May 19th, 2008, 03:14 PM
According to at least one report (I can dig up the ref is required), the earth is at the tail end on an inter-glacial period. We are 'due' for another ice age in the next one-thousand years, a blink of an eye in cosmic terms. Of course, we have no idea how the current global warming trend will affect this... what do you think ?
That is a widely accepted theory, and does encompass global warming. That's why those who research GW and eco-sciences deeply aren't so concerned about GW in the first place. Global Warming can be considered as a side effect to the ice-age. I can't quite remember the source, or the reason, so until I find it:
http://www.google.com/search?client=...UTF-8&oe=UTF-8
That should provide better answers than me. Remember not to be influenced by inaccurate hobbyists or manipulating news articles, some of which are designed to trigger panic etc. Although you probably already knew that, making this whole paragraph a pointless addition to what will soon be an RSI.
I hadn't heard that theory, unless you're referring to the idea that the thermohaline circulation might shut down, causing cooling in the North Atlantic region. The THC shutdown was proposed as a possible result of global warming, but I think the theory has few supporters today.
Other than that, it's my understanding that a near-term ice age is nothing more than speculation, the contributing factors being complex and mostly pointing in the other direction, so I'd be interested in reading your reference.
May 19th, 2008, 09:11 PM
Excluding our effects on the planet, crude estimates of future climate depend on solar variations due to astronomical changes referred to as Milankovitch Theory.Originally Posted by CShark
Sometime the earth's orbit in eliptical other times nearly circular, this is called eccentricity and has a period of about 100,000 years.
The last of course it the direction of that tilt spins much like a top in a 20,000 year period. This is called precession.
We are currently closest to the sun during the Northern hemispheric winter and this makes them a bit milder than average. But eccentricity is dropping, in other world our orbit is becoming circular which will reduce the seasonal effect of precession.
The tilt of the earth changes as well ranging between 22.1 and 24.5 degrees from perpendicular to the sun, this is called Axial obliquity and has a period of about 40,000 years. When the angle is high the seasons are exaggerated summers being very warm and winters very cold. We're now about 23.4 and decreasing so we're heading for milder seasons.
Ice age and solar radiation based on Milankovitch Theory at about 65 degree North is reasonable prediction of ice ages for the past couple hundred thousand years. If you use Milankovitch theory into the future you find a very slight cooling that doesn't approach ice age conditions for tens of thousands of years.
Here's a pretty good paper that describes Milankovitch theory and that it predicts up to 50,000 years before we see a deep ice age.
http://amper.ped.muni.cz/gw/articles.../orb_forc.html
the problem with a geological "soon" is that it's very hard to determine whether it means 10 years or 1000 years from now
historically, interglacials have lasted for an average of about 10,000 years, but there's plenty of variation in the actual figures
Yup. Much like the inversions in the earth's magnetic fields: it may be soon, but probably not in our lifetimes, and maybe not in the lifetime of anybody this century. So how soon is soon?
Even if it does happen in 1000 years, lucky you atheists don't have to worry about reincarnation.
didn't know reincarnation was part of christian dogma
And some Buddhists can be considered atheists - they do not consider the existence of a deity to be an issue - yet they may consider metempsychosis important... :P
Thanks for the response. I was reading a paper at work, which I copied, but did not keep the referenceThe title is "The Climate Shapes Man's Destiny". Let me quote a bit:
"At the moment the Earth is passing through an interglacial which has lasted for around 10,000 years following the last Ice Age, which in turn went on for some 100,000 years...Perhaps ominously for man, the pattern suggest that ice ages last around 100,000 years on average and the shorter, warmer interglacials around 10,000 years - so we are nearing the end of our current warmer period. However, there is no need for any alarm at this thought. The next ice age could be up to 1000 years away."
Also, I found this http://books.google.com/books?vid=IS...phe+%22&pgis=1 which tells of a much sooner possible cooling down.
I put this out for discussion, not as my personal opinion. I'd like to hear more about your thoughts on this.
on the other hand, the usual pattern seems to be that of an ice age gradually establishing itself, in a series of ups and downs but with an overall downward trend - definitely not as fast as the warming at the end of the most recent glacial period !
[if i remember correctly the warming climax was reached about 5000 years ago, and since then a cooling has set in, but as i said with many ups (e.g. the medieval optimum, the most recent warming period) and downs (e.g. the little ice age)]
Posting just the eccentricity. Note we're going into a period where the orbit is nearly circular--this will minimize the effects of procession--it won't matter which hemisphere faces the sun during the winter or summer because they'll be roughly the same. This is why the models suggest a very prolonged warm period with no deep ice age coming for 50,000 years.
May 20th, 2008, 11:38 PM
If what you say is true, as a ferret or jourbel I would be worried (not known for migration).
But, you know, as we age, things get drier: cracks appear..........our spirit and hydration disappears.
May 22nd, 2008, 10:12 AM
Jourbel !!@??? Do I look like a gerbilIf what you say is true, as a ferret or jourbel I would be worried (not known for migration).
But, you know, as we age, things get drier: cracks appear..........our spirit and hydration disappears.
Posting just the eccentricity. Note we're going into a period where the orbit is nearly circular--this will minimize the effects of procession--it won't matter which hemisphere faces the sun during the winter or summer because they'll be roughly the same. This is why the models suggest a very prolonged warm period with no deep ice age coming for 50,000 years.
Interesting argument. I have to agree with you Lynn, from the little I understand about how the orbit of earth effects our long-term weather, it looks like you are correct.
Nicely posted.
While the Milankovitch ideas are still enforced on the public as explanation for the ice ages, it is pretty well debunked all over the place.
First problem, the 41ka to 100ka transition is clearly visible in the oceanic proxies, (ka is thousand years)
source: http://maureenraymo.com/current_projects.php
The dominant 41ka cycle before about 0.9 million years concurs nicely with the Milankovitch cycles. The current much more dominant 100ka cycle has nothing to do with Milankovitch, which can be illustrated also comparing the NH insolation with the ice cores:
Around 425 Ka ago there was not a lot of Milankovitch effect yet we see the strongest 'climate' spike over there, alternately around 225 ka we see very agitated Milakovitch cycles, yet the 'climate' responce was rather mild.
We are just looking at something else here, unidentified, check for instance what Spencer Weart observes about those 100ka cycles.
We are working on that, free of AGW bias.As researchers extracted more precise data from the distant past, they discovered that the weak 100,000-year orbital cycle had not always dominated the ice ages after all. Go back more than a million years, and it was the 40,000-year cycle that ruled. The reason for the switch was obscure. The grand puzzle of the ice ages stood unsolved — except insofar as scientists now understood that nobody would ever jump up with a neat single solution
Note that the strong eccentricity cycle is about 430ka with a weak 95ka component, not 100ka at all.
Well, I think insolation is a crock of dinosaur dodo for explaining anything other than milder to strong winter and summer cycles on a hemisphere.While the Milankovitch ideas are still enforced on the public as explanation for the ice ages, it is pretty well debunked all over the place.
First problem, the 41ka to 100ka transition is clearly visible in the oceanic proxies, (ka is thousand years)
source: http://maureenraymo.com/current_projects.php
The dominant 41ka cycle before about 0.9 million years concurs nicely with the Milankovitch cycles. The current much more dominant 100ka cycle has nothing to do with Milankovitch, which can be illustrated also comparing the NH insolation with the ice cores:
Around 425 Ka ago there was not a lot of Milankovitch effect yet we see the strongest 'climate' spike over there, alternately around 225 ka we see very agitated Milakovitch cycles, yet the 'climate' responce was rather mild.
We are just looking at something else here, unidentified, check for instance what Spencer Weart observes about those 100ka cycles.
We are working on that, free of AGW bias.As researchers extracted more precise data from the distant past, they discovered that the weak 100,000-year orbital cycle had not always dominated the ice ages after all. Go back more than a million years, and it was the 40,000-year cycle that ruled. The reason for the switch was obscure. The grand puzzle of the ice ages stood unsolved — except insofar as scientists now understood that nobody would ever jump up with a neat single solution
Note that the strong eccentricity cycle is about 430ka with a weak 95ka component, not 100ka at all.
Notice how well the climate record lines up with eccentricity. My theory is that we have a greater average annual exposure to the sun as the eccentricity is smaller. The larger eccentricity places the orbit of the earth farther away for longer period of time, since that is the nature of eccentricity. Therefor, we have a lower annual average of heat from the sun.
Kepler's second law:
"A line joining a planet and the sun sweeps out equal areas during equal intervals of time."
I also believe eccentricity is the key. Here's an image from MyWire; Encyclopedia of Global Change; Earth Motions that shows just how low of en eccentricity we will have in 26,000 years:Posting just the eccentricity. Note we're going into a period where the orbit is nearly circular--this will minimize the effects of procession--it won't matter which hemisphere faces the sun during the winter or summer because they'll be roughly the same. This is why the models suggest a very prolonged warm period with no deep ice age coming for 50,000 years.
If you believe the article, then you believe the next ice age isn't for more than 50,000 years. I'm skeptical myself of the science being that settled. I'll try to live that long to find out.
I'll see you at the Florida Ice Fair. I'll be wearing a pink carnation, wrinkles and a frown.
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