It seems that the author of the recent paper in Nature (Shakun et al ) says that the Earth’s wobble was a contributor for ending the ice age, but won’t go so far as to call it the trigger. But I’m not even sure he can claim much of anything, because Willis has found some serious issues with the Shakun et al paper which you can read about here. It seems to me, based on the proxies and methods used, Shakun is just making a SWAG. Of course we’ll know more about the certainty as the paper is dissected in greater detail – Anthony
From National Public Radio- Shake It Off: Earth’s Wobble May Have Ended Ice Age
(h/t to WUWT reader Paul Bell)
by Christopher Joyce NPR
When viewed from outside and looking down onto the Earth from the north, the direction of precession is clockwise. When standing on Earth looking outward, the axis appears to move counter-clockwise across the sky. Image from mydarksky.org (original image with the NPR story could not be used due to licensing issues - Anthony)
But exactly what caused the big thaw isn’t clear, and new research suggests that a wobble in the Earth kicked off a complicated process that changed the whole planet.
Ice tells the history of the Earth’s climate: Air bubbles in ice reveal what the atmosphere was like and what the temperature was. And scientists can read this ice, even if it’s been buried for thousands of years.
But when it comes to the last ice age, ice has a mixed message.
The conventional wisdom is that carbon dioxide increased in the atmosphere starting about 19,000 years ago. Then the ice melted. The logical conclusion? The greenhouse effect.
But the Antarctic was getting warmer even before CO2 levels went up. So which came first in the Antarctic, warming or CO2?
“The problem is, [the Antarctic is] just one spot on the map, and it’s a dicey way to slice up global climate change by looking at one point,” says Jeremy Shakun, a climate scientist at Harvard University. So he went way beyond the Antarctic — he collected samples of ice, rock and other geologic records from 80 places around the world and found that CO2 levels did, in fact, precede global warming.
Here’s his scenario for what killed the ice age, which was published in the journal Nature this week.
About 20,000 years ago, the Earth — the whole planet — wobbled on its axis. That happens periodically. But this time, a lot more summer sunlight hit the northern hemisphere. Gigantic ice sheets in the Arctic and Greenland melted.
“That water is going to go into the North Atlantic, and that happens to be the critical spot for this global conveyer belt of ocean circulation,” Shakun says.
The conveyer belt is how scientists describe the huge, underwater loop-the-loop that water does in the Atlantic: Cold Arctic water sinks and moves south while warm water in the southern Atlantic moves north.
The trouble is that the sudden burst of fresh meltwater didn’t sink, so the conveyer belt stopped.
“It’s like, you know, sticking a fork in the conveyer belt at the grocery store,” Shakun says. “The thing just jams up; it can’t keep sinking, and the whole thing jams up.”
So warm water in the south Atlantic stayed put. That made the Antarctic warmer. Eventually, ocean currents and wind patterns changed, and carbon dioxide rose up out of the southern oceans and into the atmosphere.
Eric Wolff, a climate scientist at the British Antarctic Survey, isn’t convinced a wobble was the trigger — the planet had wobbled before and not melted the ice. But he says whatever did start the process during the ice age, the subsequent increase in CO2 created a runaway greenhouse effect worldwide.
“The CO2 increase turned what initially was a Southern Hemisphere warming into a global warming. That’s a very nice sequence of events to explain what happened between about 19,000 and 11,000 years ago,” Wolff says.
But that’s a process that has taken about 8,000 years. And Shakun’s research found that the amount of CO2 it took to end the ice age is about the same amount as humans have added to the atmosphere in the past century.
Rapidly increasing CO2 from 200 to 250 ppm is not much of a ‘forcing’,
on a log scale it’s only a third of a doubling, worth but a quarter-degree C,
a mere ‘contribution’ indeed.
Obviously the heat that melted all that ice was solar, not miniscule sky-warming.
It would certainly be nice to know that adding CO2 would keep the next glacial from occuring, for humanity’s sake, but let’s see what the skeptics say about this paper.
Yes, it must be CAGW and CO2 or the plan falls apart.
I believe the “trigger” that flips the system into the other state is Arctic summer ice. If you get enough summers of too little Arctic ice melt, maybe even Hudson Bay ice melt, the system flips into the stable cold state. It probably takes a volcanic eruption at just the right time of year at just the right place. In conjunction with a solar magnetic minimum, maybe even likely. It isn’t so much, in my opinion, the insolation being the trigger as it is there not being enough insolation to completely recover from the triggering event. Once enough ice builds, the insolation is not enough to get completely back to conditions before the event.
I believe we have been seeing that condition over the past 2000 years. Each cold period a little cooler than the one before and each subsequent warming period fails to recover to the level of the previous one. I would expect to find, if the data were available, that the Arctic sea ice for the past 2000 years has overall been trending upwards with some major variation along the way.
I’m still not sure how CO2 levels could be different to a meaningful degree in spots around the globe at the same time (unless you’re standing right next to a volcano that goes off). So either the Antarctica samples are dated wrong or those for the study are.
“Eric Wolff, a climate scientist at the British Antarctic Survey, isn’t convinced a wobble was the trigger — the planet had wobbled before and not melted the ice. But he says whatever did start the process during the ice age, the subsequent increase in CO2 created a runaway greenhouse effect worldwide.”
WTF! Where? In computers? I guess he must have fogotten the oceans rusted a while back, all due to O2.
If this had started a “runaway greenhouse effect” then why is the world not much hotter than it is? Clearly something has prevented this from happening – a mechanism for stabilising the climate.
“The trouble is that the sudden burst of fresh meltwater didn’t sink, so the conveyer belt stopped…. But that’s a process that has taken about 8,000 years….”
What a mess “sudden” means “8,000” years?
“But this time, a lot more summer sunlight hit the northern hemisphere. Gigantic ice sheets in the Arctic and Greenland melted…..So warm water in the south Atlantic stayed put. That made the Antarctic warmer. Eventually, ocean currents and wind patterns changed, and carbon dioxide rose up out of the southern oceans and into the atmosphere.”
So the Northern Hemisphere warmed first (increased insolation) but that didn’t warm the earth (somehow) that had to wait for the antartic to warm.
“So warm water in the south Atlantic stayed put. That made the Antarctic warmer. ”
Wait a minute, if the south atlantic was already warm, how dit it warm up and release more CO2.
“That’s a very nice sequence of events to explain what happened …”
This whole thing is a self-confessedly rube goldbergian mess!!!
“And Shakun’s research found that the amount of CO2 it took to end the ice age is about the same amount as humans have added to the atmosphere in the past century.”
If Shakun is right, is this not good news? Forestalling the next ice age would be man’s greatest achievement, n’est-ce pas?
oh ok….
that explains the runaway glaciation when Co2 levels are sky high
Unless I am missing something, Shakun’s theory that the “ice age” ended because of CO2 necessarily requires that the glaicers melt before the CO2 is released. If so, doesn’t the theory refute the stated conclusion? If the glaicers have melted (and, not incidently, antartica has warmed) hasn’t the “ice age” already ended? Isn’t a relative absence of ice what defines the end of an “ice age”?
Of course, it stands to reason that temps might continue to rise after the ice is gone. It also makes some that portion of the increase in CO2 (caused either directly by the warming which melted the ice or by an interruption in Ocean circulation patters) would occur before the temps reach their inter-glaicial maximum. It even makes sense that, in some portions of the world, temps might lag as the process of melting the ice and warming the Oceans would both require enormous amounts of energy. Isn’t the more natural inference that the Milankovitch cycle caused the temp increase directly and all of the other observed effects followed from that single cause?
Crosspatch,
Nice post, and one with which I completely agree. It isn’t so hard to see that we’ve been heading downward in fits and starts for 6,000 years now since the Holocene Optimum. I too agree that since we are currently only a few W/m2 above that required for a prolonged ice age (and will be at that minimum insolation for another 8,000 more years, it would only take a relatively minor event to flip us into the cold climate state.
crosspatch says:
April 6, 2012 at 10:35 am
But why the regularity of interglacials during what has been a million plus years of ice age? The regularity certainly hints at a cyclical process (Milankovitch cycles etc) with perhaps volcanic events being common enough to help the process if occurring at a time when the events would reinforce the cyclical process. And there is much we do not know about long term variability in the solar process.
But the Antarctic was getting warmer even before CO2 levels went up. So which came first in the Antarctic, warming or CO2?
What came first at the start of the ice age?
I quite like Fred Hoyle’s theory – ice ages end when a large comet or asteroid strike in an ocean somewhere vaporises a few billion tons of seawater. The extra water vapour triggers global warming.
“The problem is, [the Antarctic is] just one spot on the map, and it’s a dicey way to slice up global climate change by looking at one point,””
Correct me if I’m wrong, but the CO2 proxy is from “just one spot on the map”.
Robert Austin says:
April 6, 2012 at 10:58 am
Ho boy, you are SO right, Robert! I figure were I live here in Idaho, a return to an Ice Age will result in temperatures where the average lows every month but one will be below freezing! And the exception? July–where it will be just one degree above freezing (and that’s the AVERAGE–the actual temps will probably get below freezing every week). Looking back on my pack of seeds for garden planting, I don’t recall a single one that gave me a 1- or 2-week growing season. Not a single one!
The next Ice Age, as Anthony pointed out, will be diastrous, an extreme counter point to the current reprieve:
The last big ice age ended about 11,000 years ago, and not a moment too soon — it made a lot more of the world livable, at least for humans.
So, by this scenario, the first event is that the Northern polar areas heated and melted the Arctic ice caps, then this stopped the ocean conveyors (a ludicrous inference IMO), and this caused the Southern oceans to heat, and so released CO2. So the release of CO2 is the last thing to happen. And this is reported as that it *precedes* the warming? This is beyond pretzel logic.
It would be really nice to see some hard figures here instead of hand-waving.
How many kilojoules of energy would be required to melt kilometer thick ice down to the latitude of New York? Where did all that come from – given all we are told about TSI being constant.
Where did all the CO2 come from after a ‘little Milankovitch wobble? Going from not enough to warm the planet to current day levels -when poleward of 50 deg N/S latitude is ice covered (so no plants) the oceans are freezing (literally) and without any SUVs or coal fired power stations – takes some kind of leap of faith.
As almost all the proxies that are used in the paper seem to disagree in every metric where is the certainty of the timing, temperature and quantity of CO2? Another leap of faith?
If that relatively minor amount of CO2 was enough to melt all that ice why did it stop? Why didn’t the Earth warm “until the oceans boiled away” (Jim ‘the hat’ Hansen).?
So every ~3.5 precession cycles, the ice melts, life thrives for almost half a cycle, then it refreezes. I’ve always found this cycle interesting. Upon hearing the Arthurian legend several times and variations, it occurred to me there is an allusion to the precession cycle in the story. if one considers the king to be the guiding ‘star’ for a country where the land and king are ‘one’. With Uther Pendragan as Arthur’s father, the star went from the constellation Draconis to Ursa Minor. There is disputed etymology that the name Arthur has roots in a term for ‘bear-king’. If so, this myth holds information from a few thousand years earlier, when the pole star was in Draconis.
Don’t worry: Soon this paper will be withdrawn. What Shakun is implying can’t be true.
He also needs to explain how ice ages start with this theory if CO2 has such a big impact on climate.
Robert Austin says:
No…It is not good news that we have put such a large amount of CO2 into the atmosphere that we are not only indefinitely postponing the next ice age which we would otherwise gradually go into on a timescale of thousands to tens of thousand of years but are also likely to cause a dramatic and significant warming from the current state perhaps of about the same magnitude as the warming from the glacial period to now and over a timescale of decades to a few centuries!
Derek says:
Who says it started a runaway greenhouse effect? It didn’t…and neither is it expected to in the current anthropogenic case. (The only climate scientist I know of who is talking about the possibility of a runaway greenhouse effect is Jim Hansen and that is for the situation where we really go to town burning almost all conventional fossil fuels and maybe a lot of unconventional sources like tar sands to boot. In that case, the rise in CO2 levels will be much more larger than occurred between the last glacial period and now…as well as much, much more rapid.)
This discussion is missing the obvious point — remember that water vapor is a much stronger greenhouse gas, and water frozen deep inside glaciers stays there, never turning into water vapor. So, a little warming produces some glacier melt, which produces more water vapor, which produces more melt, and so on. The CO2 contribution to all this is a sideshow. (And obviously this process works in reverse during the onset of an ice age.)
———–
Correct me if I’m wrong, but the CO2 proxy is from “just one spot on the map”.
———–
Willis Eschenbach has just now clarified this in a separate post … CO2 is well-mixed across latitudes.
So *THAT’S* OK.
Much appreciation to Willis/WUWT for confirming the main features of the Shakun et al analysis.
The finding of Lindzen and Choi that the planet’s feedback response to a change in forcing is negative (clouds in the tropics increase or decrease to reflect more or less energy off into space which) removes the forcing amplification which is required to try to explain why the weakest of the orbital parameters eccentricity can cause the 100 kyr glacial/interglacial cycle.
http://www.leif.org/EOS/2009GL039628-pip.pdf
“On the determination of climate feedbacks from ERBE data
Richard S. Lindzen and Yong-Sang Choi
Program in Atmospheres, Oceans, and Climate
Massachusetts Institute of Technology
Climate feedbacks are estimated from fluctuations in the outgoing radiation budget from
the latest version of Earth Radiation Budget Experiment (ERBE) nonscanner data. It
appears, for the entire tropics, the observed outgoing radiation fluxes increase with the
increase in sea surface temperatures (SSTs). The observed behavior of radiation fluxes
implies negative feedback processes associated with relatively low climate sensitivity.
This is the opposite of the behavior of 11 atmospheric models forced by the same SSTs.
Therefore, the models display much higher climate sensitivity than is inferred from
ERBE…”
The discussion is pointless and goes in circles as there are multi incorrect mechanisms posited to explain what is observed. Naturally when the mechanisms are incorrect, the proxies are misinterpreted or in this case due to the extreme AGW paradigm manipulated to try to save the incorrect mechanism.
Insolation changes, due to orbital changes, are not the cause of the glacial/interglacial cycle. Temperature changes cannot and do not cause of the observed glacial/interglacial atmospheric changes in CO2. The long term reduction in atmospheric CO2 is not due to the Himalayas forming.
The theoretical assumed mechanism what controls and varies atmospheric CO2 is incorrect. The posited cause of the glacial/interglacial cycles (changes in summer insolation at 60 degree latitude north is incorrect.)
Look at figure 3 which is Greenland Icesheet temperature over the last 12,000 years Vs atmospheric CO2.
The planet warms and cools during the Dansgaard-Oeschger cycles. The Dansgaard-Oechger climate change is not an event. It is a cycle. It is a cycle.
Question 1: What the heck causes the Dansgaard-Oeschger cyles? That is rhetorical question. As I know what causes it. Hint there are cosmogenic isotope changes each and every time during the Dansgaard-Oeschger cycle. The late Gerald Bond was able to track 23 cycles. The same suspect is always at the scene of the crime. It is the bloody sun.
The assumed model for the sun is fundamentally incorrect. The sun cyclically causes a very sever climate change. The paleoclimatic data unambiguously shows there are cyclic abrupt climate changes such as the Younger Dryas. The paleoclimatic specialist refer to the Younger Dryas as Heinrich event 0. The Heinrich event is not a stupid event it is cycle. It is a cycle. An event is something that occurs randomly due to for instance comet impacts. A climate cycle requires a cyclic forcing function. A cycle is something that will happen again. All of the past interglacials ended abruptly.
The cyclic Heinrich abrupt climate change cycles are not caused by CO2 changes. The Dansgaard-Oeschger cycle is not caused by CO2 changes.
Question 2: Why the heck does CO2 not change during the Dansgaard-Oeschger cycle? Planetary temperature increases and decrease. That also is rhetorical question.
The planet cooled during the Holocene interglacial period. Why does CO2 gradually rise? Temperature is decreasing.
http://climate4you.com/images/GISP2%20TemperatureSince10700%20BP%20with%20CO2%20from%20EPICA%20DomeC.gif
http://climate4you.com/
http://arxiv.org/abs/physics/0612145v1
The Antarctic climate anomaly and galactic cosmic rays
Borehole temperatures in the ice sheets spanning the past 6000 years show Antarctica repeatedly warming when Greenland cooled, and vice versa (Fig. 1) [13, 14]. North-south oscillations of greater amplitude associated with Dansgaard-Oeschger events are evident in oxygenisotope data from the Wurm-Wisconsin glaciation[15]. The phenomenon has been called the polar see-saw[15, 16], but that implies a north-south symmetry that is absent. Greenland is better coupled to global temperatures than Antarctica is, and the fulcrum of the temperature swings is near the Antarctic Circle. A more apt term for the effect is the Antarctic climate anomaly.
http://www.agu.org/pubs/crossref/2002/2000PA000571.shtml
On the 1470-year pacing of Dansgaard-Oeschger warm events
The oxygen isotope record from the Greenland Ice Sheet Project 2 (GISP2) ice core was reanalyzed in the frequency and time domains. The prominent 1470-year spectral peak, which has been associated with the occurrence of Dansgaard-Oeschger interstadial events, is solely caused by Dansgaard-Oeschger events 5, 6, and 7. This result emphasizes the nonstationary character of the oxygen isotope time series. Nevertheless, a fundamental pacing period of ∼1470 years seems to control the timing of the onset of the Dansgaard-Oeschger events. A trapezoidal time series model is introduced which provides a template for the pacing of the Dansgaard-Oeschger events. Statistical analysis indicates only a ≤3% probability that the number of matches between observed and template-derived onsets of Dansgaard-Oeschger events between 13 and 46 kyr B.P. resulted by chance. During this interval the spacing of the Dansgaard-Oeschger onsets varied by ±20% around the fundamental 1470-year period and multiples thereof. The pacing seems unaffected by variations in the strength of North Atlantic Deep Water formation, suggesting that the thermohaline circulation was not the primary controlling factor of the pacing period.
Atmospheric CO2 does not change significantly when temperature changes. There is an estimated maximum change of 30 ppm in CO2 for the total temperature change from glacial/interglacial and visa versa. Due the change in ocean salinity atmospheric CO2 increases when there is there is more ice in the ice sheets. As the vast regions of the biosphere is covered by ice and there is massive reduction in rainforest (roughly 30% of the Amazon is converted from rainforest to savanna) there is massive reduction in vegetation which increases the amount of the CO2. The total net change in atmospheric CO2 due to ice sheets forming causing a saltier ocean and the reduction in vegetation is no net change in atmospheric CO2 and likely an increase in atmospheric CO2. (Volcanic input continues yet there is a reduction in vegetation to remove the CO2.)
There is no explanation as to what causes the reduction of 80 ppm to 100 ppm of atmospheric CO2 during the glacial/interglacial cycle. That is the so called Holy Grail of the carbon cycle specialists.
http://www.up.ethz.ch/education/biogeochem_cycles/reading_list/sigman_nat_00.pdf
A reasonable estimate for ice age ocean cooling of 2.5C in the polar surface and 5C in the low-latitude surface leads to a CO2 decrease of 30 p.p.m.v., with the low-latitude and polar temperature changes playing roughly equivalent roles in this decrease. It has recently been noted that ocean general circulation models predict a greater sensitivity of CO2 to low-latitude surface conditions than do simple ocean box models like CYCLOPS17. However, the significance of this observation is a matter of intense debate.
An opposing effect on atmospheric CO2 to that of glacial/interglacial temperature change is provided by the increased salinity of the glacial ocean, due to the storage of fresh water on land in extensive Northern Hemisphere ice sheets. Based on the approximately 120m depression of sea level during the last ice age18, the whole ocean was about 3% saltier than it is today. All else being constant, this increase would have reduced the solubility of CO2 in sea water and raised atmospheric CO2 by 6.5 p.p.m.v. Taking the estimated temperature and salinity effects together, we would expect the atmospheric CO2 concentration of the ice age world to have been 23.5 p.p.m.v. lower. Folding in the effect of a 500 Pg C transfer from the continents to the ocean/atmosphere system, we are left with an 8.5 p.p.m.v. decrease in CO2 (Table 1). There are uncertainties in each of these effects, but it seems that most of the 80±100 p.p.m.v. CO2 change across the last glacial/interglacial transition must be explained by other processes. We must move on to the more complex aspects of the ocean carbon cycle.
Timing of abrupt climate change: A precise clock by Stefan Rahmstorf
Many paleoclimatic data reveal a approx. 1,500 year cyclicity of unknown origin. A crucial question is how stable and regular this cycle is. An analysis of the GISP2 ice core record from Greenland reveals that abrupt climate events appear to be paced by a 1,470-year cycle with a period that is probably stable to within a few percent; with 95% confidence the period is maintained to better than 12% over at least 23 cycles. This highly precise clock points to an origin outside the Earth system; oscillatory modes within the Earth system can be expected to be far more irregular in period.