07-15-2017, 12:22 PM
Two simulations: World climate belts from 540 million years ago to today:
and its reverse as modern times to 540 million years ago:
Ice sheets started to form as mountain glaciers in the south polar region about 40 million years ago and largely engulfed Antarctica about 30 million years ago. Although Antarctica has been around the South Pole, it has been decidedly chilly only since about 90 million years
The glaciation of Antarctica seems to have begun begun as India slammed into Eurasia with the resulting rise of the Himalayas. The Himalayan orogeny lifted silicate rocks into a position in which they would get heavy rain. Carbon dioxide replaced the silicon dioxide, as water saturated with carbon dioxide is much more acidic than silicate rocks. The Himalayas wrenched huge amounts of carbon dioxide out of the air; carbonate rocks are commonly white, so the albedo rose over a significant part of the earth. Meanwhile, Australia separated from Antarctica, allowing what had been a comparatively-narrow strait to widen, allowing strong winds to create a barrier to any cold air flowing away from Antarctica into the middle latitudes and keeping any warm air masses out of Antarctica. Antarctica got steadily colder until it was nearly all ice-covered about 30 million years ago. Only after Antarctica was fully glaciated could ice sheets start forming in Greenland.
The color key:
Gray is for ice-sheets as in Greenland and Antarctica today in places that have no non-freezing months or places that barely escape such, like the coasts of the Arctic Ocean.
Yellow is for desert and steppe climates in tropical and non-tropical locations. Scarcity of precipitation defines the ecology, so this color does not distinguish the Gobi Desert (severely cold winters and hot summers) from the Atacama Desert (mild temperatures all year) or the Australian Outback (warm to hot all year)
Dark green is for non-arid tropical climates, whether rain-forest or savanna.
Light green is for 'warm-temperate' climates with mild winters like most of the southeastern USA (except for southern Florida, which is tropical), southern France, or southern China and Japan.
Medium green is for something that Scotese calls 'para-tropical' -- places of adequate rainfall that don't get either hot or cold at any time. These are places that look tropical in their vegetation but aren't tropical. I don't fully understand this classification, as there are few places like this today. San Francisco? Because San Francisco doesn't have a real winter it looks tropical with all the palm trees, even though it feels much like Michigan's Upper Peninsula in the summer. In contrast, Dallas, which has vegetation more like that of Detroit, is "warm temperate. Think also of Sochi, Russia, site of the 2014 Winter Olympics. Sochi is itself subtropical, but the skiing events were done nearby in the Caucasus. There are too few places like this today to fit a small world map. In some warmer times, as before India slammed into Eurasia and great ocean basins formed the southern boundary of central Asia, this group of climates and related terrains were more widespread.
Brown is for places that have cold winters (like the northeastern USA and most of Canada and Russia) and places of weak summers (like much of northwestern Europe, including England).
Average temperatures are worldwide, and we are still in one of the coldest times ever. Figure that the tropics have average temperatures around 80F in cold times and 85F in warmer times, the 57F that we now experience indicates that the polar zones are unusually cold for the norms for the last 540 million years.
If you are wondering about Antarctica warming up, it won't do so until it moves out of the south polar region. No continent is moving southward, so Antarctica is going to stay brutally cold for a very long time even in geological terms. It will be blocked from warm air currents and its cold air mass will remain hemmed in. Greenland can lose its ice cap; under current circumstances the ice sheet would not re-form. But Africa and Australia are moving northward and catching up with Eurasia, and when they do they will force the formation of large bands of mountains like the Himalayas today. I'd expect another really-nasty Ice Age. But that is a few tens of millions of years away.
Although the other plates have moved significantly in the last 100 million years, Antarctica seems not to have moved much. About 90 million years ago, Antarctica and Australia started to rift, Australia moving northward, moving about 25 degrees of latitude. About 120 million years ago India rifted away from Antarctica and has since traveled about 65 degrees due northward. Antarctica was not then at the South Pole (New Zealand was). Antarctica was in roughly the position that it was in with respect to the South Pols as early as 90 million years ago. About 150 million years ago Gondwanaland, complete with dinosaurs, comprised Antarctica, Australia, India, Africa, and South America. A strip of what is now the southeastern USA from Virginia to Louisiana and including the whole of Florida was wedged between Africa and South America
A view of the world as seen from the South Polar region going back to 540 million years ago shows some weird, often counter-intuitive geography.
Land at the South Pole has included
the main body of Antarctica (East Antarctica) for the last 90 million years or so
"West Antarctica" (the part due south of South America)
New Zealand
the open Pacific Ocean
West Antarctica again
East Antarctica again
Mozambique
South Africa
Botswana
Namibia
Angola
Brazil
Benin
Togo
Upper Volta
Mali
Mauritania
Western Sahara
the USA (states of Virginia and North Carolina)
Germany
Netherlands
Belgium
France
England
the USA (states of Mississippi and Louisiana)
Venezuela
No part of Australia was ever at the South Pole, but Tasmania was close at one point.
Except when it was in the Pacific Ocean or in what is now the Ross Ice Shelf, the South Pole has been on dry land or the Antarctic Continent. From 540 million years ago until it returned to Antarctica (or Antarctica moved under it) The North Pole has mostly been under the Arctic Ocean throughout that time.
and its reverse as modern times to 540 million years ago:
Ice sheets started to form as mountain glaciers in the south polar region about 40 million years ago and largely engulfed Antarctica about 30 million years ago. Although Antarctica has been around the South Pole, it has been decidedly chilly only since about 90 million years
The glaciation of Antarctica seems to have begun begun as India slammed into Eurasia with the resulting rise of the Himalayas. The Himalayan orogeny lifted silicate rocks into a position in which they would get heavy rain. Carbon dioxide replaced the silicon dioxide, as water saturated with carbon dioxide is much more acidic than silicate rocks. The Himalayas wrenched huge amounts of carbon dioxide out of the air; carbonate rocks are commonly white, so the albedo rose over a significant part of the earth. Meanwhile, Australia separated from Antarctica, allowing what had been a comparatively-narrow strait to widen, allowing strong winds to create a barrier to any cold air flowing away from Antarctica into the middle latitudes and keeping any warm air masses out of Antarctica. Antarctica got steadily colder until it was nearly all ice-covered about 30 million years ago. Only after Antarctica was fully glaciated could ice sheets start forming in Greenland.
The color key:
Gray is for ice-sheets as in Greenland and Antarctica today in places that have no non-freezing months or places that barely escape such, like the coasts of the Arctic Ocean.
Yellow is for desert and steppe climates in tropical and non-tropical locations. Scarcity of precipitation defines the ecology, so this color does not distinguish the Gobi Desert (severely cold winters and hot summers) from the Atacama Desert (mild temperatures all year) or the Australian Outback (warm to hot all year)
Dark green is for non-arid tropical climates, whether rain-forest or savanna.
Light green is for 'warm-temperate' climates with mild winters like most of the southeastern USA (except for southern Florida, which is tropical), southern France, or southern China and Japan.
Medium green is for something that Scotese calls 'para-tropical' -- places of adequate rainfall that don't get either hot or cold at any time. These are places that look tropical in their vegetation but aren't tropical. I don't fully understand this classification, as there are few places like this today. San Francisco? Because San Francisco doesn't have a real winter it looks tropical with all the palm trees, even though it feels much like Michigan's Upper Peninsula in the summer. In contrast, Dallas, which has vegetation more like that of Detroit, is "warm temperate. Think also of Sochi, Russia, site of the 2014 Winter Olympics. Sochi is itself subtropical, but the skiing events were done nearby in the Caucasus. There are too few places like this today to fit a small world map. In some warmer times, as before India slammed into Eurasia and great ocean basins formed the southern boundary of central Asia, this group of climates and related terrains were more widespread.
Brown is for places that have cold winters (like the northeastern USA and most of Canada and Russia) and places of weak summers (like much of northwestern Europe, including England).
Average temperatures are worldwide, and we are still in one of the coldest times ever. Figure that the tropics have average temperatures around 80F in cold times and 85F in warmer times, the 57F that we now experience indicates that the polar zones are unusually cold for the norms for the last 540 million years.
If you are wondering about Antarctica warming up, it won't do so until it moves out of the south polar region. No continent is moving southward, so Antarctica is going to stay brutally cold for a very long time even in geological terms. It will be blocked from warm air currents and its cold air mass will remain hemmed in. Greenland can lose its ice cap; under current circumstances the ice sheet would not re-form. But Africa and Australia are moving northward and catching up with Eurasia, and when they do they will force the formation of large bands of mountains like the Himalayas today. I'd expect another really-nasty Ice Age. But that is a few tens of millions of years away.
Although the other plates have moved significantly in the last 100 million years, Antarctica seems not to have moved much. About 90 million years ago, Antarctica and Australia started to rift, Australia moving northward, moving about 25 degrees of latitude. About 120 million years ago India rifted away from Antarctica and has since traveled about 65 degrees due northward. Antarctica was not then at the South Pole (New Zealand was). Antarctica was in roughly the position that it was in with respect to the South Pols as early as 90 million years ago. About 150 million years ago Gondwanaland, complete with dinosaurs, comprised Antarctica, Australia, India, Africa, and South America. A strip of what is now the southeastern USA from Virginia to Louisiana and including the whole of Florida was wedged between Africa and South America
A view of the world as seen from the South Polar region going back to 540 million years ago shows some weird, often counter-intuitive geography.
Land at the South Pole has included
the main body of Antarctica (East Antarctica) for the last 90 million years or so
"West Antarctica" (the part due south of South America)
New Zealand
the open Pacific Ocean
West Antarctica again
East Antarctica again
Mozambique
South Africa
Botswana
Namibia
Angola
Brazil
Benin
Togo
Upper Volta
Mali
Mauritania
Western Sahara
the USA (states of Virginia and North Carolina)
Germany
Netherlands
Belgium
France
England
the USA (states of Mississippi and Louisiana)
Venezuela
No part of Australia was ever at the South Pole, but Tasmania was close at one point.
Except when it was in the Pacific Ocean or in what is now the Ross Ice Shelf, the South Pole has been on dry land or the Antarctic Continent. From 540 million years ago until it returned to Antarctica (or Antarctica moved under it) The North Pole has mostly been under the Arctic Ocean throughout that time.
The ideal subject of totalitarian rule is not the convinced Nazi or the dedicated Communist but instead the people for whom the distinction between fact and fiction, true and false, no longer exists -- Hannah Arendt.