Posted on 08/28/2007 7:29:26 AM PDT by ConservativeMind
When do ice ages begin? In June, of course. Analysis of Antarctic ice cores led by Kenji Kawamura, a visiting scientist at Scripps Institution of Oceanography, UC San Diego, shows that the last four great ice age cycles began when Earths distance from the sun during its annual orbit became great enough to prevent summertime melts of glacial ice. The absence of those melts allowed buildups of the ice over periods of time that would become characterized as glacial periods.
Results of the study appear in the Aug. 23 edition of the journal Nature.
Jeff Severinghaus, a Scripps geoscientist and co-author of the paper, said the finding validates a theory formalized in the 1940s but first postulated in the 19th Century. The work also helps clarify the role of carbon dioxide in global warming and cooling episodes past and present, he said.
This is a significant finding because people have been asking for 100 years the question of why are there ice ages, Severinghaus said.
A premise advanced in the 1940s known as the Milankovitch theory, named after the Serbian geophysicist Milutin Milankovitch, proposed that ice ages start and end in connection with changes in summer insolation, or exposure to sunlight, in the high latitudes of the Northern Hemisphere. To test it, Kawamura used ice core samples taken thousands of miles to the south in Antarctica at a station known as Dome Fuji.
Scientists studying paleoclimate often use gases trapped in ice cores to reconstruct climatic conditions from hundreds of thousands of years in the past, digging thousands of meters deep into ice sheets. By measuring the ratio of oxygen and nitrogen in the cores, Kawamuras team was able to show that the ice cores record how much sunlight fell on Antarctica in summers going back 360,000 years. The teams method enabled the researchers to use precise astronomical calculations to compare the timing of climate change with sunshine intensity at any spot on the planet.
Kawamura, a former postdoctoral researcher at Scripps, used the oxygen-nitrogen ratio data to create a climate timeline that was used to validate the calculations Milankovitch had created decades earlier. The team found a correlation between ice age onsets and terminations, and variations in the season of Earths closest approach to the sun. Earth's closest pass, or perihelion, happens to fall in June about every 23,000 years. When the shape of Earth's orbit did not allow it to approach as closely to the sun in that month, the relatively cold summer on Earth encouraged the spread of ice sheets on the Northern Hemisphere's land surface. Periods in which Earth passed relatively close in Northern Hemisphere summer accelerated melt and brought an end to ice ages.
When we start to come to the point of closest approach in June, thats when the big ice melts off, said Severinghaus.
Kawamura said the new timeline will serve as a guide that will allow researchers to test climate forecast models of the effects of carbon dioxide levels in the atmosphere. The team found that the changes in Earths orbit that terminate ice ages amplify their own effect on climate through a series of steps that leads to more carbon dioxide being released from the oceans into the air. This secondary effect, or feedback, has accounted for as much as 30 percent of the warming seen as ice ages of the past have come to an end.
An important point is that climate models should be validated with the past climate so that we can better predict what will happen in the future with rising CO2 levels, said Kawamura. For that, my new timescale can distinguish the contribution to past climate change from insolation change and CO2.
In addition to Kawamura and Severinghaus, authors of the report included Takakiyo Nakazawa, Shuji Aoki, Koji Matsumoto, and Hisakazu Nakata of Tohoku University, Sendai, Japan; Frederic Parrenin of Laboratoire de Glaciologie et Geophysique de lEnvironment in Grenoble, France; Lorraine Lisiecki and Maureen Raymo of Boston University; Ryu Uemura, Hideaki Motoyama, Shuji Fujita, Kumiko Goto-Azuma, Yoshiyuki Fujii, and Okitsugu Watanabe of the National Institute of Polar Research in Tokyo, Japan; Manuel Hutterli of the British Antarctic Survey in Cambridge, England; and Francoise Vimeux and Jean Jouzel of Laboratoire des Sciences du Climat et de lEnvironment in Gif-sur-Yvette, France.
Source: UCSD
Greg, I think you mean (1/googolplex) inches closer.
Of course, I could be wrong.
BMFLR
I think the answer is 7 trillion miles in my Toyota per 1/googleplex of an inch closer to the sun, but my calculations could be off.
I’ll have to run the calculations again. I forgot how to multiply fractions.
Not my theory - I thought I was clear I was clarifying the interpretation of the theory in the article.
If you bought shore-front property, it might not be a great investment. You'd have to have bought property currently under water to make a killing of an incipient ice age, as the current shore front property will end up 50 miles inland. I understand there used to be quite a market in Florida for such property. You've still got time to trade up.
When we switch from Ice Age to “Normal Mode”, or back again, there are two feedbacks that amplify the effect of the initial cooling or warming event.
One is a CO2 outgass/uptake from/back to the oceans. The other is an albedo feedback: more land covered with a few mm of ice means higher albedo and more cooling - and vice versa.
These feedbacks are of vital importance in the switch between Ice Age and Holocene - but both are subject to a ‘saturation’ effect beyond which there are sharply diminishing returns.
Our current CO2 level is such that *doubling* the CO2 would IIRC increase the CO2 greenhouse effect by only 10%. All the quick wins for increased CO2 already happened - at the end of the last Ice Age.
Similarly our current ice coverage is so situated (e.g. considering only the summer ice at/near sea-level, it’s only on bits that are at a high slant to the direction of insolation like Greenland or the Poles) that increased solar output isn’t going to make any more headway. Again all the quick wins on Albedo reduction (e.g. melting the ice across Europe) happened at the end of the last Ice Age.
Tropical beachfront is the way to go in an ice age. You could end up with miles of property as the shore recedes.
Um...Ok, I’ve had this idea, so I will lay it out....
I watched a PBS show a couple of years ago (sorry, I forget the name), about the theory that the Sun has a dead sister star, and that the 2 reach their closest proximity in their respective orbits every 25,000 years or so.
Ice Ages occur every 20-25k years. Could there be a connection?
Flame me if you must, as long as you think about the idea first.
One is a CO2 outgass/uptake from/back to the oceans. The other is an albedo feedback: more land covered with a few mm of ice means higher albedo and more cooling - and vice versa.
These feedbacks are of vital importance in the switch between Ice Age and Holocene - but both are subject to a saturation effect beyond which there are sharply diminishing returns.
Our current CO2 level is such that *doubling* the CO2 would IIRC increase the CO2 greenhouse effect by only 10%. All the quick wins for increased CO2 already happened - at the end of the last Ice Age.
Similarly our current ice coverage is so situated (e.g. considering only the summer ice at/near sea-level, its only on bits that are at a high slant to the direction of insolation like Greenland or the Poles) that increased solar output isnt going to make any more headway. Again all the quick wins on Albedo reduction (e.g. melting the ice across Europe) happened at the end of the last Ice Age.
Cog, do you have an insight on this post?
Lawrence Solomon's "The Deniers" (a series of articles on the view of scientists who have been labelled "Global Warming Deniers"):
Other References:
Antarctic Temperature Trend 1982-2004:
This map (left) shows key areas of Antarctica, including the vast East Antarctic ice sheet. The image on the right shows which areas of the continent's ice are thickening (coloured yellow and red) and thinning (coloured blue). © (Left)British Antarctic Survey, (Right)Science
Aperiodic? The orbit of the Earth is nothing if not periodic, and predictable. Wide shift? The wider the shift, the more impact, which would argue more for the perihelion effect than against it. Or are you arguing that the periods of the Earth orbit don't match the periods of the ice ages?
What are you basing that statement on? And I will note that I probably know what you're basing it on. I'll be curious to see if I'm right.
A Saturated Gassy Argument is a long explanation of why the above is incorrect.
Similarly our current ice coverage is so situated (e.g. considering only the summer ice at/near sea-level, its only on bits that are at a high slant to the direction of insolation like Greenland or the Poles) that increased solar output isnt going to make any more headway. Again all the quick wins on Albedo reduction (e.g. melting the ice across Europe) happened at the end of the last Ice Age.
That seems right to me. Because there's so much less ice now than during continental glaciations, albedo changes due to ice are not a major effect. Cloud reflection might be, though.
I think the point is that what you say is true today, but wasn't true 12,000 years ago, and won't be true 12,000 years from now. 12,000 years in either direction, and the earth will be closest to the sun in the Northern Hemisphere summer.
The tilt of the earth can change, but I think it's on a much longer schedule than 24,000 years.
And this is all caused by CO2 changes.
So then you take it to mean that the end of result of the tipping point is that we will have seen our last Ice Age and now the planet is on an ever warming path to a time when we enter our first Steam Age?
It would be easier to convince people of that if there were as strong a temperature record for those parts of the globe outside the U.S. and if we could be convinced that what data does exist hasn’t already been run through the adjustment mill.
May I speculate? Thanks...
Based on something Wally Broecker said ages ago, if every bit of fossil fuel was burned and the CO2 ended up in the atmosphere, it would take about 10,000 years or so to get back to equilibrium, as natural processes removed the excess CO2 from the atmosphere. The main way this happens is ocean absorption and neutralization by marine calcium carbonate. It takes that long because the marine calcium carbonate is on the bottom and the water with the excess CO2 absorbed from the atmosphere has to get down there.
Based on Milankovitch forcing, the next likely glacial period isn't due for another 30,000 years after that. So the CO2 concentration of the atmosphere won't be a factor. And because we are a wet planet, not Venus, I'm not worried about a runaway greenhouse.
But an enhanced greenhouse, the path we're on now, has potential problems in the short-term, which for me is from now until 2200. Those problems have been, and are being, discussed at length elsewhere.
There's also observations of what's changing environmentally and biospherically, of course, independent of actual temperature measurements. I actually think those have stronger resonance.
But those are far more subjective in my opinion because the issue has now become so politicized as to be polarizing as we see accusations of advocacy and denial being made from two camps entrenching rather than collaborating.
While this part is business as usual here where we have a divided body politic the whole issue is largely ignored in those areas where daily survival among many peoples of different faiths, origins and class is the overwheming crux of the expense of energy, both personal and governmental.
You’re comparison doesn’t work very well. The Northern Hemisphere may not be at full heat by June 22, but neither does it take until June 22 for the Earth to begin heating up. According to what you write, we may not yet be in the coldest part of an ice age, but it would be starting to cool off. If such cycles were SO slow to initiate, they would simply blend together.
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