Steven wrote:

Alley (2000) describes some additional factors as follows:

Much research (reviewed by Jouzel et al., 1997) demonstrates that: (i) site temperature is the most important factor controlling stable isotopic composition of accumulated snow in most places; (ii) the isotopic paleothermometer can be used reliably; but (iii) the calibration of the paleothermometer can change significantly over time and space, so that local calibrations are desirable. Indeed, the documented large differences between previously expected and observed calibrations in central Greenland suggest extreme caution in use of water isotopes in paleothermometry in the absence of reliable local calibrations.

It seems to me the research here is very thorough.

I don't agree. This is why:

(small fraction of the paper:)

However in the closest other independent record is of temperatures during the last transition is found in South Greenland in a lake on the island of Angissoq. Björck et al (2003) analyze a sequence covering the time span between 14 400 and 10 500 calendar yr B.P., and find that the conditions in southernmost Greenland during the Younger Dryas stadial, 12 800–11 550 calendar yr B.P. (sic), were characterized by an arid climate with cold winters and mild summers, preceded by humid conditions with cooler summers. They contend that climate models may explain such an anomaly by local climatic phenomenon caused by high insolation and Fohn effects.

But then again, the same moist – arid - moist sequence has been identified in the Greenland summit ice cores, under the similar insolation conditions without possible föhn effects.

Jouzel et al 2007 investigate the validity of the temperature reconstruction from water isotopes in ice cores and focus on differences in sensitivities. They consider the complications with changes in the evaporative origins of the moisture, changes in seasonality of the precipitation and changes in the meteorological conditions, including humidity. Borehole temperatures diffuse over time and cannot distinguish the rapid changes of the different intervals. Moreover they note the variation in accumulation to be higher than expected for temperature alone and consider changing weather patterns. About seasonality they elaborate:

“As recently noted by Steig et al [1994], the deposition by precipitation of any atmospheric constituent that exhibits large seasonal changes and relatively small long term changes will be sensitive to the seasonal timing of the precipitation. In fact, the average --18O in a region is more logically related to the precipitation weighted temperature than to the mean annual temperature Ts in the region: If all the precipitation occurs during warm summer months for example, the “annual” --18O will naturally reflect a temperature warmer than Ts. This consideration is supported by observations of --18O in central Greenland over the past century, which are found to track the precipitation-weighted temperature more closely than Ts at Jakobshavn (a west Greenland coastal site). If major changes in seasonality occur between climates, such as a shift from summer-dominated to winter-dominated precipitation, the impact on the isotope signal could be large.

Simulations performed with the 4 x 5 resolution GISS isotope model [Charles et al., 1995] reveal virtually no systematic change in the seasonal timing of Greenland precipitation between the ice age and present-day climates. As a result simulated isotope shifts over Greenland do not correlate significantly better with shifts in “precipitation-weighted temperature” than with shifts in annual temperature Ts. (r2 increases from0.76 to 0.78). Therefore, at least for these two climates over Greenland, the GISS model results do not support Steig et al.’s suggestion that changes in seasonality have a primary influence on isotope shifts [Charles et al., 1997].”

Emphasis ours. However the results of Björck et al 2003, cool moist summers to warm dry summers in the Younger Dryas, do suggest a seasonality shift of precipitation. Note that Jouzel et al 1997 used a model to argue against the reality of “observations of --18O in central which are found to track the precipitation-weighted temperature more closely than Ts at Jakobshavn” whereas Björck et al used a model to unexplain the “anomaly” of warm Younger Dryas summers. In fact both proxies closely agree without using any models; suggesting that the climate change was more in aridity than in temperature. Seasonality of precipitation, or the absence of summer snow in the Younger Dryas, bringing the “warm” isotopes, could contribute to the explaination the “cold” average annual isotope signature.

Andre, perhaps you can email Alley directly with your paleontological objections and present the logic of your scenario.

Sure, he'll get it. I have a mailing list of 100+. He is on it.

Erratum: "Jouzel et al 2007" must be "Jouzel et al 1997". To facilitate pre peer review, it is here. Björck et al 2002 is here

On the original topic, if there was this tipping point towards disaster that we could never recover from we wouldn't exist today to talk about it. Levels of carbon dioxide have been many times higher in the past than they are today. As much as 10-12% higher in Carboniferous for example. If this tipping point existed than the planet would have become venus like long before we ever evolved.

It may seem strange but we are on original topic demonstrating that tipping points and flickering climates have been misinterpreted. It's not about the heat, it's about the humidity. Non calor, sed umor.

In case it appears that I'm denying the cold and the glacial readvances of the Younger Dryas, have a look here to understand what caused that confusion. See my last post.

andre, in almost any source I read on the topic there is strong evidence of a Gulf Stream collapse between ~12, 700 ka and 11, 700 ka when enormous amounts of freshwater had been deposited into the north atlantic, such as the redirection of meltwater from the Mississipi to the St. Lawrence, the implosion of the Laurentide Ice Sheet and draining into the Hudson Bay. See Clarke, 2003

Wouldn't this collapse necessarily lead to the dramatic temperature drop you are arguing against?

Chris wrote:
andre, in almost any source I read on the topic there is strong evidence of a Gulf Stream collapse between ~12, 700 ka and 11, 700 ka when enormous amounts of freshwater had been deposited into the north atlantic, such as the redirection of meltwater from the Mississipi to the St. Lawrence, the implosion of the Laurentide Ice Sheet and draining into the Hudson Bay. See Clarke, 2003

Wouldn't this collapse necessarily lead to the dramatic temperature drop you are arguing against?

Incidentily the link covers the 8200BP cold interval not the YD

The exact cause of events appears to come from the oceans originally.

thread start about that here

I don't believe that it's a THC shut down, probably something a bit more complicated if you look at all the evidence combined. There are pet ideas but it would be premature to elaborate on that.

andre wrote:

Perhaps you missed a few of my posts and links. No, they are unreliable because they are PROVEN empirically to be wrong. Moreover the physics for this is plain textbook. See the thread.

The only "proof" I saw was a suggestion that source moisture was drier. But you have not proved the source moisture, the topical seas, was drier. You say the source moisture was cooler, and therefore, the air masses receiving evaporation from tropical seas contained less moisture and therefore, were already depleted in heavy isotopes. To explain how tropical seas could become cooler, you explained:

andre wrote:
As I said before, Lower sea surface temperatures due to oceanic overturning.

You must be more specific here. Are you calling for a reduction in Meridional Overturning Circulation (MOC) in the Atlantic Ocean? I doubt it. So what changes in oceanic overturning are you calling for to cause circumtropical reduction in SSTs.

andre wrote:

But lower SST does not mean lower air temperature over the land.

We all know why Northern Europe is milder than similar latitudes in Canada.

Steven wrote:

andre wrote:

Perhaps you missed a few of my posts and links. No, they are unreliable because they are PROVEN empirically to be wrong. Moreover the physics for this is plain textbook. See the thread.

The only "proof" I saw was a suggestion that source moisture was drier. But you have not proved the source moisture, the topical seas, was drier. You say the source moisture was cooler, and therefore, the air masses receiving evaporation from tropical seas contained less moisture and therefore, were already depleted in heavy isotopes. To explain how tropical seas could become cooler, you explained:

andre wrote:
As I said before, Lower sea surface temperatures due to oceanic overturning.

You must be more specific here. Are you calling for a reduction in Meridional Overturning Circulation (MOC) in the Atlantic Ocean? I doubt it. So what changes in oceanic overturning are you calling for to cause circumtropical reduction in SSTs.

andre wrote:

But lower SST does not mean lower air temperature over the land.

We all know why Northern Europe is milder than similar latitudes in Canada.

Sorry, I should have said, 'The only "proof" I saw was a suggestion that source moisture was cooler, creating drier air masses from the source moisture. But you have not proved the air masses from the source moisture, the topical seas, was drier. You say the source moisture was cooler, and therefore, the air masses receiving evaporation from tropical seas contained less moisture and therefore, were already depleted in heavy isotopes.'

Andre,

I should say your seasonality point is well taken. Currently I have not found any research that reduces late glacial annual ice core layers down to the season, which seems necessary in order to finally resolve this debate. It is, however, possible to view individual annual layers in the NorthGRIP ice core, as shown here.

I know there are many chemical differences in ice core composition between seasons. For one example, there is a significant component of hydrogen peroxide in summer ice, but there is none in winter ice. H2O2 is a water soluble gas that has a short residence time of 5 to 10 days in the atmosphere. It is created in the atmosphere by the activity of ultraviolet-beta solar radiation and the interaction with other chemicals. In the polar regions, the sun shines 24 hours per day in the summer and zero hours per day in the winter. Therefore, peak production of hydrogen peroxide is in the summer and very little production in the winter. As a result, hydrogen peroxide accumulation in arctic snow occurs in the summer with little accumulation in the winter, making it an ideal annual marker in ice cores.

If seasons could be identified in annual layers and isotopic analysis could be performed from seasonal sampling, I think results from that might be the last point necessary to end the debate. (Although additional explanation will be needed to account for differences in borehole temperatures from the Bolling/Allerod, Younger Dryas, and Holocene.) But that has not occurred yet and perhaps what I am asking is not possible.

Alley (2000) has made, among many other points in his article The Younger Dryas cold interval as viewed from central Greenland, the following points:

The calibration of the ice-isotopic paleothermometer, derived by comparing shifts in ice-isotopic ratios to independent estimates of temperature change, is itself a paleoclimatic indicator (Alley et al., 1999). By assuming that space can be substituted for time in studying a system, Dansgaard (1964) estimated that a change of about 0.7 per mil in mean-annual isotopic ratio corresponds to a temperature change of 1°C. Data from Greenland indicate that major climate changes actually exhibited a dependence of about half this or slightly less (Cuffey et al., 1995 Cuffey and Clow, 1997).

Multiple causes for this large difference may exist, and two likely were important: changes in source temperature, and changes in snowfall seasonality. First, because the isotopic thermometer measures the temperature difference between moisture source and precipitation site, the correlated changes that likely occurred in temperature at the source and site would cause isotopic changes to underestimate temperature changes, as observed (Boyle, 1997).

Much or all of the signal is explainable by changes in the seasonality of precipitation in Greenland (Fawcett et al., 1997; Jouzel et al., 1997; Krinner et al., 1997). As discussed below, changes in oceanic heat transport are strongly implicated in the YD cooling. The energy balance of the high-latitude North Atlantic region is dominated by sunshine in the summer, with oceanic processes much more important in the winter. Hence, reducing oceanic heat transport is expected to cause cooling primarily in the winter.

Through a combination of reduced saturation vapor pressure plus southward shift of the storm track to follow a more-southerly sea-ice edge, oceanic wintertime cooling would be expected to be accompanied by wintertime cooling and precipitation reduction in central Greenland. Ice isotopes record temperature during snowfall, and so would not reflect extreme wintertime cooling if accompanied by wintertime drying (Fawcette et al., 1997). Atmospheric modeling supports this explanation (Fawcett et al., 1997; Krinner et al., 1997)

What I believe at this time is that at the beginning of the YD there was nearly global abrupt cooling from the Bolling/Allerod, and global abrupt warming from the YD into the Holocene. Increased aridity, as Alley and many others have said, accompanied cooling into the YD in many regions of the globe. It is possible that global cooling caused some reduction in humidity in the tropical oceans, the predominant location of source moisture for Greenland ice cores. However, at this point, I don't believe it was enough to account for even a majority of the increase in oxygen and hydrogen isotopic fractionation. Our debate seems to be a matter of degrees - no pun intended. You believe the large majority of reduction of d18O and dD during the YD was due to decreased humidity, and I still believe it to be mostly from lower temperatures.

As an aside, it behooves me to become more knowledgeable about the palynological side of the debate. Also, I have read very little on mammoth extinction and explanations therein. I understand that eventually, the twains must meet.

yes.

Steven,

The overal main point is overwhelming evidence that the interpretation of the ice cores is wrong. The 15 pages of references.

The next step is why that interpretation is wrong. I don't intend to proof that it was aridity and seasonality, I just show that the isotope signature is consistent with aridity and seasonality answering to the deep rooted ignorance fallacy: I-don't-know-anything-else-that-could-have-caused-it-so-it-must-be-temperature.

The myth of the extreme cold younger dryas with massive glacial advances is very well explainable with the carbon dating problem, changing the boundaries of the Younger dryas. I elaborate extensively on that in the paper

But I'm progrssing nicely with the paper. I See I need to make two versions. The all evidence paper in about 30-40 pages and the article limited to 9000 words ~18 pages.

andre wrote:
Steven,

The overal main point is overwhelming evidence that the interpretation of the ice cores is wrong. The 15 pages of references.

I would say that's pretty impressive, except many of the papers you refer to are pro-YD cooling.

andre wrote:
The next step is why that interpretation is wrong. I don't intend to proof that it was aridity and seasonality, I just show that the isotope signature is consistent with aridity and seasonality answering to the deep rooted ignorance fallacy: I-don't-know-anything-else-that-could-have-caused-it-so-it-must-be-temperature.

It's not a matter of "I-don't-know-anything-else-that-could-have-caused-it-so-it-must-be-temperature." Researchers have amassed a huge amount of empirical data supporting Rayleigh distillation with modification due to factors such as re-evaporation, oxygen-18 content of water vapor at the start of condensation, extent of cloud supersaturation with respect to ice at very low temperatures, geographical factors affecting stable isotope concentrations, and other factors.

andre wrote:
The myth of the extreme cold younger dryas with massive glacial advances is very well explainable with the carbon dating problem, changing the boundaries of the Younger dryas. I elaborate extensively on that in the paper

This is a 15-year old problem which has been corrected. Calibration of radiocarbon dating was worked out in the 90s.

andre wrote:
But I'm progrssing nicely with the paper. I See I need to make two versions. The all evidence paper in about 30-40 pages and the article limited to 9000 words ~18 pages.

I look forward to reading it.

From the World Glacier Monitoring Service


Glacier Mass Balance data 2003/2004 and 2004/2005

Summary of the balance years 2003/2004 and 2004/2005

Continuous mass balance statistics are calculated based on the 30 glaciers in 9 mountain ranges***. Data are now available for the years 1980-2004 and preliminary values for the year 2005 from 27 glaciers in 9 mountain ranges.

The average mass balance of the reference mountain glaciers around the world continues to decrease, with tentative figures indicating a further thickness reduction of 0.7 m and 0.6 m during 2004 and 2005, respectively. This continues the trend in accelerated ice loss during the past two and a half decades and brings the total loss since 1980 at about 9.6 m.

Results of the extreme and mean values for the year 2003/2004 and 2004/2005 have been calculated based on these 30 and 27 glaciers, respectively:


Mean specific (annual) net balance:

2003/2004 = -725 mm w.e. 2004/2005 = -625 mm w.e.

Standard deviation:

2003/2004 = 905 mm w.e. 2004/2005 = 1037 mm w.e.

Minimum value:

2003/2004 = -2820 mm w.e. 2004/2005 = -3230 mm w.e.

Maximum value:

2003/2004 = 550 mm w.e. 2004/2005 = 1100 mm w.e.

Positive balances:

2003/2004 = 20% 2004/2005 = 19%


The corresponding results of this data set from glaciers in the Americas and Eurasia are visualized in the following two figures:






Figure 1a and 1b: Mean specific net balance (top) and mean cumulative specific net balance (bottom) continuously measured on 30 glaciers in 9 mountain ranges for the period 1980 to 2004, and on 27 glaciers in 9 mountain ranges for 2005.

Steven wrote:

Continuous mass balance statistics are calculated based on the 30 glaciers in 9 mountain ranges***..

30 out of an estimated 160000 glaciers that's significant.

How are these glaciers selected?


Also Roger Pielke Sr had an interesting post a few weeks ago about glaciers:

http://climatesci.colorado.edu/2007/07/23/comment-on-why-climate-science-is-presenting-evidence-of-glacier-retreat-in-some-areas/