MIS 5c, MIS 5d and MIS 5e, which latter is the original Eemian interglacial.
8. MIS 1 - Holocene
The Holocene is our current interglacial period. It started just over 11,700 years ago with the end of the Younger Dryas and the Weichel Glaciation. In the very first millennium of the Holocene, the climate in Europe was cool with an open herbaceous and shrubby vegetation as well as scattered birch and pine, but within 1,000 years the temperature rose to about 3℃ above present-day temperature, and Europe became covered with deciduous forest. In the endless forests that covered southern Scandinavia, the Stone Age hunters hunted the European terrapin and curled pelican, which today only live in southern Europe. After another few thousand years, the level of the world's oceans rose 25 m to approximately current level. In the past 2,000-3,000 years, the climate has become colder and wetter, but with clear fluctuations. The Bronze and Middle Ages were warm periods, while the 1600s-1800s was a very cold period, which is called the Little Ice Age.
The Holocene has not yet ended, and it is unknown when a glaciation will begin.
Terraces of rice fields in the province of Yuannan in China. In the past, most of the Earth's surface was covered by forest. The wood of the trees bound a large amount of the biosphere's carbon, and therefore the carbon content of the atmosphere was not so high. Now the forests are largely burnt or rotted, and the carbon is found as CO2 in the atmosphere, say proponents of the "early anthropogenic hypothesis.
In 2003, American professor William Ruddiman put forward the "early anthropogenic (man-made) hypothesis", suggesting that humans began to change the concentration of greenhouse gases in the atmosphere already thousands of years before the industrial era. Deforestation and intensification of rice cultivation led to increases in atmospheric CO2 and CH4 levels, he believed. By comparing with natural trends in the three previous interglacials, he estimated that already in the late Holocene the concentrations of these gases in the atmosphere were increased due to human activity by 35-40 ppmv (parts per million - volume) for CO2 and about 230- 250 ppbv (parts per trillion - volume) for CH4. Ruddiman believed that the increased concentrations of greenhouse gases counteracted the "natural" cooling trend and thereby prevented the global climate from entering a new ice age.
The "early anthropogenic hypothesis" quickly came under heavy criticism, particularly with regard to the extent to which the development in the Holocene greenhouse gas concentrations can be attributed to human activities.
9. MIS 3 - Brørup
Finds from mammoths in Scandinavia from MIS 3. The finds are marked with the small mammoths. The squares are sites where the climate in MIS 3 has been explored, for example Sokli in Finland. From "Re-dating the Pilgrimstad Interstadial with OSL" by Helena Alexanderson, Timothy Johnsen and Andrew S. Murray.
The Weichel Ice Age lasted about 90,000 years, but Southern Scandinavia and Northern Europe were only completely covered by ice for a good 10,000 years during the LGM, which means "Last Glaciation Maximum". During the rest of the last ice age, northern Europe was either only partially covered by ice, as tundra with July temperatures of 8-13℃ or as open forest with birch and pine with temperatures that could briefly be quite close to today's.
In a lake near Härnösand in central Sweden, sediments have been found from 63-61,000 years before the present, that is, from around the start of MIS 3, which is identical to the Brørup softening. Pollen analyzes show that water sedge and black-green bream food grew in the lake. Willow trees grew along the bank and the landscape was characterized by scattered vegetation with birch, fir and pine. It has been concluded that the average temperature for July was 10-11℃. Härnösand lies at 62 degrees north latitude and today has an average July temperature of around 15-16℃.
The drill core from Sokli in northern Finland. The first vertical column on the left is the age of the various layers plus minus uncertainty. The depth in meters is self-explanatory. The nature of the vegetation is derived from analyzes of pollen in the different layers. The column on the far right is the current MIS periods, numbers in brackets are the differences between the different MIS. It can be seen that for most of MIS 3 there has been tundra in Sokli. From "Present day temperatures in northern Scandinavia during the last glaciation" by K.F. Helmens and more. See link below.
An interstadial in the Weichel glaciation between 50,000 to 40,000 years before present began with a 12.5℃ temperature rise in Greenland. It caused the Scandinavian ice shield to retreat to the Scandinavian mountains. The ice-free part of Scandinavia was characterized by countless lakes, scattered permafrost, sparse tundra vegetation and possibly scattered forests of pine and birch. It has been found that the July temperature in Sokli in northern Finland was between 10 and 13℃ which is to be compared with the area's current average July temperature of around 13℃. Sokli lies north of the Arctic Circle at 67 degrees north latitude.
The Milankovitch insolation was quite favorable during this period.
Pilgrimstad, Härnösand, Oulu, Sokli and Yamozero. Own work.
No later than 40,000 before the present, the ice must then have spread south very quickly to arrive at Klintholm in Denmark, perhaps between 35,000 and 30,000 before the present. However, a mammoth molar found at Pilgrimstad in Jämtland has been dated to 34-29,000 years before the present, which indicates that the land was ice-free when the mammoth lived and that the ice has spread even faster south.
10. MIS 5 - Eem
The Eem interglacial is interesting because it is our closest preceding interglacial in which we can mirror our own Holocene interglacial and seek answers to the question of how long it will be before the ice returns.
The last 150,000 years of temperature derived from analysis of ice cores. 5a to 5e stand for MIS 5a to MIS 5e, which are different stages of MIS 5. Photo Political Forum.
Eem corresponds to MIS 5. The penultimate interglacial, which has been dated to ca. 130,000 - 116,000 years before present. The duration of Eem obviously depends a lot on how one defines the beginning and end, but it is usually assumed that it lasted 11,000 to 15,000 years. It must be compared with the duration of the current interglacial, which has lasted a good 11,711 years until now, if you define the start after the Younger Dryas. If, on the other hand, one defines the start at the beginning of the Bølling-Allerød warm period, it will have lasted around 14,800 years. This roughly corresponds to half a Milankovitch precession cycle, which is 12,886 years.
The most common duration of actual glaciations over the last million years has been 90,000 years, and the most common duration of interglacials has been 10,000 years. One can thus say that Em was a relatively long interglacial, and the Holocene has already lasted longer than average.
Milankovitch parameters over 300,000 years. The lower green curve is the sum of the theoretical insolation with contributions from axis inclination, the eccentricity and the precession. It is interesting that these two warm periods seem to begin when an insolation "wave" peaks. However, it is the case that there have been several insolation maxima that were greater than or equal to the Holocenes, but which did not give rise to interglacial periods. But these two interglacials, Eem and Le Bouchet, seem to have been terminated by particularly deep insolation minima, where it can be believed that snow and ice did melt completely at 65 degrees north latitude, and thus new glaciers started. Photo unknown origin.
Despite the frequent claim that "post-industrial anthropogenic global warming" is unprecedented, it is generally agreed that the Eem was at times warmer than the present by as much as 5℃.
In the Eem interglacial, the Milankovitch parameters favored a large difference between summer and winter, and it is therefore assumed that the temperature in summer was several degrees higher than today. However, the frequent occurrence of plants such as ivy, yew, holly and boxwood shows that the winters were quite mild.
All the ice cores that have ever been drilled into the Greenland ice sheet, and which have contained ice from the Eem period, have indicated temperatures higher than today's, usually in the order of 3-5℃. Latest drilling yielded 8℃.
It could be so warm in the Eem period that the surface of the Greenland ice sheet began to thaw, and the surface water penetrated into the underlying layers of glacial ice, which today can be seen as refrozen meltwater in drill cores. This kind of refreezing of surface water has only occurred very rarely in the last 5,000 years. Only in 2012 could it be observed that the ice cap began to melt and form surface water.
In a borehole in the seabed off the coast of Greenland, pollen from spruce in layers from the Eem was three times as frequent as in layers from the Holocene.
The Greenland ice sheet in the Eem interglacial. Many believe that it was partially melted and that this water contributed to the higher level of the World Ocean. Today, the ice sheet is also about 3 km. high in the highest place. Photo unknown origin.
But the hot weather didn't last very long. After less than 5,000 years, the temperature began to drop, and then it fell steadily for about 10,000 years until the start of the Weichel glaciation. The sea level fell, the deciduous forests were gradually replaced by pine forests, which in turn were replaced by tundra.
The climate in the Eem was generally warmer and rainier than today. The climate belts were shifted to the north. Hippos lived along the Thames and the Rhine, and Europe and the Scandinavian peninsula were wooded all the way to the North Cape. Deciduous trees such as elm, hazel, hornbeam and oak grew in Europe as far north as Oulu in northern Finland on the Gulf of Bothnia. Some sources state that linden trees grew in Holland and England.
In North America, the forests spread north to the southern part of Baffin Island. The boundary between forest and prairie was several hundred kilometers further west than it is today.
The sea level was 3.5-7 meters higher than today. Opinions are divided as to where all this water came from. The latest guess is that about 25% came from a partial melting of the Greenland ice sheet, and the rest came from a melting of the Antarctica ice shield.
It was previously assumed that the Eem interglacial had a uniformly warm climate for more than 10,000 years, however, recent research has shown that the warmth did not last that long and was also interrupted by several prolonged cold periods.
Vegetation in the Eem interglacial at Grande Pile in France. Steppe means mammoth steppe. Boreal forest is an open forest with pine and birch, which today is known from northern Russia. Temperate forest is deciduous forest. There is distinguished between cold and warm temperate forest. Ognon I, Stadial I, Saint Germain I1, M lisey II, Saint Germain Ic, Montaigu event, Saint Germain Ia and M lisey I are different periods of warm and cold weather in the Eem period. The Zeifen is a short warm period which was a precursor to the Eem itself, in the same way that the Bølling-Allerød warm period was a precursor to the Holocene. The Eemian is the traditional part of the Eem, where the temperature was warmer than in the Holocene. 5a, 5b and so on denote MIS 5a MIS 5b and so on, which is a subdivision of MIS 5. "Oxygen isotope Iberian margin" refers to analyzes of sediments from the seabed off the Spanish coast regarding the frequency of the heavy oxygen isotope, which tells how much water was bound in ice sheets and thus indicates the temperature. Some approximate times are listed on the far right. From "Climate, vegetation, and CO2 dynamics during the Eemian interglacial (MIS 5e) in Europe" see link below.
The salty Eem Sea was located where the southern Baltic Sea is now. It had wide connections to both the Atlantic Ocean and the Arctic Ocean via the White Sea, so that the Scandinavian Peninsula, Finland and the Kola Peninsula were one large island. Large parts of the Northern European lowlands were covered by a shallow sea.
Eem the interglacial was warmer than the Holocene and therefore the water level in the world ocean was higher. The Eem Sea was much larger than the Baltic Sea and connected to the Barents Sea. Denmark was an island. Photo by Suomen Luonto.
In northern Russia, a little south of the Arctic Circle, a drill core has been taken in Lake Yamozero near the Timan mountains. It shows that in MIS 5a, 58,000 years before present, the lake was surrounded by spruce forest; on the drier and more fertile soil a little further away deciduous trees grew. This indicates that summers were warmer in northern Russia than they are today.
It is generally agreed that the climate in the Eem was more unstable than in the Holocene, with several cold periods lasting from decades to centuries. A remarkable shift occurred about 5,000 years into the Eem, when the temperature dropped by 6℃ to 10℃, before rising again to warm conditions.
11. MIS 7 - Le Bouchet
In the French lake Le Bouchet, located at an altitude of 1.2 kilometers in central France, pollen was found which shows that the lake was surrounded by a forest of hornbeam 240,000 years ago in the MIS 7 period. At Pianico in Northern Italy, traces of a stand of hornbeam have also been found.
Interglacials through 800,000 years. Photo Basic Glaciers.
MIS 7 lasted only a few thousand years and is traditionally considered one of the shortest and coldest interglacials. Finds from England in layers from MIS 7 indicate a temperate and dry steppe climate. This is supported by other English finds, which originate from a species of steppe elephant with straight tusks called Palaeoloxodon antiquus, as well as from several species of woolly mammoth.
In a drill sample from northwestern Greece, evidence of four forested periods has been found. The forest periods were separated by intervals with very little tree pollen, which is interpreted as an expression of relatively short cold and dry periods. The pollen distributions indicate that the summers were more rainy than today, and the winters were colder than in both the Eem period and the Holocene. At the end of the interglacial, the climate also changed to colder and drier conditions.
In the Batajnica loess area in Serbia, remains of molluscs have been found in layers from MIS 7, which indicate a temperate dry steppe climate in the middle and end of the period. In a few places in the Mediterranean area, signs of an equatorial, i.e. tropical, vegetation have been found.
Studies in Bermuda have shown evidence of an increased sea level compared to the present of about 2.5 meters, indicating at least a warm period.
12. MIS 9
This interglacial was also quite short, but however warmer than the Holocene as long as it lasted.
In early MIS 9, the forests of England consisted of oak, elm and ash, as well as several species of the evergreen yew, indicating a temperate climate. Later, the forest was dominated by oak and pine.
Bones have been found in layers from MIS 9 that originate from brown bears, which also prefer a temperate climate.
Original forest with oak and pine. Wikimedia Commons.
At Cudmore Grove on the coast of Essex, the climate has been reconstructed from pollen analyses. It turned out that the July temperature was about 2℃ warmer than today's temperature in south-east England, while January's temperature was slightly colder.
Investigations of coastal terraces by the Thames and elsewhere have shown that the water level in the world ocean was a few meters higher than today's sea level.
Some studies have shown that the sea temperature around Australia was about 4℃ warmer in MIS 9 than it is today, which allowed corals to form the foundation of the Great Barrier Reef.
The American professor William Ruddiman suggested in 2007 that among the last four interglacials, MIS 9 can be considered the closest analogue to the Holocene based on the phase between axis tilt and precession and the resulting strong biannual insolation. It is not good news for today's inhabitants of the Earth's northern regions, as this interglacial only lasted the usual 10,000 years.
13. MIS 11 - Holsten
The Holstein is interesting because it is one of the interglacials that most closely resembles the Holocene in terms of Milankovitch constellations. Both today and 400,000 years ago, the eccentricity of the Earth's orbit was low, and the orbit was and is very close to a circle.
The MIS 11 - MIS 1 analogy is not perfect. Number of years at the top represent the Holocene and Holstein at the bottom. The red (grey) curves are MIS 1 and the black are MIS 11. On the left, the precession curves are shifted by a few thousand years, so that they almost cover each other, but thereby the axis tilt curves become quite far apart. On the right, the axis inclination curves cover each other quite well, but in doing so the precession curves go completely wrong.
From "The MIS 11 - MIS 1 analogy, southern European vegetation,
atmospheric methane and the "early anthropogenic hypothesis" by P. C. Tzedakis, E. W. Wolff and others.
Loutre and Berger believe that MIS 11 represents the closest astronomical analogue to MIS 1 (Holocene), and therefore a study of this can tell us about our climatic future, and especially give us answers to the question of how long the Holocene will last.
Although similar, the insolation curves for the two periods are not exactly identical. An ongoing discussion among researchers is whether to emphasize the precession or the axis tilt in the comparison between MIS 1 and MIS 11. You have to imagine that you have MIS 1's insolation curves on a piece of transparent plastic that you can put over the MIS 11 curves to make them fit. But if the precession curves overlap, the axis inclination curves are quite different and vice versa. Emphasizing the precession would predict that the Holocene is rapidly approaching its end, it is said, as half a Milankovitch precession cycle is 12,886 years. Emphasizing the axis tilt would predict the Holocene to be a double period spanning two insolation maxima. And in that case, we can look forward to the Holocene lasting another 10,000 happy years, it is said.
Loutre and Berger believe that a comparison of vegetation trends in MIS 1 and MIS 11 favors a precessional adjustment, suggesting that the Holocene is nearing its end due to natural causes.
Comparison of parameters from five different interglacials.
For each interglacial, time progresses from right to left. The graphs for the Holocene (MIS 1) thus start 20,000 years before the present.
a) The theoretical Milankovitch insolation (solar radiation) in June at 65 degrees north latitude in W/m2. It can be seen that MIS 11 has two maxima, while all the other MIS only have one.
b) Percentage of pollen coming from heather, from Portugal. It can be seen that generally the heather areas seem to be largest when the insolation is the least.
c) Percentage of pollen from trees in Portugal that can be attributed to a temperate climate. It can be seen that, in general, the forest areas seem to be largest when the insolation is greatest.
d) Atmospheric CH4 concentration as recorded in EDC (Edica Dome C) ice cores from Antarctica. - It can be seen that the curve correlates nicely with the insolation and also with the frequency of pollen from temperate trees. Obviously, when it is warm, biological activity is high, and thus atmospheric CH4 is greatest. However, MIS 1 is an exception, as the graph for CH4 runs off and rises just around the introduction of agriculture around 5,000 to 4,000 before the present (3,000 to 2,000 BC), which favors
From "The MIS 11 - MIS 1 analogy, southern European vegetation,
atmospheric methane and the early anthropogenic hypothesis" by P. C. Tzedakis, E. W. Wolff and others. See link below.
Analyzes of pollen have shown that the Holstein interglacial in Europe was for long periods characterized by a stand of mixed temperate forest, which indicates a similar temperature level as in the present. Pollen from the Holstein period has been found in an old lakebed near Dethlingen on the Lüneburg Heath in Northern Germany. They show that the country was covered by temperate forest for almost the entire period, except for the beginning and end and in some cold periods. The pollen analyzes showed that the Northern European forests consisted of pine, noble fir, elm and oak.
I en borekerne taget i havbunden ud for Grønland fandt man tyve gange så mange pollen fra gran end den mængde, som man typisk finder i lag fra Holocæn samme sted. Hvilket indikerer at Grønland i hvert fald i en del af Holsten perioden har været ganske frodig.
The climate of the Holstein era was not perfectly stable, like you would expect from an interglacial with several maxima.
A pollen-based reconstruction of the Holstein interglacial temperature in Central Europe based on pollen from different localities points to a July temperature of 17.5 - 19.7℃, which is very similar to today's temperature.
Pollen analysis from drilling in lake bed from MIS 11 on Lüneburger Heide. The depth to the left in meters. It is thus the oldest layers which are at the bottom. The scales at the bottom for each species of pollen are the percentage that species makes up of each sample taken. The light green ones are trees and bushes, the yellow ones are herbs and the dark green ones are algae.
Note that the period ended rather abruptly in that the more heat-demanding trees, alder and oak, went back and pine and heather and grass became more predominant. Note also a clear cold period around 29 meters depth and a less significant cold period at 26 meters depth, where alder, yew, hazel and oak declined and pine, birch and grass became more dominant.
From "Vegetation dynamics and climate variability during the Holsteinian interglacial based on a pollen record from Dethlingen (northern Germany)"
Pollen analyzes from southern Portugal show that in the early phases of the Holstein era, the land was covered by an open forest consisting of juniper, pine, birch and oak. As it warmed, a Mediterranean flora of drought-tolerant shrubs and deciduous oaks became common again. Later, temperate deciduous trees became more dominant, and the last part of the interglacial is characterized by a warm landscape with conifers and an increase in the amount of herbs.
Comparison between MIS 7, MIS 13 and MIS 15 - From top to bottom the curves produce:
Atmospheric CO2 measured in the Antarctic ice core from EDC (Edica Dome C).
Deuterium (2H) in the Antarctic ice core from EDC, which indicates the temperature.
The ratio between the oxygen isotopes O16 and O18 in drill cores from the seabed. From Global Stack. This ratio indicates the temperature.
The ratio between the oxygen isotopes O16 and O18 in the drill core from the seabed in the Indian Ocean.
The ratio between the oxygen isotopes O16 and O18 in the drill core from the seabed in the South Pacific.
Sea Surface Temperature.
Pollen curve from Tenaghi Philippon in northeastern Greece.
Biological Silicon from a borehole at the bottom of Lake Baikal in Siberia.
Insolation at 65 degrees north latitude in July calculated according to the Milankovitch theory.
At the bottom, the separate insolation contributions from precession and axis tilt. The eccentricity is not shown.
From "Interglacial and glacial variability from the last 800 ka in marine,
ice and terrestrial archives" by N. Lang and E. W. Wolff.
Some old coastlines in Alaska, Bermuda, Indonesia and the Bahamas, which are about 20 meters above today's water level, are interpreted by some researchers to mean that the Holstein was a very warm period. However, other researchers believe that these high coastlines are the result of land uplift.
14. MIS 13
MIS 13 was a long interglacial with two insolation maxima. It lasted about 30,000 years. The Indian monsoon was very strong, and unusually wet conditions prevailed on the Tibetan Plateau. Drill cores from the Zoige Basin in eastern Tibet indicate a warm and wet climate. Although the insolation was long-lasting, it was not very strong, and compared to today, large areas must have been covered by ice sheets for long periods of time.
However, recently, namely in 2008, large amounts of pollen have been detected in drill cores taken from the seabed off the coast of Greenland. Pollen dates from the latter half of MIS 13. There was three times as much pollen from spruce as the amount found from the Holocene. The pollen amount from MIS 13 was greater than from any other interglacial except MIS 11, which suggests that Greenland has been relatively warm and lush at least some of the time, and the ice sheet has probably been somewhat reduced.
Artist's reconstruction of life and landscape at Pakefield in a Cromer Interglacial. The early humans must be Homo Heidelbergensis, painted by Sibbick-Happisburg.
At Pakefield, south of Lowestoft in Suffolk, England, remains of a rich fauna of herbivorous mammals have been found, including warthogs, mice, European hamsters, beavers, the now-extinct giant beaver, wild boar, fallow deer, roe deer and three species of the now-extinct Irish giant deer, a giant elk, a now-extinct species of bison, two species of horse, an extinct rhinoceros, and the largest of all, a straight-tusked elephant and a mammoth, which was a smaller ancestor of the long-haired mammoths of the later glaciations. All these animals were hunted by various predators, including lion, spotted hyena, wolf, bear and not to forget early humans, Homo Heidelbergensis.
From the plants, insects (especially beetles) and other fossil remains at Pakefield it can be inferred that the landscape consisted of swampy areas on a floodplain with reed forests and flooded areas with alder trees bordering a slowly flowing meandering river. There was plenty of aquatic plants, including white water lilies and freshwater fish such as pike, tench and roach. The temperate deciduous forest comprising oak, hornbeam, elm, maple. Other trees and shrubs grew on drier soils. The light open forest alternated with open areas of grass and herbs.
The presence of a few frost-sensitive species, such as hippopotamus, water chestnut, water fern, a species of heather and certain beetles, suggests that the summers were quite warm and the winters were probably milder than today's.>
15. MIS 15
Boreal forest, which is light open cool forest with birch, pine and some other deciduous trees. It is assumed that during the cooler interglacial periods, a large part of Europe and America was covered by this type of forest. Photo Wikimedia Commons.
MIS 15 lasted about 20,000 years, but was interrupted by a very severe cold period. It is assumed that the climate at the height of Europe was temperate. The melting of ice sheets happened very slowly, and maximum sea level occurred late in the period. The areas covered by glaciers in MIS 15 were probably larger than in the present.
16. MIS 17
Some assume that MIS-17, along with MIS-13, was the coldest interglacial in the last 800,000 years.
Near the town of Cromer in East Anglia in England, a quantity of bones from mammals from MIS 17 have been found, including teeth from squirrels, hamsters and bog pigs. In the vicinity of Cromer, bones were also found from many large animals that lived in the forest in the Pleistocene, including wild boar, fallow deer, roe deer, elk, wolf and bear, all of which are animals that like to live in a light open forest. In Denmark, a forehead bone from a red deer from a Cromer interglacial has been found.
In the interglacials of the Cromer complex, elm, beech, yew, ivy and holly were common trees in the forest. A type of duck food, called azolla, grew in small stagnant lakes.
17. MIS 19
P. C. Tzedakis believes that MIS 1 - MIS 19 is a closer and more convincing astronomical analogy than MIS 1 - MIS 11. Which leads to a significantly different conclusion about the expected natural duration of our current interglacial and the extent of the anthropogenic contribution to the Holocene methane content in the atmosphere.
Comparison between MIS 1 (Holocene) and MIS 19. Graphs relating to MIS 1 are red and graphs relating to MIS 19 are black. The top horizontal time scale in red relates to MIS 1. The bottom horizontal time scale in black relates to MIS 19 - both for a full thousand years. The top red numbers in brackets are the future.
(a) The theoretical insolation contribution of the precession.
(b) The theoretical insolation contribution of the axis inclination.
(c) The frequency of the heavy oxygen isotope in seabed drill cores obtained from the international database "LR04 benthic stack". It indicates the temperature. The red graph, which represents MIS 1, can for natural reasons only be displayed up to the present (0).
(d) The frequency of heavy hydrogen, deuterium, as found in drill core from Edica Dome C in Antarctica. This also indicates the temperature.
(e) The concentration of atmospheric methane also from the EDC ice core.
It can be seen that there is quite a good correlation between the parameters for the two periods.
From: "The MIS 11 - MIS 1 analogy, southern European vegetation,
atmospheric methane and the early anthropogenic hypothesis" by P. C. Tzedakis
PC Tzedakis concludes: The comparison between the two interglacials
suggests that the Holocene still has a quarter of an axis tilt cycle in its natural course".
The axis tilt period is 41,000 years, and a quarter is 10,250 years. We can therefore look forward to another 10,000 years of sun and warming, before the cold really arrives again, Tzedakis believes.
We can see that the MIS 19 graphs, which indicate temperature, have the characteristic form of all warm periods, namely that the heat came quickly and then faded slowly. The quarter of an axis-tilt cycle that MIS 19 lasted further beyond the present age of MIS 1 is characterized by a steadily decreasing temperature over 5 - 10,000 years, superimposed by shorter periods of heat and cold. If the MIS 1 - MIS 19 analogy holds, as many believe it does, we can expect the Holocene to develop in this way as well. Quite slowly, over thousands of years, imperceptibly for the individual generation, the temperature will drop towards actual glaciation conditions. The view is also supported by an oft-cited 1980 report by Imbrie and Imbrie, which predicts that the long-term cooling trend that began in the Stone Age about 6,000 years ago will continue through the next 23,000 years.
Tzedakist further concludes: "The discrepancy between atmospheric methane concentrations and the population of temperate trees in the late Holocene seems to favor Ruddiman's view (2003, 2007) that the CH4 increase after 5,000 years before present reflects anthropogenic emissions." This means support for Ruddiman's "early anthropogenic hypothesis".
It is a little hard to see this in the comparison of the graphs for MIS 1 and MIS 19, but in one of the graphs above from the same source, MIS 1, MIS 5e, MIS 7e, MIS 9e and MIS 11c are compared. Here it can be seen that the graphs for CH4 follow the graphs for pollen from temperate trees quite well, except for MIS 1, where the graph for CH4 runs off and rises just around the introduction of agriculture around 5,000 to 4,000 BC (3,000 to 2,000 BC).
18. The supervolcano Toba
All that remains of the supervolcano is Lake Toba, located in north-central Sumatra. Photo Quora.
Toba is a supervolcano on Sumatra in Indonesia that erupted 73,000 years before the present. The mass of the spewed lava, ash and gases was 100 times greater than that of the largest volcanic eruption in recent history, which is the volcano Mount Tambora in Indonesia, which erupted in 1815 and was the reason that 1816 became the "year without a summer" in the northern hemisphere.
The supervolcano Toba spread ash into the atmosphere and throughout southern Asia in a layer approximately 15 cm thick, which can still be traced both in India and in the South China Sea. It is believed that countless animals and early humans were wiped out on this occasion.
The Toba eruption coincided with the beginning of one of the particularly cold periods of the Weichel Ice Age, and many believe that the eruption caused a "volcanic winter" which resulted in a drop in sea surface temperature of 3-5℃, thereby accelerating the deterioration of the ice age. Analyzes of Greenlandic ice cores show that the eruption was followed by a thousand-year period of increased dust in the atmosphere and low temperatures.
