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
The extra mass on the planet caused by all these SUVs being manufactured is making the Earth heavier, so the sun is pulling it in closer.
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My God! Think about all the things we make and how much they weigh. What if it gets the earth off balance, like a washing machine, if you pile too much on one side? Have you thought of that? We could spin off into the Kuiper belt for all we know.
No, and for the same reason that the peak of Sun exposure in the northern hemisphere is June 22, but the peak of the summer heat is later, in August and September. Since the perihelion is now in January, the model suggests we may be at the start of a long cooling season that may start a new ice age in the next few thousand years.
Note that it was 12,000 years ago that the peak was in June, and 12,000 years ago that the earth started warming up from the last ice age.
So we are going into an ice age according to your theory slowhandluke. Dang. I knew property in Florida would remain a good investment.
: )
I suspect the there’s more variability within the Sun than such wide and aperiodic shifts in Earth’s orbit.
Wow! We globally wobble and warm on the “to” and cool on the “fro”....
Al Gore must be scratching his head wildly...
No update needed. You're one of an innumerable many, probably misled by bad information present in the blogosphere, which confused the global numbers with the U.S. numbers. 1998 was, by far, the warmest year globally in the temperature record. The NASA changes affected the U.S. temperature record and barely nudged the global temperature record. Point #4 is correct because it is about the global temperature record.
Not to start something, but do you, in the end, propose that global warming is man-made?
See this post: http://www.freerepublic.com/focus/f-news/1886643/posts?page=57#57
and realize that it's impossible for me or anyone to refute the basic physics of Earth's radiative balance.
In 1997, Nature magazine, science editor Roger Highfield reported that MIT’s sampling of sediments near Bermuda suggest that the last warm inter-glacial period stretched from about 118,000 to 127,000 years ago. He noted that the author, Dr. Jess Adkins of MIT pointed out the present warem period - “The holocene” has been stable for around 9,000 years.
The article, just 10 years ago was an MIT study that we were on the brink of a new ice age.
I've always suspected the sun varies, but my Timex doesn't.
Not in the Northern Hemisphere. Summer time is when the earth is farthest from the sun, while in Winter, we are closest to the sun. It's the tilt of the planet that causes us to be warm in the summer and cold in the winter.
However, I do agree that global warming is not man-made.
I think it's a little more complicated than that. It sounds like there's a timing issue.
The seasons are caused by the 23.5 degree tilt of the Earth's axis. Summer happens when a pole (north or south) is pointed sunward.
As the article states, Earth's perihelion regresses with a period of about 23,000 years. There are times when summer and perihelion line up, and there are times when they do not.
When summer (at either pole) coincides with perihelion, there's a few percentage points difference in insolation, as compared to when perihelion does not coincide with it.
It makes sense .... and it's good to have some empirical data to support the theory.
What the article doesn't mention, is where we are now in the cycle. You'd think they'd mention that....
Oh NO! We’re not in the spin cycle, are we?!? We’ll die!
Wow! We globally wobble and warm on the “to” and cool on the “fro”....
Al Gore must be scratching his head wildly...
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He’s thinking, “how can this be used to justify a larger government?”
I think the answer is obvious. It will be hard to feed so many billions of people during an ice age. This requires immediate planning to create food factories that can operate in extraordinarily cold temperatures. We only have a thousand years, maybe two, three, four or five, to prepare.
We're not.
Ice Age. See the end of the "Glacials and interglacials" section, and find reference 5 if you want the full story.
The concentrated weight of 20 million aliens who’ve moved up north is causing the Earth’s tilt to be greater than normal - we need to deport about 19.5 million to balance our wobble by redistributing or more centrally locating the weight.
I fight global warming by running my SUV all day with the air conditioner on and the windows open.
“We’re not.”
I know.
Before anything else, kudos to you Cogitator for continuously raising the level of debate on AGW.
But I have to say: we should clarify how far back the temperature record we're talking about goes. 1998 was ~ 3 degrees Centigrade cooler than the warmest parts of the Mediaeval Warm Period, and five degrees cooler than when Dinosaurs roamed the Earth.
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