Great mind of Milutin Milankovic and his theory about ice ages

[Musaka]

"What causes an ice age? Will another one occur? Since it had become generally recognized by the mid-nineteenth-century that much of Europe had once been covered by a great sheet of ice, scientists have been wondering what could cause such vast shifts in the Earth’s climate. Some began looking for underlying astronomical causes. They already knew that the tilt of Earth’s axis caused seasonal change, and also that small variations in Earth’s orbit, over tens of thousands of years, affected the amount of solar energy reaching Earth. Several scientists had proposed the existence of a cycle of global winters, but none of their figures seemed accurate, and testing their reliability was difficult. Each theory was eventually shelved.
In 1911 a young Serbian mathematician, Milutin Milankovitch, decided to chart the ice ages of the Pleistocene. (The Pleistocene is the epoch that began 1.8 million years ago and ended about 11,500 years ago. It was characterized by lengthy ice ages, when glaciers covered large regions of the continents, interrupted by short interglacial periods, when the climate was temperate.) All Milankovitch’s calculations were done by hand, and he worked at them obsessively for the next thirty years. He incorporated new information about small variations in the tilt of the Earth’s axis, and factored in small orbital changes caused by the gravitational tug of other planets. Each of these orbital variations has its own time scale, and consequently they interact in different ways over time, but each one is regular. Going back 600,000 years in his computations, he carefully calculated the effect of these factors on incoming solar radiation across the Northern Hemisphere. The charts and tabulations Milankovitch created are still used today. He also measured summer solar radiation curves in high northern latitudes, where the ice age glaciers originated, linking certain low points with four previous European Pleistocene ice ages. Ultimately, the mathematician arrived at a complete astronomical theory of glaciation.

On the basis of his analysis, Milankovitch concluded that Earth’s orbit changes in three cycles of different lengths. The shape of Earth’s orbit around the Sun changes from less to more and back to less elliptical in about 96,000 years. The Earth is tilted on its axis of rotation relative to the solar plane, currently at an angle of 23.5°. This tilt changes, however, from 21.5° to 24.5° and back again in about 41,000 years. Finally, the Earth’s axis of spin wobbles with a period of 23,000 years. The challenges for Milankovitch were to understand when the three cycles were coincident with each other and how they worked together to influence insolation (the amount of solar radiation received by the Earth). Based on his computations, Milankovitch theorized variations of more than twenty percent in the amount of sunshine reaching the northern latitudes. In his 1941 account, Canon of Insolation and the Ice Age Problem, he suggested that this caused the waxing and waning of the great continental ice sheets.
Like that of several predecessors, Milankovitch’s work was greeted with considerable excitement, but was then largely dismissed. Ice ages are difficult to date, partly because each erases much of the traces of its predecessor. However, the tables were turned by the late 1960s. Technical advances made it possible for geologists to study deep-sea sediment cores that contain a climate record going back millions of years. This climate record shows remarkably regular variations, which correlate with the mathematician’s figures and which are now known as Milankovitch cycles. However, it is also clear that astronomical factors alone cannot cause the large changes that the Earth experienced. Other factors must also influence climate but scientists still do not know how."... My question is, what are these other factors and how they influence on Earth climate? Are these factors changing of oceans currents, changing in ocean salinity, changing in SUn radiation, all these factors together with Milankovic cycles or noone of these? Shoot

[PointRadix]

Originally Posted by BeliAndjeo

On the basis of his analysis, Milankovitch concluded that Earth’s orbit changes in three cycles of different lengths. The shape of Earth’s orbit around the Sun changes from less to more and back to less elliptical in about 96,000 years. The Earth is tilted on its axis of rotation relative to the solar plane, currently at an angle of 23.5°. This tilt changes, however, from 21.5° to 24.5° and back again in about 41,000 years. Finally, the Earth’s axis of spin wobbles with a period of 23,000 years. The challenges for Milankovitch were to understand when the three cycles were coincident with each other and how they worked together to influence insolation (the amount of solar radiation received by the Earth). Based on his computations, Milankovitch theorized variations of more than twenty percent in the amount of sunshine reaching the northern latitudes. In his 1941 account, Canon of Insolation and the Ice Age Problem, he suggested that this caused the waxing and waning of the great continental ice sheets.

...

Technical advances made it possible for geologists to study deep-sea sediment cores that contain a climate record going back millions of years. This climate record shows remarkably regular variations, which correlate with the mathematician’s figures and which are now known as Milankovitch cycles. However, it is also clear that astronomical factors alone cannot cause the large changes that the Earth experienced. Other factors must also influence climate but scientists still do not know how."... My question is, what are these other factors and how they influence on Earth climate? Are these factors changing of oceans currents, changing in ocean salinity, changing in SUn radiation, all these factors together with Milankovic cycles or noone of these? Shoot

Interesting post, and very topical in the light of the current “media debate” on climate change, global warming, and the role of human activities. As you pointed out, the sediment and ice core evidence has provided paleoclimatological evidence demonstrating the dramatic shifts in the average temperature, sea level, extent of tropical-type vegetation, and other related parameters. However, I have seldom (if ever) heard direct reference to the analytical models of Milankovic in relation to current "debate" on these phenomena. Do you happen to have any links to information on his work? In terms of the other factors you mention (or question), all of these things have some influence – but it must be noted that none of these changes work (or actually initiate themselves) in isolation.

The natural climatic systems of the Earth are primarily determined by a dynamic complex of linkages, synergies and interactions among the processes, components and sub-systems of the atmosphere, hydrosphere, lithosphere and biosphere. The hydrosphere in this context includes all of the Earth’s water – oceans, rivers, lakes and the cryosphere (ice caps and snow). The main variables which characterize climate are temperature and precipitation (rainfall), humidity and cloudiness (special disturbances such as droughts and hurricances are sometimes included). These elements are in turn dependent on the meteorological variables (of weather) – such as insolation (solar radiation), wind speed and direction, ocean surface temperature, etc. To this must be added the variability of the Sun’s radiation and the Earth’s orbit, which result in an extremely complex and dynamic system.

Thus the climate system is a global complex of linkages and interactions. Inhomogeneities of all scales exist from the very large scale (e.g., 10,000 km) to the very small scale (e.g., 1 mm). This complex system is acted upon by a range of stimuli associated with the Sun, the Moon, and the Earth’s orbit around the sun. The main factors affecting climate change (natural variability) include: (1) Diurnal oscillations, due to the Earth’s rotation; (2) Tidal oscillations, due to gravitational effects of the Sun and Moon, with main periods of 12.4 hr and 24.8 hr; (3) Seasonal oscillations, due to the inclination of the equator to the ecliptic, and to changes in Sun-Earth distance; (4) Synoptic oscillations, caused by Rossby waves, with scales of 1000 km and periods of days; (5) Global oscillations with periods from weeks to months; (6) Inter-annual oscillations with periods ranging from 2 to 5 years, including El Niño/La Niña phenomena in the Pacific; and (7) Secular or long period oscillations with periods ranging from years to tens of thousands of years (the ice ages), likely due to orbital variations. (feel free to consult the search engine of your choice for clarification on any of these)

Having established the above – one of the main issues in the current debate is the possible effects of human industrial and other activities on the global climate. Despite the assertions in some quarters, anthropogenic effects are for the moment much smaller than these natural effects, the main concern being time-scales – their effects are felt within lifetimes rather than thousands of years. The critical point, is that many of the factors (“forcers” and “reactors”) in our current environment never existed in the past – many of the culprits (such as CFC) do not occur freely in nature, further to which, the rate of change of the release of naturally occurring greenhouse gases (such as carbon dioxide) over the past 200 yr or so (since the “industrial revolution”) is unprecedented and likely a result of human activities (such as deforestation). While, it is very true that global warming and climate change are a natural process on the Earth; the main issue is that the new or additional parameters added by human activities make it very difficult to use past cycles of “Ice Ages” and “Tropical Ages” to predict what is to be expected. Even if our activities are much less significant than natural variations, they definitely are not helping the situation.

[Musaka]

1. IPCC - Intergovernmental Panel on Climate Change ;2. http://www.open.ou.nl//dja/Klimaat/S...d_milank.htm;3. EO Library: Milutin Milankovitch ;4.http://www.agu.org/sci_soc/eischao.h...ovitch_cycles; 5. Precession ;...I did something wrong with links:p...hope this will be better.enjoy

[Susi]

Milankovitch is my hero <3

[Musaka]

Originally Posted by Susi

Milankovitch is my hero <3

Well, sad thing is that not too many people on Earth ever heard for him and what he done for geology, metheorology, climatology, astronomy...His discoveries in these sciences are in same rang with NIkola Tesla electricity,current and other discoveries...Because of these guys i am soooo proud i am Serb

[KaloMatt]

Yes, and both of them were born on Croatian land

[Musaka]

Originally Posted by KaloMatt

Yes, and both of them were born on Croatian land

True, MIlutin MIlankovic in Dalj,near Osijek, then Austro-Hungarian monarchy, now Croatia and NIkola Tesla in Smiljan, near Gospic,then Austo-Hungarian monarchy, now Croatia...And then somebody allow himself to say we all arent brothers..%&$#/%$# politicians