por Rasmus Benestad, com contribuições de Caspar & Eric
Em um artigo recente da Climatic Change, D.G. Martinson e W.C. Pitman III discutem uma nova hipótese que explica como o clima pode mudar abruptamente entre eras glaciais e períodos interglaciais (quentes). Eles argumentam que as mudanças na órbita da Terra ao redor do Sol em isolado não são suficientes para explicar as altas taxas de mudanças estimadas, e que deve necessariamente haver a ação de um mecanismo de feedback (ou retro-alimentação) amplificando o processo. A necessidade de um feedback não é nova, pois o sueco ganhador do Prêmio Nobel (Química), Svante Arrhenius, já havia sugerido em 1896 que o CO2 deveria agir como um mecanismo de amplificação. Além do mais, existe o feedback do albedo, pelo qual a quantidade de radiação solar que é refletida de volta ao espaço é escalonável com a área de cobertura de gelo e neve. E existem nuvens bem como outros aspectos envolvidos.
A hipótese de Martinson & Pitman III formula que a entrada de água doce funciona em consonância com o ciclo de Milankovitch e o feedback de albedo. Eles concluem que os ‘maiores’ términos podem somente acontecer após um acúmulo de gelo grande o suficiente para isolar o Artico, inibindo o fluxo de entrada de água doce até um ponto em que o aumento da salinidade na camada superficial, através de um vagaroso e contínuo crescimento do gelo marinho, causa uma inversão das águas marinhas do Ártico (pelo efeito na circulação atmosférica e nas correntes oceânicas). A inversão vertical traz água quente de baixo para cima, promovendo condições mais favoráveis ao degelo. A salinidade também tem um papel, mas a hipótese não menciona variações de gases de efeito estufa (GEE). Algumas questões: Martinson e Pitman III esqueceram disso? Ou os GEE representam somente uma pequena contribuição? E, não poderiam as mudanças nos GEE explicar boa parte da variabilidade? Por outro lado, parece plausível que mudanças na salinidade e na entrada de água doce poderiam afetar a formação de gelo marinho e a convecção profunda. Contudo, até o presente, a hipótese proposta por Martinson and Pitman III é meramente uma especulação, e estamos aguardando para ver se a hipótese pode ser testada através de experimentos de modelos numéricos (o que pode requerer modelos oceânicos e de gelo marinho com maior resolução que os atualmente usados em modelos climáticos globais). Seria interessante conduzir experimentos para avaliar a significância individual da água doce, dos GEE e o efeito combinado.
Uma reação ao trabalho de Martison e Pittman é: Onde está o cálculo de energia? Gases de efeito estufa contribuem somente com alguns W/m2, em contraste com uma forçante >40 do ciclo sazonal de Milankovich. Para esta nova idéia ter mérito, teria sido melhor ter no mínimo fluxos de calor em paralelo com a forçante radioativa do CO2. Estudos de modelagem anteriores encontraram que GEE produzem aproximadamente 50% de todo Último Máximo Glacial (inglês, LGM) para a resposta da temperatura atual (veja por exemplo Broccoli & Manabe), a outra parte sendo o albedo, etc., que respondem ao ciclo sazonal de irradiância. É muito difícil isolar completamente as causas individuais pois as mudanças nos GEE podem produzir alterações na distribuição de nuvens e gelo marinho. Mas a grosso modo, se você rodar um LGM e somente somente reduzir o nível do mar, introduzir as calotas de gelo, mudar a vegetação, adicionar alguma poeria (embora esta ainda seja grosseira), então você alcançaria ao redor de 50% do caminho que você quer ir. Mude a concentração de GEE e você chegaria mais próximo. Isso é mais ou menos o que Manabe e Stouffer mostraram há quinze anos atrás. A questão é se realmente precisamos de algo mais, e se esse ‘algo mais’ tem força suficiente.
traduzido por Ivan B. T. Lima e Fernando M. Ramos.
Just a quick question – how can hypotheses be “tested” through numerical model experiments? I thought that models threw out results which in turn are “tested” by coincidence with reality/observations? A further question is that if this paper sheds new light on a possible factor in climate change which “would require higher resolution sea-ice and ocean models than used in todays global climate models”, does this not suggest that todays global climate models are insufficiently able to project climate change?
Rasmus,
That’s a nice graph you have here, but unfortunately there are no units on the Y-axis. Can the upper 4 (coloured) lines all be converted to (say) equivalent temperature or radiative forcing (to see the relative importance), and then added (or otherwise combined) to produce a line that correlates with the black line?
I’m thinking that the earth can become imbalanced, but that could be imposible, maybe not. If a wheel is off balance it would be taken into a tire shop, set onto a machine and spun, that will let the person know where the wheel is off balance, then he will ad a weight that is required to balance the wheel. What if the weight was removed. The earth is completely round in all directions from space. The earth tilts, then we have change of weather. What if a massive amount was removed from one side of the earth to the other could that cause the earth to wabble? the removal of steel, metal,iron or maybe even “OIL” with the combination of all of these burnt into smoke. Is the smoke from all of these that i mentioned part of the cause for the ozone layer to be thinning?
Whoooosh, couple of short questions, where does the graph come from and what is it trying to show?
[Response:From Wikipedia – look up Milankovitch cycles’. -rasmus]
Nice idea Dick, but isnt that the problem the authors have too? I imagine that they certainly dont know with any degree of certainty the exact contribution from each of their forcings. So it is probably impossible/indeterminate/pointless to combine the curves except on a trial-and-error basis. It looks to me like there is sufficient randomness in the cycles they are offering (and I imagine that there are a lot of other potential candidates that they are not offering, including dear old CO2) to allow almost any solution to be found that may *corelate* plausibly with the ice record.
But such an accidental coincidence would hardly rate as truth, eh? Its a lottery, not science.
Would not the accelerated dinural movement of the magnetic poles be at least considered in the mix of solar forcings? Up until approx. 1992, the average trek of the poles have been ~10km annually. With this relatively slow movement, the megnetic flux lines were of a more congruent, harmonious pattern offering the best protection against the solar radiation. As noted on several sites describing the magnetic pole acceleration, a consensus reporting of a reduced “shield” against solar radiation have been as high as 10%, but average 6-7%. This means the effectiveness of the magnetic shield has been reduced as a result of the bending and subsequent distortion of the flux lines from the increased speed of up to 40km annually.If this movement is the beginning of the long 5k to 8k year cycle of pole reversal, than it could be expected that during any of these cycles, solar forcing would have a greater effect with increased energy passing through into the atmosphere.
I understand how the build-up of ice sheets would isolate the Arctic Ocean. But I thought sea ice would reach an equilibrium with temperature, not continue to increase. And any increase would be small relative to the volume of the ocean, so the increase in salinity would be minimal. As well, I am not familiar with the vertical structure of Arctic water, I would have assumed that water temperature decreased with depth, and anything else would be unstable and correct itself relatively quickly.
I don’t have access to the original paper, so it would help if its hypothesis was clarified.
This “new” model is a slight variation on an old idea about sea ice cycles and heat buildup in the ocean beneath the ice. They have added a fresh water input element. What isn’t clear to me is how their model copes with the Younger Dryas event and similar events that occurred in earlier cycles. Why didn’t the Younger Dryas event stop the warming for once and for all? Massive amounts of meltwater, not only from North America, but also from Scandinavia, would seem to put a cap on the heat input from the Arctic Ocean.
Re: #3 (the graph)
To answer your question, the graph shows the three astronomical cycles which affect paleoclimate, the most commonly proposed forcing calculation, and a paleoclimate record for the last million years.
1. Precession: difference between the longitude (along our orbit) toward which the axis is tilted, and the longitude of perihelion, multiplied by earth’s eccentricity. Range is from about -0.05 to +0.05.
2. Obliquity: tilt of the earth’s axis. Range from about 22 deg. to 24.5 deg.
3. Eccentricity: non-circularity of earth’s orbit. Range from about 0 to 0.05
4. 65N summer: this is the insolation (incoming solar energy) on midsummer day at latitude 65 deg.N. This is often suggested to be the main factor influencing the decay of ice sheets in the northern hemisphere. Range about 510 to 590 watts per square meter.
5. Paleoclimate: I don’t know for sure, but this record is too long (1 million years) to be an ice core, so I’m guessing it’s a stacked sediment core, showing delta-O18 from ocean foraminifera. Is this the “LR04” stack?
I don’t understand the energy reference. The paper refers to a few W/m2 for greenhouse gases and >40 for Milankovich. I was under the impression that greenhouse gases swamp Milankovich annual contribution to the energy budget, but that the Milankovich inputs are “slow and steady”, i.e. not so much each year, but continuous.
Re: #10
The few W/m^2 for greenhouse gases apply to the entire planet. The 40 (or more) W/m^2 due to Milankovitch cycles apply only to one specific latitude (usually 65 deg.N), but an increase at one latitude is compensated by a decrease at other latitudes. The global forcing from Milankovitch cycles is generally not more than 0.3 W/m^2.
re #10, is that correct RC concerning Milankovitch cycles only causing increasing anountsof sunshine to fall on certain parts of the planet rather than all of it for GHG concentrations ?
[Response: Yes it is. Tamino’s comments are almost invariably accurate, and this one is no exception. As Tamino notes, Milankovic cycles do lead to a slight modulation of the annual average, but it is very small, especially for the 100KYr cycle. The big numbers are in what Milankovic does to the seasonal cycle amplitude. In some sense, the search for a theory of glacial-interglacial cycles amounts to a search for the “rectifier” which turns the modulation of the amplitude of the seasonal forcing into a rectified signal in global ice volume. –raypierre]
A few comments.
In the context of this post, the question “What triggers ice ages?” only applies to the late Pleistocene (since about 800,000 years ago). From the onset of northern-hemisphere glaciation (about 3 million years ago) to the “mid-Pleistocene transition” (about 800,000 years ago), glacial advance and retreat follows a strong 41,000-year cycle, which has led to its being called “the 41 ky world” (Raymo & Nisancioglu 2003, Paleoceanography, 18, 1011). This is surely due to the changes of earth’s obliquity, since changes in the amplitude of the climate signal correspond to changes in the amplitude of the obliquity cycle (Lisiecki & Raymo 2007, Quaternary Science Reviews, 26, 56).
But since the mid-Pleistocene transition (not precisely since, this happens intermittently before that time) glacial changes are dominated by a 100,000-year cycle. The behavior during the “late Pleistocene” was originally attributed to changes in earth’s eccentricity, but that idea has now fallen out of favor. Huybers & Wunsch (2005, Nature, 434, 491) and Huybers (Quaternary Science Reviews, 26, 37) have convincingly shown that even during the late Pleistocene, the timing of deglaciations is strongly correlated to the obliquity cycle. They find no such relationship for the precession cycle or the eccentricity cycle.
Huybers (Quaternary Science Reviews, 26, 37) has proposed a simple model in which deglaciation is triggered when the obliquity cycle is high, and when ice mass is sufficiently high. The match of his model to actual paleoclimate is impressive, but that doesn’t necessarily mean it’s right — especially since Huybers made no suggestion about what the physical mechanism is which brings this about. The fresh-water theory fits this idea neatly; it provides a physical mechanism whereby deglaciation can be triggered only when total ice extent is sufficiently large.
Personally, I disagree both with Huybers’ model and the fresh-water theory. I have my own theory, of course! With any luck, you can read about it in an upcoming issue of GRL.
Rasmus : “Previous modeling studies find that GHG make up roughly 50% of the total LGM to present temperature response…”
Martinson and Pitman III discuss of the “abrupt terminations” of glacial period. The CO2 rise is a slower process (with an initial lag of several centuries) and it counts for 50% in a 15.000 yrs equilibrium comparison (from LGM to mid-Holocene, for example). I’ve not access to Martison / Pitman III paper, but it seems you don’t exactly speak of the same phenomenon (that is, the CO2 objection may be not pertinent for the question of abrupt transition).
It would be really informative to see an FFT of those temporal plots. the location of peaks in each spectrum would help nail down which of the causal factors play more relevant roles.
Re 1: In a sense, a hypothesis is already a model, but because it’s verbal it’s poorly specified and hard to simulate accurately and thus hard to reject. Translating the hypothesis to a numerical model forces you to confront the ambiguities; along the way there are many points where you might reject the hypothesis because of a discovery from first principles (violation of conservation laws, dimensional inconsistency, qualitative failure to replicate the hypothesized behavior mode, absurd behavior in extremes, etc.). If the hypothesis implemented in a model passes those tests, then you need data to calibrate and verify, but data by itself is often a weak test. Presumably in this case you’d start with a model that’s already been tested against a lot of data and thus serves as a compact proxy for that information.
Re 6:
A layman’s answer to your questions:
The magnetic field of the earth only shields against charged particles coming from the sun (the so-called “solar wind”) and charged particles coming from outer space (some varieties of cosmic rays). The total energy in these particles is insignificant compared to the energy in the form of light from the sun, so the variation of the magnetic field will not have a direct effect on Earth climate.
A weakening magnetic field might lead to more cloud formation because more air molecules would be ionized by incoming high-energy radiation, and ionized air molecules are nucleation sites for cloud droplets. More clouds means higher albedo, which in turn might mean a cooler climate.
[Response: Note also that more low clouds would unambiguously mean a cooling effect, but more high clouds could lead to either a warming effect or a cooling effect, depending on the altitude of the clouds and the typical particle size in the GCR-induced clouds (if any). –raypierre]
Surprising there isn’t a more obvious relationship between solar forcing and the growth and ebb of the ice. I’m glad you posted this article.
Re: #15
The FFT is a poor choice, because is requires the data to be evenly spaced in time (which often it is not), and requires the number of data points to be a power of 2 (which it almost never is).
I applied the DCDFT (date-compensated discrete Fourier transform) to generate Fourier power spectra of all five signals shown in the original plot (assuming that the last graph is the LR04 stack). I’ve posted them on my blog.
Re: #9
When giving the range of 65N insolation, I mistakenly looked at the data for insolation at the pole (90N). The correct range for 65N insolation is aobut 390 to 490 watts per square meter.
[[What if a massive amount was removed from one side of the earth to the other could that cause the earth to wabble? …the removal of steel, metal,iron or maybe even “OIL” with the combination of all of these burnt into smoke. ]]
Wobble. Yes, it does. But the effect is far too tiny to detect. Compare the mass of iron ore mined since the beginning of the industrial revolution to the mass of the Earth. There’s no comparison. Don’t worry about it.
[[Is the smoke from all of these that i mentioned part of the cause for the ozone layer to be thinning? ]]
Probably not. That seems to be from human use of chloroflurocarbons for spray cans and refrigerants. The Montreal Protocol of 1979 banned use of these, and industry now uses substitutes.
On the subject, Robert Ehrlich has a recent paper on solar forcing of ice ages. He claims to have solved all but one of the major “problems” of Milankovitch forcing:
Solar Resonant Diffusion Waves as a Driver of Terrestrial Climate Change
ABSTRACT
A theory is described based on resonant thermal diffusion waves in the sun that explains many details of the
paleotemperature record for the last 5.3 million years. These include the observed periodicities, the relative strengths
of each observed cycle, and the sudden emergence in time for the 100 thousand year cycle. Other prior work
suggesting a link between terrestrial paleoclimate and solar luminosity variations has not provided any specific
mechanism. The particular mechanism described here has been demonstrated empirically, although not previously
invoked in the solar context. The theory, while not without its own unresolved issues, also lacks most of the problems
associated with Milankovitch cycle theory.
http://arxiv.org/PS_cache/astro-ph/pdf/0701/0701117.pdf
I think the paper has now been published, earlier this month, but can’t remember where. Still, its an interesting read.
Another provocative paper, well worth reading, is by Carl Wunsch and attempts to uage the contribution of orbital variations to climate change:
http://ocean.mit.edu/~cwunsch/papersonline/milankovitchqsr2004.pdf
He argues that stochastic variation is responsible, although wimps out of actually coming up with an explanation. His alternative hypothesis regarding abrupt climate change was rubbish too, but thats another story.
Thanks tamino – those graphs deserve to be disseminated. It’s quite a bit more informative thanthe original.
Sorry, off topic, but this is in the news today and seems rather alarming:
Scientists Sound Alarm Over Melting Antarctic Ice Sheets
by Steve Connor, Science Editor in San Francisco
February 16, 2007
The lndependent/UK
Excerpt:
While the water under the Antarctic ice is not itself related to global warming, the suprisingly large amount of water, the surprising speed with which it moves, and its effect of “lubricating” the movement of the Antarctic ice, may affect how the ice sheets respond to warming. This new discovery is of course not accounted for in the IPCC AR4 and suggests we may be in for some unpleasant surprises from Antarctica.
Re #21 and Ehrlich
It’s to be published in the Journal of Atmospheric and Solar-Terrestrial Physics (will be doi.10.1016/j.jastp.2007.01.005).
[And SteveF, you will know, this is currently newolder’s favourite anti-AGW “evidence”, which it isn’t so far as I can see.]
1,000 kyear — no significant continental drift in that time span, right? Just checking.
[[1,000 kyear — no significant continental drift in that time span, right? Just checking. ]]
Actually, I think there might well be significant continental drift over that period. I assume by 1,000 kyear you mean 106 years? It wouldn’t be as obvious as over 100 million years, but it would be enough to distort maps noticeably.
Re: #25, #26
There’s not a lot of tectonic movement in a “mere” million years, but it may not take a lot to have a climate impact. For example, closure of the Isthmus of Panama, and restriction of the Indonesian seaway, have been suggested as reasons for the onset of northern-hemisphere glaciation 3 million years ago (but that’s 3 million, not 1 million).
Re #21: SteveF, thanks for the link to the new paper. Regarding Wunsch, both he and Huybers (who was Wunsch’s grad student) have done follow-up papers, one of which was linked by Tamino in #19.
Re #23: SA (and what a great handle that is, BTW), the moment I saw this I wondered if it could explain the other recent results showing a sudden slowdown in two of the Greenland outlet glaciers. Despite being trumpeted in certain circles as meaning that there’s really nothing to worry about regarding the Greenland ice sheet, the authors made a point of noting (although not in this press release) that an additional source of mass loss needs to be identified in order to reconcile their results with the GRACE data (which do not show a reduction in mass loss for the same period). Similar subglacial water activity in Greenland would seem to fill the bill nicely, in particular because it would also explain the sharp changes in outlet glacier speed.
See also the interesting tone taken by this IPY press release.
Re #25, #26, #27: The Indio-Australian plate moves generally north at a very high rate for a tectonic plate. So in a mere one million years the Himalayan Mountains and in general the Tibetian Plateau would have been modified. To the east, the boundary between the Indian Ocean and the South China Sea would have been altered.
Can anyone add something about how the biology is changing in that time span?
That would, I’d guess, be interesting as a very fast feedback effect if, say, plankton’s changing year by year as one or more of those other signals change.
Might be some proxy for total primary productivity, or biomass, or respiration, or photosynthesis, or chemistry of diatom shells or lack thereof in each slice of the sediment core.
Not sure how to tease that out, just wondering if Gaia’s in there swinging behind some of that variation.
#23
If there is running water and lakes beneath the ice in Antarctica, could it be that the earth is warming substantially and causing the ice to melt from the bottom up? Interesting!
Re #30: Hank Roberts — Not directly the answer to your latest question, but at each major sea low stand, East Asia expands to the east and Southeast Asia grows into Sundaland. Both locations will continue to contribute to biological productivity in contrast to the expanded deserts in many other locations.
I’ve always been impressed by the rapidity with which glacial periods end, despite the expected high feedback of all that ice cover. I don’t follow climate science in detail, with all the ins and outs of competing models, but as an interested non-specialist I hope to live long enough to see a consensus explanation emerge!
Bob M. wrote: “I’ve always been impressed by the rapidity with which glacial periods end …”
Speaking of which:
Is it reasonable to think this is the other side of this question ‘What ends hot ages’, especially artificial ones, WITH INSUFFICIENT ARTIFICIAL HELP? I keep hearing about how much hotter it’s going to be in 2100, but nothing about after that, as though one way or another it’s going to end there. With all the forms of positive feedback we already see, what’s going to create negative feedback while life is still possible on Earth, like before the oceans have finished evaporating and adding to greenhouse gasses? It also seems many changes are occurring faster than scientists previously expected. Does someone have some hope for our grandchildren and beyond? Is it possible that even climate scientists believe only what their minds can tolerate and ignore the rest?
Re #23
What is alarming other than the word alarm in the title? You say there is a surpisingly large amount of water, what amount of water would you expect? And the water is moving at a surprising speed, what speed would not surprise you?
I find this new information interesting and important but not alarming.
re: “Scientists Sound Alarm Over Melting Antarctic Ice Sheets”
13-Feb-2007
Antarctic Temperatures Disagree with Climate Model Predictions
Ohio State University
http://www.newswise.com/articles/view/527313/
“A new report on climate over the world’s southernmost continent shows that
temperatures during the late 20th century did not climb as had been predicted by
many global climate models.”…
…”Bromwich said that the increase in the ozone hole above the central Antarctic
continent may also be affecting temperatures on the mainland. “If you have less
ozone, there’s less absorption of the ultraviolet light and the stratosphere
doesn’t warm as much.”
That would mean that winter-like conditions would
remain later in the spring than normal, lowering temperatures.
“In some
sense, we might have competing effects going on in Antarctica where there is
low-level CO2 warming but that may be swamped by the effects of ozone
depletion,” he said. “The year 2006 was the all-time maximum for ozone depletion
over the Antarctic.”
Bromwich said the disagreement between climate model
predictions and the snowfall and temperature records doesn’t necessarily mean
that the models are wrong.
“It isn’t surprising that these models are not
doing as well in these remote parts of the world. These are global models and
shouldn’t be expected to be equally exact for all locations,” he said.”….
———–
Sea Level Rise, After the Ice Melted and Today
Vivien Gornitz
NASA GISS: Science Briefs, (Jan 2007)
http://www.giss.nasa.gov/research/briefs/gornitz_09/
…”Meltwater from glacial Lake Agassiz (southwest of Hudson Bay) draining catastrophically into the North Atlantic via Lake Superior and the St. Laurence seaway was once thought to have initiated ocean circulation changes leading to the Younger Dryas cold period. Regional removal of ice sheets, however, occurred nearly 1000 years later, and hence draining of Lake Agassiz could not likely have caused the Younger Dryas cold reversal. This cold spell may have instead been triggered by increased outflow into the Arctic Ocean, the Fram Strait east of Greenland, and ultimately the eastern North Atlantic, between 12,900 and 12,800 years before present, as suggested by the glacial model of Tarasov and Peltier. On the other hand, Leventer et al. indicate that the timing of deglaciation in eastern Antarctica roughly coincides with the onset of meltwater pulse 1B. “….
Another hypothesis for why the glacial periods terminate and restart is GCR modulation by changes in the intensity of the earth’s magnetic field. GCR changes of course as we all know, it is hypothesized affect global cloud cover. I am not sure why the response to the hypothesis that changes in the intensity of the geomagnetic field, triggers/controls the timing of the ice ages in this forum was “rubbish”. The rubbish comment noted that geomagnetic field intensity changes do not correlate with the ice age cycles. Perhaps we are looking at different data.
The following is data from the review paper “Time Variations in Geomagnetic Field Intensity”
http://ssn.dgf.uchile.cl/home/informe/2001RG000104b.pdf
See Page 4-22, Figure 9: Geomagnetic field intensity level derived from composite volcanic records, not sea floor sediments, for the past 45 kyr.
Obviously, Figure 9 shows that 40 kyrs ago the earth’s magnetic field intensity was 75% less (2×10^22Am^2) than the geomagnetic field’s current intensity (8×10^22Am^2) and that the earth’s magnetic field intensity peaked at around (12×10^22Am^2)and has dropped 30% in the last 1000 years and that the geomagnetic field intensity is now dropping at the rate of 5%/100yrs.
Comments:
1)The geomagnetic field researchers do not even have a hypothesis as to why there are cyclic changes in the geomagnetic field intensity. Something is fundamental incorrect with the most basic assumptions concerning what creates the geomagnetic field, and what causes it to change. Rather than address the absolute failure of their model, they have thoughtfully decided to ignore the problematic data.
2)The paper I referenced states that the proxy magnetic field intensity derived from sea floor sediment data does not match obital frequencies however other papers state that it does. The real problem is the volcanic data and sea sediment data (proxy data that is used to determine the intensity of the geomagnetic field) indicates that climate changes directly affects the intensity of geomagnetic field. As there is no explanation as to how climate changes could possibly affect the intensity of the earth’s magnetic field, it was decided that it would be easier to believe that proxy sea floor sediment data should be adjusted (“corrected”)for sea water temperature.
3)Other indications of the absolute failure of the geomagnetic field model is the so called heat flux problem or the recent discovery of very,very rapid geomagnetic field intensity and inclinition changes (All researchers agree that the very, very rapid field changes could not possibly be due to changes in the earth’s core. If the problematic data is correct, the earth’s magnetic field is not generated in the core.)
Re # 31 The existence of lakes beneath Antarctic ice is nothing new – this has been known for decades:
Science 5 October 1962
Vol. 138. no. 3536, pp. 34 – 36
(http://tinyurl.com/2yzwg3)
Science 28 May 1965
Vol. 148. no. 3674, pp. 1226 – 1227
(http://tinyurl.com/292wvs)
Lake Vostok, for example, has a maximum depth greater than 500 m, is deeper than Lake Tahoe, and has a surface area similar to that of Lake Ontario. It is the largest of at least 68 lakes located 3 to 4 km beneath the East Antarctic Ice Sheet.
As the article cited in #23 indicates, the existence of these lakes is not related to global warming. Rather, “they are maintained in a liquid state by geothermal heating, pressure, and insulation by the overlying ice.”
Science 10 December 1999
Vol. 286. no. 5447, pp. 2094 – 2095
(http://tinyurl.com/2gwpn6)
What is new, and newsworthy, is that the extensive system of liquid water under the ice may provide a better understanding of ice sheet dynamics:
An Active Subglacial Water System in West Antarctica Mapped from Space
Helen Amanda Fricker, Ted Scambos, Robert Bindschadler, Laurie Padman
Satellite laser altimeter elevation profiles from 2003-2006 collected over the lower parts of Whillans and Mercer ice streams, West Antarctica, reveal 14 regions of temporally varying elevation which we interpret as the surface expression of subglacial water movement. Vertical motion and spatial extent of 2 of the largest regions are confirmed by satellite image differencing. A major, previously unknown subglacial lake near the grounding line of Whillans Ice Stream is observed to drain 2.0 km3 of water over ~3 years, while elsewhere a similar volume of water is being stored subglacially. These observations reveal a widespread, dynamic subglacial water system which may exert an important control on ice flow and mass balance.
Science (Published Online February 15, 2007)
http://tinyurl.com/ys49wu
I don’t think anyone is suggesting that global warming has any impact on the temperature of the earth’s interior – the earth’s core has that well under control.
Not sure how relevant this article is and I’ve not come across this possiblity discussed here,
http://www.livescience.com/forcesofnature/061222_super_volcanoes.html
William, would you please give references for where you’re getting your beliefs?
A link, a date, an article name, something to help the curious reader find your sources, please.
This is all I could find — mentions rapid field changes but not support for your statements about them.
http://www.agu.org/cgi-bin/SFgate/SFgate?&listenv=table&multiple=1&range=1&directget=1&application=fm05&database=%2Fdata%2Fepubs%2Fwais%2Findexes%2Ffm05%2Ffm05&maxhits=200&=%22GP21A%22
Edit, please:
wrong: They argue that the changes in Earth’s orbit around the Sun in isolation is not sufficient to explain the estimated high rate of change ….
right: They argue that the changes in Earth’s orbit around the Sun in isolation ARE not sufficient to explain the estimated high rate of change ….
.
in the Wickapedia artile on ice ages some of the blame goes to the creation of the Himalayas increacing the World’s rainfall. Why should the creation of the Himalayas increase world rainfall?
Wang Dang wrote: “What is alarming other than the word alarm in the title? You say there is a surpisingly large amount of water, what amount of water would you expect? And the water is moving at a surprising speed, what speed would not surprise you?”
Chuck Booth wrote: “The existence of lakes beneath Antarctic ice is nothing new – this has been known for decades … What is new, and newsworthy, is that the extensive system of liquid water under the ice may provide a better understanding of ice sheet dynamics”
What is alarming is that the volume of water and the extent and rapidity of its movement is suprisingly much greater than previously believed, and that a possible, perhaps likely, effect of this on ice sheet dynamics is to make the ice sheets less stable and more likely to respond more quickly to global warming than previously expected.
Re 41 and 38, especially the latter.
The cool reception to the suggestion that GCR’s are involved in glacial-interglacial cycles comes because there is overwhelming evidence that Milankovic is the basic pacemaker, which needs to be supplemented with an amplifying feedback (certainly involving CO2) and some kind of rectifier of the seasonal cycle. It would be extremely improbable for GCR’s to just happen to give the same periodicities as Milankovic. It is not out of the question that solar fluctuations, either through luminosity or perhaps GCR, play a role in Pleistocene climate transitions, including abrupt changes like Heinrich events. In systems that have a threshold, or switch, a little bit of noise whether from solar variability or something else, can tip the balance once you get near the transition point. Stefan has proposed some ideas about Heinrich events based on this line of reasoning.
The Pleistocene does offer some possibilities to directly look for evidence of GCR influence. One of the critical periods to look at is the Laschamp Magnetic Excursion. I’ll take the liberty of quoting in full from the abstract of Lloyd Keigwin’s paper ( http://www.agu.org/pubs/crossref/2005/2003JB002943.shtml ):
“We have recovered two new high-resolution paleomagnetic records of the Laschamp Excursion (~41,000 calendar years B.P.) from deep-sea sediments of the western North Atlantic Ocean. The records document that the Laschamp Excursion was characterized locally by (1) declination changes of ±120°, (2) inclination changes of more than 140°, (3) ~1200-year oscillations in both inclination and declination, (4) near 90° out-of-phase relationships between inclinations and declinations that produced two clockwise loops in directions and virtual geomagnetic poles (VGPs) followed by a counterclockwise loop, (5) excursional VGPs during both intervals of clockwise looping, (6) magnetic field intensities less than 10% of normal that persisted for almost 2000 years, (7) marked similarity in excursional directions over ~5000 km spatial scale length, and (8) secular variation rates comparable to historic field behavior but persisting in sign for hundreds of years. All of these features, with the exception of anomalously large directional amplitude, are consistent with normal magnetic field secular variation. Comparison of our Laschamp Excursion paleomagnetic records with other late Quaternary excursion records suggests that there is a group of excursions, which we term class I, which have strikingly similar patterns of field behavior and likely share a common cause as part of the overall core dynamo process. Three general models of secular variation are described that can qualitatively produce class I excursions. On the basis of these observations we conclude that class I excursions, epitomized by the Laschamp Excursion, are more closely related to normal secular variation and are not necessarily a prelude to magnetic field reversal.”
With these monumental changes in the shielding effect of the Earth’s magnetic field, you’d expect to see fairly massive climate consequences if the GCR crowd are right. After all, the implied changes in GCR flux are huge compared to what is expected from the gentle modulation of the Earth’s magnetic field arising from recent solar activity changes (not that there’s any trend in those that would explain recent warming). Readers can look for themselves at the Greenland ice core record and decide whether there’s anything of consequence going on around 41K before present that looks any different from other glacial-interglacial cycles.You can look at the GISP data yourself by downloading
http://nsidc.org/data/gisp_grip/data/gisp2/isotopes/gispd18o.dat
If there’s an effect there, it’s pretty subtle.
Re: #45
Raypierre, the data you link to only goes back a little over 1000 years! I’m sure you meant to link to some other file.
[Response:Oops, sorry. I copied over the wrong link. It’s fixed now. Thanks for checking. –raypierre]
Re#44
Maybe I am confusing surprised and alarmed. As I understand it, this is a first observation of its kind and it tells us we don’t know as much as we thought we did. I am not surprised, because I had no preconcieved notion of how much water is under the ice and how it moves. To spin this into alarm is a little premature.
BTW I am not surprised that you are alarmed, but I might be alarmed if you were only surprised.
I wonder if you comment on the fact that the historical climate records of GISS, the National Climate Data Centre and the Hadley Centre have been adjusted started in 2000.
It looks like the older temperature records from the 1930s for example have been adjusted downwards by 0.2C and the newest temperature records have been adjusted upwards by 0.3C.
These adjustments would account for all of the recorded 0.6C increase in temperatures in the 20th century.
I imagine readers would like to know this has occurred and why.
[Response: The adjustments are only for US stations and come from time of day adjustments, station location adjustments etc. and were clearly documented in Hansen et al, 2001 and references therein. -gavin]
[Response: …and the citation of 0.6C as the net observed warming is considerably out of date and a significant underestimate. More recent assessments (e.g. IPCC ’07 SPM) place the number close to 0.8C, and even that number is fairly conservative. -mike]
Re #48: The regulars over at Climate Audit would like to know, anyway. The complexity of climate science is such that folks who come to it already convinced that it’s all a vast conspiracy can engage in endless discussion that they think proves their points, but in fact proves nothing.
There is an important role to be played by climate scientists in educating the piblic and policymakers about the science, a role that is exemplified by this blog. It’s rather less constructive for climate scientists to spend their time engaging in endless rounds of nit-picking with denialists who are in the end unconvincable. We had quite enough of that with the hockey stick.
*Why* is it important to pay close attention to making the historical record in the U.S. as accurate as possible? It’s not so some huge deal can be made of, e.g., 1934 now being thought to have been slightly cooler than 1999, because in and of itself that’s pretty meaningless, but rather because data accuracy in turn affects the accuracy of climate model projections and in particular (in the case of this data) regional projections for the U.S.
Of course the Climate Audit regulars think the models are hopelessly defective as well, but that’s another discussion.
A tidbit about what cycles:
” … coccoliths evolved fairly recently. The earliest appeared just 200 million years ago. Their effect was only to expand the world’s calcium carbonate sinks from the shallow continental shelves to some of the deeper ocean (Westbroek 1991).”