This is an attempt to redefine the graph made famous by Al Gore in An Inconvenient Truth that showed temperature leading CO2.
From a press release embargoed until 1PM EST 4/4:
Work that may clarify the relationship between carbon dioxide (CO2) levels and temperature at the end of the last ice age is presented in this week’s Nature. The study reveals that rising temperatures were preceded by CO2 increases during the last deglaciation, contrary to prior findings derived from ice cores that were thought to represent larger global patterns. These results support an important role for CO2 in driving global climate change.
Antarctic ice-core records indicate that CO2 may have influenced climate changes during the Pleistocene ice ages, which began around 2.6 million years ago and ended about 11,700 years ago. However, the exact role of CO2 in producing climate changes has remained unclear, partly because ice-core records only reflect local temperatures. To better understand the relationship between CO2 and global climate change, Jeremy Shakun and colleagues reconstruct global surface temperatures for the last deglaciation. They show that rising temperatures are correlated with, and generally lag behind, increasing levels of CO2.
The reconstructed global temperatures were produced using proxy records of temperature variability, such as those recorded in planktonic microorganisms. Anomalies in the correlations, such as in the Antarctic where the CO2 changes lag behind temperature, are explained by redistribution of heat between the Northern and Southern Hemispheres, the authors suggest.
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Here is the long form press release (h/t to junkscience.com):
Rising CO2 levels linked to global warming during last deglaciation
CORVALLIS, Ore. – Many scientists have long suspected that rising levels of carbon dioxide and the global warming that ended the last Ice Age were somehow linked, but establishing a clear cause-and-effect relationship between CO2 and global warming from the geologic record has remained difficult.
A new study, funded by the National Science Foundation and published in the journal Nature, identifies this relationship and provides compelling evidence that rising CO2 caused much of the global warming.
Lead author Jeremy Shakun, who conducted much of the research as a doctoral student at Oregon State University, said the key to understanding the role of CO2 is to reconstruct globally averaged temperature changes during the end of the last Ice Age, which contrasts with previous efforts that only compared local temperatures in Antarctica to carbon dioxide levels.
“Carbon dioxide has been suspected as an important factor in ending the last Ice Age, but its exact role has always been unclear because rising temperatures reflected in Antarctic ice cores came before rising levels of CO2,” said Shakun, who is a National Oceanic and Atmospheric Administration (NOAA) Post-doctoral Fellow at Harvard University and Columbia University.
“But if you reconstruct temperatures on a global scale – and not just examine Antarctic temperatures – it becomes apparent that the CO2 change slightly preceded much of the global warming, and this means the global greenhouse effect had an important role in driving up global temperatures and bringing the planet out of the last Ice Age,” Shakun added.
Here is what the researchers think happened.
Small changes in the Earth’s orbit around the sun affected the amount of sunlight striking the northern hemisphere, melting ice sheets that covered Canada and Europe. That fresh water flowed off of the continent into the Atlantic Ocean, where it formed a lid over the sinking end of the Atlantic Meridional Overturning Circulation – a part of a global network of currents that brings warm water up from the tropics and today keeps Europe temperate despite its high latitudes.
The ocean circulation warms the northern hemisphere at the expense of the south, the researchers say, but when the fresh water draining off the continent at the end of the last Ice Age entered the North Atlantic, it essentially put the brakes on the current and disrupted the delivery of heat to the northern latitudes.
“When the heat transport stops, it cools the north and heat builds up in the Southern Hemisphere,” Shakun said. “The Antarctic would have warmed rapidly, much faster than the time it takes to get CO2 out of the deep sea, where it was likely stored.
“The warming of the Southern Ocean may have shifted the winds as well as melted sea ice, and eventually drawn the CO2 out of the deep water, and released it into the atmosphere,” Shakun said. “That, in turn, would have amplified warming on a global scale.”
The researchers constructed a record of global surface temperature from 80 temperature reconstructions spanning the end of the Ice Age and found that average temperature around the Earth correlated with – and generally lagged behind – rising levels of CO2.
Peter Clark, an Oregon State University scientist and co-author on the paper, said changes in solar radiation were the likely trigger for the series of effects that followed. His 2009 study, published in Science, confirmed an earlier theory that wobble in the Earth’s axis, which changes the amount of sunlight captured by Earth, first caused melting of the large northern ice sheets.
“It has long been known that Earth’s slow wobble is caused primarily by the gravitational influences of the larger planets, such as Jupiter and Saturn, which pull and tug on the Earth in slightly different ways over periods of thousands of years,” said Clark, a professor in OSU’s College of Earth, Ocean, and Atmospheric Sciences.
Shakun said there is “an enormous amount” of carbon sequestered in the deep ocean.
“The Southern Ocean is connected to all the deep ocean basins,” he pointed out, “so the most likely mechanisms to draw it out of the ocean were certainly there.”
The question now, the researchers say, is how human-generated carbon dioxide will affect the planet when there isn’t an ice age.
“CO2 was a big part of bringing the world out of the last Ice Age,” Shakun said, “and it took about 10,000 years to do it. Now CO2 levels are rising again, but this time an equivalent increase in CO2 has occurred in only about 200 years, and there are clear signs that the planet is already beginning to respond.”
“While many of the details of future climate change remain to be figured out, our study bolsters the consensus view that rising CO2 will lead to more global warming,” Shakun added.
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The paper is at http://www.nature.com/nature/journal/v484/n7392/full/nature10915.html and named:
Global warming preceded by increasing carbon dioxide concentrations during the last deglaciation
Jeremy D. Shakun, Peter U. Clark, Feng He, Shaun A. Marcott, Alan C. Mix, Zhengyu Liu, Bette Otto-Bliesner, Andreas Schmittner & Edouard Bard
Abstract:
The covariation of carbon dioxide (CO2) concentration and temperature in Antarctic ice-core records suggests a close link between CO2 and climate during the Pleistocene ice ages. The role and relative importance of CO2 in producing these climate changes remains unclear, however, in part because the ice-core deuterium record reflects local rather than
global temperature. Here we construct a record of global surface temperature from 80 proxy records and show that temperature is correlated with and generally lags CO2 during the last (that is, the most recent) deglaciation. Differences between the respective temperature changes of the Northern Hemisphere and Southern Hemisphere parallel variations in the strength of the Atlantic meridional overturning circulation recorded in marine sediments. These observations, together with transient global climate model simulations, support the conclusion that an antiphased hemispheric temperature response to ocean circulation changes superimposed on globally in-phase warming driven by increasing CO2 concentrations is an explanation for much of the temperature change at the end of the most recent ice age.
METHODS SUMMARY
The data set compiled in this study contains most published high-resolution
(median resolution, 200 yr), well-dated (n5636 radiocarbon dates) temperature
records from the last deglaciation (see Supplementary Information for the full
database). Sixty-seven records are from the ocean and are interpreted to reflect sea
surface temperatures, and the remaining 13 record air or lake temperatures on
land. All records span 18–11 kyr ago and,85% of them span 22–6.5 kyr ago. We
recalibrated all radiocarbon dates with the IntCal04 calibration (Supplementary
Information) and converted proxy units to temperature using the reservoir corrections
and proxy calibrations suggested in the original publications. An exception
to this was the alkenone records, which were recalibrated with a global
core-top calibration41. The data were projected onto a 5u35u grid, linearly
interpolated to 100-yr resolution and combined as area-weighted averages. We
used Monte Carlo simulations to quantify pooled uncertainties in the age models
and proxy temperatures, although we do not account for analytical uncertainties
or uncertainties related to lack of global coverage and spatial bias in the data set. In
particular, the records are strongly biased towards ocean margins where high
sedimentation rates facilitate the development of high-resolution records. Given
these issues, we focus on the temporal evolution of temperature through the
deglaciation rather than on its amplitude of change. The global temperature stack
is not particularly sensitive to interpolation resolution, areal weighting, the
number of proxy records, radiocarbon calibration, infilling of missing data or
proxy type. Details on the experimental design of the transient model simulations
can be found in ref. 25.
The temperature stacks and proxy data set are available in Supplementary Information.
Full Methods and any associated references are available in the online version of
the paper at www.nature.com/nature.
PDF files
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- Supplementary Information (9.2M)
- This file contains Supplementary Text and Data, Supplementary Figures 1-30, Supplementary Tables 1-3, additional References and Supplementary Appendices 1-2.
Excel files
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- Supplementary Data (2.4M)
- This file contains Supplementary Data.
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Don Easterbrook has some initial thoughts on the Nature paper.
The paper is based on many assumptions without supporting data. Here are a few examples:
1. They assume that CO2 is capable of causing climate changes, even though 95% of the greenhouse gas (GHG) effect is from water vapor. In order to seriously consider CO2 as a causal mechanism, you first need to prove that very tiny increases in CO2 do indeed increase atmospheric water vapor. However, during recent warming, purported to be caused by increased CO2, atmospheric water vapor has not gone up, it has decreased slightly. CO2 by itself cannot cause significant warming because there is little of it in the atmosphere (0.038%) and CO2 accounts for only a few percent of the GHG effect.
2. They assume that the AMOC is the only driver of climate change, totally ignoring the influence of the Pacific Ocean, which covers almost half of the Earth’s surface and we can see in the modern data a strong influence of ENSO as a driver of climate changes (actually a closer correlation than the AMOC). They offer no evidence that the AMOC is the main and only driver of climate change.
3. They assume a hemispheric ‘see-saw’ of climate changes in which the North and South Hemispheres are out of phase, despite strong evidence in both hemisphere that climate changes were closely simultaneous, not out of phase with one another (Easterbrook, 2011).
4. The dismiss all other causal mechanisms by simply stating that they are only of ‘regional importance’, similar to the tactic of dismissing the MWP and Little Ice Age as only regional climate changes, not global. They also totally ignore the complete lack of correlation of CO2 with Holocene climate changes. They don’t even mention the very strong correlation of variation in 10Be and 14C with climate changes, suggesting a solar cause.
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The Antarctic Ice core graph is particularly troublesome.
In the long scale graph at top, I pointed out that the resolution of the temperature reconstruction diminished as the sample got older. Willis responded to my query with this:
The resolution for temperature drops, as does the CO2 resolution, because the ice is getting more compressed and so there is more and more time between equally spaced samples. Here’s one of my old graphs of the same data, showing the same phenomenon:
Where I think they go wrong is the claim that they can somehow reconstruct, not just the couple thousands of years of temperature that Mann claimed, but nearly a million years of temperature … and that the timelines for the two wouldn’t have errors.
My rule of thumb about these kinds of things is, no error bars … no science.
w.
Other rebuttals are in the works. I will add to this posting as they develop.
Pat Michaels writes to junkscience.com:
I am very unexcited about this. I have always thought that the timing of carbon dioxide changes and warming/cooling is pretty much irrelevant… What is interesting about this latest “finding” is that it demonstrates, yet again, the unfalsifiability of climate change “science”. The standard argument on the ice cores has been that temperature preceding carbon dioxide changes is simply evidence for positive feedback rather than lack of forcing. Now the argument will revert back to the other way around — that CO2 causes all the major pleistocene (which we are still in — see Greenland) climate fluctuations.
About that carbon dioxide–it’s just another attempt to explain the true mystery of climate change, which is why major glaciations ever go away.
My mantra is that “it’s not the heat, it’s the sensitivity”, which is obviously overestimated in climate models, for a variety of reasons that should be obvious.
Tom V. Segalstad Associated Professor of Resource and Environmental Geology, at the
University of Oslo writes:
There are some serious problems with ice cores.
I’ll be surprised if the new Nature paper cites our paper by Jaworowski, Segalstad & Ono (1992): Do glaciers tell a true atmospheric CO2 story? in the professional peer-reviewed Elsevier journal “Science of the total environment”, Vol. 114, pp. 227-284 (1992). The paper is available on my website here: http://www.co2web.info/stoten92.pdf
There’s a follow-up paper (abstract) on the stable isotope temperature measurement technique in ice cores here: http://www.co2web.info/aig.pdf
I checked the references of the Shakun et al paper published today, and the paper Segalstad mentions is not part of the references section. I guess it was too inconvenient to mention.
sunshinehours1 says:
April 5, 2012 at 10:51 am
John Finn, the interesting thing about HADCET is seasonally ranked data.
Warmest DJF 1869, 1834, 1989, 2007
Warmest MAM 2011, 1893, 2007, 1945
Warmest JJA 1976, 1826, 1995, 2003
Warmest SON 2006, 2011, 1731, 1730
I don’t see any catastrophic warming …
I never mentioned catastrophic warming. I’ m disagreeing with Smokey’s claim that recent warming is a continuing trend back to the LIA – or back to 1659 in the case of the CET graphs. Mind, though, it is perhaps worth pointing out that of the 16 years specified above only 7 (less than half) are in the first 300-year period (up to 1959) while the rest are in the 50-odd year period up to 2011.
You can talk about trends … but if UHI is .25C or .5C which I think is most likely ….
CET is adjusted for UHI. I know this to be the case because I live in the CET region and I know that the local stations have higher recorded temperatures than those in the CET data. In fact, on the CET site, you can check the actual measured temperatures for each month and compare them with the recorded values. The recorded values tend to be about 0.3-0.4 deg below the measured values.
There’s an argument to suggest that there is some over-compensation for UHI. Where I live experienced a significant decrease in population throughout the 1970s and 1980s yet the local station data shows a greater warming trend than the CET data over the last few decades. Also the 100- year trend (up to 2000) at the rural Armagh Observatory is almost exactly the same as the CET trend.
beng says:
April 5, 2012 at 8:47 am
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Gail Combs says:
April 5, 2012 at 6:12 am
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Gail, you have it right. Since the ice changes/65N summer insolation are so tightly correlated, it leaves little else to affect the ice changes — unless CO2 level changes are the same as the Milankovitch changes (which they are obviously not).
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Actually that is ONE of the factors.
Geologist think Plate Tectonics are also a factor.
As I under stand it A shift in the Caribbean tectonic plate joined North and South America… changed the flow of the ocean currents and caused the creation of the Gulf Stream.The Gulf Stream introduced warm and saline water masses to the north creating deepening of the thermocline. http://www-odp.tamu.edu/publications/202_SR/synth/synth_5.htm
The configuration of the planet is still pretty much the same BTW
Lots of discussion at: The End Holocene, or How to Make Out Like a ‘Madoff’ Climate Change Insurer
@John Finn,
Still waiting for your accounts of challenging Michael Mann: [“I can point to a number of online ‘exchanges’ I’ve had with AGW proponents (including Michael Mann). In fact one particular case involving Mann was cited on WUWT. I’ve been challenging AGW issues for several years.”].
If you’re challenging AGW, why do your arguments sound like you’re a true believer? The short term trends are still well within the long term parameters. Natural variablility causes natural fluctuations. Wake me when the global temperature breaks through the upper band. So far, it’s not happening.
If CO2 had a role in increasing temperatures and bringing us out of the last ice age, where did the CO2 come from? An ice covered Earth?
The most important thing is that it is a metastudy, which is an implicit admission of observational failure.
Joel Shore says: @ur momisugly April 5, 2012 at 9:28 am
….So, of the rise in CO2 that we see in the atmosphere (from ~280 ppm before the industrial revolution) to 390+ ppm today, humans are responsible for all of it. In fact, the change in concentration would have been about twice as large as we observed if all of the excess CO2 remained in the atmosphere. However, about half of what we emit rapidly segregates in the biosphere and ocean mixed layer….
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And Thank Gaia we are recycling the CO2 that is locked up in coal. I am sure plants would thank us if they could talk. Without plants higher life forms would become extinct. There is plenty of evidence that we were entering into a “Carbon Dioxide Starvation Age”
If you look at the very long term, the amount of CO2 has decreased in fits and starts and the amount of O2 has increased. The Cambrian Period was nearly 7000 ppm of CO2, the Late Ordovician Period was ~ 4400 ppm of CO2. and the Cretaceous between ~ 700 and 1400 ppmv.
This is supported by plant biology and evolution.
C3 and C4 photosynthesis are the two most common photosynthetic pathways contributing to global primary productivity, with Crassulacean Acid Metabolism (CAM), a third pathway found in succulents, being of limited importance to global productivity (Sage and Monson 1999; Still et al. 2003). Atmospheric CO2 is the carbon source for all three pathways; one key distinguishing feature among them, however, is that both C4 and CAM photosynthesis involve a CO2-concentrating mechanism to create high CO2 concentrations at the site of photosynthetic carboxylation. In contrast, C3 photosynthesis relies solely on diffusion of CO2 from the outside atmosphere to the sites of photosynthetic CO2 fixation (Fig. 10.1). Hence, it is clear that changes in the atmospheric CO2 levels will more likely influence the photosynthetic activities of C3 than of C4 and CAM plants….
C4 photosynthesis is found only among the most advanced land plants. C4 is known to occur among the Angiosperms but has not been reported among older taxonomic groups, such as Gymnosperms (e.g., pines and other coniferous trees) or the Pteridopyhta (e.g., ferns)….
Within both monocots and dicots, C4 photosynthesis has polyphyletic origins and appears to occur among only the most recently derived taxa, suggesting an evolutionary origin of only 10 to 15 million years ago.… C4 photosynthesis is found most commonly among herbaceous vegetation (both as annuals and as perennials)….
…while C4 taxa represent only approx 2% of the total species, they account for 25% to 30% of the global terrestrial primary productivity (Still et al. 2003)…. Second, there is ample evidence to suggest that herbivores (both insect and mammal) exhibit dietary preferences for one photosynthetic pathway over the other (summarized in Caswell et al. 1973; Ehleringer and Monson 1993; Sage and Monson 1999)…. http://www.ehleringer.net/Jim/Publications/328.pdf
So the lowering of CO2 levels was slowly pushing about 97% of the plant species towards extinction.
Since CO2 is more soluble in cold water and the Holecene was characterized by an already low level of CO2 would the onset of the next glaciation also have been the demise of C3 plants due to CO2 starvation?
Would there have been enough CO2 partial pressure for the C4 plants to survive?
I am just an amateur, but doens’t the Al Gore famously made graphic show CO2 rising after the temp rises? Just a thought 😉
Someone may have pointed this out already, but this appears to be an attempt to get the “last word” in the record supporting a particular ideology.
As opposed to any form of “science.”
Simon says:
April 4, 2012 at 4:56 pm
Myrrh says
“So give the evidence. Give it now. Do not run away. Do not ignore this request. Do not refer to some amorphous ‘it’s in all the text books’ or ‘it is well known’ – DAMN WELL PRODUCE IN ALL ITS DETAIL.”
It’s only been known for over a hundred years, but read this http://en.wikipedia.org/wiki/Greenhouse_effect
All there.
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I’ve just demanded that I’m not given this effin excuse again!
Don’t keep passing the buck, it really is so very tiresome. I’m asking for convincing proof, surely you must have it somewhere..? Show and tell. You fetch. You explain. You show and tell. Convince me.
“The greenhouse effect is a process by which thermal radiation from a planetary surface is absorbed by atmospheric greenhouse gases, and is re-radiated in all directions. Since part of this re-radiation is back towards the surface and the lower atmosphere, it results in an elevation of the average surface temperature above what it would be in the absence of the gases.”
Show and tell. You fetch. You explain. You show and tell. Convince me.
That’ll do for a start. Get on with it.
Joel Shore says:
April 5, 2012 at 12:24 pm
“You haven’t even made a case at all! I assume you think that some of it might be due to ocean outgassing from warming.”
You made the assertion so you must make the case. No one remotely knowledgeable about climate science would claim that mankind is responsible for (110/280 = 40%) a forty percent increase in CO2 concentration during the last 162 years. The claim is absurd on its face. If you do not agree then justify your claim.
“CO2 change slightly preceded much of the global warming …”
Wow, this kind of exactness to timing over millions of years.
“Here is what the researchers think happened.” Wow this kind of inexactness….
The finding that CO2 rise followed temp rise was noted decades ago and was witnessed a zillion times on a microscale by all who have opened a warm beer or soft drink. The finding of CO2 most obviously following temp was the embarrasing Greenland records and that is why attention shifted to Antarctica where it apparently wasn’t so patently obvious. Like the LIA and the MWP, the reverse CO2-temp findings have been a troubling thorn to the CAGW folks. And like these other confounding issues, it was only a matter of time before some “team” sought to extract the thorn.
Well I have a question for these CO2 control knobs. Once you have a warm period like the Paleocene-Eocene Thermal Maximum, what cools things down 8-10C and puts the CO2 back in the ocean? Here, surely they will agree that the temperature led CO2 downwards and it accomplished this large temperature change naturally. If the earth’s wobble can do that all by itself then the present hysteria is totally off the wall.
This paper, as all others emanating from the climate establishment, takes it for granted that any observed warming is caused by the enhanced greenhouse effect of carbon dioxide. There is just this one problem with their assumption: the chief greenhouse gas on earth is not carbon dioxide but water vapor. They both absorb outgoing infrared (long-wave) radiation and it is their combined absorption of radiant energy that causes the atmosphere to get warm.
But now consider this: when we don’t change the amount of carbon dioxide in the air we have a stable climate. There are local temperature and humidity variations, to be sure, but long-term drift is absent. What guarantees this?
To prevent a long term temperature drift the IR absorption by greenhouse gas concentration that determines IR transmittance of the atmosphere must respond to any such temperature drift. And water vapor is the only greenhouse gas that can easily do that. Starting from this qualitative picture Ferenc Miskolczi brought in radiation theory and showed that for a stable climate to exist the optical thickness of the atmosphere in the infrared had to have a value of 1.86 (15% transmittance). This transmittance is determined by the combined absorption of infrared radiation by all the greenhouse gases present, but the adjustment is maintained by water vapor, the only adjustable greenhouse gas in the lot.
The blogosphere was hostile to the idea because it wiped out the sacrosanct Arrhenius law. But Miskolczi went on to test it using NOAA database of weather balloon observations that goes back to 1948. He found that the IR transmittance of the atmosphere had been constant for the previous 61 years as his theory predicted. During that same period of time the amount of carbon dioxide in air increased by 21.6 percent. This means that the addition of all this carbon dioxide to air had no effect whatsoever upon the absorption of of IR by the atmosphere. And no absorption means no greenhouse effect, case closed.
This is an empirical observation, not derived from any theory, and it overrides any theoretical calculations that do not agree with it. Specifically, it overrides any calculations based on climate models that use the greenhouse effect to predict warming. In accord with this, a close examination of the temperature history of the last 100 years reveals that there has been no greenhouse warming at all during this entire period.
Starting with the twentieth century, the first part of the twentieth century warming started in 1910 and stopped in 1940. There was no corresponding increase of carbon dioxide at the beginning of this warming which means that according to the laws of physics it cannot be greenhouse warming. Bjørn Lomborg attributes this warming to solar influence and I agree with him. There was no warming in the fifties, sixties, and seventies while carbon dioxide relentlessly increased. There is no satisfactory explanation for this lack of warming, only various contorted excuses to explain it away.
The true reason for this lack of warming is clear from Miskolczi’s work. There was no warming in the eighties and nineties either according to the satellite temperature measurements. There was only a short spurt of warming between 1998 and 2002 caused by the warm water that the super El Nino of 1998 had carried across the ocean. And there was no warming from that point on to the present while carbon dioxide just kept on going up on its merry way. And if you still think Arctic warming proves the existence of greenhouse warming think again: Arctic warming is not greenhouse warming and is caused by Atlantic Ocean currents carrying warm Gulf Stream water into the Arctic.
Taking all this history and Miskolczi’s theory into account the attempt in the Nature article to explain the end-Pleisticene warming as greenhouse warming is nothing more than hopelessly misguided global warming doctrine.
Theo Goodwin says:
I don’t need to waste my time proving everything to your satisfaction (which is impossible anyway because your objections are not based on science but on ideology). It is the accepted view in the scientific community. If you don’t want to believe it, you are welcome not to. It will just make you look “AGW skeptics” look even sillier in the eyes of the scientific community (if such a thing is possible).
Merovign says:
April 5, 2012 at 2:46 pm
Someone may have pointed this out already, but this appears to be an attempt to get the “last word” in the record supporting a particular ideology.
As opposed to any form of “science.”
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Oh that much is obvious. This is a pure propaganda piece not science.
They know darn well the climate will be cooling over the next couple of decades. Just because they trash any studies that do not support “The Cause” does not mean they are not paying close attention to them. Nopenhagen, where a world wide carbon tax (and World Government) was supposed to be formed bombed. Public opinion is starting to nose dive and therefore they have to push the agenda through very shortly. This paper gets bundled with a bunch of others into the next IPCC report and is sold as AAA rated just like Subprime Mortgage Bonds were sold as “AAA rated mortgage backed securities” We know what the effect of that con-job was. If they manage to sell this con it will be even worse.
This is an attempt to erase the warmth preceding CO2 increase. Note the runaway greenhouse effect in this morning’s NPR piece on this.
Text of NPR piece on the Nature article this morning
http://www.npr.org/2012/04/05/150000446/shake-it-off-earth-s-wobble-may-have-ended-ice-age
April 5, 2012
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.
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?
A carving of a beast on a bone, found years ago in Vero Beach, is now seen as important early art.
“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.
Joel Shore says:
“…ideology…”
If I had a nickel for every time Joel Shore blamed his inadequacy on ‘ideology’ my piggy bank would be full.
The CBC has jumped all over this:
“Last ice age ended by carbon dioxide increase. Climate skeptics’ popular argument discredited by clear global trend”
http://www.cbc.ca/news/technology/story/2012/04/05/environment-climate-co2-ice-age-end.html?cmp=rss
The ignorant climate doomsday cult just does not give up. Too bad we did not cut the CBC’s funding completely. I can get propaganda for free from Suzuki’s Desmogblog, don’t need to pay 1.1 billion for it at the CBC.
It seems to me that at some point in the elevation of the percentage of CO2… the heat from the Sun will stop reaching the surface of the Earth.
Fairly certain we’d all be narc’d out on it by that point.
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.”
This is why I hate the concept of Meridianal Overturning Circulation (MOC). The meridian is several axes of longitude transecting the north and south Atlantic oceans. It was discovered and named by observant European and American sailors who ruled the seas in the 19th century. It is a simple convection cell where the Gulf Stream flows north and sinks and the bottom water flows south and warms.
Bathospheres in the 60’s painted a far more complex and amazing picture and subsequent isotopic dating showed that the thermohaline circulation was neither meridianal nor predominantly overturning (but hey, aside from that what’s not to like about the name?).
By accident of geography the North Atlantic is the only outlet for Arctic Ocean bottom water. Seawater becomes haline (saline) not only from evaporation of warm surface water, but also from freezing of cold surface water.
I seriously doubt the meltwater put a fork in the thermohaline circulation, but it could slow it down.
The output of propaganda by the MSM; the ongoing revelations of scientific and financial fraud, of bankruptcy and missing billions; the fevered demands/ pleas by warmists to view their model outputs as scientific evidence of change in the physical world (other than what’s happening between their own ears); increasing frequency of ad-hominem attack that lately has even included a shrill call from an academic to “treat” AGW “deniers” – reminiscent of tactics used by the Nazis and the Bolsheviks and their ideologue friends; and even just last week a call from the leader of Greens in Australia (which holds the balance of power) for one-world government…
Others have said it, and I agree with them: the most important single thing that threatens the plans of tyrants is opportunity for unregulated mass communication via the internet. And it is here that the next front in the age-old conflict between totalitarianism and libertarianism will be fought.
Reading these comments prompted me to think: “OK, so what really ended the last Ice Age.”
There must have been some major feedback system – there is no way the modest change in CO2 levels could have been responsible for the dramatic increase in temperature, likewise nor could the positive effect of Milankovitch cycles have been sufficient.
It can only have been increasing levels of water vapour in the atmosphere, which created ‘the greenhouse effect’ we are enjoying today.
So:
1. In the beginning (~12,000 years ago), a natural climate cycle causes a very modest amount of warming.
2. Consequently, a little more ice melts (now the water can vaporise), frosts melt more easily – atmospheric water vapour levels rise, so temperature increases, then the process starts to feed on itself.
3. The surface area of the oceans increase as they start to rise as a consequence of glacier melt, likewise so do inland lakes, making more surface area from which water can evaporate.
4. Eventually as temperature rises, more life can exist on Earth – a combination of warmer oceans and greater amounts of life result in CO2 levels starting to rise.
It is self-evident that atmospheric water vapour levels today are a significant multiple of what they were 15,000 years ago.
So CO2’s impact in this process of creating the last 10,000 years’ ambient temperatures?
Answer: Almost nothing.
Gail Combs says:
April 5, 2012 at 2:25 pm
I fail to understand why anyone would demonize CO2 or try to convince people we are all going to die if the levels of CO2 rise when the evidence points to more CO2 is better especially at the end of an interglacial.
A very important argument about recent C4 evolution indicating a biosphere flora under stress from decreasing CO2. A candle of reason in a dark age of ideological irrationality and fanaticism. We need to lower CO2 like we need a hole in the head.
The Oregon nest of Talebanic AGW fascist-fanaticism has come up with an interesting innovation here – the Younger-Dryas two-step. The same nest from which only last week professor Kari Norgaard proclaimed Soviet style political psyciatry as a solution for climate change skepticism.
There were two rises in global temperatures at the start of the current interglacial – a first abortive one and then a second, after the Younger Dryas (a cold glacial period interrupting the initiation of the interglacial). Here comrade Shakun cherry-picks global temp proxies to show temperature rise apparently later than CO2 rise. What they have probably done is selected proxy records which track the second, post Younger-Dryas, temperature rise, not the first.
From the study it is revealing that at the start of deglaciation that both global and Antarctic temperatures were rising for a 1000 years BEFORE CO2 started to rise.
For CO2 to lag and then lead rises in global temperatures but not Antarctica seems very odd behaviour!
– The item was released on Wednesday lunchtime before Easter, not giving much time for rebuttal, before the meme has settled into peoples brains over Easter. (maybe just a coincidence)
– It was reported on the BBC Science in Action radio prog on Thu, but I not they were not over alarmist.
– In an item about the part retitling of the new British film, the word “Scientists” was replaced by “Misfits” for US & the rest of the world
QUOTE “another example of what some commentators in the United States see as a growing anti-science culture? Science in Action spoke to Dr Eugenie Scott, Director of the National Center for Science Education, a non-profit organisation that helps defend the teaching of subjects such as evolution and climate change which they perceive as being under attack in the US.”ENDQUOTE
-… the presenter directed the talk to be about creationist disruptions & kept her from stirring on Climate Change. http://www.bbc.co.uk/programmes/p00q88gq#synopsis