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 Earth’s 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, Kawamura’s team was able to show that the ice cores record how much sunlight fell on Antarctica in summers going back 360,000 years. The team’s 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 Earth’s 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, that’s 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 Earth’s 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 l’Environment 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 l’Environment in Gif-sur-Yvette, France.
Source: UCSD
My son, a geology major, has spent the summer studying evidence of glaciers on Mars. We have a huge amount of high quality images from our satelites orbiting Mars. While it is too early in the research to draw solid conclusions, it appears that the climate of Mars shifts DRAMATICALLY and periodically so that rain and snow accumulate. He’s finding lots of evidence of glaciation and it’s not billions of years old. What drives the dramatic temperature shifts on Mars? It appears that the orbit, inclination, and perhaps solar activity are the major drivers. However, I don’t think we will have a good handle on all of the factors involved in climate change for a long time. We need a lot more research like this. Somehow, I don’t think the global warming alarmists will be happy about actual data and research.
That's a non sequitur. I was talking about peaks; of course there is a warming period before the peak. The energy delivered by solar radiation in the Northern Hemisphere increases before the Jun 22 peak, the resulting heat of the Earth increases before the Aug/Sep peak. Even on a daily basis, the warmest part of the day is not always at Noon, but usually later in the afternoon.
The ice ages cycles are slow, but clearly have not blended together to an average. Every 100,000 years or so, we get 10-20,000 years of non-ice age.
Cycles of different periods do blend together most of the time, but regardless of the variation in the period, eventually the cycles will all hit a peak (or low) at the ame time.
I've never owned beach front property, nor discussed such ownership with anyone who knew anything about it. Would such a deed say from 'this point to the water's edge'? Or, does it give a certain area, leaving the shore to the ownership of the local government?
>> That’s a non sequitur. I was talking about peaks; of course there is a warming period before the peak. <<
No, the issue at hand is why we aren’t cooling off, not why we haven’t reached a nadir.
But the temperature graphs I’ve seen don’t look anything like a 24,000-year cycle, either.
I’ve never owned beach front property, nor discussed such ownership with anyone who knew anything about it. Would such a deed say from ‘this point to the water’s edge’? Or, does it give a certain area, leaving the shore to the ownership of the local government?
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A lot of deeds own to the water’s edge. Depends on local laws I think. Some property doesn’t carry rights to the beach.
Why aren't we cooling off? Maybe because we are just barely past a high in the sunspot cycle.
And, it's the wrong question anyway. Why was the global warming rate higher before the 1950's than it was after? The supposed C02 increase came in the later period. Global warming should be zooming up now that the economies of China and India are zooming up, but it isn't.
In regard to the man-made GW theory, the question isn't why aren't we cooling, but why aren't we warming in the last decade. The sun-made GW theory is clear that the Sun is at a peak, warming should be slowing, and cooling to happen some years ahead.
I thought climate models were validated with rock concerts and movies.
>> Why aren’t we cooling off? Maybe because we are just barely past a high in the sunspot cycle. <<
That hardly explains the fact that we haven’t been cooling off for a couple thousand years.
>> And, it’s the wrong question anyway. <<
It depends what your interests are.
>> Why was the global warming rate higher before the 1950’s than it was after? <<
It’s not. That was true in the late 1980s, when skepticism of global warming began.
>> Global warming should be zooming up now that the economies of China and India are zooming up, but it isn’t. <<
This much is true, but I’d caution you the same way I’d caution the global warming alarmists: Don’t use single-factor analyses or short time frames to detect long-term trends. We’re discussing climate change, not weather change.
>> In regard to the man-made GW theory, the question isn’t why aren’t we cooling, but why aren’t we warming in the last decade. The sun-made GW theory is clear that the Sun is at a peak, warming should be slowing, and cooling to happen some years ahead. <<
True, but again: don’t look, in experiential data, for any easy confirmation in a given theory for the next few decades.
Neat graphics. Here’s a question:
I notice that oceanic and peninsular regions near Antarctica are heating up, while the inland regions are cooling off. Any chance that the lack of melting ice to cool off the oceans is a factor in ocean warming?
That's plausible. But I don't know of any research that attempts to answer that question.
You are correct. The year was 1934 and perhaps not so coincidently the worst hurricane, i.e. the one with the lowest barometric pressure, was the so-called Florida Keys hurricane of 1935.
Where in the world do you get this logic? That we are at a current high in the sunspot cycle does explain the current warming. That we were at a long term low in the sunspot cycle in the 1700s does explain the nasty winter at Valley Forge.
We are still cooler than the 1400's but warmer than the 1700's. And the 1400's were cooler than the Roman Warm spell.
We've been warming and cooling a bunch over that last 2000 years, and are currently somewhere in the middle of the range of that period.
>> Where in the world do you get this logic? <<
*Bangs head on desk*
Because the topic is whether ice ages are caused by the progression of the perihelion! Yet in trying to explain my difficulties with the current theory, you’ve just asserted a completely unrelated theory. Not that both couldn’t be factors, but I’m questionning why we aren’t in a cooling trend of thousands of years, and you’re responding to me with trends of decades or centuries.
>> We’ve been warming and cooling a bunch over that last 2000 years, and are currently somewhere in the middle of the range of that period. <<
Yes: According to the theory which is the topic of the thread, we should see a a marked cooling trend over the last few thousand years. If we liken the 24,000 year cycle to the yearly cycle of seasons, we should be right about at December 22. Even if the trend from the Roman Warm spell to the Medieval Warm spell to our present relative maximum forms a downward slope, that places us right about at the end of July to early August, when the dog days are interrupted by an occasional mild day.
Why does the first decline from peak temperature happen in late July, instead of late June? Because the Earth takes time to heat up, putting temperature about a month out of phase with the length of daylight and angle of midday sun.
OK, maybe the phase is further shifted with this 24,000-year cycle. But it can’t shift more than 6,000 years, because the temperature maximum can’t take place after heating drops below average. And it seems like we’re about 10,000 or 12,000 years out of phase.
Does the temperature in a teapot go lower when you turn the heat down? Or does it just get warmer slower? It all depends on other factors, and on time. If the perihelion effect is at the bottom now, the cooling effect might just be starting. Especially since it's likely that Solar radiation levels swamp the perihelion effect over shorter intervals.
Since past times (Medieval Warming, Roman Warm) that I mentioned were both warmer and about 1 and 2 thousand years ago, I think I did answer your question indirectly. There is evidence of cooling over the last 2000 years. And also evidence of other cycles in the warming and cooling of shorter times.
>> Does the temperature in a teapot go lower when you turn the heat down? Or does it just get warmer slower? <<
A wholly invalid comparison. No-one just lit the sun, recently. We’re talking this factor approaching its MINIMUM. You’re still treating the issue like it’s July 10th in the cycle, and it’s already January.
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