Nature Ice Age , Sahara desert, Earth's wobble and the Gulf Stream

oriental said:

Paleo-rivers of the Sahara may have aided human migration.

http://www.sciencedaily.com/releases/2013/09/130911184712.htm

http://www.livescience.com/39575-ancient-saharan-rivers-existed.html

http://www.livescience.com/21070-green-sahara-hosted-african-dairy-farms.html

Those involved with the human evolution should look at the role of the Sahara played.

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bicicleur said:

climate is not stable, it changes all the time, with or without human activity
a new ice age would be much more catastrophical to humans than global warming
i'm sure humans will end up trying to manipulate and controll the global climate

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it changes all the time, with or without human activity

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http://www.google.ca/url?sa=t&rct=j...bA-XEryexsxFuvejojzID3Q&bvm=bv.91665533,d.cGU

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[h=2]The puzzle of coexisting warm and cold climate animals[/h] Ice Age fossils often display a strange mix of animals that would not be expected to coexist. Remains of animals adapted to the cold are found much farther south than expected. Warmth-loving animals are found as fossils much farther north than they would venture today. Yet, they apparently thrived in the Ice Age environment. This peculiar mixture of animals has been given a special name — disharmonious associations.
These disharmonious associations were the rule rather than the exception. This mix of cold-tolerant and warm-tolerant animals occurred over the whole Northern Hemisphere,24 including Siberia, Alaska, and the Yukon Territory.25 Disharmonious associations are also found in the Southern Hemisphere.26

Disharmonious associations apply not only to large mammals, but also to small mammals, plants, insects, birds, amphibians and reptiles! Graham and Lundelius27 write:

Late Pleistocene communities were characterized by the coexistence of species that today are allopatric [not climatically associated] and presumably ecologically incompatible. … Disharmonious associations have been documented for late Pleistocene [Ice Age] floras … terrestrial invertebrates … lower vertebrates … birds … and mammals.
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One of the most outstanding examples is the existence of hippopotamus fossils associated with fossils of reindeer, musk oxen, and woolly mammoths found in England, France, and Germany.28 Sutcliffe29 states:

Finding conditions so favourable the hippopotamus (today an inhabitant of the equatorial regions) had been able to spread northwards throughout most of England and Wales, up to an altitude of 400 meters [1,300 feet] on the now bleak Yorkshire moors.
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Furthermore, hippo fossils are not rare but rather common in England:

Remains of hippopotamuses are known from probably about a hundred localities within England and Wales.30
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In North America too, most late Pleistocene faunas and floras are disharmonious.31 Reindeer mingled with warmth-loving animals as far south as Alabama and Georgia. Badgers, black-footed ferrets, ground sloths, camels, and giant beavers that prefer temperate climates are found much farther north in Alaska in association with woolly mammoths and other cold-tolerant animals.32
Disharmonious associations have garnered much controversy. Although difficult to explain, most scientists have now accepted that the disharmonious associations during the Ice Age are real.33 The reason for the dilemma is that an Ice Age climate is assumed to have been much colder than present-day climates. However, the evidence from the Ice Age fossils instead implies an equable climate with mild winters and cool summers. This climatic deduction from observed fossil evidence is disconcerting, as Kenneth Cole34 realizes when considering very cold Ice Age computer simulations:

Although paleoecologists often conclude that past climates were equable, it is difficult to create equable climates in continental interiors using climate circulation models.
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The explanation of disharmonious association during the Ice Age has resulted in over 150 years of controversy. Cole35 again writes:

One of the longest-running philosophical debates in paleoecological interpretation concerns the importance of mixed, or disharmonious, assemblages which represent past communities with no modern analog. These mixed assemblages challenge our world view. … Mixed assemblages are usually explained by invoking past climates more “equable” than that of today.
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Indeed, disharmonious associations do challenge the mainstream Ice Age world view. There does not appear to be any likely solution to this enigma on the horizon.
[h=2]Mass extinctions at the end of the Ice Age[/h] It is difficult enough to accept that animals, as well as plants and insects, were disharmonious during the Ice Age. But scientists also are faced with explaining why this mix of animals came to an abrupt end with mass extinctions at the close of the Ice Age — at a time the climate was supposed to be warming and the living area expanding.
Not only did the woolly mammoth die out in Siberia at the end of the Ice Age, it died out everywhere. Tolmachoff36 summarizes the problem of the disappearance of the woolly mammoth:

We must explain the extinction of an animal which was living in great numbers, apparently very prosperously, over a large area, in variable physicogeographical conditions to which it was well adapted, and which died out in a very short time, geologically speaking.
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One slightly unexpected turn of events has recently occurred. Whereas scientists believed the woolly mammoth became extinct at the very end of the Ice Age, fossils of mammoths have been discovered on Wrangel Island north of Siberia in the Arctic Ocean that have been dated to about 2000 BC by carbon-14.37 So apparently the woolly mammoth managed to survive past the end of the Ice Age on an isolated island. It is possible that the carbon-14 dates are wrong, or that the Ice Age ended around 4,000 years ago.
Many of the other animals of the mammoth steppe became extinct or disappeared from whole continents at the same time as the woolly mammoth. In North America alone, 135 species in 33 genera of large mammals disappeared.38 Twenty-two genera of birds went extinct from North America at the end of the Ice Age.39 Other continents were hit hard with extinctions during and soon after the Ice Age, including South America and Australia. In all, 167 genera of large mammals greater than 100 pounds (45 kg) disappeared from entire continents.40 Why?
Scientists do not know why the extinctions occurred, and the question has tortured their minds for more than 200 years! Mass extinctions at the end of the Ice Age, when the climate and environment was improving, remains an enigma to this day. Ward41 writes:

This great extinction — truly a mass extinction — represents one of paleontology’s most fundamental mysteries.
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Climate scientist Gavin Schmidt, of NASA’s Goddard Institute for Space Studies, explained that around 8,000 years ago, the Earth’s orbit was slightly different to how it is today. The tilt changed from around 24.1 degrees to the present-day 23.5 degrees.
“Additionally, the Earth had its closest approach to the Sun in the northern hemisphere (with) summer in August,” Schmidt said. “Today, that closest approach is in January. So, summertime in the north was warmer back then than it is now.”
The changes in the Earth’s orbital tilt and precession (or the wobbling motion) occur because of gravitational forces emanating from other bodies in the solar system. To understand exactly what happens, picture a spinning top when it is slightly disturbed. Just like a top, the Earth too wobbles slightly about its rotational axis. This tilt changes between roughly 22 and 25 degrees about every 41,000 years, while the precession varies on about a 26,000-year period. These cycles have been determined by astronomers and validated by geologists studying ocean sediment records.
- See more at: http://www.astrobio.net/news-exclus...shift-shaped-the-sahara/#sthash.OKK077kp.dpuf

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