I was watching the CTV news recently and it was mentioned that the last occurence of severe global warming happened 100,000 years ago when the orbit of the Earth around the sun was somehow changed/different. This is the first I have ever heard of this. Is it true? What would cause such a thing to happen?

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The world breaks everyone and afterward many are strong in the broken places. ~ Ernest Hemingway ...

Hard to tell from the brief description, but they might be talking about Milankovitch cycles, regular changes in the Earth's orbit and orientation to the Sun that has been correlated with climate changes. The largest cycle is about 100,000 years.

[quibble]The 100,000-year eccentricity cycle has the smallest effect on actual seasonal insolation, but appears to correlate with the largest signal in the temperature record. This mismatch is called the "100,000 year problem", imaginatively enough. [/unquibble]

Grant Hutchison

Yeah, I'm not defending the science. It's a problem--the cycle appears to be real in the climated data though, but whether or not it can be explained by the Milankovitch cycles is considered an open question. My advisor has done a lot of work in the area, and is convinced that it can be explained, through some sort of feedback.

Regardless, that is my best guess as to what was being discussed, from the OP.

Yes indeed. I'd guess the same.
Hence my need for [quibble] tags.

Grant Hutchison

There's also a stronger 400,000 year cycle where the Earth's eccentricity cycles from its minimum value to its maximum value.

The more eccentric an orbit is, the more insolation the planet receives. The eccentricity of Earth's orbit varies between about 0.005 at its roundest, and 0.05 at its most eccentric. At its most eccentric, Earth receives about 1/10 of 1 percent more insolation than it does at its roundest over the course of 1 year. Earth's orbit is currently heading towards more circular. So if this were the only factor to consider, Earth should currently be cooling.

But total insolation throughout the year isn't the biggest factor. When the orbit is at its most eccentric, Earth receives about 20% more insolation at perihelion than at aphelion. And since the northern and southern hemispheres of Earth are not equally efficient at absorbing the available insolation (I believe the Southern Hemisphere, being mostly ocean is better at absorbing solar radiation), whichever hemisphere is in summer while Earth is at perihelion makes a big difference.

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If there is a 100,000 year cycle, and 100,000 years ago was the last severe round of global warming, could the current global warming be part of that cycle?

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I'm not a scientist, but I play one on the internet.
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Based on insolation, the earth is currently in the position that is believed to start a glacial cycle. (Insolation is currently the same as during the coldest period of the last glacial cycle.)

When this interglacial period ("Holocene") started, the Northern Hemisphere was closest to the sun in the summer and farthest from the sun in the winter and the orbital tilt has maximum. (The critical latitude for insolation is 60N.)

The Northern hemisphere is now farthest from the sun in the summer and closest in the winter and has less orbital tilt, both of which result in colder Northern Hemisphere summers.

Here is some more background concerning the last interglacial and the glacial cycles in general.

The glacial/interglacial periods are cyclic. There have been roughly 22 cycles so far. The interglacial period is fairly short, typically less than 10 kyrs. In the past the interglacial period has ended abruptly.

The Antarctic ice sheet provides a record of the last 8 cycles. This graph from Wikipedia shows the last 4 cycles.

http://en.wikipedia.org/wiki/Image:V...core-petit.png

Each of those long dips in temperature corresponds to a glacial cycle. The last glacial cycle is called the Wisconsin, as the North American ice sheet came down into the state of Wisconsin.

This map (from Wikipedia) shows the extent of the ice sheet during the last glacial maximum. Note the vegetation difference in North America, as compared to current conditions. Canada has no vegetation as it is covered by an ice sheet. The vegetation in central US is tundra.

http://en.wikipedia.org/wiki/Image:L...tation_map.png

This paper shows (from Atlantic sea floor sediment, the proxy parameter the researcher measured is an isotope of oxygen, O18. By measuring the amount of O18 the researcher can determine the temperature changes) temperature changes in the Northern hemisphere over the last 3 million years. As the graph (figure 1) indicates the glacial period has become gradually colder over the last 3 MM years and longer. The glacial period is now roughly 100 k years.

http://www.maureenraymo.com/2003_Raymo+Nisancioglu.pdf

[quote=tony873004;1134721]The more eccentric an orbit is, the more insolation the planet receives. The eccentricity of Earth's orbit varies between about 0.005 at its roundest, and 0.05 at its most eccentric. At its most eccentric, Earth receives about 1/10 of 1 percent more insolation than it does at its roundest over the course of 1 year. Earth's orbit is currently heading towards more circular. So if this were the only factor to consider, Earth should currently be cooling.[quote]

Interesting stuff. The way it was reported was very vague...hence my being vague... maybe global warming will be offset by what Tony is talking about.

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The world breaks everyone and afterward many are strong in the broken places. ~ Ernest Hemingway ...

No, the rate of change is too rapid. The average temp has increased by about 1 degree over the last 100 years. For a 100,000 year cycle, that kind of change should take 10,000+ years, unless we are talking about 100+ degree changes over the course of the cycle (not the case, since basically only bacteria could have survived such extreme temperatures).

Pretty much all of the long term oscillations in the global climate (such as those resulting in ice ages) are the result of gradual variations in the orbit of the Earth. Those variations are significant only on the scale of 1000's of years or more, not on the 10's of years for the current global warming. That is why, even though we may be on an upswing in one of those cycles, they are not taken to be a likely explanation for Global Warming.

How can we possibly know this? To have a reasonable assessment of global temperature 100 years ago we would need samples from a sufficient number of standard volumetric cells from all over the Earth (oceanic and atmospheric), taken with reasonable simultaniety, to be sure that whatever data are available are not resulting from local variations. Otherwise, we have no "benchmark" against which to calculate the 100 year differential. I would be astonished to learn that the data gathered 100 years ago was sufficiently globally sampled to provide a reasonable reference for any calculation of the degree of global temperature increase. The melting of ice on a global scale is solid evidence of global warming in a general sense, but assigning accuracies at the single degree level per 100 years seems unwarranted as does predicting various disasterous results by schedule.

Has anyone modeled the likely effects of exchanges of energy between magnetic fields of the sun and the Earth as a function of the inclination of the Earth's axis and the waxing and waning of the Earth's magnetic field strength? My guess is that the medium of energy exchange is related to kinetic energy imparted by various strengths and orientations of Earth's magnetic field to charged particles in the ionosphere which bang against normal molecules and atoms giving more rise to atmospheric temperatures in some cases than in others. If the configuration of Earth's magnetic fields which favor temperature rises last over tens of years, a few degrees temperature increase may occur. The effect may be global if both poles of the Earth's field are similarly affected.

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For those inclined to oppose human meddling with the structure of the universe or the composition and configuration of objects and groups of objects within the universe, consider:
Whether there is a limit to the magnitude of a modulation of chaos below which order remains invariant? Or, is order but a fiction invented by perspectives applied over finite, however large, time intervals?

Records from ice cores, for one, go back 100,000's of years. From that, you can see what typical variations are over 100 year time scales and the past 100 years far exceed normal variations.

We have a reasonable understanding of the energy scales involved here and it is not significant. The energy here is minuscule compared to the radiation from the Sun.

Even if we were mistaken and the energy of the high speed particles was in any way significant, you would see large increases of temperature at the poles where those particles are funneled. But that is not the case.

Do you really believe that ice cores are capable of revealing a few degrees per century change in global temperature? Do you even know or care how accurately we have measured the rise in global temperature over the last century free from effects local to the scarce measurement points from which data are available?

Note that you are able to see that polar tempertures may be subject to local effects, but that you neither consider nor explain what local effects may have been inadvertantly used to mis-determine the general rise in global temperature. The chart entitled "Global Temperature and Atmospheric CO2 over Geologic Time" in
http://mysite.verizon.net/mhieb/WVFo...s_climate.html shows a drop in global temperature to current levels with CO2 levels ten times the current level. Who knows how accurate these guesses are?

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For those inclined to oppose human meddling with the structure of the universe or the composition and configuration of objects and groups of objects within the universe, consider:
Whether there is a limit to the magnitude of a modulation of chaos below which order remains invariant? Or, is order but a fiction invented by perspectives applied over finite, however large, time intervals?

This thread is drifting a bit. perhaps I may inject some statements.

1. The 'warming' 100,000 years ago was actually from about 135-110,000 years ago, is known as the Eemian or Sangamonian interglacial.

2. The longest ice core on record, EPICA Dome C goes back 740,000 years and shows the 100,000 years cycle in concert with the sediment cores from the oceans, which show a remarkable resemblance.

The last 500,000 years:



The Milankovitch cycles amount to 403,000 years for eccentricity with a weak 95,000 years component superimposed, a 41,000 years cycle for obliquity and 19,000 - 22,000 years cycles for precession the perihelion. The strong 100,000 years cycle is not related to these Milankovitch cycles here:



See for instance the weak solar forcing variation around 400,000 years ago going together with the strongest spike in the ice core. That doesn't make sense.

Also it should be noted that the 100,000 cycle came into being some 900,000 years ago, before that the 41,000 years cycle was dominent albeit much weaker.

3. Ice core readings: Because the oceanic isotope spikes from the sediment cores dove tail with the Anarctic ice cores, it signifies at least one global signal. However if one closes in on all elements, it might be a combination of aridity, seasonality of precipitation and actual temperatures and I think that these changes are likely initiated in the ocean, not by solar forcing.

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Quid est ergo tempus.
Augustinus

Adam’s paper, “Sudden climatic transitions during the Quaternary” (see link below), is a good review of abrupt climate change. The paleoclimatic data indicates that some forcing factor(s) is causing world wide, rapid, sever, semi periodic climate changes.

Insolation changes slowly, due to orbital changes and hence could not possibly be the cause of the semi periodic, sever climate changes. Insolation at the time of what ever mechanism(s) is forcing the climate, would determine the sensitivity of each Hemisphere and specific latitudes to the sudden cooling or warming forcing.

It should also be noted that the orbital insolation changes are primarily globally neutral. For example if the Northern Hemisphere experiences colder winters and warmer summers due to orbital changes, the Southern Hemisphere experiences warmer winters and colder summers and visa versa. (i.e. Globally neutral). Adam's paper notes that the paleclimatic data shows that there is sudden cooling in both summer and winter, in the Northern Hemisphere due to the global forcing change, which rules out changes in ocean currents as the mechanism, as changes in ocean currents only effects either winter or summer (Ocean current changes also are not theoretically capable of causing the magnitude of the changes).

There are recent papers that show the temperature change occurred world wide. (i.e. The change is not limited to either the Northern or Southern Hemisphere.)

http://ethomas.web.wesleyan.edu/adamsetal99.pdf

Excerpt from Adam et al.’s paper, “Sudden climate transitions during the Quaternary”.

This paper states that the length of the interglacial period is determined by what ever is causing the millennial variability (planetary response to the semi periodic forcing function(s)) in the climatic record.

“The Duration of Forest Stages in Southern Europe and Interglacial Climate Variability” by Tzedakis et al.

http://www.sciencemag.org/cgi/conten.../sci;1102398v1

Comment:
The paleoclimatic data show that there are roughly 200 yr, 600 yr, 1500 yr, 2500 yr, and 6000 yr to 8000 yr, rapid increases and decreases, of planetary temperature. The changes vary in magnitude. The cooling events are more sever and occur more frequently than the warming events. The 6000 year to 8000 year change is the most sever.

As referenced in my last comment, this is the finding that supports global synchronous, climate change.

http://www.nsf.gov/news/news_summ.js...100348&org=ATM

Here is a link to another paper by the same authors that provides data which supports synchronous climatic change in the current interglacial period.

http://www.geology.wisc.edu/~davem/abstracts/05-2.pdf

With regular intervals mammoth mummies are discovered in the Siberian permafrost high north on the Arctic coast, for instance the Jarkov Mammoth the Fishhook mammoth and the Yukagir Mammoth. All are dated between 18,500 and 20500 carbon years, roughly 23-24,000 years ago at the onset of the last glacial maximum when Greenland was oh some 10 degrees colder than today.

Extensive research has recvealed that the mammoths were part of a productive grassy steppe with horses, antilopes (Saiga), lions etc. And that less than 500 miles from the North Pole in the high arctic tundra that only supports a musk oxs.

Obviously, none of those simultaneous ice ages studies addresses this refuting evidence. If you can't explain this, you can't explain the ice ages, the very basis of the current global warming scare.

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Quid est ergo tempus.
Augustinus

So they all got caught in a sudden onslaught of ice? Yikes!