Here is a short article on exactly what we have done.Here's some more reading for ya.....
The history of ice on Earth
The history of ice on Earth
By Michael Marshall
Primitive humans, clad in animal skins, trekking across vast expanses of ice in a desperate search to find food. That’s the image that comes to mind when most of us think about an ice age.
But in fact there have been many ice ages, most of them long before humans made their first appearance. And the familiar picture of an ice age is of a comparatively mild one: others were so severe that the entire Earth froze over, for tens or even hundreds of millions of years.
In fact, the planet seems to have three main settings: “greenhouse”, when tropical temperatures extend to the poles and there are no ice sheets at all; “icehouse”, when there is some permanent ice, although its extent varies greatly; and “snowball”, in which the planet’s entire surface is frozen over.
Why the ice periodically advances – and why it retreats again – is a mystery that glaciologists have only just started to unravel. Here’s our recap of all the back and forth they’re trying to explain.
Snowball Earth
2.4 to 2.1 billion years ago
The Huronian glaciation is the oldest ice age we know about. The Earth was just over 2 billion years old, and home only to unicellular life-forms.
The early stages of the Huronian, from 2.4 to 2.3 billion years ago, seem to have been particularly severe, with the entire planet frozen over in the first “snowball Earth”. This may have been triggered by a 250-million-year lull in volcanic activity, which would have meant less carbon dioxide being pumped into the atmosphere, and a reduced greenhouse effect.
Deep freeze
850 to 630 million years ago
During the 200 million years of the Cryogenian period, the Earth was plunged into some of the deepest cold it has ever experienced – and the emergence of complex life may have caused it.
One theory is that the glaciation was triggered by the evolution of large cells, and possibly also multicellular organisms, that sank to the seabed after dying. This would have sucked CO2 out of the atmosphere, weakening the greenhouse effect and thus lowering global temperatures.
There seem to have been two distinct Cryogenian ice ages: the so-called Sturtian glaciation between 750 and 700 million years ago, followed by the Varanger (or Marinoan) glaciation, 660 to 635 million years ago. There’s some evidence that Earth became a snowball at times during the big freezes, but researchers are still trying to work out exactly what happened.
Mass extinction
460 to 430 million years ago
Straddling the late Ordovician period and the early Silurian period, the Andean-Saharan ice age was marked by a mass extinction, the second most severe in Earth’s history.
The die-off was surpassed only by the gargantuan Permian extinction 250 million years ago. But as the ecosystem recovered after the freeze, it expanded, with land plants becoming common over the course of the Silurian period. And those plants may have caused the next great ice age.
Plants invade the land
360 to 260 million years ago
Like the Cryogenian glaciation, the Karoo ice age featured two peaks in ice cover that may well have been distinct ice ages. They took place in the Mississipian period, 359 to 318 million years ago, and again in the Pennsylvanian 318 to 299 million years ago.
These ice ages may have been the result of the expansion of land plants that followed the Cryogenian. As plants spread over the planet, they absorbed CO2 from the atmosphere and released oxygen (PDF). As a result CO2 levels fell and the greenhouse effect weakened, triggering an ice age.
There is some evidence that the ice came and went in regular cycles, driven by changes in Earth’s orbit. If true, this would mean that the Karoo ice age operated in much the same way as the current one.
Antarctica freezes over
14 million years ago
Antarctica wasn’t always a frozen wasteland. It wasn’t until around 34 million years ago that the first small glaciers formed on the tops of Antarctica’s mountains. And it was 20 million years later, when world-wide temperatures dropped by 8 °C, that the glaciers’ ice froze onto the rock, and the southern ice sheet was born.
This temperature drop was triggered by the rise of the Himalayas. As they grew higher they were exposed to increased weathering, which sucked CO2 out of the atmosphere and reduced the greenhouse effect.
The northern hemisphere remained relatively ice-free for longer, with Greenland and the Arctic becoming heavily glaciated only around 3.2 million years ago.
Latest advance of the ice
2.58 million years ago
The Quaternary glaciation started just a few million years ago – and is still going on. So its history is relatively recent, in geological terms, and can be studied in far more detail than the others’. It’s evident that the ice sheets have gone through multiple stages of growth and retreat over the course of the Quaternary.
During “glacial” stages, the temperature was low and ice extended far away from the poles. During “interglacials”, the temperature was somewhat warmer and the ice retreated. Brief, inconclusive periods of advancing ice – typically lasting less than 10,000 years – are called “stadials”; conversely, periods when the ice retreated, but only briefly, are called “interstadials”.
The main trigger for the Quaternary glaciation was the continuing fall in the level of CO2 in the atmosphere due to the weathering of the Himalayas. However, the timing of the glacials and interglacials was driven by periodic changes in Earth’s orbit that change the amount of sunshine reaching various parts of the planet. The effect of these small orbital changes was amplified by positive feedbacks, such as changes in greenhouse gas levels.
During the first two-thirds of the Quaternary, the ice advanced and retreated roughly every 41,000 years – the same tempo as the changes in the tilt of Earth’s axis. About a million years ago, the ice switched to a 100,000-year cycle for reasons that were until recently a mystery. Now more detailed information about the timing of the ice’s movements may have helped glaciologists find an answer.
To make matters more complicated still, the ice didn’t advance and retreat simultaneously all around the world. Often it would begin advancing on one continent, with the others only being covered thousands of years later, and then linger on a few continents several millennia after it had disappeared from the others.
So there were actually many overlapping glaciations within the Quaternary, each separately named: the Bavelian and Cromerian complexes of glacials and interglacials; the Elsterian glacial; the Holsteinian interglacial and the Saalian glaciation, among others.
Between 130,000 and 114,000 years ago, the ice retreated during the Eemian interglacial – and then advanced again to create the glacial that most people know as “the ice age”.
Our ice age
110,000 to 12,000 years ago
The cool temperatures of the Quaternary may have allowed our brains to become much larger than those of our of hominid ancestors. While that’s still open to debate, it’s plausible that the most recent glacial period left its mark on our species.
Neanderthals, with whom we shared the planet until just before the last glacial maximum, 20,000 years ago, may have struggled to survive as the rising and falling ice ate away at their habitat – although many other explanations for their extinction have been suggested. What is beyond doubt is that Homo sapiens survived and turned to farming soon after the ice retreated, setting the stage for the rise of modern civilisation.
As the glacial period drew to a close and temperatures began to rise, there were two final cold snaps. First, the chilly “Older Dryas” of 14,700 to 13,400 years ago transformed most of Europe from forest to tundra, like modern-day Siberia. After a brief respite, the Younger Dryas, between 12,800 to 11,500 years ago, froze Europe solid within a matter of months – probably as a result of meltwater from retreating glaciers shutting down the Atlantic Ocean’s “conveyor-belt” current, although a cometary impact has also been blamed.
Twelve thousand years ago, the great ice sheets retreated at the beginning of the latest interglacial – the Flandrian – allowing humans to return to northern latitudes. This period has been relatively warm, and the climate relatively stable, although it has been slightly colder than the last interglacial, the Eemian, and sea levels are currently at least 3 metres lower – differences that are being closely scrutinised by researchers keen to understand how our climate will develop.
But this respite from the ice is likely to prove short-lived, at least in geological terms. Human effects on the climate notwithstanding, the cycle will continue to turn, the hothouse period will some day come to an end – and the ice sheets will descend again.
And here is another lil tidbit...
Sahara Desert Was Once Lush and Populated
At the end of the last Ice Age, the Sahara Desert was just as dry and uninviting as it is today. But sandwiched between two periods of extreme dryness were a few millennia of plentiful rainfall and lush vegetation.
During these few thousand years, prehistoric humans left the congested Nile Valley and established settlements around rain pools, green valleys, and rivers.
The ancient climate shift and its effects are detailed in the July 21 issue of the journal Science.
When the rains came
Some 12,000 years ago, the only place to live along the eastern Sahara Desert was the Nile Valley. Being so crowded, prime real estate in the Nile Valley was difficult to come by. Disputes over land were often settled with the fist, as evidenced by the cemetery of Jebel Sahaba where many of the buried individuals had died a violent death.
But around 10,500 years ago, a sudden burst of monsoon rains over the vast desert transformed the region into habitable land.
This opened the door for humans to move into the area, as evidenced by the researcher's 500 new radiocarbon dates of human and animal remains from more than 150 excavation sites.
"The climate change at [10,500 years ago] which turned most of the [3.8 million square mile] large Sahara into a savannah-type environment happened within a few hundred years only, certainly within less than 500 years," said study team member Stefan Kroepelin of the University of Cologne in Germany.
Frolicking in pools
In the Egyptian Sahara, semi-arid conditions allowed for grasses and shrubs to grow, with some trees sprouting in valleys and near groundwater sources. The vegetation and small, episodic rain pools enticed animals well adapted to dry conditions, such as giraffes, to enter the area as well.
Humans also frolicked in the rain pools, as depicted in rock art from Southwest Egypt.
In the more southern Sudanese Sahara, lush vegetation, hearty trees, and permanent freshwater lakes persisted over millennia. There were even large rivers, such as the Wadi Howar, once the largest tributary to the Nile from the Sahara.
"Wildlife included very demanding species such as elephants, rhinos, hippos, crocodiles, and more than 30 species of fish up to 2 meters (6 feet) big," Kroepelin told LiveScience.
A timeline of Sahara occupation [See Map]:
- 22,000 to 10,500 years ago: The Sahara was devoid of any human occupation outside the Nile Valley and extended 250 miles further south than it does today.
- 10,500 to 9,000 years ago: Monsoon rains begin sweeping into the Sahara, transforming the region into a habitable area swiftly settled by Nile Valley dwellers.
- 9,000 to 7,300 years ago: Continued rains, vegetation growth, and animal migrations lead to well established human settlements, including the introduction of domesticated livestock such as sheep and goats.
Both articles address the fact of the changing climate as a natural occurrence. There is nothing man has done to bring it about, nor is there anything man can do to stop it.
- 7,300 to 5,500 years ago: Retreating monsoonal rains initiate desiccation in the Egyptian Sahara, prompting humans to move to remaining habitable niches in Sudanese Sahara. The end of the rains and return of desert conditions throughout the Sahara after 5,500 coincides with population return to the Nile Valley and the beginning of pharaonic society.
Perhaps there's some troglodyte living in a cave somewhere that actually doesn't know about ice ages and warming and cooling trends. This isn't news.
Just as obviously humans before the Industrial Revolution had no influence on that. But you can't sit in your easy chair an flatly declare we don't in the present day, simply because it's what you would like to be true. The fact is you have nowhere near the perspective to make such an assessment. At all. That's just delusions-of-omniscience arrogance.
As is the deliberate conflation of "weather" with "climate".
So then explain just what we humans have done in the last 300 years to contribute to the Global Climate Change......and include links to back it up.
Prior to the industrial revolution, our primary influence was the clearing of forests, and creation of much faster erosion through poor farming methods. But when we started burning fossil fuels, and releasing CO2 into the air by the giga-ton, we started to become a force to be reckoned with. Since there is massive inertia in the system, and since CO2 levels will persist long after we stop emitting, the affects we feel today are the result of what was in the atmosphere 30 to 50 years ago. So we are going to see much greater effects down the road from what is in the atmosphere today.
Very easy to do. First, we have increased the GHGs in the atmosphere very significantly. CO2 by over 40%, CH4 by about 250%. Second, we know from the absorption spectra of CO2 and CH4 that they absorb longwave IR, and warm the atmosphere, and, by back radiaton, the ground.Here's some more reading for ya.....
The history of ice on Earth
The history of ice on Earth
By Michael Marshall
Primitive humans, clad in animal skins, trekking across vast expanses of ice in a desperate search to find food. That’s the image that comes to mind when most of us think about an ice age.
But in fact there have been many ice ages, most of them long before humans made their first appearance. And the familiar picture of an ice age is of a comparatively mild one: others were so severe that the entire Earth froze over, for tens or even hundreds of millions of years.
In fact, the planet seems to have three main settings: “greenhouse”, when tropical temperatures extend to the poles and there are no ice sheets at all; “icehouse”, when there is some permanent ice, although its extent varies greatly; and “snowball”, in which the planet’s entire surface is frozen over.
Why the ice periodically advances – and why it retreats again – is a mystery that glaciologists have only just started to unravel. Here’s our recap of all the back and forth they’re trying to explain.
Snowball Earth
2.4 to 2.1 billion years ago
The Huronian glaciation is the oldest ice age we know about. The Earth was just over 2 billion years old, and home only to unicellular life-forms.
The early stages of the Huronian, from 2.4 to 2.3 billion years ago, seem to have been particularly severe, with the entire planet frozen over in the first “snowball Earth”. This may have been triggered by a 250-million-year lull in volcanic activity, which would have meant less carbon dioxide being pumped into the atmosphere, and a reduced greenhouse effect.
Deep freeze
850 to 630 million years ago
During the 200 million years of the Cryogenian period, the Earth was plunged into some of the deepest cold it has ever experienced – and the emergence of complex life may have caused it.
One theory is that the glaciation was triggered by the evolution of large cells, and possibly also multicellular organisms, that sank to the seabed after dying. This would have sucked CO2 out of the atmosphere, weakening the greenhouse effect and thus lowering global temperatures.
There seem to have been two distinct Cryogenian ice ages: the so-called Sturtian glaciation between 750 and 700 million years ago, followed by the Varanger (or Marinoan) glaciation, 660 to 635 million years ago. There’s some evidence that Earth became a snowball at times during the big freezes, but researchers are still trying to work out exactly what happened.
Mass extinction
460 to 430 million years ago
Straddling the late Ordovician period and the early Silurian period, the Andean-Saharan ice age was marked by a mass extinction, the second most severe in Earth’s history.
The die-off was surpassed only by the gargantuan Permian extinction 250 million years ago. But as the ecosystem recovered after the freeze, it expanded, with land plants becoming common over the course of the Silurian period. And those plants may have caused the next great ice age.
Plants invade the land
360 to 260 million years ago
Like the Cryogenian glaciation, the Karoo ice age featured two peaks in ice cover that may well have been distinct ice ages. They took place in the Mississipian period, 359 to 318 million years ago, and again in the Pennsylvanian 318 to 299 million years ago.
These ice ages may have been the result of the expansion of land plants that followed the Cryogenian. As plants spread over the planet, they absorbed CO2 from the atmosphere and released oxygen (PDF). As a result CO2 levels fell and the greenhouse effect weakened, triggering an ice age.
There is some evidence that the ice came and went in regular cycles, driven by changes in Earth’s orbit. If true, this would mean that the Karoo ice age operated in much the same way as the current one.
Antarctica freezes over
14 million years ago
Antarctica wasn’t always a frozen wasteland. It wasn’t until around 34 million years ago that the first small glaciers formed on the tops of Antarctica’s mountains. And it was 20 million years later, when world-wide temperatures dropped by 8 °C, that the glaciers’ ice froze onto the rock, and the southern ice sheet was born.
This temperature drop was triggered by the rise of the Himalayas. As they grew higher they were exposed to increased weathering, which sucked CO2 out of the atmosphere and reduced the greenhouse effect.
The northern hemisphere remained relatively ice-free for longer, with Greenland and the Arctic becoming heavily glaciated only around 3.2 million years ago.
Latest advance of the ice
2.58 million years ago
The Quaternary glaciation started just a few million years ago – and is still going on. So its history is relatively recent, in geological terms, and can be studied in far more detail than the others’. It’s evident that the ice sheets have gone through multiple stages of growth and retreat over the course of the Quaternary.
During “glacial” stages, the temperature was low and ice extended far away from the poles. During “interglacials”, the temperature was somewhat warmer and the ice retreated. Brief, inconclusive periods of advancing ice – typically lasting less than 10,000 years – are called “stadials”; conversely, periods when the ice retreated, but only briefly, are called “interstadials”.
The main trigger for the Quaternary glaciation was the continuing fall in the level of CO2 in the atmosphere due to the weathering of the Himalayas. However, the timing of the glacials and interglacials was driven by periodic changes in Earth’s orbit that change the amount of sunshine reaching various parts of the planet. The effect of these small orbital changes was amplified by positive feedbacks, such as changes in greenhouse gas levels.
During the first two-thirds of the Quaternary, the ice advanced and retreated roughly every 41,000 years – the same tempo as the changes in the tilt of Earth’s axis. About a million years ago, the ice switched to a 100,000-year cycle for reasons that were until recently a mystery. Now more detailed information about the timing of the ice’s movements may have helped glaciologists find an answer.
To make matters more complicated still, the ice didn’t advance and retreat simultaneously all around the world. Often it would begin advancing on one continent, with the others only being covered thousands of years later, and then linger on a few continents several millennia after it had disappeared from the others.
So there were actually many overlapping glaciations within the Quaternary, each separately named: the Bavelian and Cromerian complexes of glacials and interglacials; the Elsterian glacial; the Holsteinian interglacial and the Saalian glaciation, among others.
Between 130,000 and 114,000 years ago, the ice retreated during the Eemian interglacial – and then advanced again to create the glacial that most people know as “the ice age”.
Our ice age
110,000 to 12,000 years ago
The cool temperatures of the Quaternary may have allowed our brains to become much larger than those of our of hominid ancestors. While that’s still open to debate, it’s plausible that the most recent glacial period left its mark on our species.
Neanderthals, with whom we shared the planet until just before the last glacial maximum, 20,000 years ago, may have struggled to survive as the rising and falling ice ate away at their habitat – although many other explanations for their extinction have been suggested. What is beyond doubt is that Homo sapiens survived and turned to farming soon after the ice retreated, setting the stage for the rise of modern civilisation.
As the glacial period drew to a close and temperatures began to rise, there were two final cold snaps. First, the chilly “Older Dryas” of 14,700 to 13,400 years ago transformed most of Europe from forest to tundra, like modern-day Siberia. After a brief respite, the Younger Dryas, between 12,800 to 11,500 years ago, froze Europe solid within a matter of months – probably as a result of meltwater from retreating glaciers shutting down the Atlantic Ocean’s “conveyor-belt” current, although a cometary impact has also been blamed.
Twelve thousand years ago, the great ice sheets retreated at the beginning of the latest interglacial – the Flandrian – allowing humans to return to northern latitudes. This period has been relatively warm, and the climate relatively stable, although it has been slightly colder than the last interglacial, the Eemian, and sea levels are currently at least 3 metres lower – differences that are being closely scrutinised by researchers keen to understand how our climate will develop.
But this respite from the ice is likely to prove short-lived, at least in geological terms. Human effects on the climate notwithstanding, the cycle will continue to turn, the hothouse period will some day come to an end – and the ice sheets will descend again.
And here is another lil tidbit...
Sahara Desert Was Once Lush and Populated
At the end of the last Ice Age, the Sahara Desert was just as dry and uninviting as it is today. But sandwiched between two periods of extreme dryness were a few millennia of plentiful rainfall and lush vegetation.
During these few thousand years, prehistoric humans left the congested Nile Valley and established settlements around rain pools, green valleys, and rivers.
The ancient climate shift and its effects are detailed in the July 21 issue of the journal Science.
When the rains came
Some 12,000 years ago, the only place to live along the eastern Sahara Desert was the Nile Valley. Being so crowded, prime real estate in the Nile Valley was difficult to come by. Disputes over land were often settled with the fist, as evidenced by the cemetery of Jebel Sahaba where many of the buried individuals had died a violent death.
But around 10,500 years ago, a sudden burst of monsoon rains over the vast desert transformed the region into habitable land.
This opened the door for humans to move into the area, as evidenced by the researcher's 500 new radiocarbon dates of human and animal remains from more than 150 excavation sites.
"The climate change at [10,500 years ago] which turned most of the [3.8 million square mile] large Sahara into a savannah-type environment happened within a few hundred years only, certainly within less than 500 years," said study team member Stefan Kroepelin of the University of Cologne in Germany.
Frolicking in pools
In the Egyptian Sahara, semi-arid conditions allowed for grasses and shrubs to grow, with some trees sprouting in valleys and near groundwater sources. The vegetation and small, episodic rain pools enticed animals well adapted to dry conditions, such as giraffes, to enter the area as well.
Humans also frolicked in the rain pools, as depicted in rock art from Southwest Egypt.
In the more southern Sudanese Sahara, lush vegetation, hearty trees, and permanent freshwater lakes persisted over millennia. There were even large rivers, such as the Wadi Howar, once the largest tributary to the Nile from the Sahara.
"Wildlife included very demanding species such as elephants, rhinos, hippos, crocodiles, and more than 30 species of fish up to 2 meters (6 feet) big," Kroepelin told LiveScience.
A timeline of Sahara occupation [See Map]:
- 22,000 to 10,500 years ago: The Sahara was devoid of any human occupation outside the Nile Valley and extended 250 miles further south than it does today.
- 10,500 to 9,000 years ago: Monsoon rains begin sweeping into the Sahara, transforming the region into a habitable area swiftly settled by Nile Valley dwellers.
- 9,000 to 7,300 years ago: Continued rains, vegetation growth, and animal migrations lead to well established human settlements, including the introduction of domesticated livestock such as sheep and goats.
Both articles address the fact of the changing climate as a natural occurrence. There is nothing man has done to bring it about, nor is there anything man can do to stop it.
- 7,300 to 5,500 years ago: Retreating monsoonal rains initiate desiccation in the Egyptian Sahara, prompting humans to move to remaining habitable niches in Sudanese Sahara. The end of the rains and return of desert conditions throughout the Sahara after 5,500 coincides with population return to the Nile Valley and the beginning of pharaonic society.
Perhaps there's some troglodyte living in a cave somewhere that actually doesn't know about ice ages and warming and cooling trends. This isn't news.
Just as obviously humans before the Industrial Revolution had no influence on that. But you can't sit in your easy chair an flatly declare we don't in the present day, simply because it's what you would like to be true. The fact is you have nowhere near the perspective to make such an assessment. At all. That's just delusions-of-omniscience arrogance.
As is the deliberate conflation of "weather" with "climate".
So then explain just what we humans have done in the last 300 years to contribute to the Global Climate Change......and include links to back it up.
And here is a presentation to the AGU by one of the top scientists and glaciaologists on earth, Dr. Richard Alley that discusses the known historical affect of CO2;
You see, GHGs don't care whether they came from a Trapp volcanic eruption cooking coal seams, or mankind burning fossil fuels, they simply do what the physics say they should do.
I'm fully aware your mission on this board is to take issue with everything I post even when it agrees with what you post, but you really need to take a remedial reading course.
You asked, specifically, what have we done in the last 300 years and wanted details.
What I'm telling you is I can't definitively quantify that in terms of effect.
I could pull up stats on this and that (and it appears another poster already has) but I can't tell you what it means for the planetary system BECAUSE, and I'll just post this again until it sinks in to your thick contrarian skull, I don't believe I have the perspective to judge that, just as I don't believe YOU have the perspective to judge the reverse of it.
Capice?
It all returns to this simple-as-can-be fact: YOU asserted a negative, to wit the flat declaration that nothing we do can affect the climate.
I then pointed out to you that you have no basis upon which to stand to assert that absolute negative.
Which you don't. Because you can't.
Notice this --- you're asserting the negative; I am not asserting a positive. The only burden of proof is yours.
When you and I reach our ten thousandth birthdays, let's meet back here and see what we found out.
Get it now?
Very easy to do. First, we have increased the GHGs in the atmosphere very significantly. CO2 by over 40%, CH4 by about 250%. Second, we know from the absorption spectra of CO2 and CH4 that they absorb longwave IR, and warm the atmosphere, and, by back radiaton, the ground.Here's some more reading for ya.....
The history of ice on Earth
The history of ice on Earth
By Michael Marshall
Primitive humans, clad in animal skins, trekking across vast expanses of ice in a desperate search to find food. That’s the image that comes to mind when most of us think about an ice age.
But in fact there have been many ice ages, most of them long before humans made their first appearance. And the familiar picture of an ice age is of a comparatively mild one: others were so severe that the entire Earth froze over, for tens or even hundreds of millions of years.
In fact, the planet seems to have three main settings: “greenhouse”, when tropical temperatures extend to the poles and there are no ice sheets at all; “icehouse”, when there is some permanent ice, although its extent varies greatly; and “snowball”, in which the planet’s entire surface is frozen over.
Why the ice periodically advances – and why it retreats again – is a mystery that glaciologists have only just started to unravel. Here’s our recap of all the back and forth they’re trying to explain.
Snowball Earth
2.4 to 2.1 billion years ago
The Huronian glaciation is the oldest ice age we know about. The Earth was just over 2 billion years old, and home only to unicellular life-forms.
The early stages of the Huronian, from 2.4 to 2.3 billion years ago, seem to have been particularly severe, with the entire planet frozen over in the first “snowball Earth”. This may have been triggered by a 250-million-year lull in volcanic activity, which would have meant less carbon dioxide being pumped into the atmosphere, and a reduced greenhouse effect.
Deep freeze
850 to 630 million years ago
During the 200 million years of the Cryogenian period, the Earth was plunged into some of the deepest cold it has ever experienced – and the emergence of complex life may have caused it.
One theory is that the glaciation was triggered by the evolution of large cells, and possibly also multicellular organisms, that sank to the seabed after dying. This would have sucked CO2 out of the atmosphere, weakening the greenhouse effect and thus lowering global temperatures.
There seem to have been two distinct Cryogenian ice ages: the so-called Sturtian glaciation between 750 and 700 million years ago, followed by the Varanger (or Marinoan) glaciation, 660 to 635 million years ago. There’s some evidence that Earth became a snowball at times during the big freezes, but researchers are still trying to work out exactly what happened.
Mass extinction
460 to 430 million years ago
Straddling the late Ordovician period and the early Silurian period, the Andean-Saharan ice age was marked by a mass extinction, the second most severe in Earth’s history.
The die-off was surpassed only by the gargantuan Permian extinction 250 million years ago. But as the ecosystem recovered after the freeze, it expanded, with land plants becoming common over the course of the Silurian period. And those plants may have caused the next great ice age.
Plants invade the land
360 to 260 million years ago
Like the Cryogenian glaciation, the Karoo ice age featured two peaks in ice cover that may well have been distinct ice ages. They took place in the Mississipian period, 359 to 318 million years ago, and again in the Pennsylvanian 318 to 299 million years ago.
These ice ages may have been the result of the expansion of land plants that followed the Cryogenian. As plants spread over the planet, they absorbed CO2 from the atmosphere and released oxygen (PDF). As a result CO2 levels fell and the greenhouse effect weakened, triggering an ice age.
There is some evidence that the ice came and went in regular cycles, driven by changes in Earth’s orbit. If true, this would mean that the Karoo ice age operated in much the same way as the current one.
Antarctica freezes over
14 million years ago
Antarctica wasn’t always a frozen wasteland. It wasn’t until around 34 million years ago that the first small glaciers formed on the tops of Antarctica’s mountains. And it was 20 million years later, when world-wide temperatures dropped by 8 °C, that the glaciers’ ice froze onto the rock, and the southern ice sheet was born.
This temperature drop was triggered by the rise of the Himalayas. As they grew higher they were exposed to increased weathering, which sucked CO2 out of the atmosphere and reduced the greenhouse effect.
The northern hemisphere remained relatively ice-free for longer, with Greenland and the Arctic becoming heavily glaciated only around 3.2 million years ago.
Latest advance of the ice
2.58 million years ago
The Quaternary glaciation started just a few million years ago – and is still going on. So its history is relatively recent, in geological terms, and can be studied in far more detail than the others’. It’s evident that the ice sheets have gone through multiple stages of growth and retreat over the course of the Quaternary.
During “glacial” stages, the temperature was low and ice extended far away from the poles. During “interglacials”, the temperature was somewhat warmer and the ice retreated. Brief, inconclusive periods of advancing ice – typically lasting less than 10,000 years – are called “stadials”; conversely, periods when the ice retreated, but only briefly, are called “interstadials”.
The main trigger for the Quaternary glaciation was the continuing fall in the level of CO2 in the atmosphere due to the weathering of the Himalayas. However, the timing of the glacials and interglacials was driven by periodic changes in Earth’s orbit that change the amount of sunshine reaching various parts of the planet. The effect of these small orbital changes was amplified by positive feedbacks, such as changes in greenhouse gas levels.
During the first two-thirds of the Quaternary, the ice advanced and retreated roughly every 41,000 years – the same tempo as the changes in the tilt of Earth’s axis. About a million years ago, the ice switched to a 100,000-year cycle for reasons that were until recently a mystery. Now more detailed information about the timing of the ice’s movements may have helped glaciologists find an answer.
To make matters more complicated still, the ice didn’t advance and retreat simultaneously all around the world. Often it would begin advancing on one continent, with the others only being covered thousands of years later, and then linger on a few continents several millennia after it had disappeared from the others.
So there were actually many overlapping glaciations within the Quaternary, each separately named: the Bavelian and Cromerian complexes of glacials and interglacials; the Elsterian glacial; the Holsteinian interglacial and the Saalian glaciation, among others.
Between 130,000 and 114,000 years ago, the ice retreated during the Eemian interglacial – and then advanced again to create the glacial that most people know as “the ice age”.
Our ice age
110,000 to 12,000 years ago
The cool temperatures of the Quaternary may have allowed our brains to become much larger than those of our of hominid ancestors. While that’s still open to debate, it’s plausible that the most recent glacial period left its mark on our species.
Neanderthals, with whom we shared the planet until just before the last glacial maximum, 20,000 years ago, may have struggled to survive as the rising and falling ice ate away at their habitat – although many other explanations for their extinction have been suggested. What is beyond doubt is that Homo sapiens survived and turned to farming soon after the ice retreated, setting the stage for the rise of modern civilisation.
As the glacial period drew to a close and temperatures began to rise, there were two final cold snaps. First, the chilly “Older Dryas” of 14,700 to 13,400 years ago transformed most of Europe from forest to tundra, like modern-day Siberia. After a brief respite, the Younger Dryas, between 12,800 to 11,500 years ago, froze Europe solid within a matter of months – probably as a result of meltwater from retreating glaciers shutting down the Atlantic Ocean’s “conveyor-belt” current, although a cometary impact has also been blamed.
Twelve thousand years ago, the great ice sheets retreated at the beginning of the latest interglacial – the Flandrian – allowing humans to return to northern latitudes. This period has been relatively warm, and the climate relatively stable, although it has been slightly colder than the last interglacial, the Eemian, and sea levels are currently at least 3 metres lower – differences that are being closely scrutinised by researchers keen to understand how our climate will develop.
But this respite from the ice is likely to prove short-lived, at least in geological terms. Human effects on the climate notwithstanding, the cycle will continue to turn, the hothouse period will some day come to an end – and the ice sheets will descend again.
And here is another lil tidbit...
Sahara Desert Was Once Lush and Populated
At the end of the last Ice Age, the Sahara Desert was just as dry and uninviting as it is today. But sandwiched between two periods of extreme dryness were a few millennia of plentiful rainfall and lush vegetation.
During these few thousand years, prehistoric humans left the congested Nile Valley and established settlements around rain pools, green valleys, and rivers.
The ancient climate shift and its effects are detailed in the July 21 issue of the journal Science.
When the rains came
Some 12,000 years ago, the only place to live along the eastern Sahara Desert was the Nile Valley. Being so crowded, prime real estate in the Nile Valley was difficult to come by. Disputes over land were often settled with the fist, as evidenced by the cemetery of Jebel Sahaba where many of the buried individuals had died a violent death.
But around 10,500 years ago, a sudden burst of monsoon rains over the vast desert transformed the region into habitable land.
This opened the door for humans to move into the area, as evidenced by the researcher's 500 new radiocarbon dates of human and animal remains from more than 150 excavation sites.
"The climate change at [10,500 years ago] which turned most of the [3.8 million square mile] large Sahara into a savannah-type environment happened within a few hundred years only, certainly within less than 500 years," said study team member Stefan Kroepelin of the University of Cologne in Germany.
Frolicking in pools
In the Egyptian Sahara, semi-arid conditions allowed for grasses and shrubs to grow, with some trees sprouting in valleys and near groundwater sources. The vegetation and small, episodic rain pools enticed animals well adapted to dry conditions, such as giraffes, to enter the area as well.
Humans also frolicked in the rain pools, as depicted in rock art from Southwest Egypt.
In the more southern Sudanese Sahara, lush vegetation, hearty trees, and permanent freshwater lakes persisted over millennia. There were even large rivers, such as the Wadi Howar, once the largest tributary to the Nile from the Sahara.
"Wildlife included very demanding species such as elephants, rhinos, hippos, crocodiles, and more than 30 species of fish up to 2 meters (6 feet) big," Kroepelin told LiveScience.
A timeline of Sahara occupation [See Map]:
- 22,000 to 10,500 years ago: The Sahara was devoid of any human occupation outside the Nile Valley and extended 250 miles further south than it does today.
- 10,500 to 9,000 years ago: Monsoon rains begin sweeping into the Sahara, transforming the region into a habitable area swiftly settled by Nile Valley dwellers.
- 9,000 to 7,300 years ago: Continued rains, vegetation growth, and animal migrations lead to well established human settlements, including the introduction of domesticated livestock such as sheep and goats.
Both articles address the fact of the changing climate as a natural occurrence. There is nothing man has done to bring it about, nor is there anything man can do to stop it.
- 7,300 to 5,500 years ago: Retreating monsoonal rains initiate desiccation in the Egyptian Sahara, prompting humans to move to remaining habitable niches in Sudanese Sahara. The end of the rains and return of desert conditions throughout the Sahara after 5,500 coincides with population return to the Nile Valley and the beginning of pharaonic society.
Perhaps there's some troglodyte living in a cave somewhere that actually doesn't know about ice ages and warming and cooling trends. This isn't news.
Just as obviously humans before the Industrial Revolution had no influence on that. But you can't sit in your easy chair an flatly declare we don't in the present day, simply because it's what you would like to be true. The fact is you have nowhere near the perspective to make such an assessment. At all. That's just delusions-of-omniscience arrogance.
As is the deliberate conflation of "weather" with "climate".
So then explain just what we humans have done in the last 300 years to contribute to the Global Climate Change......and include links to back it up.
And here is a presentation to the AGU by one of the top scientists and glaciaologists on earth, Dr. Richard Alley that discusses the known historical affect of CO2;
You see, GHGs don't care whether they came from a Trapp volcanic eruption cooking coal seams, or mankind burning fossil fuels, they simply do what the physics say they should do.
Very easy to do. First, we have increased the GHGs in the atmosphere very significantly. CO2 by over 40%, CH4 by about 250%. Second, we know from the absorption spectra of CO2 and CH4 that they absorb longwave IR, and warm the atmosphere, and, by back radiaton, the ground.Here's some more reading for ya.....
The history of ice on Earth
The history of ice on Earth
By Michael Marshall
Primitive humans, clad in animal skins, trekking across vast expanses of ice in a desperate search to find food. That’s the image that comes to mind when most of us think about an ice age.
But in fact there have been many ice ages, most of them long before humans made their first appearance. And the familiar picture of an ice age is of a comparatively mild one: others were so severe that the entire Earth froze over, for tens or even hundreds of millions of years.
In fact, the planet seems to have three main settings: “greenhouse”, when tropical temperatures extend to the poles and there are no ice sheets at all; “icehouse”, when there is some permanent ice, although its extent varies greatly; and “snowball”, in which the planet’s entire surface is frozen over.
Why the ice periodically advances – and why it retreats again – is a mystery that glaciologists have only just started to unravel. Here’s our recap of all the back and forth they’re trying to explain.
Snowball Earth
2.4 to 2.1 billion years ago
The Huronian glaciation is the oldest ice age we know about. The Earth was just over 2 billion years old, and home only to unicellular life-forms.
The early stages of the Huronian, from 2.4 to 2.3 billion years ago, seem to have been particularly severe, with the entire planet frozen over in the first “snowball Earth”. This may have been triggered by a 250-million-year lull in volcanic activity, which would have meant less carbon dioxide being pumped into the atmosphere, and a reduced greenhouse effect.
Deep freeze
850 to 630 million years ago
During the 200 million years of the Cryogenian period, the Earth was plunged into some of the deepest cold it has ever experienced – and the emergence of complex life may have caused it.
One theory is that the glaciation was triggered by the evolution of large cells, and possibly also multicellular organisms, that sank to the seabed after dying. This would have sucked CO2 out of the atmosphere, weakening the greenhouse effect and thus lowering global temperatures.
There seem to have been two distinct Cryogenian ice ages: the so-called Sturtian glaciation between 750 and 700 million years ago, followed by the Varanger (or Marinoan) glaciation, 660 to 635 million years ago. There’s some evidence that Earth became a snowball at times during the big freezes, but researchers are still trying to work out exactly what happened.
Mass extinction
460 to 430 million years ago
Straddling the late Ordovician period and the early Silurian period, the Andean-Saharan ice age was marked by a mass extinction, the second most severe in Earth’s history.
The die-off was surpassed only by the gargantuan Permian extinction 250 million years ago. But as the ecosystem recovered after the freeze, it expanded, with land plants becoming common over the course of the Silurian period. And those plants may have caused the next great ice age.
Plants invade the land
360 to 260 million years ago
Like the Cryogenian glaciation, the Karoo ice age featured two peaks in ice cover that may well have been distinct ice ages. They took place in the Mississipian period, 359 to 318 million years ago, and again in the Pennsylvanian 318 to 299 million years ago.
These ice ages may have been the result of the expansion of land plants that followed the Cryogenian. As plants spread over the planet, they absorbed CO2 from the atmosphere and released oxygen (PDF). As a result CO2 levels fell and the greenhouse effect weakened, triggering an ice age.
There is some evidence that the ice came and went in regular cycles, driven by changes in Earth’s orbit. If true, this would mean that the Karoo ice age operated in much the same way as the current one.
Antarctica freezes over
14 million years ago
Antarctica wasn’t always a frozen wasteland. It wasn’t until around 34 million years ago that the first small glaciers formed on the tops of Antarctica’s mountains. And it was 20 million years later, when world-wide temperatures dropped by 8 °C, that the glaciers’ ice froze onto the rock, and the southern ice sheet was born.
This temperature drop was triggered by the rise of the Himalayas. As they grew higher they were exposed to increased weathering, which sucked CO2 out of the atmosphere and reduced the greenhouse effect.
The northern hemisphere remained relatively ice-free for longer, with Greenland and the Arctic becoming heavily glaciated only around 3.2 million years ago.
Latest advance of the ice
2.58 million years ago
The Quaternary glaciation started just a few million years ago – and is still going on. So its history is relatively recent, in geological terms, and can be studied in far more detail than the others’. It’s evident that the ice sheets have gone through multiple stages of growth and retreat over the course of the Quaternary.
During “glacial” stages, the temperature was low and ice extended far away from the poles. During “interglacials”, the temperature was somewhat warmer and the ice retreated. Brief, inconclusive periods of advancing ice – typically lasting less than 10,000 years – are called “stadials”; conversely, periods when the ice retreated, but only briefly, are called “interstadials”.
The main trigger for the Quaternary glaciation was the continuing fall in the level of CO2 in the atmosphere due to the weathering of the Himalayas. However, the timing of the glacials and interglacials was driven by periodic changes in Earth’s orbit that change the amount of sunshine reaching various parts of the planet. The effect of these small orbital changes was amplified by positive feedbacks, such as changes in greenhouse gas levels.
During the first two-thirds of the Quaternary, the ice advanced and retreated roughly every 41,000 years – the same tempo as the changes in the tilt of Earth’s axis. About a million years ago, the ice switched to a 100,000-year cycle for reasons that were until recently a mystery. Now more detailed information about the timing of the ice’s movements may have helped glaciologists find an answer.
To make matters more complicated still, the ice didn’t advance and retreat simultaneously all around the world. Often it would begin advancing on one continent, with the others only being covered thousands of years later, and then linger on a few continents several millennia after it had disappeared from the others.
So there were actually many overlapping glaciations within the Quaternary, each separately named: the Bavelian and Cromerian complexes of glacials and interglacials; the Elsterian glacial; the Holsteinian interglacial and the Saalian glaciation, among others.
Between 130,000 and 114,000 years ago, the ice retreated during the Eemian interglacial – and then advanced again to create the glacial that most people know as “the ice age”.
Our ice age
110,000 to 12,000 years ago
The cool temperatures of the Quaternary may have allowed our brains to become much larger than those of our of hominid ancestors. While that’s still open to debate, it’s plausible that the most recent glacial period left its mark on our species.
Neanderthals, with whom we shared the planet until just before the last glacial maximum, 20,000 years ago, may have struggled to survive as the rising and falling ice ate away at their habitat – although many other explanations for their extinction have been suggested. What is beyond doubt is that Homo sapiens survived and turned to farming soon after the ice retreated, setting the stage for the rise of modern civilisation.
As the glacial period drew to a close and temperatures began to rise, there were two final cold snaps. First, the chilly “Older Dryas” of 14,700 to 13,400 years ago transformed most of Europe from forest to tundra, like modern-day Siberia. After a brief respite, the Younger Dryas, between 12,800 to 11,500 years ago, froze Europe solid within a matter of months – probably as a result of meltwater from retreating glaciers shutting down the Atlantic Ocean’s “conveyor-belt” current, although a cometary impact has also been blamed.
Twelve thousand years ago, the great ice sheets retreated at the beginning of the latest interglacial – the Flandrian – allowing humans to return to northern latitudes. This period has been relatively warm, and the climate relatively stable, although it has been slightly colder than the last interglacial, the Eemian, and sea levels are currently at least 3 metres lower – differences that are being closely scrutinised by researchers keen to understand how our climate will develop.
But this respite from the ice is likely to prove short-lived, at least in geological terms. Human effects on the climate notwithstanding, the cycle will continue to turn, the hothouse period will some day come to an end – and the ice sheets will descend again.
And here is another lil tidbit...
Sahara Desert Was Once Lush and Populated
At the end of the last Ice Age, the Sahara Desert was just as dry and uninviting as it is today. But sandwiched between two periods of extreme dryness were a few millennia of plentiful rainfall and lush vegetation.
During these few thousand years, prehistoric humans left the congested Nile Valley and established settlements around rain pools, green valleys, and rivers.
The ancient climate shift and its effects are detailed in the July 21 issue of the journal Science.
When the rains came
Some 12,000 years ago, the only place to live along the eastern Sahara Desert was the Nile Valley. Being so crowded, prime real estate in the Nile Valley was difficult to come by. Disputes over land were often settled with the fist, as evidenced by the cemetery of Jebel Sahaba where many of the buried individuals had died a violent death.
But around 10,500 years ago, a sudden burst of monsoon rains over the vast desert transformed the region into habitable land.
This opened the door for humans to move into the area, as evidenced by the researcher's 500 new radiocarbon dates of human and animal remains from more than 150 excavation sites.
"The climate change at [10,500 years ago] which turned most of the [3.8 million square mile] large Sahara into a savannah-type environment happened within a few hundred years only, certainly within less than 500 years," said study team member Stefan Kroepelin of the University of Cologne in Germany.
Frolicking in pools
In the Egyptian Sahara, semi-arid conditions allowed for grasses and shrubs to grow, with some trees sprouting in valleys and near groundwater sources. The vegetation and small, episodic rain pools enticed animals well adapted to dry conditions, such as giraffes, to enter the area as well.
Humans also frolicked in the rain pools, as depicted in rock art from Southwest Egypt.
In the more southern Sudanese Sahara, lush vegetation, hearty trees, and permanent freshwater lakes persisted over millennia. There were even large rivers, such as the Wadi Howar, once the largest tributary to the Nile from the Sahara.
"Wildlife included very demanding species such as elephants, rhinos, hippos, crocodiles, and more than 30 species of fish up to 2 meters (6 feet) big," Kroepelin told LiveScience.
A timeline of Sahara occupation [See Map]:
- 22,000 to 10,500 years ago: The Sahara was devoid of any human occupation outside the Nile Valley and extended 250 miles further south than it does today.
- 10,500 to 9,000 years ago: Monsoon rains begin sweeping into the Sahara, transforming the region into a habitable area swiftly settled by Nile Valley dwellers.
- 9,000 to 7,300 years ago: Continued rains, vegetation growth, and animal migrations lead to well established human settlements, including the introduction of domesticated livestock such as sheep and goats.
Both articles address the fact of the changing climate as a natural occurrence. There is nothing man has done to bring it about, nor is there anything man can do to stop it.
- 7,300 to 5,500 years ago: Retreating monsoonal rains initiate desiccation in the Egyptian Sahara, prompting humans to move to remaining habitable niches in Sudanese Sahara. The end of the rains and return of desert conditions throughout the Sahara after 5,500 coincides with population return to the Nile Valley and the beginning of pharaonic society.
Perhaps there's some troglodyte living in a cave somewhere that actually doesn't know about ice ages and warming and cooling trends. This isn't news.
Just as obviously humans before the Industrial Revolution had no influence on that. But you can't sit in your easy chair an flatly declare we don't in the present day, simply because it's what you would like to be true. The fact is you have nowhere near the perspective to make such an assessment. At all. That's just delusions-of-omniscience arrogance.
As is the deliberate conflation of "weather" with "climate".
So then explain just what we humans have done in the last 300 years to contribute to the Global Climate Change......and include links to back it up.
And here is a presentation to the AGU by one of the top scientists and glaciaologists on earth, Dr. Richard Alley that discusses the known historical affect of CO2;
You see, GHGs don't care whether they came from a Trapp volcanic eruption cooking coal seams, or mankind burning fossil fuels, they simply do what the physics say they should do.
You see, GHGs don't care whether they came from a Trapp volcanic eruption cooking coal seams, or mankind burning fossil fuels, they simply do what the physics say they should do
and that sounds like it's a natural occurrence.
Very easy to do. First, we have increased the GHGs in the atmosphere very significantly. CO2 by over 40%, CH4 by about 250%. Second, we know from the absorption spectra of CO2 and CH4 that they absorb longwave IR, and warm the atmosphere, and, by back radiaton, the ground.Here's some more reading for ya.....
The history of ice on Earth
The history of ice on Earth
By Michael Marshall
Primitive humans, clad in animal skins, trekking across vast expanses of ice in a desperate search to find food. That’s the image that comes to mind when most of us think about an ice age.
But in fact there have been many ice ages, most of them long before humans made their first appearance. And the familiar picture of an ice age is of a comparatively mild one: others were so severe that the entire Earth froze over, for tens or even hundreds of millions of years.
In fact, the planet seems to have three main settings: “greenhouse”, when tropical temperatures extend to the poles and there are no ice sheets at all; “icehouse”, when there is some permanent ice, although its extent varies greatly; and “snowball”, in which the planet’s entire surface is frozen over.
Why the ice periodically advances – and why it retreats again – is a mystery that glaciologists have only just started to unravel. Here’s our recap of all the back and forth they’re trying to explain.
Snowball Earth
2.4 to 2.1 billion years ago
The Huronian glaciation is the oldest ice age we know about. The Earth was just over 2 billion years old, and home only to unicellular life-forms.
The early stages of the Huronian, from 2.4 to 2.3 billion years ago, seem to have been particularly severe, with the entire planet frozen over in the first “snowball Earth”. This may have been triggered by a 250-million-year lull in volcanic activity, which would have meant less carbon dioxide being pumped into the atmosphere, and a reduced greenhouse effect.
Deep freeze
850 to 630 million years ago
During the 200 million years of the Cryogenian period, the Earth was plunged into some of the deepest cold it has ever experienced – and the emergence of complex life may have caused it.
One theory is that the glaciation was triggered by the evolution of large cells, and possibly also multicellular organisms, that sank to the seabed after dying. This would have sucked CO2 out of the atmosphere, weakening the greenhouse effect and thus lowering global temperatures.
There seem to have been two distinct Cryogenian ice ages: the so-called Sturtian glaciation between 750 and 700 million years ago, followed by the Varanger (or Marinoan) glaciation, 660 to 635 million years ago. There’s some evidence that Earth became a snowball at times during the big freezes, but researchers are still trying to work out exactly what happened.
Mass extinction
460 to 430 million years ago
Straddling the late Ordovician period and the early Silurian period, the Andean-Saharan ice age was marked by a mass extinction, the second most severe in Earth’s history.
The die-off was surpassed only by the gargantuan Permian extinction 250 million years ago. But as the ecosystem recovered after the freeze, it expanded, with land plants becoming common over the course of the Silurian period. And those plants may have caused the next great ice age.
Plants invade the land
360 to 260 million years ago
Like the Cryogenian glaciation, the Karoo ice age featured two peaks in ice cover that may well have been distinct ice ages. They took place in the Mississipian period, 359 to 318 million years ago, and again in the Pennsylvanian 318 to 299 million years ago.
These ice ages may have been the result of the expansion of land plants that followed the Cryogenian. As plants spread over the planet, they absorbed CO2 from the atmosphere and released oxygen (PDF). As a result CO2 levels fell and the greenhouse effect weakened, triggering an ice age.
There is some evidence that the ice came and went in regular cycles, driven by changes in Earth’s orbit. If true, this would mean that the Karoo ice age operated in much the same way as the current one.
Antarctica freezes over
14 million years ago
Antarctica wasn’t always a frozen wasteland. It wasn’t until around 34 million years ago that the first small glaciers formed on the tops of Antarctica’s mountains. And it was 20 million years later, when world-wide temperatures dropped by 8 °C, that the glaciers’ ice froze onto the rock, and the southern ice sheet was born.
This temperature drop was triggered by the rise of the Himalayas. As they grew higher they were exposed to increased weathering, which sucked CO2 out of the atmosphere and reduced the greenhouse effect.
The northern hemisphere remained relatively ice-free for longer, with Greenland and the Arctic becoming heavily glaciated only around 3.2 million years ago.
Latest advance of the ice
2.58 million years ago
The Quaternary glaciation started just a few million years ago – and is still going on. So its history is relatively recent, in geological terms, and can be studied in far more detail than the others’. It’s evident that the ice sheets have gone through multiple stages of growth and retreat over the course of the Quaternary.
During “glacial” stages, the temperature was low and ice extended far away from the poles. During “interglacials”, the temperature was somewhat warmer and the ice retreated. Brief, inconclusive periods of advancing ice – typically lasting less than 10,000 years – are called “stadials”; conversely, periods when the ice retreated, but only briefly, are called “interstadials”.
The main trigger for the Quaternary glaciation was the continuing fall in the level of CO2 in the atmosphere due to the weathering of the Himalayas. However, the timing of the glacials and interglacials was driven by periodic changes in Earth’s orbit that change the amount of sunshine reaching various parts of the planet. The effect of these small orbital changes was amplified by positive feedbacks, such as changes in greenhouse gas levels.
During the first two-thirds of the Quaternary, the ice advanced and retreated roughly every 41,000 years – the same tempo as the changes in the tilt of Earth’s axis. About a million years ago, the ice switched to a 100,000-year cycle for reasons that were until recently a mystery. Now more detailed information about the timing of the ice’s movements may have helped glaciologists find an answer.
To make matters more complicated still, the ice didn’t advance and retreat simultaneously all around the world. Often it would begin advancing on one continent, with the others only being covered thousands of years later, and then linger on a few continents several millennia after it had disappeared from the others.
So there were actually many overlapping glaciations within the Quaternary, each separately named: the Bavelian and Cromerian complexes of glacials and interglacials; the Elsterian glacial; the Holsteinian interglacial and the Saalian glaciation, among others.
Between 130,000 and 114,000 years ago, the ice retreated during the Eemian interglacial – and then advanced again to create the glacial that most people know as “the ice age”.
Our ice age
110,000 to 12,000 years ago
The cool temperatures of the Quaternary may have allowed our brains to become much larger than those of our of hominid ancestors. While that’s still open to debate, it’s plausible that the most recent glacial period left its mark on our species.
Neanderthals, with whom we shared the planet until just before the last glacial maximum, 20,000 years ago, may have struggled to survive as the rising and falling ice ate away at their habitat – although many other explanations for their extinction have been suggested. What is beyond doubt is that Homo sapiens survived and turned to farming soon after the ice retreated, setting the stage for the rise of modern civilisation.
As the glacial period drew to a close and temperatures began to rise, there were two final cold snaps. First, the chilly “Older Dryas” of 14,700 to 13,400 years ago transformed most of Europe from forest to tundra, like modern-day Siberia. After a brief respite, the Younger Dryas, between 12,800 to 11,500 years ago, froze Europe solid within a matter of months – probably as a result of meltwater from retreating glaciers shutting down the Atlantic Ocean’s “conveyor-belt” current, although a cometary impact has also been blamed.
Twelve thousand years ago, the great ice sheets retreated at the beginning of the latest interglacial – the Flandrian – allowing humans to return to northern latitudes. This period has been relatively warm, and the climate relatively stable, although it has been slightly colder than the last interglacial, the Eemian, and sea levels are currently at least 3 metres lower – differences that are being closely scrutinised by researchers keen to understand how our climate will develop.
But this respite from the ice is likely to prove short-lived, at least in geological terms. Human effects on the climate notwithstanding, the cycle will continue to turn, the hothouse period will some day come to an end – and the ice sheets will descend again.
And here is another lil tidbit...
Sahara Desert Was Once Lush and Populated
At the end of the last Ice Age, the Sahara Desert was just as dry and uninviting as it is today. But sandwiched between two periods of extreme dryness were a few millennia of plentiful rainfall and lush vegetation.
During these few thousand years, prehistoric humans left the congested Nile Valley and established settlements around rain pools, green valleys, and rivers.
The ancient climate shift and its effects are detailed in the July 21 issue of the journal Science.
When the rains came
Some 12,000 years ago, the only place to live along the eastern Sahara Desert was the Nile Valley. Being so crowded, prime real estate in the Nile Valley was difficult to come by. Disputes over land were often settled with the fist, as evidenced by the cemetery of Jebel Sahaba where many of the buried individuals had died a violent death.
But around 10,500 years ago, a sudden burst of monsoon rains over the vast desert transformed the region into habitable land.
This opened the door for humans to move into the area, as evidenced by the researcher's 500 new radiocarbon dates of human and animal remains from more than 150 excavation sites.
"The climate change at [10,500 years ago] which turned most of the [3.8 million square mile] large Sahara into a savannah-type environment happened within a few hundred years only, certainly within less than 500 years," said study team member Stefan Kroepelin of the University of Cologne in Germany.
Frolicking in pools
In the Egyptian Sahara, semi-arid conditions allowed for grasses and shrubs to grow, with some trees sprouting in valleys and near groundwater sources. The vegetation and small, episodic rain pools enticed animals well adapted to dry conditions, such as giraffes, to enter the area as well.
Humans also frolicked in the rain pools, as depicted in rock art from Southwest Egypt.
In the more southern Sudanese Sahara, lush vegetation, hearty trees, and permanent freshwater lakes persisted over millennia. There were even large rivers, such as the Wadi Howar, once the largest tributary to the Nile from the Sahara.
"Wildlife included very demanding species such as elephants, rhinos, hippos, crocodiles, and more than 30 species of fish up to 2 meters (6 feet) big," Kroepelin told LiveScience.
A timeline of Sahara occupation [See Map]:
- 22,000 to 10,500 years ago: The Sahara was devoid of any human occupation outside the Nile Valley and extended 250 miles further south than it does today.
- 10,500 to 9,000 years ago: Monsoon rains begin sweeping into the Sahara, transforming the region into a habitable area swiftly settled by Nile Valley dwellers.
- 9,000 to 7,300 years ago: Continued rains, vegetation growth, and animal migrations lead to well established human settlements, including the introduction of domesticated livestock such as sheep and goats.
Both articles address the fact of the changing climate as a natural occurrence. There is nothing man has done to bring it about, nor is there anything man can do to stop it.
- 7,300 to 5,500 years ago: Retreating monsoonal rains initiate desiccation in the Egyptian Sahara, prompting humans to move to remaining habitable niches in Sudanese Sahara. The end of the rains and return of desert conditions throughout the Sahara after 5,500 coincides with population return to the Nile Valley and the beginning of pharaonic society.
Perhaps there's some troglodyte living in a cave somewhere that actually doesn't know about ice ages and warming and cooling trends. This isn't news.
Just as obviously humans before the Industrial Revolution had no influence on that. But you can't sit in your easy chair an flatly declare we don't in the present day, simply because it's what you would like to be true. The fact is you have nowhere near the perspective to make such an assessment. At all. That's just delusions-of-omniscience arrogance.
As is the deliberate conflation of "weather" with "climate".
So then explain just what we humans have done in the last 300 years to contribute to the Global Climate Change......and include links to back it up.
And here is a presentation to the AGU by one of the top scientists and glaciaologists on earth, Dr. Richard Alley that discusses the known historical affect of CO2;
You see, GHGs don't care whether they came from a Trapp volcanic eruption cooking coal seams, or mankind burning fossil fuels, they simply do what the physics say they should do.
You see, GHGs don't care whether they came from a Trapp volcanic eruption cooking coal seams, or mankind burning fossil fuels, they simply do what the physics say they should do
and that sounds like it's a natural occurrence.
The GHGs from the coal seams and the Trapp Volcanics was a natural occurance, and resulted in the greatest extinction the earth has ever seen. Mankind burning fossil fuel is hardly a natural occurance, and we are changing the climate far faster than the Trapp Volcanics did. Did you bother to read any of the references that I listed, or are you going to simply continue posting your ignorance on this board.
Fact: There is more C02 in our atmosphere than there has ever been. The build up in C02 comes from burning fossil fuels. C02 in the atmosphere leads to atmospheric warming.Here's some more reading for ya.....
The history of ice on Earth
The history of ice on Earth
By Michael Marshall
Primitive humans, clad in animal skins, trekking across vast expanses of ice in a desperate search to find food. That’s the image that comes to mind when most of us think about an ice age.
But in fact there have been many ice ages, most of them long before humans made their first appearance. And the familiar picture of an ice age is of a comparatively mild one: others were so severe that the entire Earth froze over, for tens or even hundreds of millions of years.
In fact, the planet seems to have three main settings: “greenhouse”, when tropical temperatures extend to the poles and there are no ice sheets at all; “icehouse”, when there is some permanent ice, although its extent varies greatly; and “snowball”, in which the planet’s entire surface is frozen over.
Why the ice periodically advances – and why it retreats again – is a mystery that glaciologists have only just started to unravel. Here’s our recap of all the back and forth they’re trying to explain.
Snowball Earth
2.4 to 2.1 billion years ago
The Huronian glaciation is the oldest ice age we know about. The Earth was just over 2 billion years old, and home only to unicellular life-forms.
The early stages of the Huronian, from 2.4 to 2.3 billion years ago, seem to have been particularly severe, with the entire planet frozen over in the first “snowball Earth”. This may have been triggered by a 250-million-year lull in volcanic activity, which would have meant less carbon dioxide being pumped into the atmosphere, and a reduced greenhouse effect.
Deep freeze
850 to 630 million years ago
During the 200 million years of the Cryogenian period, the Earth was plunged into some of the deepest cold it has ever experienced – and the emergence of complex life may have caused it.
One theory is that the glaciation was triggered by the evolution of large cells, and possibly also multicellular organisms, that sank to the seabed after dying. This would have sucked CO2 out of the atmosphere, weakening the greenhouse effect and thus lowering global temperatures.
There seem to have been two distinct Cryogenian ice ages: the so-called Sturtian glaciation between 750 and 700 million years ago, followed by the Varanger (or Marinoan) glaciation, 660 to 635 million years ago. There’s some evidence that Earth became a snowball at times during the big freezes, but researchers are still trying to work out exactly what happened.
Mass extinction
460 to 430 million years ago
Straddling the late Ordovician period and the early Silurian period, the Andean-Saharan ice age was marked by a mass extinction, the second most severe in Earth’s history.
The die-off was surpassed only by the gargantuan Permian extinction 250 million years ago. But as the ecosystem recovered after the freeze, it expanded, with land plants becoming common over the course of the Silurian period. And those plants may have caused the next great ice age.
Plants invade the land
360 to 260 million years ago
Like the Cryogenian glaciation, the Karoo ice age featured two peaks in ice cover that may well have been distinct ice ages. They took place in the Mississipian period, 359 to 318 million years ago, and again in the Pennsylvanian 318 to 299 million years ago.
These ice ages may have been the result of the expansion of land plants that followed the Cryogenian. As plants spread over the planet, they absorbed CO2 from the atmosphere and released oxygen (PDF). As a result CO2 levels fell and the greenhouse effect weakened, triggering an ice age.
There is some evidence that the ice came and went in regular cycles, driven by changes in Earth’s orbit. If true, this would mean that the Karoo ice age operated in much the same way as the current one.
Antarctica freezes over
14 million years ago
Antarctica wasn’t always a frozen wasteland. It wasn’t until around 34 million years ago that the first small glaciers formed on the tops of Antarctica’s mountains. And it was 20 million years later, when world-wide temperatures dropped by 8 °C, that the glaciers’ ice froze onto the rock, and the southern ice sheet was born.
This temperature drop was triggered by the rise of the Himalayas. As they grew higher they were exposed to increased weathering, which sucked CO2 out of the atmosphere and reduced the greenhouse effect.
The northern hemisphere remained relatively ice-free for longer, with Greenland and the Arctic becoming heavily glaciated only around 3.2 million years ago.
Latest advance of the ice
2.58 million years ago
The Quaternary glaciation started just a few million years ago – and is still going on. So its history is relatively recent, in geological terms, and can be studied in far more detail than the others’. It’s evident that the ice sheets have gone through multiple stages of growth and retreat over the course of the Quaternary.
During “glacial” stages, the temperature was low and ice extended far away from the poles. During “interglacials”, the temperature was somewhat warmer and the ice retreated. Brief, inconclusive periods of advancing ice – typically lasting less than 10,000 years – are called “stadials”; conversely, periods when the ice retreated, but only briefly, are called “interstadials”.
The main trigger for the Quaternary glaciation was the continuing fall in the level of CO2 in the atmosphere due to the weathering of the Himalayas. However, the timing of the glacials and interglacials was driven by periodic changes in Earth’s orbit that change the amount of sunshine reaching various parts of the planet. The effect of these small orbital changes was amplified by positive feedbacks, such as changes in greenhouse gas levels.
During the first two-thirds of the Quaternary, the ice advanced and retreated roughly every 41,000 years – the same tempo as the changes in the tilt of Earth’s axis. About a million years ago, the ice switched to a 100,000-year cycle for reasons that were until recently a mystery. Now more detailed information about the timing of the ice’s movements may have helped glaciologists find an answer.
To make matters more complicated still, the ice didn’t advance and retreat simultaneously all around the world. Often it would begin advancing on one continent, with the others only being covered thousands of years later, and then linger on a few continents several millennia after it had disappeared from the others.
So there were actually many overlapping glaciations within the Quaternary, each separately named: the Bavelian and Cromerian complexes of glacials and interglacials; the Elsterian glacial; the Holsteinian interglacial and the Saalian glaciation, among others.
Between 130,000 and 114,000 years ago, the ice retreated during the Eemian interglacial – and then advanced again to create the glacial that most people know as “the ice age”.
Our ice age
110,000 to 12,000 years ago
The cool temperatures of the Quaternary may have allowed our brains to become much larger than those of our of hominid ancestors. While that’s still open to debate, it’s plausible that the most recent glacial period left its mark on our species.
Neanderthals, with whom we shared the planet until just before the last glacial maximum, 20,000 years ago, may have struggled to survive as the rising and falling ice ate away at their habitat – although many other explanations for their extinction have been suggested. What is beyond doubt is that Homo sapiens survived and turned to farming soon after the ice retreated, setting the stage for the rise of modern civilisation.
As the glacial period drew to a close and temperatures began to rise, there were two final cold snaps. First, the chilly “Older Dryas” of 14,700 to 13,400 years ago transformed most of Europe from forest to tundra, like modern-day Siberia. After a brief respite, the Younger Dryas, between 12,800 to 11,500 years ago, froze Europe solid within a matter of months – probably as a result of meltwater from retreating glaciers shutting down the Atlantic Ocean’s “conveyor-belt” current, although a cometary impact has also been blamed.
Twelve thousand years ago, the great ice sheets retreated at the beginning of the latest interglacial – the Flandrian – allowing humans to return to northern latitudes. This period has been relatively warm, and the climate relatively stable, although it has been slightly colder than the last interglacial, the Eemian, and sea levels are currently at least 3 metres lower – differences that are being closely scrutinised by researchers keen to understand how our climate will develop.
But this respite from the ice is likely to prove short-lived, at least in geological terms. Human effects on the climate notwithstanding, the cycle will continue to turn, the hothouse period will some day come to an end – and the ice sheets will descend again.
And here is another lil tidbit...
Sahara Desert Was Once Lush and Populated
At the end of the last Ice Age, the Sahara Desert was just as dry and uninviting as it is today. But sandwiched between two periods of extreme dryness were a few millennia of plentiful rainfall and lush vegetation.
During these few thousand years, prehistoric humans left the congested Nile Valley and established settlements around rain pools, green valleys, and rivers.
The ancient climate shift and its effects are detailed in the July 21 issue of the journal Science.
When the rains came
Some 12,000 years ago, the only place to live along the eastern Sahara Desert was the Nile Valley. Being so crowded, prime real estate in the Nile Valley was difficult to come by. Disputes over land were often settled with the fist, as evidenced by the cemetery of Jebel Sahaba where many of the buried individuals had died a violent death.
But around 10,500 years ago, a sudden burst of monsoon rains over the vast desert transformed the region into habitable land.
This opened the door for humans to move into the area, as evidenced by the researcher's 500 new radiocarbon dates of human and animal remains from more than 150 excavation sites.
"The climate change at [10,500 years ago] which turned most of the [3.8 million square mile] large Sahara into a savannah-type environment happened within a few hundred years only, certainly within less than 500 years," said study team member Stefan Kroepelin of the University of Cologne in Germany.
Frolicking in pools
In the Egyptian Sahara, semi-arid conditions allowed for grasses and shrubs to grow, with some trees sprouting in valleys and near groundwater sources. The vegetation and small, episodic rain pools enticed animals well adapted to dry conditions, such as giraffes, to enter the area as well.
Humans also frolicked in the rain pools, as depicted in rock art from Southwest Egypt.
In the more southern Sudanese Sahara, lush vegetation, hearty trees, and permanent freshwater lakes persisted over millennia. There were even large rivers, such as the Wadi Howar, once the largest tributary to the Nile from the Sahara.
"Wildlife included very demanding species such as elephants, rhinos, hippos, crocodiles, and more than 30 species of fish up to 2 meters (6 feet) big," Kroepelin told LiveScience.
A timeline of Sahara occupation [See Map]:
- 22,000 to 10,500 years ago: The Sahara was devoid of any human occupation outside the Nile Valley and extended 250 miles further south than it does today.
- 10,500 to 9,000 years ago: Monsoon rains begin sweeping into the Sahara, transforming the region into a habitable area swiftly settled by Nile Valley dwellers.
- 9,000 to 7,300 years ago: Continued rains, vegetation growth, and animal migrations lead to well established human settlements, including the introduction of domesticated livestock such as sheep and goats.
- 7,300 to 5,500 years ago: Retreating monsoonal rains initiate desiccation in the Egyptian Sahara, prompting humans to move to remaining habitable niches in Sudanese Sahara. The end of the rains and return of desert conditions throughout the Sahara after 5,500 coincides with population return to the Nile Valley and the beginning of pharaonic society.
Both articles address the fact of the changing climate as a natural occurrence. There is nothing man has done to bring it about, nor is there anything man can do to stop it.
