List of periods and events in climate history

The climate history of the Earth describes the sequence of weather and climate events in the past. Depending on the viewing period is about a few decades or several billions of years. The sciences which have made it their mission to study climate history, the paleoclimatology and the Historical Climatology.

Accurate and regarded as relatively reliable data are available only from the recent past of the last 150 years. Information about the Earth's climate prior to that date must be generally classified as less certain.

Data recovery

Past climate events can be reconstructed on the basis of various studies. For this purpose, different climate archives are as dendrochronology ( tree ring analysis ), the study of sediments (mainly of deposits in lakes and oceans ), ice cores, Faunenvergesellschaftungen, corals, speleological investigations and the evaluation of historical representations and chronicles. Be applied in order to elicit their data these " archives " a variety of methods. So can be done to the content of carbon isotopes of organic radicals with the radiocarbon dating measurements to determine the age of the radicals. The determination of oxygen isotope ratios of fossil shellfish and ice cores provides information on the course of the climate and the flow of ice ages. 10Be the isotope may be used to determine the previous sunlight. By means of the pollen and the Diatomeenanalyse can be reconstructed former ecological conditions.

Early climate history

The climate history begins with the formation of the Earth around 4.6 billion years ago. In the early stages of the Earth shortly after the formation of the near-surface temperature was about 180 ° C. The cooling lasted very long, 4 billion years ago was below the temperature for the first time the 100 - ° C limit. The climate at this time was therefore not only hot, but also very dry. So there were no oceans, rain or other liquid water on Earth, and the composition of the reducing primitive atmosphere was very different from today's atmosphere. Regardless of the environment came to this point, the Chemical Evolution in motion, in which organic molecules are formed, which were essential building blocks of the emergence of life.

With the progressive cooling of water vapor reached for the first time in the history of the earth its condensation point, so that liquid water could form. Without this the emergence of life and the subsequent biological evolution on Earth would have been impossible.

After the first water was condensed, gradually the water cycle and thus the hydrosphere was formed. The oldest evidence of oceans on Earth are present in rocks, which have now reached an age of 3.2 billion years.

2.6 billion years ago, was formed in the course of development of the Earth's atmosphere by the activity of cyanobacteria, the first oxygen in the primitive atmosphere, reaching approximately 2.2 billion years before significant concentrations. The water vapor condensed mostly and was bound as water in seas and lakes. With the steam and a large part of the carbon dioxide from the atmosphere disappeared. He was consumed by the cyanobacteria, which used it in the course of photosynthesis as a carbon source. The carbon was removed from the normal cycle because the cyanobacteria were not metabolized by other organisms, but is deposed on the sea floor, where they dispersed were deposited in the sediments or fossilized in coastal, light-filled shallow water as stromatolites. Only by building a oxidizing oxygen atmosphere was possible, over a long period have been no significant concentration increases as the oxygen released initially only oxidized iron compounds. This resulted in large deposits of so-called Bändererze which have remained as productive reservoirs and intensively mined. The oxygen concentration in the atmosphere of increased further, so that this aerobic life on Earth has been possible. The change in the concentration of greenhouse gases and their composition also changed the radiation budget of the earth and brought the greenhouse effect in motion that warms the earth ever since.

This very early part of the climate history is divided into four parts. The Precambrian here describes the greatest period of about 3.8 to 0.57 billion years. He is so far relatively poorly reconstructed, because the rocks were subject to far-reaching changes from this period, so that there are few data from this era, which can be used for the reconstruction of the climate. Nevertheless, the early part of the climate history is particularly interesting, as were the first ice age in it. The first of them is about 2.3 billion years back. From about the end of the Precambrian, it is now possible to reconstruct the climate enough and understand. This is possible mainly through the analysis of sediments.

Methane hypothesis

In the early days of the earth, the luminosity of the Sun was only 70 percent of the current value. That would not have been sufficient to prevent a global glaciation. Geological evidence favors the contrary, rather for a higher soil temperature than in the middle of the last 100,000 years. This contradiction is called the paradox of the faint young sun.

To explain the heating of the atmospheric greenhouse effect is discussed in Science:

• Ammonia is indeed one of the most effective greenhouse gas, but it is destroyed in the atmosphere quickly by UV rays that could directly reach the earth in the time before 2.3 billion years due to the lack of ozone.
• Carbon dioxide - a greenhouse gas - passed through the volcanic activity in Earth's atmosphere. In the absence of oxygen, CO2 reacts with the iron oxide to siderite (iron (II) carbonate). This reaction would use at a concentration of 3.040 ml / m³. In the rock strata from the time of 2.2 -2.8bn years no siderite is found. The CO2 concentration must therefore have been lower at the time and would not have been sufficient to prevent a global glaciation.
• The methane favored hypothesis is that in the period before 2.3 billion years ( the beginning of the oxygen producing photosynthesis) the greenhouse gas methane caused the necessary heating, produced by anaerobic archaebacteria.

Without an oxidizing atmosphere, which would convert methane to carbon dioxide and carbon monoxide, the residence time of methane in the atmosphere could be 10,000 years as it is today in about 10 years. Many Methangärer need hydrogen gas and CO2, which are ejected from volcanoes, to build their structures and as an energy source. The methanogens today prefer an ambient temperature of about 40 ° C. So the warmer the earth was the greenhouse gas methane, the better they were able to multiply and the more methane was formed, so that global warming would have to achieve in the higher life would not have been possible values ​​. Since methane reacts with sunlight to longer hydrocarbons, which attach themselves to dust particles in the air, there was a high altitude haze that prevented further warming.

The fact that the atmosphere at that time must have been largely free of oxygen, prove sediments that are older than about 2.2 billion years old. They contain divalent iron in large amounts, which can be formed only in the absence of oxygen. In younger rocks is almost invariably only to find hematite, a trivalent iron oxide. This is an indication that large quantities of oxygen - apparently formed by photosynthesis - entered the atmosphere. Since oxygen is toxic to the Methangärer and other anaerobic organisms, they died from either or settled in the oxygen-free ecological niches at the bottom of the deep sea and in swamps (see also carbon cycle). The decrease in the oxidation of methane Methangärer and oxygen resulted in a reduction of the methane content of the atmosphere and thus to a reduction of the greenhouse effect.

Ice Age

An ice age is a time period in which there were icy poles on the ground or are. Today we can not imagine a world without ice, but ice ages are the exception rather than the rule. The icing of both polar caps means that our earth climate is currently in an ice age. This is an " exceptional situation " because ice-free poles - even " akryogenes (not eisbildendes ) Hot Air " called - the actual " normal" state of the earth. During most of the climate history of the earth, with the exception of some high mountains, was almost free of ice. These warmer periods make up about 80 to 90 percent of the Earth's history. With regard to the periodic recurrence of cold and warm periods is always referenced as a cause among other things, the Milankovitch cycles.

The first documented ice age, which began about 2.3 billion years ago and lasted about 300 million years was the " Archaic Ice Age ", which was probably caused by the large oxygen catastrophe. Regional this ice age has other names, such as it is called in North America " Huron Ice Age", by Lake Huron, are found in the rock layers numerous indications.

The second ice age in Earth's history had to wait a relatively long time in coming. It was only in 950 million year old rock layers, ie more than 1 billion years later, references can be found out that ice formed again on earth. This ice age bears the name " Algonkisches ice age " or " Griesjö - icing ". There are so far only in Europe notes on this ice age by traces of ice movement in the rocks. From this it is deduced that only one lying in what is now Europe pole of the earth was covered with ice.

The next two ice ages followed by 750-620 million years after a warm period. They performed with a relatively short distance, both hemispheres were icy. It refers to the Ice Age as " stubbornness tables icing ", " Marinoische icing " and " Varanger glaciation ", collectively the " Eokambrisches Ice Age ". Evidence that at this time the entire globe was covered by ice to the equator, are discussed under the name Snowball Earth.

The following " Silurian - Ordovician ice age " began 440 million years. This probably only rather weak ice age was limited to the area of ​​today's Sahara and is therefore also called " Sahara icing ". Some scientists a distribution is represented to South America and South Africa.

The following two Ice Age were more pronounced again. 280 million years ago was the " Permo-Carboniferous ice age " instead, which is also known as " Gondwana glaciation ".

The last ice age began 2.6 million years ago and continues to this day. In this period the history of man falls. It is " Quaternary Ice Age " and is by far the best researched, because the evidence of glaciation in many areas of the world are still in good condition. At this recent period of Earth's history can be divided into different climate archives a wealth of data about the climate found. In addition to very cold phases, the cold periods ( glacials ), in which large parts of Antarctica, Europe, Asia, South and North America were glaciated, there were warm periods ( interglacials ), where the climate approximately corresponded to the present. The still ongoing Holocene, which began around 9620 BC, is one such interglacial.

The current ice age

Prior to about 2.6 million years ago the youngest ice age, the Quaternary, which continues to this day began. During the Tertiary, the temperature was gradually decreased so that Antarctica was covered by an ice cap since the Oligocene around 30 million years ago. Prior to about 3.2 million years ago, so it occupy at least deep sea sediments, the temperature dropped again significantly. In the Gelasian formed with some delay at the North Pole ice cap one, and continues to this day fluctuations in temperature began.

In the period from 3.2 to 1.6 million years ago, a cycle time of 41,000 years for the temperature fluctuations could be determined. In the temperature over the last 2.6 million years, ie within the Pleistocene, occur in the observed temperature fluctuations in cycles of about 100,000 years. At the temperatures here the reference is to be noted: In terms of the climate history of the last 100 million years, it is currently cold, as we move in the Quaternary Ice Age. Embedded in the Ice Age, it is currently relatively warm because we are in for about 11,625 years in a warm period of the Ice Age, the Holocene.

In just the last 850,000 years there have been a variety of hot and cold periods. According to studies of oxygen isotopes in marine sediments occurred in this period, at least nine alternating between cold and warm periods. The ice advances and retreats have left this country to a complicated patchwork of deposits. In northern Germany today following sections are distinguished, some of which contain several cold and warm periods:

• Some 850,000 years: Cromer complex
• From about 400,000 years: Elster glaciation
• From about 320,000 years: Holstein interglacial
• From about 300,000 years: Saale Glacial
• From about 126,000 years: Eemian
• ( so named regional Weichsel glaciation, Würm glaciation ) Last glacial period: from about 115,000 years
• Since about 11,625 years: recent warm period or Holocene

In the hot and cold periods, there is the problem that they have different names in the affected regions. So the last glacial period is called in the Alps " Würm glacial period ", in Northern Europe " Weichsel glaciation ," England " Devensian " in Russia " Valdai " and in North America, " Wisconsin ". In addition, let the common names are not so readily equate, as has been shown with increasing knowledge that even the phases of the last glacial period not always correspond to each other, and that this is almost impossible for the older hot and cold periods.

The different temperatures within the hot and cold periods are called " stadials " for relatively cold periods and as " interstadials " for relatively warm periods indicated. In the Würm glacial period alone, there were three stadials, 60,000, 40,000 and 18,000 years ago. At that time the temperature more, although only about four to five Kelvin down from today's Erdmitteltemperatur from what envisaged, that is about three times as much ice could form as it is today. 18,000 years ago, which had the effect that the sea level was lower by about 135 meters than at present. The Gulf Stream was thereby greatly weakened, and the North Sea almost disappeared. Only in the tropics, the climate was similar. The January mean temperature in Germany at that time was approximately -20 ° C, 0.3 ° C today In the animal world had the great impact. In northern Germany, for example, the polar bear was at this time at home.

This shows that even by today's standards very severe winter is not comparable with a winter in a cold period. The change of the Vistula Glacial to the current warm period is seen by scientists as an abrupt climate change, although in the course of several thousand years, he took place ( in front of 15,000 to 7,000 years ago ). The change between the cold and the warm period is dated to 11,000 years before present.

Contribution of coral reefs to the last temperature increase

In the period from front of 16,000 to 10,000 years ago before our time

• The temperature rose in the Antarctic of -8 ° C. to slightly below 0 ° C;
• The carbon dioxide content of the atmosphere increased from 180 ml ​​/ m³ to 260 ml / m³, a proportion of this increase is due to the lower solubility with increasing temperature of carbon dioxide in the oceans;
• The sea level rose to 100 meters.

Around 10,000 years ago, the regions were flooded, where coral reefs could exist. They require a relatively high water temperatures and shallow, light-filled water. The coral had their heyday in the period 9000-6000 years ago. Their rate of growth and the further rise in sea level of 20 meters talking just the scale. Today, the growth rate of the coral reefs has been greatly reduced because of the sea level hardly increases. Since the precipitation of Kalkgehäuses of coral carbon dioxide -free (see carbon cycle), the carbon dioxide content in the past 14,000 years, according to estimates by scientists through the coral reefs to about 50 ml / m³ increased. It is believed that kalkbildendes plankton an equally high proportion of the CO2 increase in the atmosphere is like the coral.

The current warm period

Even in the current warm period, the Holocene, there are still many relative climate changes. In approaching the present time, the reconstruction of the climate always manages detailed and diverse. But the oldest three-quarters of the Holocene are still largely unexplored. Only with the development of the first civilizations of the observation is accurate. Research in the Sahara and the Mediterranean Seebodenuntersuchungen showed that in North Africa today desert was not predominantly about 10,000 years ago, but a grass savannah, which was populated by a variety of animals and people offered habitat. Testify fossil plants as well as rock and cave paintings. A thesis is based on a cyclic greening of the desert areas of North Africa, the cycle time is about 22,000 years. Consequently, a steady long-term change in climate is part of a natural cycle in which there are " winners and losers ".

The change from the last ice age to the current interglacial period was relatively fast, but still took several thousand years. This was due mainly to the fact that the large ice sheets could not melt as fast. The Scandinavian ice sheet had disappeared about 7,000 years ago, and thus melted compared to the shields in North America and northern Asia relatively quickly. The Lauren tables ice sheet in North America was completely dissolved until 4000 years ago. A melting of the Antarctic Ice Sheet today would take at least 15,000 years.

Years ago, about 8000 to 4000 present warm period had passed its peak, so that a slow development of the next ice age may be suspected. However, this movement is so slow that the temperature decreases over a period of a thousand years, only about 0.1 ° C. This small change but it is covered by so many other influences on the climate, that it can be practically realized only over a very long period in the middle. These overlapping changes have recorded an average over a large area, such as on the southern hemisphere, not more than about 1 ° C temperature rise or descent.

The " Holocene temperature optimum " or " Atlantic period " lasted at least on the northern hemisphere from about 7000 BC to 4000 BC, with distinctive breaks between 6500-6100 BC ( the so-called 8.2ka event by the inflow of the North American Eisstausees Lake Agassiz into the Atlantic ), and by about 5200 BC from previously unknown causes.

So it was during the Holocene always "smaller" climate variability ( Misox fluctuation, Piora fluctuation), which noticeably affected the vegetation and therefore on the fauna and humans. In this context, the two terms " Pluvial " are ( relatively precipitation -rich phase ) and " Interpluvial " ( relatively dry phase ) is used. This is necessary because in the history of the temperature and precipitation fluctuations proceeded not always parallel. About 2,000 years ago there was in the period between about 100 BC and 500 AD, the " optimum of the Roman period ." As this air slowly era came to an end and the climate deteriorated ( " pessimum the Migration Period " ), the time of the great migrations of people came (around 370-570 AD). It may be just coincidence, but there are many such parallels between climate and human history.

After this relatively "bad" time for humanity once again developed a warmer era. From about 800 AD followed the Medieval Warm Period. Initially, the precipitation was still within bounds, which changed towards the end of this phase, as the precipitation rates rose sharply. From this period, many German place names that refer to wine, although the wine is no longer a time it was possible there.

It remains that we are now in a relatively warm phase of an interglacial period, which in turn is part of the Ice Age.

Global warming and the future of the climate

The latest findings of climate research suggest that the anthropogenic greenhouse gas emissions substantially increase since the beginning of industrialization, the natural greenhouse effect, and thus exert a growing influence on the climate. The average global temperatures have increased ± 0.18 ° C during the 20th century by 0.74 ° C. Most pronounced is the warming from 1976 to today. By the end of the 21st century expect climate scientists with a global warming of 1.1 to 6.4 ° C, depending on the different model calculations and depending on the future behavior of mankind. This heating is accompanied by partly drastic consequences that may increase with increasing heating on.