Most modern climate scientists want to explain all climate changes with varying levels of greenhouse gases in the atmosphere. Only the way in which the gases find its way into the atmosphere can vary. Their preferred explanation is that it is humans, who emit CO2 and methane and thereby change the climate for the worse.
However, in the geological past, humans did not exist, and they can therefore hardly be held responsible for the very dramatic climate changes of the past, which far exceed the fairly insignificant changes of the last 50-100 years.
The special feature of the climate in the Paleogene and Neogene periods - formerly called the Tertiary - is that the average temperature of the globe fell over 50 million years from the Eocene Optimum's 25℃ to the Pleistocene Ice Age's 5-8℃.
The mysterious PETM warm period at the end of the Paleocene, when the temperature over a period of a few thousand years suddenly increased by 8℃ above the temperature of the time, is still an unsolved mystery.
Today, traditional CO2-based climate research has been challenged by Henrik Svensmark's theory that cosmic radiation affects the cloud cover, which is the most important cause of variations in the globe's temperature.
1. The cooling of the Earth over 50 million years
This article deals with the geological period, which was previously called the Tertiary, but which has now been divided and renamed into the Paleogene and Neogene periods following the decision of the International Stratigraphic Commission of 1968. The Paleogene will thus include the sub-periods Paleocene, Eocene and Oligocene, and the Neogene will include Miocene and Pliocene.
Time progresses from right to left.
The Geological Eons - Hadal was the glowing inferno just after Earth's creation. In the Archean, the first rocksand and an atmosphere of nitrogen were formed, methane and water condensed. In the Proterozoic, cyanobacteria produced oxygen, which oxidized iron and methane; at the end of the period, life arose on the sea floor. The Phanerozoic refers to the part of Earth's history where there has been visible tangible life.
The entire period prior to the Phanerozoic is often called the Precambrian, which means pre-Cambrian, as it was previously believed that life arose in the Cambrian (earliest period in the Paleozoic) about 540 million years ago.
The Phanerozoic is divided into the Paleozoic, Mesozoic and Cenozoic eras. The Paleozoic is the era of early life in which plants, insects, fish, molluscs, corals and many more living organisms evolved. The Mesozoic is the era of the dinosaurs and the Cenozoic is the era of the mammals.
The Paleogene and Neogene are the subject of this article, and they include the Paleocene, Eocene, Oligocene, Miocene, and Pliocene subperiods.
Own work.
The early geologists divided the Cenozoic into only two periods, the Tertiary and the Quaternary. Tertiary was the part of the age of mammals where humans did not exist, and Quaternary denoted the time when humans existed. But as a result of the Stratigraphic Commission's decision in 1968, there are now, as I said, three periods in the Cenozoic, namely the Paleogene, Neogene and Quaternary.
There is much evidence that the Earth's average temperature throughout the 542 million years of the Phanerozoic has had a slightly increasing trend until a maximum in the middle of the Cretaceous, however interrupted by the three ice ages, the Andean-Saharan, the Karoo and today's Pleistocene ice age. One can guess that it was due to the Sun's ever-increasing brightness.
The average temperature of the globe through the Phanerozoic as a deviation from today's temperature according to Anton Uriarte - however, the geological periods have been added. Time progresses from right to left. It can be seen that the temperature has generally been slightly increasing until the Cretaceous period, after which it fell towards the Pleistocene ice age period, which we live in now. Furthermore, the curve has some similar minima at the other two ice ages in the Phanerozoic, namely the Andean-Saharan Ice Age at the transition between the Ordovician and Silurian, and the Karoo Ice Age in the late Carboniferous and early Permian. Photo Anton Uriarte.
The Sun is a star in the main series of the Hertzsprung-Russell diagram. It will stay in the main sequence for about 11 billion years, during which time it will increase its luminosity threefold overall. At the beginning of the Paleogene 65 million years ago, the Sun had reached a good 99% of today's brightness, and as we know, it has since caught up.
The most interesting thing about the Paleogene and Neogene periods from a climate point of view is that the average temperature of the globe fell quite steadily and constantly over 50 million years from the Cretaceous and Eocene Maximum perhaps 27-28℃ to today's 14℃.
The content of CO2 in the atmosphere in the Phanerozoic according to Robert Berner Yale University - however added the geological periods. Time progresses from left to right. The current CO2 content in the atmosphere is set to 1 (today). It can be seen that the CO2 content had a maximum in the Cambrian, and then it has been decreasing except for a minimum in the Carboniferous period. There are several reconstructions of the CO2 content in the past atmosphere, all of which are different. But the trend is the same: for the vast majority of time, the concentration has been much higher than in today's atmosphere. Graf Robert Berner.
The global climate of the Paleogene began with the short-lived "global winter" caused by the impact of the Chicxulub meteor, which killed the dinosaurs. But then the late Cretaceous warm and humid climate continued for another few million years, until the temperature rose again to the rare PETM, which stands for Paleocene–Eocene Thermal Maximum.
The PETM was a geologically quite short time interval characterized by a sudden average global temperature increase of 5-8 ℃. The PETM began at the transition between the Paleocene and Eocene periods. It lasted about 200 thousand years.
Variations in atmospheric oxygen content through the Phanerozoic according to Robert Berner Yale University - but added to the geological periods. Time progresses from left to right. Graf Robert Berner.
At the same time as the Earth cooled down through the Paleogene and Neogene, there was a corresponding constant decrease in the atmosphere's CO2 content, with the concentration falling by a factor of 10 from at least 4,500 ppm down to the Ice Age's around 200 ppm, the latter being dangerously low and close to wiping out all life. However, since the end of the last ice age, the CO2 concentration has climbed to today's around 400 ppm.
According to Robert Berner of Yale University, from the middle of the Triassic until a few million years into the Jurassic, the percentage of oxygen in the atmosphere gradually dropped to a Phanerozoic low of about 15-17% before rising again to a maximum of about 27% in the very last part of the Cretaceous. At the start of the Paleogene, the oxygen content in the atmosphere was around 25%, and it has since fallen to today's 21%.
A research team from the Russian "Institute of Physics of the Earth" in Karelia has drawn up a curve for the Earth's rotation speed through the Phanerozoic calculated on the basis of magnetic measurements. Time progresses from right to left. It can be seen that at the start of the Cenozoic a day lasted a good 23.5 hours and - at the end of the period the length of the day was very close to today's 24 hours.
The Paleogene and Neogene lasted a combined 63 million years. During this vast span of time, Earth's average temperature dropped steadily from Cretaceous greenhouse temperatures of between 20 and 26°C down to the Pleistocene Ice Age average temperature of about 5°C. We are still living in this ice age period, only we are lucky enough that the glaciers have temporarily retreated in the last twelve thousand years and made way for an interglacial period, which we call the Holocene. For comparison, the Earth's annual average temperature today is 14℃.
Throughout the Paleogene and Neogene, which make up most of the Cenozoic, the temperature was generally falling, but the curve is, however, superimposed by several periods of particularly warm or cold climate, such as the PETM at the transition from the Paleocene to the Eocene, the Eocene maximum and a marked temperature drop at the start of the Oligocene, which led to the first appearance of a permanent ice sheet in Antarctica, a warm period between the Oligocene and Miocene, the Miocene Maximum and the relatively warm climate of the Pliocene.
A reconstruction of Earth's temperature through the Paleogene and Neogene taken from -
Wikipedia
- Time progresses from left to right, and therefore the present is on the right. It can be seen that the general trend is a steady cooling from the greenhouse temperatures of the Cretaceous period to the freezer of the Pleistocene ice ages, however superimposed by shorter or longer periods of extraordinary cold or heat.
The curve is constructed on the basis of samples of deposits on the bottom of the Arctic Ocean. The large scale on the right indicates the content of the oxygen isotope O-18 in sediments. The ratio of the oxygen isotopes O-16 and O-18 in shellfish remains indicates the temperature at which the shellfish died. This is compared with analyzes of radioactive decay from the same layer, which indicates the time.
The letters above and below represent the geological periods. The five epochs of the Paleogene and Neogene (former Tertiary) are Pal for Paleocene, Eo for Eocene, Ol for Oligocene, Mio for Miocene and Pli for Pliocene. Plt represents the Pleistocene (Pleistocene), which is the present ice age. Note the typical fluctuations between ice ages proper and interglacials. The Holocene, which is the present since the end of the last ice glaciation, is a relatively short period that is not shown.
The scale on the left "Polar Ocean Equivalent delta-T (C)" shows the temperature as a difference from today. It is supplemented by the "Equivalent Vostok delta-T (C)" scale in the lower right corner, which shows results from ice core drilling at the Russian Vostok station in Antarctica, as deviations from present-day temperature.
During the Paleogene, mammals evolved from the small, simple species that poked around in the undergrowth in the Cretaceous period - probably an important food item for the dinosaurs - to a large group of different animals that competed to take over the dinosaurs' ecological niches.
In modern times, researchers have a marked tendency to explain all climatic phenomena with variations in the atmosphere's content of CO2 and methane, the greenhouse effect of these gases and the resulting temperature variations and "tipping points", which results in a rather narrow-minded research
But there are other possible explanations such as changes in ocean currents due to continental drift or changes in the salinity of the sea, variations in the activity of the Sun, changes in Earth's albedo due to mountain raising or ice formation and variations in cosmic radiation and consequent changes in cloud formation.
Besides, the Sun has been shining for billions of years, and we have only been studying it for a few hundred years. What do we know about what phenomena can occur? We must not think that we have reached the peak of scientific knowledge.
2. The theory of the Earth cooling due to reduced CO2
The Earth's atmosphere today contains around 400 ppm CO2, which is 0.04 in volume percent. It is 4 ten-thousandths, that is a completely insignificant part of the atmospheric air. Nevertheless, the vast majority of scientists, politicians, journalists and educators have passionately professed their belief that a marginal change in this already insignificant volume is the most important factor in the evolution of the Earth's climate.
An overall presentation of atmospheric CO2 and average global temperature in the Phanerozoic. Time progresses from left to right. The vertical axis on the left is the CO2 concentration in the atmosphere in ppm. The vertical axis on the right is the temperature in degrees Celsius. Both parts were decreasing in the Tertiary, which is the Paleogene and Neogene, but in the Earth's earlier periods the correlation between temperature and the CO2 content of the atmosphere is however very poor, which shows that there is no cause and effect relationship.
During warm periods, the Earth's average temperature has been around 25℃ and in regular ice age periods 5℃, which is to be compared with the Earth's current annual average temperature, which is about 14℃. Denmark's annual average temperature is 8℃. Graf R. Scotese and R. A. Berner 2001.
In light of this belief, many assume that the high content of CO2 in the Cretaceous atmosphere was the cause of a greenhouse effect, which created the high temperatures, and consequently that the decreasing concentration of CO2 in the atmosphere was the decisive cause of the temperature drop through the Paleogene and Neogene the periods.
The supposed effect of greenhouse gases in the atmosphere - Most of the Sun's shortwave radiation is converted to heat when it hits the Earth's surface. The thereby heated soil, rocks and water emits long-wave heat radiation. Some of this heat radiation escapes into space, but another part is captured by the greenhouse gases in the atmosphere and reflected back to Earth. Next, the theory's supporters reason that when the volume of greenhouse gases in the atmosphere increases or decreases, the Earth's temperature will increase or decrease. Photo HowStuffWorks
The theory that increased CO2 content in the atmosphere is the cause of increased temperature states that CO2 is a greenhouse gas that allows the short-wave solar rays to pass through and thereby heat the Earth's surface, while it does not allow the long-wave heat radiation from the Earth's surface to escape into space. In this way, it lets the heat in, but does not allow it to escape again, much like the glass in gardeners' greenhouses.
Since the atmosphere's CO2 content has been steadily decreasing over the last 50 million years, at the same time as the Earth's temperature has also been decreasing during this period, it is tempting to assume that it is a case of cause and effect.
However, when you go further back in the Earth's history and compare the curves for CO2 concentration in the atmosphere and temperature in the earlier periods of the Phanerozoic, you have to recognize that there is no obvious correlation, which really rules out cause and effect.< br>
The Earth's carbon cycle - The plants absorb carbon in the form of CO2 with their photosynthesis. Some plants are eaten by animals and humans, which exhale CO2 into the atmosphere. When plants, animals and people die, they will rot and most of their carbon content will return to the atmosphere.
However, this important circuit is not completely closed. All the Earth's CO2 originally comes from volcanoes. Active volcanoes as well as emissions from the fault zones between the Earth's tectonic plates add ever-larger amounts of CO2 to the atmosphere. In addition, the cycle has a leak, the CO2 in the air dissolves in rain and becomes acid rain, which reacts with bare rocks in the Earth's mountains, the weathering products in the form of carbonates are washed away by water and carried by the rivers to the bottom of the sea, where they remain as sediments. Furthermore, carbonaceous sediments are formed directly from organic matter everywhere on Earth, which is why archaeologists and geologists must always dig to find the past. Own work.
CO2 is not the only type of gas with this property, methane is an even stronger greenhouse gas, but however it is oxidized rather quickly by the oxygen in the air. Water vapor is also a greenhouse gas; it is not as strong as the other two, but on the other hand there is a lot of it.
Some mento in cola-light cause its dissolved CO2 to turn to gas at high speed, creating an almost explosive foam. Photo unknown origin.
Today, the contribution of water vapor to the atmosphere's greenhouse effect is limited to tropical and subtropical regions. Because of the cold, the absolute humidity at higher latitudes is very low; for example, the water vapor content in the air in the Antarctic winter is about 0.00001%, while humid regions at the equator can have an absolute humidity of up to 4.0%. In the Jurassic and Cretaceous times, the air at the poles was much warmer, and their absolute humidity was therefore also much higher than today, and consequently the contribution of water vapor to the greenhouse effect was also considerably greater.
We often read that environmental alarmists state that the content of greenhouse gases in the atmosphere has now reached a "tipping point with no return" and that man-made "global warming" threatens our safe life. But earlier in Earth's history - for example in the Cretaceous period - the CO2 content in the atmosphere was far, far greater than it is now, and nevertheless it fell little by little.
Limestone gargoyle that has guarded Notre Dame in Paris since the Middle Ages. The surface is heavily degraded by acid rain. Photo Pinterest.
Plants absorb carbon in the form of CO2 from the atmosphere by their photosynthesis. Some plants are eaten by animals and humans, who thereby absorb carbon. Animals and humans exhale carbon into the atmosphere in the form of CO2. When plants, people and animals wither and die, they decay into CO2, which is returned to the atmosphere. Forest fires and other burning also bring large amounts of carbon back into the atmosphere in the form of CO2.
Some have calculated that the Earth's plants annually produce 150 Gigatons (nine zeros) of organic carbon compounds with their photosynthesis, and a similar amount is returned to the atmosphere each year by decay, fires, respiration and oxidation.
As we know from cola and soda, large amounts of CO2 can dissolve in water. One liter of cola contains more than two liters of CO2 at normal pressure and temperature. We also know that if we heat the cola, CO2 will escape as bubbles because more CO2 can dissolve in cold liquid than in hot.
Weathered rock at the Matterhorn in the Alps on the Swiss border
and Italy. All rain on Earth contains CO2 and is therefore slightly acidic, and therefore all exposed rocks will slowly decompose and the decomposition products will be carried away by the rivers. Photo Quora.
Thus, atmospheric CO2 is also dissolved in the Earth's oceans. In cold periods, the oceans can contain more CO2 than in warm periods. This means that the Earth's oceans act as a CO2 store, absorbing CO2 in cold periods and releasing it again in warm periods.
Together, these processes form a stable equilibrium, which annually circulates 200-300 Gigatons of carbon around the various circuits. All life on Earth depends on this balance.
However, the circuit is not close. CO2 is constantly added to the system, and there are also several leaks where CO2 disappears and is not recycled.
Many of the Earth's high mountains were created in the Paleogene and Neogene periods by the remnants of Gondwanaland pushing against Eurasia. The dark brown is Eurasia and the light brown is the remains of Gondwanaland. The black lines show the many newly formed mountains. Photo uk.m.wikipedia.org/wiki.
Much of the CO2 in the atmosphere originally comes from volcanoes, whose eruptions are irregular and unpredictable. In addition, a corresponding amount of CO2 constantly seeps from the Earth's interior through the fault zones between the tectonic plates. Only in recent times have humans added CO2 to the atmosphere by burning fossil fuels, which also originally got their carbon from the Earth's interior.
When CO2-containing rain falls on bare mountains, it will react chemically with the rocks and form various carbonates, which are carried by the rivers to the bottom of the sea. It is not very much CO2 annually that leaks out of the carbon cycle in this way, but over the course of 65 million years it will still become something.
Monsoon rain over Himalayas. Photo ukendt oprindelse.
Most of the Earth's great mountain ranges were formed during the Paleogene and Neogene. Only twenty million years ago, the Indian subcontinent began to push against Asia, creating the Himalayas and the Tibetan Highlands. Twenty million years ago, the collision between Africa and Europe created the Alps. The Andes began to rise in earnest fifty million years ago. Only in the Paleogene and Neogene periods the Rocky Mountains were formed.
Lawn that grows over tiles. If the garden owner does not take action, the tiles will be completely covered in perhaps 10-15 years. Own photo.
Most of Earth's great mountain ranges were formed during the Paleogene and Neogene. Only twenty million years ago, the Indian subcontinent began to push against Asia, thereby creating the Himalayas and the Tibetan Highlands. Twenty million years ago, the collision between Africa and Europe created the Alps. The Andes began to rise in earnest fifty million years ago. Only during the Paleogene and Neogene did the Rocky Mountains form.
In other words, it was precisely in the Paleogene and Neogene that huge areas of bare rock were formed, which were continuously eroded by the weakly acidic rain, thereby constantly leaking carbon out of the carbon cycle.
Archaeologists and geologists mostly have to dig down to find the past. All this material that they have to descend through is created by processes that represent the output of the biosphere's carbon cycle. Acid rain erodes rocks, and photosynthesis and biological activity create organic decay that does not return to the carbon cycle. Photo Pinterest.
How can it be that archaeologists and geologists always have to dig down through different archaeological and geological "layers" to find the past? Where does all this material come from? It comes largely from erosion and biological activity, both of which processes consume CO2 from the atmosphere and take it out of the biosphere's carbon cycle.
In the geological short term, the carbon content of the biosphere is an equilibrium between input and output. Active volcanoes and seeping through fault zones add carbon to the biosphere in the form of CO2 in the atmosphere, and erosion of rocks and various organic decays remove CO2 from the biosphere. During periods with many active volcanoes, the CO2 content in the atmosphere has been high, for example in the Cambrian and in the Cretaceous period. The CO2 content of the atmosphere in carbon was low due to large output in the form of formation of coal sediments. Nowadays, the CO2 content is also low, perhaps due to extensive chemical decomposition of bare mountains and little volcanic activity.
Some have calculated that if no CO2 is added at all, the atmosphere and oceans will be depleted of CO2 in about 2.5 million years, and all photosynthesis and thus all life will then cease.
3. The theory of the Earth's cooling due to increased albedo
Albedo describes a surface's ability to reflect sunlight and thus the energy contained in the Sun's light. A completely white surface, such as snow, has an albedo of 0.9, while coal has an albedo of 0.04.
The Drake Passage. Photo Anton Uriarte.
When the Drake Passage opened between Antarctica and South America, and the Tasman Sea south of Australia were formed, Antarctica was isolated from the rest of Gondwana. Due to the rotation of the Earth, the circumpolar ocean currents arose around Antarctica, which climatically isolated the continent. Thus, the continent could no longer exchange heat and cold with the World Ocean and the other continents. Therefore, 34 million years ago, for the first time in the Cenozoic, ice formed at the South Pole.
Ice has a very high albedo, which makes such areas very difficult to heat, as most of the sun's rays are reflected back into space. The Antarctic ice's high albedo contributed not only to the continent's low temperature, but also to that the Earth's total heat input from the Sun becoming smaller.
It is believed that all the great mountain ranges and plateaus, that were formed during the Paleogene and Neogene, especially the Himalayas and the Tibetan Plateau, the Alps and the Andes Mountains, reflect more sunlight back to space than the forests, swamps and grasslands that existed there before the mountain rise, because they have a higher albedo, and among other things because they are more often covered by ice and snow. This is the reason for a low temperature in these mountains, but also the reason that the Earth overall does not absorb as much of the Sun's heat as before, which contributed to the steadily falling average temperature.
When one stand well dressed on a cold, windswept plateau in Tibet or Bolivia, one can probably get the idea that this part of the world does not receive as much solar energy as a beach in Hawaii or a jungle in Central Africa.
4. The theory of the Earth's cooling due to changing ocean currents
During the Paleogene and Neogene, Antarctica was cut off from South America by the formation of the Drake Passage and also cut off from Tasmania and Australia by the formation of the Tasman Sea. This created open sea all the way around Antarctica, which allowed the waves to now freely roll around the globe and get stronger with each turn, creating the strong current, huge waves and raging storms south of Cape Horn, which sailors have always feared.
During the Cretaceous and the beginning of the Paleogene, the Tethys Sea was an enormously shallow tropical archipelago where the surface water was significantly warmed by a very warm climate. Due to evaporation, the salinity and thus the density increased, the warm saline water sank to the bottom and flowed towards Antarctica as a warm bottom current. Photo Anton Uriarte.
Thereby, Antarctica was climatically isolated, so that the continent could no longer exchange heat and cold with the rest of the planet. Then began the cooling of Antarctica, and the first ice sheet formed on this continent.
During the Cretaceous and early Paleogene, Europe was an archipelago in the vast shallow tropical Tethys Sea. As in the Mediterranean today, the evaporation was very strong. Therefore, the salt concentration in the surface water was increased, and the thereby heavier heated water sank to the bottom and flowed as a warm bottom current towards the colder waters at the South Pole. Here the warm water came to the surface on the coasts of Antarctica and thereby contributed to a relatively warm climate on this continent.
Even today there is a very large evaporation from the Mediterranean. More water evaporates than is supplied from rain and rivers. The heavy saline water sinks to the bottom, and a warm saline bottom current flows out through Gibraltar and spreads into the North Atlantic. The map shows salinity at a depth of 1000 m. High salinity is marked in red. Photo Mercator.
However, during the Paleogene and Neogene, the Tethys Sea was reduced to the Mediterranean, Black Sea, Caspian Sea, Red Sea and Persian Gulf, which were cut off from the World Ocean and therefore could no longer supply the warm bottom current to the coasts of Antarctica, and this contributed to the cooling of this continent.
The Mediterranean Sea is one of the remnants of the Tethys Sea, and it has a very strong evaporation. Even today, a warm saline bottom current flows out through the Strait of Gibraltar, while cold and less saline water flows in at the surface.
5. The theory of the Earth's cooling due to increased cosmic radiation
Generally, we imagine that clouds are formed by the air's water vapor content. But this is only partially true, as water vapor is a transparent gas. Clouds are formed by aerosols, which are clumps of air molecules, here among water.
Cosmic particles enter Earth's atmosphere at high speed and energy. They ionize thousands of air molecules - including water vapor molecules, which then easily gather together in clusters called aerosols. Clouds consist of aerosols. Drawing Simon Swordy NASA.
The Danish researcher Henrik Svensmark and his colleagues have demonstrated that the extent of cloud cover according to data taken down from satellites has a remarkable correlation with counts of cosmic radiation from space carried out in ground stations. He concluded that increased cosmic radiation is a cause of increased cloud cover on Earth and thus lower temperature; and conversely, that reduced cosmic radiation is the cause of reduced cloud cover and thus higher temperature.
This discovery has given rise to a completely new theory about the causes of the Earth's climate variations.
Top of clouds seen from airplane window - They are always very white, only from below some clouds can appear dark. Photo unknown origin.
The cosmic radiation originates from the supernovas of the Milky Way. The intensity of the radiation that enters the atmosphere depends on the intensity of the basic radiation, but also on the strength of the Sun's magnetic field, as much of the cosmic radiation from outer space is deflected by this magnetic field.
The Sun has a very strong magnetic field, which is several thousand times stronger than Earth's. Currently, the Sun's field is about 2,000 gauss, which should be compared to the Earth's field, which is 1 gauss. It stretches far into space, well past Pluto's orbit. The Sun's magnetic field protects the Earth from cosmic radiation.
Sunspots are areas on the Sun with intense magnetic activity. Sunspots - and thus the strength of the Sun's magnetic field - vary with a cycle of 11 years.
Svensmark's sunspot theory assumes that the Sun's activity, which is indicated by the number of sunspots, affects the amount of cosmic radiation that reaches the Earth.
Low and high clouds act differently in relation to the Sun's radiation. Low clouds have a high albedo and reflect a lot of solar radiation back to space. High clouds, on the other hand, have a lower albedo and reflect only a little of the Sun's rays back into space. Low clouds have a relatively high infrared emission, which sends much of the heat back into space as long-wave infrared radiation, while high clouds only send a little heat into space. Low clouds are dense and allow little of the sun's rays to penetrate them, while high clouds are thin and transparent. Photo The Conversation.
If the Sun's magnetic field is strong - many sunspots - it will deflect much of the cosmic radiation and not so many low-lying clouds will form, and the Earth's temperature will therefore be relatively high.
If the Sun's magnetic field is weaker - few or no sunspots - it will not deflect as much cosmic radiation, and more low clouds will form, and the Earth's temperature will therefore be relatively low.
According to Svensmark, the temperature variations over the past centuries, including the warming in the 20th century, can be explained satisfactorily based on this context. In short, periods of high cosmic radiation coincide with periods of lower temperatures.
A cloud passes the Sun - an experience we all know, and which illustrates the cooling effect of low clouds. Photo Yandex.
It has been shown that especially the low-lying cloud cover, that is clouds at a height of less than 3 kilometers, is affected by cosmic radiation. Low-lying clouds cover on average more than a quarter of the Earth's surface and exert a strong cooling effect.
The tops of low clouds are very white, as we have often seen when looking out the window of an airplane for 10 km. height. Clouds have a high albedo, and therefore they reflect a large part of the sunlight back into space - sunlight that would otherwise have warmed the Earth's surface.
Cloud cover is significantly cooling. We have often felt it ourselves, when we lie on the sand at the beach after a swim, bathed in the sun. Then a cloud slips in front of the sun, and we immediately feel the heat disappear.
One might object that nights with cloud cover are usually less cold than starry nights because the clouds retain the heat. But the solar energy that the clouds initially send back to space during the day is lost forever, therefore the net effect of cloud cover must be cooling.
This new theory about the causes of the Earth's climate changes especially challenges the widespread theory that variations in the atmosphere's content of greenhouse gases are the decisive cause of the Earth's climate changes.
The movements of the solar system in the Milky Way. Both the Sun and the Milky Way itself, including the arms, move clockwise, but the Sun moves faster than the arms, as do most of the other stars. The stars in the arms are thus constantly replaced, but the arms remain.
You can imagine that when the Sun moves in a circular path around the center of gravity of the Milky Way, it is like we are driving on the motorway. Occasionally we encounter increased traffic, perhaps caused by convoys of trucks, caravans and other passenger cars, which patiently stay behind these while waiting for an opportunity to move forward again. At some point we will get through the increased traffic density and can increase speed again. But if we could look back, we would see that the increased traffic density behind us still exists, only now with other cars.
In the same way, the Sun and other stars in their orbits around the center of the Milky Way form Milky Way arms, which consist of stars that are constantly replaced, which arms can also be observed in other galaxies. We can imagine that the increased gravity from other stars in an arm inhibits the speed of the individual stars through this Milky Way arm and thus ensures its existence.
The vertical axis is kiloparsecs; one parsec being 3.26 light years. One revolution takes 230 million years, it is said (That is, the time from the Sun being in the Orion Spur, for example, until it is again in the same arm after one revolution). The star density and thus the risk of super novae and consequent cosmic radiation, cloud cover and cooling are assumed to be greatest when passing through the arms of the Milky Way. From COSMOCLIMATOLOGY:a by Henrik Svensmark.
Henrik Svensmark's theory is very convincing in explaining climate variations in relatively recent times, hat is since the end of the glaciation. But it can also explain why ice age periods and very warm periods have alternated during the Phanerozoic - representing much greater fluctuations in the Earth's temperature.
The Sun is just one of the Milky Way's hundreds of billions of stars.
The solar system does not have a fixed place in one of the arms of the Milky Way, but orbits independently around the center of the galaxy, a round trip that takes 230 million years, says Martin Enghoff from DTU Space. Most of the Milky Way stars do this. It is believed that the arms of the Milky Way are transitory formations, where stars are constantly being replaced, a bit like random queues on the motorway.
Currently, the solar system is in the Orion Spur arm.
Cosmic radiation is created by super novas, which are exploding stars. Therefore, the cosmic radiation must be most intense, when the Solar System passes one of the arms of the Milky Way, where the density of stars is greatest. One must also imagine that the strength of the radiation is associated with a certain statistical uncertainty, as it depends on how many, how big and how close the super novae that the solar system is exposed to on its passage through a galaxy arm.
The strength of cosmic radiation over time can be reconstructed from the amount of the isotope Beryllium-10 in sediments.
Nir Shaviv from the Hebrew University of Jerusalem, Henrik Svensmark from Denmark's National Space Institute and Jan Veizer from the University of Ottawa, break down the influence on the Earth's temperature from three inputs as follows:
The vertical axis shows the temperature in degrees Celsius and the horizontal axis shows the time in millions of years before present throughout the Phanerozoic. Time progresses from left to right. The top black line is the most recent reconstruction of the temperature, as described by Scotese et al, and the yellow dotted line behind it is an earlier reconstruction shown for comparison. The green line is the prediction from their model, based on the addition of the contributions from the three colored lines below it. The red line is the contribution of CO2, which gradually decreases throughout the Phanerozoic, because CO2 in the atmosphere has been steadily decreasing. The purple line is the contribution from the Sun, which gradually increases over time, due to the Sun's ever-increasing luminosity. The lower gray line is the contribution from the cosmic radiation and the varying cloud formation and represents the largest contribution.
It can be seen that the cosmic radiation varies quite a lot. This is because either the Solar System is located in one of the arms of the Milky Way, where there is a high density of stars and therefore a lot of cosmic radiation, or it is located in the areas between the arms, where there are fewer stars and less cosmic radiation. Photo Climate Discussion Nexus.
Nir Shaviv and Jan Veizer believe that the Andean Saharan, Karoo and Pleistocene Ice Ages were triggered when the Solar System passed through the Perseus arm, the Norma arm and the Oriun Spur respectively, where the star density was high and the cosmic radiation was strong. When the solar system entered the Orion Spur arm 2.5 million years ago, the current Pleistocene Ice Age was triggered.
6. Paleocene
The Paleocene is the earliest period of the Paleogene. It began with the K/T catastrophe 65 million BC, which wiped out all dinosaur species at same time, and ended with the mysterious Paleocene-Eocene-Thermal-Maximum, where the temperature over a period of a few thousand years rose by 8℃ above the temperature at the time.
Reconstruction of the World in the Paleocene. The Arctic Ocean was quite isolated from the rest of the World Ocean. There was only access through three narrow straits. Namely the strait between Scandinavia and Greenland, the Bering Strait and a strait where the West Siberian lowland is now located. The Indian subcontinent was still heading towards Asia. Europe was taking shape but was still an archipelago in the Tethys Sea. North and South America were separate. South America still had a connection with Antarctica. Map from scotese.com.
The climate of the Paleocene was a continuation of the warm and humid greenhouse climate of the Cretaceous, the temperature was even still increasing throughout the period. Earth's average temperature was perhaps 18-20℃, which to be compared with Earth's present-day annual average of 14℃.
Reconstruction of landscape in the Paleocene. An artistic representation of the extraordinary large snake Titanoboa Cerrejon. Photo Smithsonian Magazine.
Some authors write that the CO2 content in the atmosphere in the Paleocene was up to 2,000 ppm. Robert Berner of Yale University believes that it was well over twice that of today, around 700 ppm.
The oxygen content in the atmosphere was barely 25%, which should be compared with today's 21%. It is believed that insects in particular were favored by a high oxygen content in the air.
The length of the day was a good 23.5 hours. The sun shone almost with the brightness of today.
All over the Earth the climate was hot and humid with subtropical vegetation in Greenland and Patagonia. Crocodiles swam along the Greenland coast, and in Earth's tropical forests, small rodent-like animals, birds, reptiles and giant snakes fought for the ecological niches that had become vacant after the dinosaurs' demise. It teemed with insects and flowering plants.
Petrified tree trunk from the Paleocene at Stenkul Fjord on Ellesmere Island - It is believed to belong to the species Metasequoia, which is a kind of redwood tree related to the Californian giant trees - Photo Anne Jefferson in Highly Allochthonous.
Most of the Earth had a tropical climate and there was a lot of rain and very little difference between summer and winter. Almost the entire Earth was covered in dense impenetrable primeval forests. There was no ice at the poles, and the polar regions were overgrown with coniferous and deciduous trees.
High to the north, on Axel Heibergs Island and Ellesmere Island, which lie on the Arctic Ocean at the height of Thule, many finds of fossilized leaves and logs from the Paleocene have been made.
Left: Axel Heiberg Island.
Right: Ellesmere Island. Photo Wikimedia Commons.
In the Cerrejon coal mine in Colombia, many leaves from the Paleocene jungle have been found. Fossils of a giant snake have also been found in the mine, which has been named Titanoboa, it is estimated to have been almost 13 meters long and weighed more than a ton. Some scientists estimate from the shape of the leaves and the very size of the snake Titanoboa that the temperature in the Paleocene Colombian jungle was around 30-32℃, which should be compared to today's 27℃ in the jungle around the coal mine.
The Paleocene ended dramatically 55 million years ago with the mysterious Paleocene-Eocene-Thermal-Maximum (PETM), which was a sudden global warming that lasted about 80,000 years. Quite suddenly, seen through geological eyes, it became unbearably hot on Earth. the average temperature rose towards 7℃ in relation to the greenhouse climate that prevailed in the Paleocene already.
Fossilized leaves from the Paleocene, found in the Cerrejon coal mine in Colombia, compared with leaves from the modern jungle of Colombia. The gray ones are fossils from the coal mine, and the green ones are leaves from the modern jungle in the same place. They are very similar. Photo Fabiany Herrera Florida Museum.
All modern explanatory models for the mysterious PETM warming period involve the effect of greenhouse gases in the atmosphere. Modern climate scientists cannot get away from greenhouse theories.
Volcanic activity is erratic and unpredictable. At the end of the Paleocene, Greenland and North America separated from Europe and opened up the North Atlantic, which of course was accompanied by extensive volcanism, as we still see in Iceland today. It could have emitted large amounts of CO2 from the Earth's interior.
Some have deduced from the carbon-12/carbon-13 isotope ratio that a gigantic meteor of the carbon type hit the earth and spread its carbon all over the world, carbon, which then was oxidized to CO2 by the oxygen of the atmosphere. It could be fitting that the oxygen content of the atmosphere was decreasing during the period.
Left: Fossilized leaf from Cerrejón, which resembles the family Malvaceae, which in Denmark is called the katost family. Photo Florida Museum.
On the right: Common katost is a very common Danish weed. Photo unknown origin.
The oldest and still most popular hypothesis is that carbon came from large deposits of methane hydrate that were released from the ocean floor; perhaps because Earth's temperature exceeded a critical value above which methane hydrate is no longer stable, or the release was caused by volcanic eruptions. The released methane bubbled up and was quickly oxidized to CO2 by the oxygen in the air. Methane hydrate is a white substance that looks like ice. It consists of water molecules and methane. It is only stable at cold temperatures and high pressure. It is found today in the World Oceans along the continental shelves and under the arctic tundra.
Some researchers have suggested that global warming was caused by extensive peat fires all over the Earth, which had produced CO2. This can be made probable by the fact that the oxygen content in the atmosphere was quite high, and fires could therefore start very easily. It is easy to imagine that there may also have been fires in open coal deposits, such as the eternally burning coal mines that we know today from China, the USA and Australia.
Left: Location of possible methane hydrate deposits in today's sea. It has been suggested that the oceans' methane hydrate can be picked up and used as an energy source - The black areas are areas with possible methane hydrate occurrences in today's oceans. Photo People-Edu.
Right: Clumps of methane hydrate brought up from the seabed in the Gulf of Mexico in 2002. Photo Wikipedia
Even today, when the oxygen content of the atmosphere has dropped to 21%, thousands of underground coal mines and coal deposits are burning all over the Earth. Some have been ignited by humans in historic times, and others have been burning for thousands of years. In China, coal fires are mentioned as early as 1,000 AD. in a report by Li Dao Yuan who explored northwestern China for the "Northern Song Dynasty" (960-1280 AD). Marco Polo (1254-1324 AD) mentions the "burning mountains along the Silk Road", which may have been ancient coal fires in Xinjiang. Scientists estimate that a burning coal deposit in New South Wales, Australia, has been burning for 6,000 years.
Left: Burning coal mine near Denniston, New Zealand. Photo Alan Liefting. Wikimedia Commons.
In the middle: Burning Mountain in New South Wales, Australia. According to Smithsonian Magazine, researchers estimate that it is the oldest known coal fire in the world, as they believe that the mountain has been burning for 6,000 years. Photo Beruthiel English Wikipedia
Right: Smoke and toxic gases rise from an underground coal fire in Centralia, Pennsylvania, which has now been burning for 62 years since it was accidentally ignited in 1962. Photo CC Jrmski CFJC Today.
Recent research has shown that the PETM 55 million years ago was not entirely unique. There have been other sudden and unexplained periods of heat. For example, a sudden minor warm period has been detected in the Eocene 53.7 million years ago, which has been named ETM-2.
7. Eocene
PETM, ETM-2 and the Eocene Optimum. Foto Wikipedia.
The Eocene lasted from the end of the warm period PETM 55 million. years before the present and until the steep temperature drop 34 million years before the present, which marked the beginning of the Oligocene, when continuous ice formed on Antarctica for the first time in the Cenozoic.
The Atlantic Ocean continued to expand, and the distance between North America, Greenland and Europe became ever greater. This process is still going on today, accompanied by volcanic activity in Iceland, just as it was certainly accompanied by extensive volcanic activity in the Eocene.
At the end of the Eocene, the Indian subcontinent made contact with Asia and thus began the creation of the Himalayan mountains and the Tibetan Plateau. Likewise, at the end of the Eocene, South America was completely separated from Antarctica.
Reconstruction of landscape from the Eocene. Foto Jakub Cichack.
The preceding Paleocene climate was warm, but at the beginning of the Eocene it was even more unbearably hot and humid. After the short-lived and mysterious Paleocene-Eocene Maximum (PETM), temperatures continued to rise to the Eocene Optimum of about 25℃ in global annual average temperature, which should be compared with today's global average temperature of 14℃ and the Danish annual average temperature of 8℃.
Canal in Sommerset in south-west England attacked by the fast-growing Azolla. - Photo Hans Splinter.
The increasing temperature curve from the beginning of the Eocene to the Eocene Optimum, 49 million. years before the present, was however briefly interrupted by another brief and sudden increase in temperature, which lasted perhaps 80,000 years. It is called Elmo Event or ETM-2.
In the "Eocene Optimum" around 49 million years before the present it was almost as warm as in the PETM. Then the temperature started to drop and it continued to do so for the next 50 million years down towards the Pleistocene ice ages that we really live in now.
American researchers believe that during the Eocene Optimum, the Arctic Ocean was filled with a duckweed-like aquatic plant called Azolla. The so-called "Azolla Event" lasted approximately one million years. Some CO2-oriented researchers believe that the aquatic plant had a unique ability to absorb CO2, and when it then sank to the bottom, the carbon bound thereby escaped the carbon cycle. In doing so, the plant significantly reduced atmospheric CO2, which reduced the greenhouse effect and thereby triggered the temperature drop that was to continue for the next 49 million years.
Bill Hagopian holds a 54-million-year-old piece of wood from the Eocene excavated on Ellesmere Island. - Photo Brian Schubert.
During Earth's history, warm periods, "hothouses", have alternated with glacial periods, "Icehouses". The Eocene Optimum was a culmination of the recent "hothouse" where sea surface temperatures near the poles were at times 14 -16℃ higher than it is today, while the corresponding temperature difference in tropical waters was not nearly as dramatic. There was a more uniform climate across the Earth. This shows that the Eocene greenhouse climate represented a completely different weather system to the one we know today.
40-50 million years ago, the arctic islands of Axel Heiberg Island and Ellesmere Island were covered in lush forests dominated by fast-growing redwood trees, called Metasequoias, which are related to the redwood trees found in northern California today.
Petrified stumps and tree trunks on the islands bear witness to the Eocene forests of the past. The trees seemed to have adapted to the midnight sun and the arctic winter with three months of total darkness. They grew about 30-40 meters tall and grew densely.
Petrified piece of wood from the Eocene from Axel Heibergs Island. Foto Lyn Anglin/NRCAN
In the hillsides you can find 28 layers of compressed fossil forests, interrupted by layers of silt or sand. 28 times the forests have succumbed, and the fallen tree trunks have been covered with sand or silt.
It suggests that the trees grew on a large floodplain, perhaps something like the Mississippi Delta in southern Louisiana. Until the US Army Corps of Engineers tamed the river and forced it to flow in its current channels, the Mississippi River periodically shifted its course from east to west and back again over thousands of years. This created a very wide delta floodplain and periodic floods, which killed the trees that fell into the water and were eventually covered with silt or sand.
The crocodile-like Allognathosuchus, which lived on Ellesmere Island in the Eocene. FotoGhedoghedo Wikipedia.
At Strathcona Fjord on Ellesmere Island, fossils of more than 40 different Eocene vertebrates have been found, including giant tortoises, a type of alligator called Allognathosuchus, a type of rhinoceros called Brontotheres, the hippopotamus-like Coryphodon, a tapir called Thuliadanta and an early horse. In addition, fossils have been found of various predators that do not resemble any living species, such as Creodonts, Mesonychid, a small swimming predator, as well as at least five different kinds of rodents.
The Eocene ended abruptly with a marked, almost vertical drop in global temperature of perhaps about 4℃ down to the somewhat cooler climate of the Oligocene. As a result, permanent ice formed on Antarctica for the first time in the Cenozoic.
8. Oligocene
In the Oligocene, a temporary temperature drop occurred compared to the steadily decreasing trend throughout the Tertiary, it lasted about 9 million years. Only in the last few million years of the Oligocene did the temperature rise again. Foto Wikipedia.
After the long and constant temperature drop in the last half of the Eocene, the beginning of the Oligocene was marked 34 million years ago with a marked and sudden temperature drop of around 4-5℃. This initiated a cold period called Oi-1, which lasted perhaps a million years. After Oi-1, temperatures rose again but only by 1-2℃, and the climate remained relatively cool throughout most of the Oligocene.
Oligocene started 34 million years ago. before the present and lasted until 23 million years before the present, a total of 11 million years.
However, the climate in the Oligocene was still warmer than today's climate. The gradual cooling of the earth was favorable for the development of mammals.
Ice cap in Antarctica with the volcano Mount Erebus in the background. The ice on Antarctica is dazzling white and has a higher albedo than the Greenland ice sheet. The area of the Antarctic ice sheet is larger than the area of Australia. Foto Chimu Blog.
Many believe that the rather sudden drop in temperature at the beginning of the Oligocene was due to South America and Antarctica drifting apart and the Drake Passage opening. Some time before, Antarctica had moved away from Australia-Tasmania, opening the Tasman Sea. The latter event created the cold circumpolar current around Antarctica as we know it today. Waves could now roll unimpeded around the Earth and be amplified with each round.
The circumpolar current around Antarctica. Foto Anton Uriarte.
Thereby, Antarctica was climatically isolated, and the continent could no longer exchange heat and cold with the rest of the Earth. Therefore, for the first time in the Cenozoic, permanent ice formed at the South Pole. The ice on Antarctica is dazzling white and therefore has a high Albedo, which meant that a very large part of the Sun's rays were now reflected back into space, whereby the Earth's heat input became less than before, and the temperature drop was amplified.
Some believe that the cause of the Oligocene temperature drop was even more complex. They believe that Antarctica had previously been warmed by a warm bottom current of relatively salty water, which flowed from the vast shallow tropical Tethys Sea towards the coasts of the southern continent, where it rose to the surface and gave off its heat. At the beginning of the Oligocene, however, Africa and Eurasia began to close in on the Tethys Sea. The two huge tectonic plates pushed against each other and Europe and the Middle East slowly rose from the sea. The Tethys Sea was gradually reduced to include the Mediterranean Sea, the Black Sea, the Caspian Sea, the Persian Gulf and the Red Sea. As the Tethys Sea was thus greatly reduced, and the remnants no longer had an effective connection to the World Ocean, it could no longer supply the warm bottom current to the southern polar rains.
Reconstruction of Europe in the Oligocene. The African and Eurasian plates are pushing against each other and Europe is rising from the ocean. The Tehtys Sea is now greatly reduced and its connection to the World Ocean is greatly cut off and therefore it is no longer able to deliver a warm bottom current of saline water to the coasts of Antarctica. Map scotese.com
It has been found that the temperature of the deep sea in the Oligocene was below 3℃, which should be compared with 12-15℃ during PETM and about 2℃ today. It shows that there was no longer any warm bottom flow heading towards the southern polar regions. It is very likely that the dramatic temperature drop at the beginning of the Oligocene marks a shift in the Earth's climate system, at least as far as the southern hemisphere is concerned; a shift from a weather system with a large heat exchange between Antarctica and the rest of the Earth to a weather system with a climatically isolated Antarctica covered by a growing ice sheet.
In the Northern Hemisphere, the climate developed somewhat reverse. The Faroe and Shetland shelves separated and the entire North Atlantic continued to expand, and this created an ever wider connection between the Polar Sea and the World Ocean, which allowed more efficient exchange of cold and warm water. Greenland remained ice-free, and was only covered by ice sheets many millions of years later.
Many northern forests were transformed into tundra and further south other forest areas were transformed into steppe. In the Oligocene, the first elephants with trunks appeared, and the first primitive three-toed horses roamed the endless steppe.
Volcanic basalt plateaus in Ethiopia and Somalia from the Oligocene 30 million years ago. They are the size of the whole of Spain. Foto Anton Uriarte.
30 million years ago, a series of volcanic eruptions occurred in the border area between Ethiopia and Somalia. An area the size of Spain was covered by a layer of lava up to two meters thick. It may have been the result of a series of smaller eruptions spread over many thousands of years. Ash clouds from the volcanoes may have contributed to the Oligocene's significant temperature drop.
In the last few million years of the Oligocene, Earth's temperature rose again to pre-Oi-1 levels - for reasons that are still not fully explained. The Antarctic ice sheet disappeared again.
9. Miocene
Mi-1, Mid Miocene climatic Optimum and the drop in temperature in the last half of the Miocene. Foto Wikipedia.
The transition from Oligocene to Miocene is marked by a marked cold period, which is called Mi-1. Some have found evidence that ice formation in Antarctica caused the water level in the world's oceans to drop. As a result, shallow areas were exposed to wind and sun, which caused severe erosion.
Analyzes of sediments taken from the bottom of the Ross Sea in Antarctica indicate that the transition from the Oligocene to the Miocene was accompanied by cyclical changes in the volume of ice in Antarctica very similar to the cyclically recurring ice ages that we know from the - geologically speaking - still ongoing ice ages of the Pleistocene.<
After the Mi-1 cold period, temperatures rose again and remained high throughout the first half of the Miocene. The ice sheet on Antarctica melted away again, the Arctic tundra areas were once again overgrown with pine forest.
The world in the Miocene 20 million years before present - Note that the Indian subcontinent has come into place and is seriously pushing against the Eurasian plate and thereby creating the Tibetan Plateau. The Drake Passage is open and there is still a connection between the Atlantic Ocean and the Pacific Ocean through the Panama Strait between North and South America. The Tethys Sea is now completely closed and reduced to a series of bodies of water. Map from scotese.com.
Between 17 and 14.5 million years before present, a new temperature maximum called the "Mid Miocene Climatic Optimum" occurred. Fossils from both the sea and the land indicate that the temperature was about 6℃ higher than today's temperatures.
The Tibetan Plateau with all the great and famous rivers that have their source on it. Photo meltdownintibet.
But from the "Mid-Miocene Climatic Optimum" and throughout the rest of the period, the temperature fell steadily to about 1-2℃ above present temperature. However, some researchers believe they have identified a significant cold period in the period from 14.2 to 13.8 million. before the present with a temperature drop of about 6-7℃.
During the last few million years of the Miocene, ice sheets formed for the first time on both Antarctica and Greenland.
The formation of the Tibetan Plateau happened gradually. Already at the end of the Eocene, the Indian subcontinent made contact with the Eurasian plate, but only in the Miocene did the uplift of the Himalayas and the Tibetan Highlands begin in earnest.
The Himalayas and part of Tibet seen from space. Photo Space Earth Desktop Wallpapers.
The highlands' bare rocks provide optimal opportunities for erosion. The silicate rocks are broken down by acid rain, and the carbonaceous erosion products are carried to the ocean floor by the rivers, where they will remain for millions of years; which, in the opinion of many, led to the CO2 content in the atmosphere decreasing, and the Earth's climate thereby slowly - over millions of years - becoming increasingly colder - these scientists believe.
The Himalayas and nearby mountain ranges are high and steep, and since they are near the warm Indian Ocean, they are flooded every year by intense monsoon rains, which cause severe erosion. The large rivers Ganges, Indus, Brahmaputra, Yangtze and Mekong carry the carbonaceous corrosion products with them to the bottom of the sea. At the same time, the rivers carry with them a quantity of other carbon-containing organic matter into the sea in the form of fallen trees, grass, branches, leaves and twigs etc., which are also evaded from the carbon cycle.
A road along a river in the Himalayas is washed away by heavy monsoon rains. Just a month before, the nearby village had experienced another severe storm with devastating rain. Residents say a hillside collapsed and a huge amount of rock debris toppled the wall of the local school, resulting in the roof collapsing and killing 19 students. Photo The Himalayan.
It has been calculated that these large rivers, which all flow from the Tibetan highlands, contain 25% of all dissolved matter that flows into the world's oceans, and is largely deposited on the seabed as sediments, thus leaking out of the carbon cycle .
It has also been calculated that in just a few million years these two processes have caused a significant drop in the atmosphere's CO2 content, which - according to the prevailing popular theory - has led to a drop in the Earth's temperature.
The area of The Tibetan Plateau is about one million km2. This entire area was raised to an average height of 5,000 m above sea level. The rocks and gravel of the plateau are lighter than the original forests and plains that covered the area before the uplift, and thus have a higher albedo than before. As the temperature at such altitudes is very low, a larger part of the surface became covered by ice and snow, which also increased the albedo and thus further reduced Earth's total heat input from the Sun.
Reconstruction of Europe in the middle of the Miocene 13 million. years before the present. The Tethys Sea is greatly reduced and the new Mediterranean Sea has a few narrow accesses to the World Ocean. Map scotese.com.
Another important event at the end of the Miocene was the desiccation of the Mediterranean. It has been proven that under the bottom of the Mediterranean lie thick layers of salt and gypsum, which indicate that it has been completely or partially dried up several times, as we know it today from the Dead Sea. The event is called "the Messinian Salinity Crisis".
At the beginning of the Tertiary period, 65 million years ago, the areas that today make up southern Europe, North Africa and the Middle East were part of a large shallow tropical archipelago called the Tethys Sea.
During the Tertiary period, the African and Eurasian tectonic plates slowly closed in on the Tethys Sea, and eventually its connection with the World Ocean was completely cut off. When at the same time the pressure of the two plates against each other caused the seabed to rise, the Tethys Sea was reduced to a series of smaller bodies of water, which are the Mediterranean, the Black Sea, the Caspian Sea, the Persian Gulf and somewhat later the Red Sea.
Evaporite deposits in the Mediterranean. When the Messinian Salinity Crisis was at its height at the end of the Miocene, the Mediterranean was reduced to several isolated salt lakes similar to the Dead Sea with surfaces several hundreds of meters below sea level. Photo University of Utah.
In the beginning, the Mediterranean was still connected to the world ocean through varying straits north and south of present-day Gibraltar. However, at the end of the Miocene, about 5-6 million years ago, these straits opened and closed cyclically, so that the Mediterranean was alternately an inland sea and alternately part of the World Ocean. It is obvious to put these cyclical openings and closings of the Straits of Gibraltar's predecessors in connection with the cyclical temperature fluctuations, which are evident in sediment analyzes from precisely the end of the Miocene.
At this time, ice sheets had formed both on Antarctica and Greenland, and it is easy to imagine that cyclical temperature changes were connected with cyclical changes in the amount of ice sheets, as is known from the later Pleistocene Ice Ages. That is, when it was relatively cold, the ice sheet grew and the water level in the world ocean fell, and therefore the Mediterranean Sea was cut off from the world ocean. When it got warmer again, part of the ice sheet melted, the water level in the world oceans rose, and the Mediterranean returned to contact with the world oceans and filled up.
Still today, a warm bottom current of water with a high salt content flows out of the Mediterranean through the Strait of Gibraltar and a cold surface current of less salty water flows into the Mediterranean. The boundary layer between the two opposing currents was exploited by Submarines during the Second World War to sneak in and out of the Mediterranean Sea unseen - From Blog sobre Geociencia, see link below.
Evaporation from the Mediterranean is very high, even today. More water evaporates from the surface than is added from the rivers and from rain directly over the sea. If we imagine that the Straits of Gibraltar, the Suez Canal and the Dardanelles were closed, the Mediterranean Sea would dry up in only 1,000 years, leaving a 70 m thick layer of salt and gypsum on the bottom.
In 1970, the marine research vessel Glomar Challenger found thick layers of evaporation products on the sea floor at a depth of 3 km. According to reports, layers of evaporation products, mostly salt and gypsum, have been found in some places, which are 2-3 kilometers thick.
If a drying out of the Mediterranean Sea will create a salt layer of 70 m. then about 30-40 consecutive cycles of filling and drying are needed to create a layer of salt and gypsum of 2-3 kilometers. This shows that the Mediterranean has been drained and filled again - not once, but several times.
10. Pliocene
The Pliocene is the latest and shortest period of the Tertiary. It began 5 million. years before the present and ended 2.6 million years before present.
The vertical axis represents the temperature in the Pliocene calculated from the relative frequency of the heavy oxygen isotope O-18, as deviation from the 1960-90 average. Calculated from samples of small shellfish from the Pliocene taken from the seabed. Time progresses from left to right and is millions of years before the present. It can be seen that during most of the Pliocene the temperature was slightly higher than today, only at the end of the period did it became cold, and the ice age was at the door. Photo Wikipedia.
The climate in the Pliocene is generally thought to have been slightly warmer than today. The temperature was perhaps about three degrees warmer at the beginning and in the middle of the Pliocene. The climate was particularly mild at high latitudes, and some species of both plants and animals were found hundreds of kilometers north of where their most closely related species are found today. Smaller ice sheets in Antarctica and Greenland caused a sea level that is believed to have been about 30 meters higher than today.
The general cooling trend during the Pliocene was associated with increased desiccation of some areas where forest was replaced by grassland. This was, for example, the case in East Africa, and thus the stage was set for the development of man.
When the forest disappeared some apes crawled down from the trees, stood up on their hind legs and looked around for opportunities on the new grassland. Some believe that Australopithecus, or at least their ancestors, developed here during the Pliocene.
The biggest tectonic event in the Pliocene was the creation of the Panama Isthmus and thus a land-locked connection between South and North America.
Until now, a large part of the warm Gulf Stream had escaped to the Pacific Ocean through the strait between South and North America, and the Gulf Stream, which flowed towards Greenland and Northern Europe, was significantly weaker than it is today. However, after the closure of the "Panama Strait" the entire Gulf Stream flowed north, and that, all else being equal, must have been the cause of a milder climate along the coasts of the North Atlantic.
Artistic reconstruction of a landscape from the Pliocene. Painted by J. Matternes, Smithsonian. USGS Science for a changing world.
But paradoxically, permanent sea ice formed in the Arctic Ocean - precisely in the Pliocene. This means that some of the sea ice did not manage to melt during the summer; as the situation still is today.
Some have explained this apparent paradox by saying that before the "Strait of Panama" was closed, the water of the Gulf Stream contained less salt, and the water was therefore lighter and floated more on the surface of the ocean. Therefore, the warm current could more easily flow through the entire Arctic Ocean and keep it ice-free, at least in summer.
After the closure of the "Panama Strait" all the warm water from the Gulf of Mexico flows north. This water has been exposed to a strong evaporation in the tropical waters, and therefore its salt concentration is relatively high, and the water is therefore heavier than water that contains less salt.
Atlantic surface water salinity 2011. The sun and trade winds blowing over the tropical Atlantic (purple arrows) cause a net loss of freshwater (evaporation minus rain) from the northeast Atlantic, making the waters there very salty. A flow of very salty water from the Mediterranean through Gibraltar also contributes to the salinity. As this warm, salty water from the tropical Atlantic flows northward into the subpolar regions of the North Atlantic with the Gulf Stream (dark blue arrows), the surface water is cooled by evaporation, resulting in the formation of cold, salty surface water that eventually becomes heavy enough to sink to the bottom in the area south of Greenland and in the Norwegian Sea. This forms the North Atlantic Deep Water (NADW). This NADW then flows southward along the floor of the Atlantic Ocean (green arrows). This circulation of northward flowing surface water and southward flowing deep ocean water is what oceanographers call the "Atlantic Meridional Overturning Circulation" (AMOC). Thereby we can realize that if the Gulf Stream had been less saline, it could possibly have flowed through a larger part of the Arctic Ocean. Photo Jennifer Hertzberg Research Gate.
However, the warm saline water is just light enough to stay on the surface as it flows north. But as soon as it cools in the waters around Greenland, Iceland and Northern Norway, it becomes too heavy, the density increases, and the water sinks to the bottom and begins its journey back to the tropical waters as a cold bottom current. And therefore, when today's warm Gulf Stream does not come far enough north to flow through the Arctic Ocean and keep it ice-free in summer, it may be because the salinity is too high.
In modern times, variations in the extent of sea ice in the Arctic Ocean can be observed. Right now the sea ice seems to be receding. It is easy to attribute this to global warming, after all, it is ice that is melting. But it is quite possible that changes in the flow, salinity or temperature of the Gulf Stream are also of great importance.
Ocean Currents in the Atlantic and Arctic Oceans in the Present and Early Pliocene - Some believe that in the early Pliocene, while the Panama Strait was still open, the Gulf Stream was less salty. The warm water could therefore more easily stay on the surface and thus more easily penetrate the Arctic Ocean and keep it ice-free. It is believed that some of the warmest, saltiest water escaped through the strait, and the resulting current to the north was therefore less salty and did not sink to the bottom so early. Foto unknown origin.
One must also assume that the closure of the Panama Strait contributed to the build-up of the Greenland ice sheet, and during the ice ages also to the Scandinavian and North American ice sheets. It may sound paradoxical that an increased flow of warm water to the north is the cause of increased ice formation. But we have to remember that the formation of ice caps requires a lot of precipitation in the form of snow, and the Gulf Stream is precisely the cause of a lot of precipitation, as we know it from the rainy climate in the British Isles and in Western Norway. When the current comes further north, it still causes precipitation, but in the form of snow. In East Siberia it is even colder than in Greenland, but there is no ice sheet - only frozen tundra, because there not very much precipitation.
The climate in the Pliocene was characterized by increasingly large cyclical variations between warm and cold weather, which foreshadowed the coming interplay between glacials and interglacials.
