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Past Climates and Ice Ages


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#1
TT-SEA

Posted 20 April 2017 - 08:16 PM

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Hang on, lemme go get in my time machine and find out.

 

 

 

I would love to go back 1,000 or 5,000 years and see what my area looked like.   It would be fascinating because the mountains would all look the same.  


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#2
crf450ish

Posted 20 April 2017 - 08:24 PM

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That would be so fun... time travel to different weather events.

I would love to go back 1,000 or 5,000 years and see what my area looked like. It would be fascinating because the mountains would all look the same.



I'd like to see lake Missoula busting lose and carving out the scab lands.
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#3
Phil

Posted 20 April 2017 - 08:33 PM

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That would be so fun... time travel to different weather events.

I would love to go back 1,000 or 5,000 years and see what my area looked like. It would be fascinating because the mountains would all look the same.


I'd love to travel back to the last glacial maximum about 20,000 years ago. Would have been insane to live in that climate.

-PNW was a dry tundra, with savanna-esque grasslands and relatively little precip thanks to the frigid katabatic winds blowing off the ice sheet.

- Florida was almost as warm as today, perhaps even warmer at certain times, while Virginia was colder than modern day Barrow AK. Insane thermal gradient.

- California/SW US had the climate of the modern day PNW/coastal Alaska. Much wetter (the tropical Pacific was actually in a semi-permanent El Niño state through most of the last ice age, ironically). Conifers grew at the coasts down to Mexico, and a solid winter sea ice pack slid down the entire west coast, even down to San Diego, driven by the NPAC anticyclone.

- No ice sheets over Alaska/NE Siberia, where a huge, relatively warm anticyclone dominated. Would have been a -EPO type pattern on steroids.

- Most of Canada and the Northern US had a climate as cold as modern day Antarctica, with ice sheets towering miles high, altering planetary waves, etc.

- The northern half of the US saw the majority of its seasonal snowfall during the heart of summer. :lol:
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#4
dolt

Posted 20 April 2017 - 10:39 PM

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I'd love to travel back to the last glacial maximum about 20,000 years ago. Would have been insane to live in that climate.

-PNW was a dry tundra, with savanna-esque grasslands and relatively little precip thanks to the frigid katabatic winds blowing off the ice sheet.

- Florida was almost as warm as today, perhaps even warmer at certain times, while Virginia was colder than modern day Barrow AK. Insane thermal gradient.

- California/SW US had the climate of the modern day PNW/coastal Alaska. Much wetter (the tropical Pacific was actually in a semi-permanent El Niño state through most of the last ice age, ironically). Conifers grew at the coasts down to Mexico, and a solid winter sea ice pack slid down the entire west coast, even down to San Diego, driven by the NPAC anticyclone.

- No ice sheets over Alaska/NE Siberia, where a huge, relatively warm anticyclone dominated. Would have been a -EPO type pattern on steroids.

- Most of Canada and the Northern US had a climate as cold as modern day Antarctica, with ice sheets towering miles high, altering planetary waves, etc.

- The northern half of the US saw the majority of its seasonal snowfall during the heart of summer. :lol:

I respect your knowledge and contributions to this forum.  I'm curious, do you have a personal theory of what caused the last few ice ages?  Extreme solar minimums?  Volcanic eruptions?

 

My guess is that it was caused by massive and long lived volcanic eruptions.  I'm hopeful that the exact cause will be solved and proven within my lifetime.



#5
tenochtitlan

Posted 20 April 2017 - 11:23 PM

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I'd love to travel back to the last glacial maximum about 20,000 years ago. Would have been insane to live in that climate.

-PNW was a dry tundra, with savanna-esque grasslands and relatively little precip thanks to the frigid katabatic winds blowing off the ice sheet.

- Florida was almost as warm as today, perhaps even warmer at certain times, while Virginia was colder than modern day Barrow AK. Insane thermal gradient.

- California/SW US had the climate of the modern day PNW/coastal Alaska. Much wetter (the tropical Pacific was actually in a semi-permanent El Niño state through most of the last ice age, ironically). Conifers grew at the coasts down to Mexico, and a solid winter sea ice pack slid down the entire west coast, even down to San Diego, driven by the NPAC anticyclone.

- No ice sheets over Alaska/NE Siberia, where a huge, relatively warm anticyclone dominated. Would have been a -EPO type pattern on steroids.

- Most of Canada and the Northern US had a climate as cold as modern day Antarctica, with ice sheets towering miles high, altering planetary waves, etc.

- The northern half of the US saw the majority of its seasonal snowfall during the heart of summer. :lol:

It's crazy how much our success as humans comes down to the climate's stability. Even after we've gone through the Green Revolution and have so much technology to fall back on, we would still be screwed if a return to those conditions took place. I'm afraid we're in for a rude awakening pretty soon, either because of climate change, or a continuation of the mass extinction event we're causing, or some combination of the two.



#6
Phil

Posted 20 April 2017 - 11:39 PM

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I respect your knowledge and contributions to this forum. I'm curious, do you have a personal theory of what caused the last few ice ages? Extreme solar minimums? Volcanic eruptions?

My guess is that it was caused by massive and long lived volcanic eruptions. I'm hopeful that the exact cause will be solved and proven within my lifetime.


Thank you. I'm always trying to learn and find answers.

As for ice ages, as far as we know, the boundary states that "precondition" the glacial inceptions and terminations is set by long term variations in Earth's axial tilt (obliquity), synchronicity of its wobble to orbit (precession), and the shape of its orbit (eccentricity). Of particular importance is obliquity, which appears to control the most essential functions such as the meridional thermal gradient and poleward transport of mass, heat, and moisture. Contrary to popular belief, the maximum insolation at 65N holds little value in predicting the initiation and termination of ice ages. Rather, it's the amplitude of the equator-pole thermal gradient (driven by obliquity) that appears to precondition the system state to flip between quasi-stable modes of circulation.

However, both the glacial inceptions and the glacial terminations occur much too quickly to be a function of long term orbital harmonics alone. For example, the last interglacial (Eemian) ended very abruptly, perhaps within 70 years. Within a century or less, the Earth system transitioned from a state warmer than today (sea levels were up to 4 meters higher) into a full ice age state. Some estimates suggest NH temperatures dropped up to 4C within 150yrs.

Another example is the termination of the last ice age. Around 13,000 years ago, the system entered its "unstable" period between quasi-stable states, as is typical towards the beginnings and ends of ice ages, and NH temperatures warmed an astounding 4-7C within a few years, while sea levels rose at close to a foot per year. After a few thousand years, something happened, and the system could not maintain its interstadial state, and once again the NH abruptly cooled 3-5C within a year or less (this is now mostly agreed upon). This return to ice age conditions lasted 1-2 thousand years before terminating so abruptly that it took scientists decades to accept it. In perhaps a few months, the system abruptly switched from its glacial circulation state into its interglacial circulation state, and temperatures warmed once again by 4-7C across the NH.

So, the conclusion that most scientists derive is that the climate system holds certain preferred modes of variability, uniquely distinct from one another, and if forced beyond particular thresholds, will "jump" from state-to-state.

The big "trigger" in this case appears to be the meridional temperature gradient of the oceans, in response to orbital forcings. At some particular threshold, this gradient becomes sharp enough (or weak enough) to somehow trigger a runaway reorganization of the ocean/atmosphere circulations into one of their other preferred modes of operation.
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#7
Phil

Posted 20 April 2017 - 11:50 PM

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It's truly amazing how rapid the fillibrations between climate states were during the Younger Dryas episode. Even more telling is the fact they appear to have been forced by shifts in tropical convection. (The moisture source in this case would be the NH SSTs above 20N).

http://science.scien...nt/321/5889/680

The last two abrupt warmings at the onset of our present warm interglacial period, interrupted by the Younger Dryas cooling event, were investigated at high temporal resolution from the North Greenland Ice Core Project ice core. The deuterium excess, a proxy of Greenland precipitation moisture source, switched mode within 1 to 3 years over these transitions and initiated a more gradual change (over 50 years) of the Greenland air temperature, as recorded by stable water isotopes. The onsets of both abrupt Greenland warmings were slightly preceded by decreasing Greenland dust deposition, reflecting the wetting of Asian deserts. A northern shift of the Intertropical Convergence Zone could be the trigger of these abrupt shifts of Northern Hemisphere atmospheric circulation, resulting in changes of 2 to 4 kelvin in Greenland moisture source temperature from one year to the next.



#8
tenochtitlan

Posted 20 April 2017 - 11:55 PM

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Thank you. I'm always trying to learn and find answers.

As for ice ages, as far as we know, the boundary states that "precondition" the glacial inceptions and terminations is set by long term variations in Earth's axial tilt (obliquity), synchronicity of its wobble to orbit (precession), and the shape of its orbit (eccentricity). Of particular importance is obliquity, which appears to control the most essential functions such as the meridional thermal gradient and poleward transport of mass, heat, and moisture. Contrary to popular belief, the maximum insolation at 65N holds little value in predicting the initiation and termination of ice ages. Rather, it's the amplitude of the equator-pole thermal gradient (driven by obliquity) that appears to precondition the system state to flip between quasi-stable modes of circulation.

However, both the glacial inceptions and the glacial terminations occur much too quickly to be a function of long term orbital harmonics alone. For example, the last interglacial (Eemian) ended very abruptly, perhaps within 70 years. Within a century or less, the Earth system transitioned from a state warmer than today (sea levels were up to 4 meters higher) into a full ice age state. Some estimates suggest NH temperatures dropped up to 4C within 150yrs.

Another example is the termination of the last ice age. Around 13,000 years ago, the system entered its "unstable" period between quasi-stable states, as is typical towards the beginnings and ends of ice ages, and NH temperatures warmed an astounding 4-7C within a few years, while sea levels rose at close to a foot per year. After a few thousand years, something happened, and the system could not maintain its interstadial state, and once again the NH abruptly cooled 3-5C within a year or less (this is now mostly agreed upon). This return to ice age conditions lasted 1-2 thousand years before terminating so abruptly that it took scientists decades to accept it. In perhaps a few months, the system abruptly switched from its glacial circulation state into its interglacial circulation state, and temperatures warmed once again by 4-7C across the NH.

So, the conclusion that most scientists derive is that the climate system holds certain preferred modes of variability, uniquely distinct from one another, and if forced beyond particular thresholds, will "jump" from state-to-state.

The big "trigger" in this case appears to be the meridional temperature gradient of the oceans, in response to orbital forcings. At some particular threshold, this gradient becomes sharp enough (or weak enough) to somehow trigger a runaway reorganization of the ocean/atmosphere circulations into one of their other preferred modes of operation.

Great analysis :) I'd also add that continental distribution, and major tectonic events, can have an effect on ocean currents and atmospheric patterns, and maybe could lead to an ice age. For example the formation of the Isthmus of Panama took place a couple hundred thousand years before the Pleistocene began, so maybe those events are connected, or maybe it has something to do with there being a continent placed over one of the poles.


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#9
Phil

Posted 20 April 2017 - 11:55 PM

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This is another fascinating read:

http://m.pnas.org/co.../38/14308.short

Slowing down as an early warning signal for abrupt climate change

In the Earth's history, periods of relatively stable climate have often been interrupted by sharp transitions to a contrasting state. One explanation for such events of abrupt change is that they happened when the earth system reached a critical tipping point. However, this remains hard to prove for events in the remote past, and it is even more difficult to predict if and when we might reach a tipping point for abrupt climate change in the future. Here, we analyze eight ancient abrupt climate shifts and show that they were all preceded by a characteristic slowing down of the fluctuations starting well before the actual shift. Such slowing down, measured as increased autocorrelation, can be mathematically shown to be a hallmark of tipping points. Therefore, our results imply independent empirical evidence for the idea that past abrupt shifts were associated with the passing of critical thresholds. Because the mechanism causing slowing down is fundamentally inherent to tipping points, it follows that our way to detect slowing down might be used as a universal early warning signal for upcoming catastrophic change. Because tipping points in ecosystems and other complex systems are notoriously hard to predict in other ways, this is a promising perspective.



#10
Phil

Posted 21 April 2017 - 12:00 AM

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Great analysis :) I'd also add that continental distribution, and major tectonic events, can have an effect on ocean currents and atmospheric patterns, and maybe could lead to an ice age. For example the formation of the Isthmus of Panama took place a couple hundred thousand years before the Pleistocene began, so maybe those events are connected, or maybe it has something to do with there being a continent placed over one of the poles.


Thanks. I definitely agree with your first and last sentences. A continent at/near one of the poles is a hallmark of all ice ages.

As for why we began the descent into the current ice age a few millions years ago, I personally believe the rise of the Himalayas played a significant role, by deflecting planetary waves and inhibiting the poleward transport of heat/moisture from the IO/Indo-China domain into Siberia.

#11
tenochtitlan

Posted 21 April 2017 - 12:03 AM

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Thanks. I definitely agree with your first and last sentences. A continent at/near one of the poles is a hallmark of all ice ages.

As for why we began the descent into the current ice age a few millions years ago, I personally believe the rise of the Himalayas played a significant role, by perturbing/deflecting Rossby waves, and inhibiting the poleward transport of heat and moisture from the IO/Indo-China domain.

Yeah, that makes sense. Come to think of it, the Himalayas are the only really big east-west mountain range on Earth right now on the edge of the subtropics. And it's true that they prevent the transfer of heat to and from the Indian subcontinent--you can see that in the winter averages and extremes for places in North India, which are really warm for that latitude. (At least compared to places further east at those latitudes.)


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#12
Chris

Posted 25 April 2017 - 09:38 AM

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Vegetation now vs glacial maximum. It's kinda hard to imagine the PNW being a desert tundra with no virtually no trees.

Tim would probably enjoy it. :lol:

5DB435AF-7503-4D6A-B1D1-48DA2DB2EA87_zps

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#13
Phil

Posted 25 April 2017 - 09:38 AM

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Here's another interesting paper:

http://www.sciencedi...277379107003356

The transition from interglacial to glacial climate has attracted much attention in paleoclimatic research, partly because orbital forcing dictates that such a return to a new ice age is inescapable (albeit in the distant future only). The detailed series of steps that leads to glacial inceptions remains poorly understood, however, and studies of past glacial inceptions are often compromised by incomplete records, imprecise chronological control, and/or uncertainties associated with proxy-transfer functions. Here we present results from U–Th-dated speleothems from a cave in the Austrian Alps (Entrische Kirche cave) which grew continuously between ca 127 and 114 ka and intermittently also during subsequent stadials and interstadials. The alpine setting of this cave is prone to periglacial and glacial processes as well as temperature and precipitation changes which are recorded in these cave deposits. We use high-resolution stable isotope data to constrain paleoenvironmental changes associated with the demise of the Last Interglacial, unprecedented in detail for central Europe. Peak interglacial conditions are characterized by high δ18O values and high growth rates from ca 127 to 124 ka. A major drop in δ18O by 3‰ occurred at ca 118 ka, which coincided with cold event C26 in the North Atlantic. This isotopic shift, which occurred at or close to isotopic equilibrium, cannot be explained by simple uniform cooling. Modelling suggests that enhanced seasonality, dominated by significant changes in winter precipitation, are required to reconcile the isotope data with the fact that calcite deposition continued across the MIS 5e/d transition (i.e., no cave freezing). This period of enhanced seasonality lasted for several millennia during which the catchment area of the cave remained geomorphologically stable and ice free. Eventually, speleothem growth terminated at ca 114 ka, which is in line with widespread ice-rafting in the North Atlantic (cold event C24) and the onset of fully stadial conditions during MIS 5d.



#14
Chris

Posted 20 November 2017 - 09:45 AM

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Sorry to regurgitate this, but it's just amazing luck that the LIA wasn't glacial inception. A real head scratcher. We were well on our way to starting the ice age until the cooling terminated around the year 1700. The glacial anomalies in Norway (Gjerde et al 2016) reflect this:

ZFl0fV2.png

Then again, rapid warm/cold climate oscillations were a theme during the glacial inception following the Eemian, so maybe Mother Nature is just toying with us. Certainly, our orbital picture looks quite grim, going forward.



#15
Andie

Posted 05 May 2019 - 12:33 PM

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A simple straight forward look at the epochs and how history has been written on the back of climate.
Warmth provides prosperity, while the cold sends us into economic and historical challenge.


https://edmhdotme.wo...obal-warming-2/

Our current beneficial, warm Holocene interglacial has been the enabler of mankind’s civilisation for the last 10,000 years. The congenial climate of the Holocene epoch spans from mankind’s earliest farming to the scientific and technological advances of the last 100 years.

However all the Northern Hemisphere Ice Core records from Greenland show:

the last millennium 1000AD – 2000AD has been the coldest millennium of the entire Holocene interglacial.
each of the notable high points in the Holocene temperature record, (Holocene Climate Optimum – Minoan – Roman – Medieval – Modern), have been progressively colder than the previous high point.
for its first 7-8000 years the early Holocene, including its high point “climate optimum”, had virtually flat temperatures, an average drop of only ~0.007 °C per millennium.
but the more recent Holocene, since a “tipping point” at ~1000BC, has seen a temperature diminution at more than 20 times that earlier rate at about 0.14 °C per millennium.
the Holocene interglacial is already 10 – 11,000 years old and judging from the length of previous interglacials the Holocene epoch should be drawing to its close: in this century, the next century or this millennium.
the beneficial warming at the end of the 20th century to the Modern high point has been transmuted into the “Great Man-made Global Warming Alarm”.
eventually this late 20th century temperature blip will come to be seen as just noise in the system in the longer term progress of comparatively rapid cooling over the last 3000+ years.
other published Greenland Ice Core records as well as GISP2, (NGRIP1, GRIP) corroborate this finding. They also exhibit the same pattern of a prolonged relatively stable early Holocene period followed by a subsequent much more rapid decline in the more recent past.
When considering the scale of temperature changes that alarmists anticipate because of Man-made Global Warming and their view of the disastrous effects of additional Man-made Carbon Dioxide emissions in this century, it is useful to look at climate change from a longer term, century by century and even on a millennial perspective.

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Before You Diagnose Yourself With Depression or Low Self-Esteem,...First Make Sure You Are Not In Fact, Just Surrounded By A$$holes.

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