Traduit par Valérie Masson Delmotte
A partir de nouvelles observations satellitales, un article récent de Francis & Hunterfournit une discussion intéressante sur les raisons de la diminution actuelle de l’extension de glace de mer (banquise) dans l’Arctique. On invoque souvent à propos de la glace de mer une rétroaction positive parce que la glace modifie l’albédo planétaire (la manière dont notre planète réfléchit le rayonnement solaire vers l’espace avant que cette énergie n’entre dans “le système climatique”). Pourtant, l’histoire est plus complexe, car la glace de mer agit également comme un couvercle isolant posé sur la surface de la mer.
Certains effets sont subils, ainsi, la planète perd davantage de chaleur depuis les mers libres que depuis les zones couvertes de banquise (une partie de cette chaleur est absorbée par l’atmosphère, mais les régions englacées ont un climat d’hiver plus continental : sec et froid). La perte de chaleur par l’océan dépend bien sur de la température de surface de la mer (SST, acronyme de “Sea surface temperature”). Les mers libres sont aussi une source d’humidité, par contraste avec les les zones de banquise (parce qu’elles sont froides, et non parce qu’elles sont sèches); mais l’humidité atmosphérique est aussi influencée par le transport d’humidité lié aux vents (advection de vapeur d’eau).
Francis & Hunter ont découvert une corrélation positive entre le manque de glace de mer et le rayonnement infra-rouge incident, un phénomène qu’ils attribuent principalement à l’effet de la nébulosité. Par conséquent, les nuages jouent un rôle important, à la fois en modifiant l’albédo et également en piégeant les pertes thermiques. Francis & Hunter suggèrent que les changements de rayonnement infra-rouge sont plus importants que la modulation du rayonnement solaire incident par les nuages.
Par le passé (IPCC TAR), les modèles de la glace de mer étaient connues pour leurs difficultés à fournir des simulations réalistes. Une partie du problème pourrait cependant provenir du couplage entre l’océan et la composante atmosphérique. Je ne sais pas si ces aspects ont été améliorés dans le prochain rapport IPCC; cependant, Francis & Hunter proposent plusieurs facteurs qui pourraient affecter la localisation du front de glace de mer, comme l’influence de l’océan, du débit des rivières, des effets non linéaires, l’effet des vents et du transport de chaleur, et trouvent qu’ils jouent des rôles différents en différents endroits.
Les régions polaires ont des nuits blanches en été avec un ensoleillement 24h sur 24 (mais avec un angle rasant) et l’obscurité totale 24h sur 24 en hiver. La rétroaction d’albédo de la glace de mer ne peut être active qu’en été, où il y a du rayonnement solaire à réfléchir. L’extension de glace de mer varie aussi selon les saisons, avec une zone d’eau libre plus étendue en été et une couverture de banquise plus large en hiver. Enfin, la glace de mer est déplacée par les vents de surface. Au final, l’effet de changements d’extension de glace de mer sera différent selon les saisons. Une diminution d’extension de la glace de mer en hiver entraînera une perte de chaleur plus grande depuis l’océan libre – cependant, à partir du moment où les températures chuteront suffisamment, il se formera à nouveau de la glace. L’océan libre fournira aussi des conditions plus favorables à la genèse de dépressions polaires (tempêtes). Le refroidissement de la couche de surface et le mélange par l’exposition aux vents pourrait ensuite modifier les courants océaniques et peut-être la formation des eaux profondes. En été, il est probable que c’est l’effet de l’augmentation de l’absorption de rayonnement de courte longueur d’onde qui va dominer.
Une autre question intéressante est la suivante : comment la perte de glace de mer peut-elle affecter la “machine thermique planétaire”, quand davantage de chaleur est perdue aux hautes latitudes? Si la perte de chaleur dans l’Arctique est amplifiée quand la glace de mer se réduit et découvre une surface de la mer avec une température plus élevée? Ceci pourrait être totalement contre-balancé par une diminution de l’albédo local et par une augmentation du transport de chaleur par l’océan et l’atmosphère, ou par une intensification de l’AGW. Il est probable qu’un “effet de serre amplifié par la nébulosité” dans l’Arctique pourrait supprimer une partie de la perte de chaleur par l’océan, et cet effet est cohérent avec les conclusions de Francis & Hunter. Ainsi, l’augmentation de la nébulosité et l’augmentation du rayonnement infra-rouge incident qui en résulte pourraient agir comme une rétroaction positive supplémentaire pour la surface de l’Arctique, en plus de l’effet d’albédo, alors que la perte supplémentaire de chaleur agit comme une rétro-action négative. Quoique subtiles, les résultats de Francis & Hunter ont des implications importantes pour le bilan de chaleur de notre planète.
Les rétroactions positives qui ont lieu à l’échelle locale pourraient donner lieu à des variations locales plus fortes. En plus de l’effet de la dérive de la banquise sous l’effet des vents, de telles rétroactions pourraient expliquer les grandes anomalies locales de température et l’amplitude de la variabilité naturelle dans l’Arctique. Les régions polaires représentent des régions relativement “petites” en terme de degrés de liberté, une facette qui est souvent négligée. De plus, les fluctuations de température montrent une bonne cohérence sur de larges régions (il y a cependant une anti-corrélation dans la structure en dent de scie associée à la NAO, Oscillation Nord Atlantique). Les profils de moyennes zonales (la valeur moyenne de mesures effectuées par bandes de latitude autour du globe) intègrent la comparaison de zones très étendues autour de l’équateur à des zones plus resserées près des pôles (en tenant compte de la surface des différents “anneaux”). A cause de la corrélation spatiale, cependant, les bandes équatoriales includent beaucoup plus de degrés de liberté que celles près des pôles. De tels profils latitudinaux de moyennes zonales reviennent donc à comparer des valeurs moyennes d’échantillons de tailles différentes (un peu comme comparer des valeurs journalières à des moyennes mensuelles ou annuelles). L’implication de cette analyse est que des évènements comme le réchauffement du début du siècle (dans l’Arctique) ne sont pas aussi significatifs qu’un réchauffement de même amplitude apparent dans un profil zonal aux latitudes plus basses.
Thanks for that rasmus.
On various discussion groups I have gone on about regional albedo feedbacks in the Arctic (and Antarctic Peninsular) rather more than the insulating effects of sea ice. Cloud feedback as described here is news to me.
As a slight digression:
I get quite irritated that the media continually stress ice-melt = sea-level-rise. Even leaving aside sea ice displacement meaning the loss of sea ice is not a major direct contributor to sea level change. I see a quite different and, in my opinion, more immediate concern.
What bothers me is that the jet stream seems to be caused by the equator-pole energy transport (like the Hadley Walker cells). And the jet stream has a significant effect on our weather here in the UK, notably the track of pressure systems. The loss of ice and the enhanced high latitude warming in the northern hemisphere seems to be changing the difference between equator and pole (at least in a qualitative sense). So before we get to the stage of ‘no summer sea-ice’, which is another media obsession, we are likely to see weather impacts due to that change.
I understand what you mean by “events such as the early century warming are not as significant as when the a warming of similar magnitude is seen in the zonal mean profile at lower latitudes.” But the sort of levels of warming seen in the Arctic seem to be due for later this century in lower latitudes, i.e. they’re of less immediate concern.
Basically I’d like to know if I am wrong to be concerned that we are likely to see changes in the UK and Europe as a result of the ice loss and high latitude warming well before the N. pole is sea-ice ‘free’ in the summer.
Rasmus, when you write:
ITIYM that the long stretched areas are near the equator.
Regards
Luke
[Response:Oops! Thanks! -rasmus]
Partly as an addendum to comment #1, I’d like to hear if anyone knows of any research which attempts to quantify the likely change to the planetary heat balance in a zero summer sea ice scenario, such as we may see well before 2040. Would the much lower albedo result in higher temperatures over a broad enough region to accelerate the crossing of other ‘tipping points’ elsewhere, such as the release of large quantities of methane/CO2 from Siberian peat? Or would it have an effect mainly restricted to the Arctic Ocean and adjacent areas, and have little effect on overall planetary temperatures? I know there are no easy answers, but surely there is some work which at least hazards a guess?
Our friend Lumo is at it again. Deniers are trotted this post out as evidence GW isn’t real. Please address this. We really are in a propaganda war.
http://motls.blogspot.com/2006/12/2006-probably-coldest-year-in-last.html
Isn’t he that solar guy?
The URL above for the Francis & Hunter paper leads to a password-protected AGU site. OK, I’m an AGU member, but for those who are not — if you don’t know the trick of Googling the authors’ names and some keywords, I did it for you, and as is often the case, they have posted a PDF of the paper:
http://marine.rutgers.edu/~francis/pres/Eos_11-14-2006EO460001.pdf
[Response:Thanks! -rasmus]
RE # 5
Thank you Spencer. And, a good reminder to all. Many journal article authors have home pages or links to their papers and often one can find the subscripted article there. It might require googling second, third, etc. author names. But, how badly do you want the paper?
RE # 5
Thank you Spencer. And, a good reminder to all. Many journal article authors have home pages or links to their papers and often one can find the subscripted article there. It might require googling second, third, etc. author names. But, how badly do you want the paper?
Here’s an interesting article from years ago regarding the effects of an ice-free Arctic.
http://www.americanheritage.com/articles/magazine/ah/1960/3/1960_3_40_print.shtml
Here is the part where they describe what and how.
The Arctic Ocean, they point out, is a sea almost separate from the other waters of the earth. Its connection with the Pacific at the Bering Strait is so narrow and shallow it allows no significant interchange of waters. The passage between the Arctic and the North Atlantic is broader, but across its bottom, between Norway and Greenland, extends a shallow sill, less than three hundred feet deep in most places.
The currents flowing across the sill bring warm Atlantic water into the polar sea, and although the net gain each year is tiny, over thousands of years it is enough to make the Arctic Ocean very much warmer. As a result, the ice on the water becomes thinner, patches of open water grow larger, and eventually the time comes when the ocean is completely free of ice.
A polar sea without ice opens a new stage in the glacial cycle. The warm, open water gives off a great deal of water vapor by evaporation; the moisture is swept south and overland by the winds where it cools off and falls as rain or snow. The open Arctic is such a prolific producer of precipitation that the increased winter snowfall amounts to more than the oblique rays of the sun can melt away during the short northern summer. The snow accumulates and packs into ice until, after tens of thousands of years, the ice cap has become two miles or so thick. The day comes when the tremendous pressure begins to push the ice outward and another continental glacier is on its way.
But even as they form, icecaps carry the mechanism for their own destruction – according to the Ewing-Donn theory. With so much moisture becoming locked up in ice, ocean levels slowly drop until the Bering Strait becomes dry land and the flow over the Norway-Greenland sill becomes greatly restricted, so that not enough warm water can flow into the polar ocean to keep it from freezing. The Arctic Ocean cools off and finally freezes over again. Since very little moisture evaporates from ice, the snowfalls become much lighter – and far to the south the glacier front comes to a stop.
Once again the situation is changed. With snowfall reduced, the glacier is not replenished at the old rate, and so begins to shrink. Water from the melting ice makes the oceans rise, only a fraction of an inch a year but, in the fullness of time, enough to let the currents increase their flow over the northern sill, bringing ever more warm water into the gelid Arctic.
In this year 1960 A.D., we are (still according to the Ewing-Donn theory) at the point in the cycle where the Arctic Ocean is almost ready to shed its old, old, covering of ice. The north-polar ice is going very fast; it covers twelve per cent less area and is forty per cent thinner than it was only fifteen years ago. At that rate it could disappear completely in less than a human lifetime, although we cannot say whether this is a normal climate fluctuation or a steady trend.
I have recently become concerned about the continuing reduction in pH of the oceans as a result of their absorption of carbon dioxide. If the Arctic Ocean is losing ice at a greater rate than previously thought, won’t this increase the rate at which carbon dioxide is absorbed? There would be more open ocean, and cold water absorbs carbon dioxide at a greater rate than warm water. Has this been taken into account in the projections of ocean pH decreases?
Re #8: I also wonder about the effect of Arctic ice cap reduction on uptake of carbon dioxide. I used to think that “cold water absorbs carbon dioxide at a greater rate than warm water,” until I read this paper by Sabine et. al in Science which shows the opposite. Cold water may hold more CO2, but the amount it absorbs from the air depends on how saturated it already is.
So my question is how much CO2 will be absorbed by newly exposed ocean water. Is it possible that because it used to be covered with ice it may be under-saturated, and thus absorb more than Antarctic ocean water? I suspect any change in CO2 absorption will to too small to have much affect on either levels in the atmosphere or ocean acidification, which may be why Rasmus did not mention it in his article.
I must be drinking too much eggnog these days, because I don’t really understand what this blog entry is saying. How do all these competing effects balance out? What’s the net effect? What exactly did Francis & Hunter find? And what do you mean by “degrees of freedom”: sampling locations, model grid points, or an inherent cellular structure to the climate system?
George
[Response:The competeing effects do not cancel each other, but some are positive feed-backs and one is a negative feed-back. Francis & Hunter found that the downward long-wave radiation associated with a retreating sea-ice extent is more important (a stronger effect) than cloud modulation of SW also associated with the sea-ice extent. Degrees of freedom is commonly used in statistics, but can also describe how much information you really need to describe something after stripping away redundant information (spatial correlation). For instance, if I know the temperature at my home, I hve pretty good idea about the temperature at my neighbours property, since they are closely related. Hence, I need only to know the temperature at my place to make inferrences about the temperature in my neighbourhood. -rasmus]
I was wondering if anyone happens to have the current sea ice extent anomaly handy? Many thanks in advance.
re #8: The Ewing-Donn model was pioneering and played an important role in stirring up interest in climate change, and especially fast-feedback climate change, but it was soon shown not to work. Just for one thing, the straits are in fact deep enough so that the Arctic and Atlantic Oceans would exchange water even in the midst of an ice age. For a brief history see my essay on simple climate models.
Here you go, Steve. Looks like about 700,000km^2 below 1979-2000 mean for the time of year – and a rather wobbly line, too.
Re #12: Go to http://nsidc.org/data/seaice_index/
It has monthly anomalies going back to 1978 relative to a 1979-2000 reference period. The November 2006 Arctic anomaly was -1.2 mill. sq. km., the lowest November in the record.
Hello Steve,
Cryosphere Today. http://arctic.atmos.uiuc.edu/cryosphere/
The most ‘current’ source I have. The following graph gives the most update total and anomaly.
This years press release for NSIDC,
http://nsidc.org/news/press/2006_seaiceminimum/20061003_pressrelease.html
From Cryosphere Today http://arctic.atmos.uiuc.edu/cryosphere/IMAGES/current.365.jpg I read the most recent figure of anomaly as about -0.7 Million Km^2 from ’79-’00 mean. Sorry I can’t find a more accurate figure than that.
Here’s an anomaly plot I just found:
http://arctic.atmos.uiuc.edu/cryosphere/IMAGES/current.365.jpg
And here’s a striking and amazing “looking from the top down” Arctic image – I never fail to be amazed by either images like this, or, to see things up close and personal:
http://arctic.atmos.uiuc.edu/cryosphere/IMAGES/arctic.jpg
(BTW – thinking about doing a trip up the Dempster Highway at some point – if I don’t fit it in summer 2007 I’ll go the following summer)
Your comment regarding sea-ice/ocean feedback points to the recent paper by Holland, et al.(1). This report describes simulations of future sea-ice extent using the NCAR CCSM3, which point to the possible complete loss of sea-ice at the end of the melt season as soon as 2040. These simulations employ the sea-ice model of Briegleb et al., 2004, which incorporate the albedo data collected during the SHEBA experiment. These data indicate a strong difference between the albedo of sea-ice and open water, with some reduction in sea-ice albedo when melt ponds are expected.
The instruments which were used to measure the albedo (Eppley PPS emispherical pyranometers) measure the energy falling on a horizontal surface, not the direct beam energy normal to the incident radiation.
http://www.eol.ucar.edu/rtf/projects/sheba/rad.isff.html
The result is a cosine dependence on the measured energy. At polar latitudes, the sun never rises high above the horizon, even during mid-summer, thus the direct beam energy is not well characterized. The difference between direct and diffuse solar energy is important because the albedo is a function of zenith angle, which is especially so for the direct SW beam impinging on water. The direct beam energy is much stronger on clear days, yet it’s impact is muted because of the higher albedo at the surface. However, the direct beam SW energy which is reflected by the surface may then be reflected/absorbed by clouds. The SW energy reflected downwards will likely have been scattered and arrive at the surface as diffuse energy and be more easily absorbed, as will the downward radiated IR.
My point is that changes in clouds, ie., an increase in average summer clouds, may not have the effect seen in the paper from EOS. That’s because increasing clouds will cut the direct SW energy before it arrives at the surface, thus less energy will actually be trapped by the interactions between the sea-ice and the clouds above. This effect may not be visible from the position of the AVHRR satellite instrument, which tends to look downward nearly along the zenith direction. The instrument views a swath of 2399 km from an altitude of 833 km, for a field of view roughly +/- 55 degrees wide (neglecting the Earth’s curvature). As a result, any changes which occur outside that swath, such as reflections at zenith angles greater than 55 degrees at the surface, can not be viewed or measured.
1. Holland, M. M., C. M. Bitz, B. Tremblay (2006), “Future abrupt reductions in the summer Arctic sea ice”, GRL 33, L23503, doi:10.1029/2006GL028024.
RE # 18
To add to Steve’s link:
Dr. Will Chapman’s Cryosphere Today web page offers an archive of daily polar sea ice cap concentrations (1979 – present)at:
http://arctic.atmos.uiuc.edu/cryosphere/archive.html
Try building a slide show using September 25 images from 1979 to 2006 to get the real effect of the meltback.
I followed the progress of the return ice since mid-September and the ice sheet closed in later and more slowly than any year in the past 30.
RE: #20 – By my read, the anomaly actually reached zero in November then backed off into negative territory, bottoming out at -1M km^2, later recovering slightly again, as noted above, to about – 0.7M km^2 of late. Much of what has driven the negative anomaly since September, has been two things:
1) A persistent High pressure ridge over easternmost Siberia, which delayed the onset of the Chukchi Sea and Western Bering Sea freeze for a few weeks. (Since then, Chukchi froze over and Bering Sea ice has started to spread rapidly southward)
2) Persistent Easterly winds around Svalbard (on the NE sides of multiple very deep Hudson Bay Lows), which have repeatedly compressed the ice edge westward toward Greenland. There must be some huge pressure ridges in that particular ice area as a result.
Most other places in the NH have been flirting with zero anomaly locally since September or October, depending on the location. (There were however some oddities in the measurements of Kara Sea ice during October, but given how glitch-like they look on that regional plot, they must have been instrument related and not indicative of actual extent in that area.)
It will be interesting to see what happens with NH extent between now and March or April.
RE: #21 – I missed one other notable contributor to the negative anomaly this fall, namely, the Barents Sea. That is truly an odd one. Fenno-scandia, just to the SW of there, got early snow fall this year (October) and the western portions of it have remained snow covered since then, Norway has been pretty much covered nation wide with only the immediate coastal areas in the South having thawed at all. So, with Barents, it may be a remnent of last years warmer than normal SSTs, or winds – the air temperatures in that area should be supporting more widespread sea ice formation by now.
[Response:There is a website called SeNorge.no giving up-to date (or for any date since 1961!) information about snow-cover, temperatures and precipitation. I think you mean the northern part or the mountains (whivh is common). Otherwise, the winter so far has been extremely mild for Norway and people are longing after snow. -rasmus]
Re: #19 Continuing the thoughts offered above.
The AVHRR is a cross track high resolution scanner. The resulting swath is a little larger than 1 km wide, thus the zenith angle sensitivity is centered around zero degrees along the ground track.
http://www2.ncdc.noaa.gov/docs/klm/html/c3/sec3-1.htm
As the satellite passes over the poles, it’s ground track is such that the instrument swath is nearly perpendicular to the sun vector. Thus, any SW energy reflected from the surface or from clouds would be missed by the fact that the instrument is looking nearly straight down.
One should note that the ERBE scanning instrument had similar limitations. Even the wide FOV ERBE instrument was similarly limited in the effective zenith angle sensed…
Have a great Winter Solstice Celebration (aka: Christmas)!
Lord Monckton has spoken. Silence!
http://ff.org/centers/csspp/pdf/20061121_gore.pdf
RE: In reply to the English Gentleman’s (CobblyWorlds) question: “Basically I’d like to know if I am wrong to be concerned that we are likely to see changes in the UK and Europe as a result of the ice loss and high latitude warming well before the N. pole is sea-ice ‘free’ in the summer”
Based on the paleoclimatic record the Polar Circulation Index becomes activated when the planet cools, rather than when it warms. For example see figure 1 in Alley’s paper that shows the GISP2 ice core data (The wiggle lines indicate a massive increase in sea salt and dust that is being transported to the Greenland Ice sheet, as compared to the current climate. Bad thing from the standpoint of UK.) It appears the earth’s climate is unstable when it cools a few degrees, as that starts the formation of the massive ice sheets in the Northern Hemisphere.
http://www.pnas.org/cgi/reprint/97/4/1331.pdf
But it seems all right thinking people believe the earth will continue to warm rather than suddenly cool. Oh, by the way the planet did suddenly cool, about 8,200 years ago. Does any one have an explanation for the sudden cooling?
http://www.geo.arizona.edu/palynology/geos462/8200yrevent.html
I guess it must only be a coincidence that the sun’s large scale magnetic field has doubled in the last 100 years and that the solar activity is the highest in the last 8000 years.
http://cc.oulu.fi/~usoskin/personal/nature02995.pdf
As to the definition of suddenly. The Younger Dryas climate event occurred within 5 layers of ice core data.
I have found a number of interesting papers that seem to provide a logical explanation for the observed climatic changes.
Re “The URL above for the Francis & Hunter paper leads to a password-protected AGU site. OK, I’m an AGU member, but for those who are not — if you don’t know the trick of Googling the authors’ names and some keywords, I did it for you, and as is often the case, they have posted a PDF of the paper:”
I think the tendency of journals to become more and more secretive of their contents, to demand money to see even long past publications, and to go all-electronic and subscription-only rather than sending paper copies to libraries, is an extremely destructive and ill-omened trend. When science becomes the exclusive preserve of scientists with academic or corporate backing, and when the latter can only cite journals which they themselves have access to, it will give them little credibility with the public.
I wrote a paper on stellar astronomy in 1997 which was turned down by ApJ, but a revised version later passed peer review at PASP. It was never published, because I couldn’t come up with the $3,600 they wanted in printing fees. A university or corporate scientist could just tap their employer, but I was SOL because I was working alone and as an amateur. For that reason, and that reason alone, I have no track record of publication in a peer-reviewed journal.
[Response:Please see link provided in #5. -rasmus]
Re “I guess it must only be a coincidence that the sun’s large scale magnetic field has doubled in the last 100 years and that the solar activity is the highest in the last 8000 years.”
Global warming has been significant in the past 30-40 years, and in that time frame the Solar constant has not changed measurably at all. We’ve been measuring it since the 1960s with direct satellite observations (e.g. by Nimbus-7 and the ERBE). Relying on proxies when direct measurements are available smacks of cherry-picking the input data to get the results you want.
I’m not sure to understand all the interest of Francis & Hunter paper. Apart albedo, shouldn’t we expect a classical water vapour feedback (and so DLF forcing) as arctic ice is melting and arctic seas / ocean warming ?
Re # 26
Scientific journals have always been copyrighted, as far as I know. That they were available in university libraries, was the result of the universities paying subscription fees. For the past few decades , the increased costs for journals and the growing number of journals has forced libraries to cut back on the number of journal subscriptions. The folks who publish journals want to make a living too, thus they must cover their expenses. As inflation has pushed up costs for everything since the 1970’s, it’s become more expensive to publish. Scientific journals do not have the wide circulation that popular magazines enjoy, thus the subscription costs are greater. That said, there is a symbiotic relationship between paid researchers and the journals that publish their work. The researchers need the journals to broadcast and archive their work and the journals need papers to print…
BTW, I had to pay the cost or a paper I wrote a few years back. I had the choice to use color graphics or B&W for my figures. The color pages cost more and offered little extra in terms of information content, so I saved lots of bucks by going with B&W graphs.
In Reply to Comment 27: “Global warming has been significant in the past 30-40 years, and in that time frame the Solar constant has not changed measurably at all. We’ve been measuring it since the 1960s with direct satellite observations (e.g. by Nimbus-7 and the ERBE). Relying on proxies when direct measurements are available smacks of cherry-picking the input data to get the results you want.”
There appears to be a misunderstanding concerning the difference between the term “solar constant” (Measurement of radiation that travels through space) and the term “solar magnetic field” (A magnetic field is a condition of space.)
The following is an excerpt from a paper that notes the solar magnetic field has increased by 40% since 1964.
http://www.nature.com/nature/journal/v399/n6735/abs/399437a0.html
“Moreover, changes in the heliospheric magnetic field have been linked with changes in total cloud cover over the Earth, which may influence global climate. Here we show that measurements of the near-Earth interplanetary magnetic field reveal that the total magnetic flux leaving the Sun has risen by a factor of 1.4 since 1964: surrogate measurements of the interplanetary magnetic field indicate that the increase since 1901 has been by a factor of 2.3. This increase may be related to chaotic changes in the dynamo that generates the solar magnetic field. We do not yet know quantitatively how such changes will influence the global environment.”
Comments:
1) The solar magnetic field is an interplanetary magnetic field which, along with the geomagnetic field, and the conductive solar wind, diverts galactic cosmic rays from striking the earth’s atmosphere and surface.
2) As the solar magnetic field, the geomagnetic field, and the solar wind all change with time, the magnitude of the GCR that strikes and passes through the earth’s atmosphere also changes with time. GCR it is hypothesized affects the amount of cloud cover on the planet. If the cloud cover is less the planet is warmer and visa versa, an relative increase in cloud cover causes the planet to cool.
Lastly in response to the comment: “smacks of cherry-picking the input data to get the results you want.” It appears significant planetary cooling is imminent, based on the paleoclimatic record and a hypothesis that is explained in a dozen scientific papers. What possible motive could I have to start this discussion? A wager? A genuine concern for humanity?
The sea ice animations from the NSIDC are nice but I prefer to look at visible light images which are actual pictures afterall and have not been heavily modified by a computer software program (and hence subject to bias of the programmer.)
Here is the Beaufort Sea on July 25, 2006 and 2005 (which to us is the height of the summer.) Frozen solid.
http://earthobservatory.nasa.gov/NaturalHazards/shownh.php3?img_id=13738
[Response: Minimum sea ice extent is September, not July. -gavin]
Re #30: I don’t quite see how this relates to sea ice, but since I’m quite puzzled by this cosmic rays affect climate theory, I’ll risk getting further off topic.
As I understand it, the basic theory is that incoming charged particles provide additional cloud condensation nucleii (like the cloud chambers used as detectors in early subatomic physics), that the rate of incoming particles is modulated by the magnetic fields of the sun and earth, and that therefore the amount of cloud cover varies with the particle flux, which in turn drives climate, so we can stop worrying about CO2. Am I missing something?
Now for the things about this theory that really puzzle me. First, there are occasions when a solar flare hits earth, which should significantly increase the particle flux, and hence cloud cover. It seems to me (though I must admit I’m not a climate scientist) that an obvious and quite simple test of the theory would be to use satellite images to calculate cloud cover during such events, and compare it to long-term averages. I don’t see this being done – why not?
Second, the current generation of climate models seem to do a pretty good job, based on already-known physics. Even if the cosmic ray theory is borne out by evidence, where is the room for it to be anything more than another, and not very significant, forcing factor?
[Response:Please see an earlier post on Galactic Cosmic Rays (GCR) and climate (also here; you can also find all solar-related posts by selecting ‘Index’ st the top of the page.). The bottom line is: there is no systematic trend in GCR or other solar indices that can explain the warming over the past ~50 years. -rasmus]
This is what I get out of it: the Arctic-ice-albedo situation is more complicated than earlier thought (due to clouds, sun-filled summers, dark winters, etc), but NET EFFECT, the ice loss and all these other related factors (some negative feedbacks) act as a positive feedback and enhance global warming. If this is wrong, and the net effect of all these factors is a negative feedback, please let me know.
Next question (assuming the net effect is a positive feedback), do all these factors (net effect) actually mean is it worse than scientists had earlier thought, about the same, not as bad (though still a net positive feedback), or not sure (due to it being so complicated)? Please select one and let me know.
And finally, what about Mark’s questions (#3) and other factors not discussed here — do all these effects re Arctic ice lead scientists to believe there is a greater and/or earlier chance (assuming we continue increasing our GHG emissions – business as usual) of melting hydrates and permafrost releasing vast stores of methane into the atmosphere than scientists believed before the study, or is the assessment of this about the same, or scientists are not sure if this study indicates a greater/lesser/same chance of this?
[Response:The climate models indicate a ‘polar amplification‘, which implies a positive net feedback. -rasmus]
Re #13
I took a look at your article and would like to know if there is more available information casting doubt on the Ewing-Donn model. Somehow the problem with the depths of the Atlantic and Artic doesn’t satisfy me enough to throw the whole theory out. What if the mixing between the oceans were drastically reduced due to changes in ocean circulation? When I read the initial post, I goggled Ewing-Donn and didn’t come up with a lot (but I did find your article). Unfortunately, probably most of the debates and articles from that time may not have made it into digitized form yet.
In response to comment 32:
First, basic facts, to provide a physical framework for discussions concerning the GCR effect.
The Solar Wind, is a charged plasma, (made up protons and electrons), with a current velocity of 662 km/s. The solar wind does not penetrate the earth’s magnetic field.
See the attached link for details concerning the current state of the sun. (There have been recent notes in this area and related chat rooms of abnormal solar observations.)
http://www.dxlc.com/solar/
Protons are accelerated in a solar flare up to around 10 Mev. GCR protons have a typical energy range of 100 Mev to 10 Gev. The solar system is currently traveling through the spiral arms of the galaxy, a region where the GCR more than doubles in magnitude. It is hypothesized that the increase in GCR, when the solar system moves through the spiral arms, is the reason (trigger) why the earth is currently in an ice epoch.
Galactic Cosmic Rays (GCR), which are mostly protons, travel at about 150,000 km/s to just less than the speed of light, 300,000 km/s. A portion of the GCR penetrate the sun’s and earth’s magnetic field and through secondary reactions with molecules in the earth’s atmosphere, create charged nuclei, which affect cloud formation.
I do not have time to reply to your other questions concerning GCR and models now. Attached is a link to a paper ‘The Glacial cycles and Cosmic Rays’ that provides a reasonable explanation of the GCR hypothesis and known issues with Milankovitch’s insolation model. http://arxiv.org/pdf/physics/0407005
Also attached is a link to Shaviv’s third paper “On climate response to changes in the cosmic ray flux and radiative budget”. http://arxiv.org/pdf/physics/0409123
Re “Lastly in response to the comment: “smacks of cherry-picking the input data to get the results you want.” It appears significant planetary cooling is imminent, based on the paleoclimatic record and a hypothesis that is explained in a dozen scientific papers. What possible motive could I have to start this discussion? A wager? A genuine concern for humanity?”
A desire to discredit the idea of anthropogenic global warming?
Interesting about the loss of ocean heat due to artic ice melt. Most sources claim that it would inrease albedo and lead to a positive feedback. Now it seems to be more complicated.
Re: the posting about the effects of the melt on Europe. It should lead to a weakening and/or a migration north of the jet stream. This should lead to Britain suffering a big drop in summer rainfall among other things. Has any research been done on this?
Re #30 and #36: Perhaps William Astly can elaborate on why significant planetary cooling is imminent. The paleoclimatic record suggests we may possibly lose about a watt per square meter if we return to Little Ice Age conditions, which is considerably smaller than the greenhouse forcing expected in the coming century.
No matter what the reality of an external cooling event, it has no relevance to the reality of anthropogenic global warming.
Reading this post and comments I find my non-scientific brain a little thickened rather then illuminated. I am betting that all of you could come up with a sentence or two that did not include a lot of climate related jargon, but spoke directly of the issues involved. Take the last sentence of the post, “Such latitudinal profiles of zonal means are analogous to comparing mean values of different sample sizes (a bit like comparing daily values to monthly and annual means). The implication is that events such as the early century warming are not as significant as when the a warming of similar magnitude is seen in the zonal mean profile at lower latitudes”
Imaging sitting around the table with your presumably intelligent and thoughtful relatives and using a sentence like this. Can you hear the laughter at your expense or the resentful conversations as they drive away about there pompous over educated brother in law?
I understood the purpose of this blog to be an attempt to communicate to a broader spectrum of the population. So could you please continue to describe things in the kind detail you need to, but on occasion through us non-science types a sentence that explains your point in conversational terms?
I greatly appreciate what you are trying to do and the pull that you all must feel towards using the specific language that you are comfortable with, however this topic is to important and so often poorly written about in our newspapers, that an effort towards plain language does seem very worthwhile in regards to educating the public.
[Response:Sorry. I’ll try, but I’m not sure I’ll succeed. Consider the following facts: 1. Basically as you move away from the poles to the equator, the distnce you would increase if you decided to circum-navigate the earth while staying at the same distance from the pole (i.e. at the same latitude). This is due to Earth’s spherical shape. 2. Climate models indicate that the Arctic warms at a faster rate than the rest of the planet, and hence it is of interest to compare the warming at the different latitudes (eg. at 30N compared to 80N). How do you then compare these two latitudes? You can choose to compare the mean temperature change for 30N and 80N respectively, and you do that by computing the average around the planet – along the circle of constant latitude. Since the distance for the circle at 30N is longer than at 80N [d ~2 pi a cos(latitude), where ‘a’ is the Earth’s radius…], one compares apples with pears because the two latitudes represent different length/surface area. One may resolve this by choosing a wider strip near 80N and a more narrow strip near 30N, so that their area are the same. But this does not work either, because the temperatures are related to nearby temperatures (the temperature varies smoothly/slowly with distance). Even if you measure the temperature at 80N, the temperature at other near-by latitudes (eg 75N) are not independent. You have to go a certain distance before the temperature you measure is unaffected by the temperature where you started off (spatial autocorrelation, in jargon terms). The distance you have to travel before the temperature is unrelated to the one at the out-set is called the ‘de-correlation length’. The thin strip at 30N will have a longer circumference which spans far more de-correlation lengths than at 80N, and using a wider strip at 80N will not compensate for this even if the area is the same. Well, I think this one was hard to explain in lay-man terms… I hope someone understood what I tried to say. -rasms]
In reply to comment 38: “Perhaps William Astley can elaborate on why significant planetary cooling is imminent. The paleoclimatic record suggests we may possibly lose about a watt per square meter if we return to Little Ice Age conditions, which is considerably smaller than the greenhouse forcing expected in the coming century.”
The current conditions (those that determine the magnitude of the GCR effect) have changed from those in the 17th century.
The geomagnetic field is 20% less than at the time of the Little Ice Age. See figure 1 a) geomagnetic field strength over the last 7000 years in the attached paper. The geomagnetic field was been dropping at the rate of about 5% per century, starting at about the time of Maunder minimum.
http://adsabs.harvard.edu/abs/2006GeoRL..3308103U
A better analogue to current conditions is shown in the link in comment 25. That link provides paleoclimatic data that shows that the most sever cooling in the Holecence (5C cooling on the Greenland Ice sheet) occurred 8200 years ago. It is hypothesized that this is a Heinrich event as opposed to a Maunder event.
In reply to comment 36: “A desire to discredit the idea of anthropogenic global warming?”
I believe, sudden, rapid, and sever global cooling is possible and likely based on the paleoclimatic and paleo-geomagnetic records. There is a correlation of the rapid changes to the earth’s magnetic field that have occurred in the past and paleoclimatic changes (which supports the GCR hypothesis and is the reason for the recent papers.). The question as to what is causing the rapid changes in the geomagnetic dipole field, has not been answered, however, it seems reasonable that the forcing function is solar.
Attached is a link to a public version of Yamazaki’s paper (See figure 1 e) relative paleointensity over the last 2.5MMyr). Also attached is a link to a public version of Usoskin’s paper (In my last comment it has noted the geomagnetic field is 20% less now than in the 17th century, but neglected to provide a link to a public version of the paper.)
http://www.sciencemag.org/cgi/content/full/295/5564/2435
http://cc.oulu.fi/~usoskin/personal/2006GL0259211_pub.pdf
“Disappearing world: Global warming claims tropical island
For the first time, an inhabited island has disappeared beneath rising seas.
Environment Editor Geoffrey Lean reports
Published: 24 December 2006
Rising seas, caused by global warming, have for the first time washed an inhabited island off the face of the Earth. The obliteration of Lohachara island, in India’s part of the Sundarbans where the Ganges and the Brahmaputra rivers empty into the Bay of Bengal, marks the moment when one of the most apocalyptic predictions of environmentalists and climate scientists has started coming true.”
http://news.independent.co.uk/environment/article2099971.ece
Brian Schmidt and James Annan would like to talk to William Astley
The sentence you quote (last one from the main post) is sort of a picture puzzle. Let me try as an amateur, for whatever comparison it’s worth:
‘Such latitudinal profiles of zonal means are analogous to comparing mean values of different sample sizes (a bit like comparing daily values to monthly and annual means). The implication is that events such as the early century warming are not as significant as when the a warming of similar magnitude is seen in the zonal mean profile at lower latitudes”
—-
I think that expands to something like
….”lower” latitudes (nearer the Equator (0 degrees latitude) than the Poles (90 degrees North or South latitude).
From “lower latitudes” since science started (a few hundreds of years ago) temperature averages for any “zone” you define are calculated from many measurements over centuries. The records would date from at least when ships began carrying thermometers, and sooner for ‘below freezing’ info).
Zonal average in shipping zones would be an average made up from a lot of numbers across several centuries.
The more numbers you have, the more years between collecting the numbers, or both, the better, for any statistical work, even just calculating an average or average per time period. Doing it across a big area gives more confidence that the average is close to useful, as well. So from lower latitude zones we have better statistics.
Zonal averages in the polar waters are from the places where the lines of latitude get closer together (they meet at the Pole). Visits from ships carrying thermometers began later, are rarer, and were taken over a smaller area. So an average calculated from those records is less reliable.
Now draw a picture of the globe and show on it what you call ‘average temperatures’ for whatever zones you choose to draw on it; then show recent variations from those “averages” — the variations from the longterm average in a higher latitude zone don’t mean as much, because we’re comparing today’s measurement to averages based on fewer numbers, collected over fewer years in fewer places, when looking at variation near the Poles. We can’t be as sure that a given change is significant, when it’s measured nearer the Poles, because we don’t have as reliable an average number.
————
Whew. This formally makes the argument for scientific writing, it packs explanations quite densely. Comments welcome on whether I understood it, let alone explained it.
[Response:Sorry. Zonal mean means taking the average around the planet at one latitude. Because the circumference varies with latitude, the length over which the average is made – and the number of independent measurements – increase. The term is not in particular related to shipping and historical data (although historicl data can be presented as zonal mean). -rasmus]
Re “I believe, sudden, rapid, and sever global cooling is possible and likely based on the paleoclimatic and paleo-geomagnetic records.”
I believe you don’t know what you’re talking about.
Re #35: Thanks for the links to those papers, though I’m not sure that I understood them in detail. I must say that they’ve increased my puzzlement. I’d think that anyone presenting a theory as novel as that linking GCRs and climate would want to present as much supporting evidence, but there are several things that seem obvious to me (non-specialist though I am). For instance, there’s a long record of geomagnetic field reversals, with the geomagnetic field presumably being near-zero for some time at each reversal. Shouldn’t there be obvious correlations between the reversals and climate cycles? On the other hand, if solar magnetic fields have an effect, then shouldn’t we see correlations between climates of Earth & Mars?
I think the real problem, once again, is with the argument that despite a lack of supporting evidence this mechanism (or any other claimed mechanism) should displace rather than supplement the current model of the effects of CO2 increases. That model is, after all, ultimately derived from fairly simple physics and directly measured data.
As for the case for a sudden severe cooling in the near future, I simply don’t see it. Where is the predictive capability of the GCR theory? Why should it displace the predictions from the CO2 model? It is, after all, the model’s predictions of future warming that are worrisome, not its explanation of observed warming to date.
[Response:It’s difficult to say what happened in the far past, but we have fairly good data for the last 50 years. Basically, there is no systematic trend in the modern GCR (presumably the data which is most reliable) that can explain the recent warming. There are also other difficulties with the GCR-theory too (if you have access to GRL, see here). Everything in the GCR-idea and the recent warming hinges on whether there have a trend in GCR or not. So far, the GCR-theory proponents have not offered any explanation for how GCR can cause a warming if there has been no trend in the GCR since 1952. -rasmus]
Hence, clouds play a role, both in terms of influencing the albedo as well as trapping out-going heat
Well yeah. Actually it’s a pretty good confirmation of the effects of GHG. Take a winter’s night in the country (away from city heat islands) with clouds in the sky vs a clear star filled sky and you’ll definitely feel the difference.
Thanks Rasmus. Your clarification makes me wish for a new year’s typographical feature here for RC — being able to show mistakes in a s-t-r-i-k-e-t-h-r-o-u-g-h- font (grin). Thanks for clarifying what ‘zonal’ means, it’s way different than I thought.
#41: If you’re interested in putting some money up to back your position against the global warming position, please contact me. However, I advise against it.
#46 Rasmus Comment
As I understand it, the GCR-idea does not deny human influences on global warming and does not really provide a good estimate of what the magnitude of GCR influences might be. It doesn’t try to account for all or even most of recent warming.
So saying there has there has been no recent trend in GCR is really knocking down a straw man. The GCR theory is in my view is much more related to explaining trends over thousands of years rather than the last hundred.