Guest commentary from Dirk Notz, MPI Hamburg
“Well, it’s not really good timing to write about global warming when the summer feels cold and rainy”, a journalist told me last week. Hence, at least here in Germany, there hasn’t been much reporting about the recent evolution of Arctic sea ice – despite the fact that Arctic sea ice extent in July, for example, was the lowest ever recorded for that month throughout the entire satellite record. Sea-ice extent in August was also extremely low, second only to August 2007 (Fig. 1). Whether or not we’re in for a new September record, the next weeks will show.
Figure 1: Evolution of Arctic sea-ice extent in July and August from 1979 until 2011. (NSIDC)
A rainy summer might be one reason for an apparent lack of public attention with respect to the ongoing sea-ice loss. Another reason, however, is possibly the fact that we scientists have failed to make sufficiently clear that a major loss of sea ice during the early summer months is climatologically more important than a record minimum in September. This importance of sea-ice evolution during the early summer months is directly related to the role of sea ice as an efficient cooling machine: Because of its high albedo (reflectivity), sea ice reflects most of the incoming sunlight and helps to keep the Arctic cold throughout summer. The relative importance of this cooling is largest when days are long and the input of solar radiation is at its maximum, which happens at the beginning of summer. If, like this year, sea-ice extent becomes very low already at that time, solar radiation is efficiently absorbed throughout all summer by the unusually large areas of open water within the Arctic Ocean. Hence, rather than being reflected by the sea ice that used to cover these areas, the solar radiation warms the ocean there and thus provides a heat source that can efficiently melt the remaining sea ice from below. In turn, additional areas of open water are formed that lead to even more absorption of solar radiation. This feedback loop, which is often referred to as the ice-albedo feedback, also delays the formation of new sea ice in autumn because of the accompanying surplus in oceanic heat storage.
Measurements from ice buoys show that indeed melting at the bottom of the sea ice has increased significantly in recent years. While field experiments that were carried out in the 20th century showed unambiguously that surface melting used to be the dominant mechanism for the thinning of Arctic sea ice, now in larger and larger areas melting at the underside of the ice is almost equally important. Such melting from below is particularly efficient since the temperature at the ice-ocean interface is fixed by the phase equilibrium that must be maintained there. Hence, any heat provided by the ocean to this interface will lead to thinning of the ice in summer and to slower ice growth in winter. At the surface, the ice temperature is not fixed as long as the ice isn’t melting, and heat input from the atmosphere can in part be compensated for by a change in surface temperature and an accompanying change in outgoing long-wave radiation at the ice surface.
In addition to these climatological reasons, there is another reason for why a public focus on just the September sea-ice extent is possibly misleading: Such focus might give the impression that sea-ice extent is stable in other seasons but summer. That this is not the case becomes obvious from the graphical distribution of extreme sea-ice extent for each individual month that is shown in Figure 2. The figure shows in red the years with the five lowest values of sea-ice extent for a certain month and in blue the years with the five highest values. A retreat of sea ice throughout the entire year is obvious. In fact, the sea-ice extent for every month since June 2010 has been among the five lowest values ever recorded by satellites.
Figure 2: Distribution of record minima and record maxima of Arctic sea-ice extent (NSIDC). The years with the five lowest values of sea ice extent for a certain month are marked in red, those with the five highest values of sea-ice extent are marked in blue. The darkness of the color indicates the ranking: the darkest red marks the lowest value, the darkest blue the highest.
Such widespread loss of Arctic sea ice has sometimes given rise to the concern that the total loss of Arctic sea ice at least during summer time can no longer be avoided. In this context, usually the ice-albedo feedback is mentioned, since it provides a mechanism that can in principle lead to a so-called “tipping point” beyond which the loss of the remaining sea ice becomes unstoppable. However, recent research shows that this scenario is too pessimistic. For example, in a paper published in Geophysical Research Letters in January 2011, Tietsche et al. [1] used climate model simulations to examine the evolution of Arctic sea ice after an extreme loss event. In their model simulations, they artificially removed all Arctic sea ice at the beginning of June for selected years and examined if the ice would recover from such extreme event.
Their main result is shown in Fig. 3: It took only about two years after each complete sea-ice removal until the ice had recovered to roughly the extent it had before the removal. Hence, sea ice extent is primarily defined by the prevailing climate conditions; the ice-albedo feedback mechanism is, in isolation, too weak to stabilize a very low sea-ice cover. In examining the mechanisms behind this finding, Tietsche et al. found that unusually large amounts of heat indeed accumulate in the ocean during the ice-free summer. However, this heat is efficiently released to the cold atmosphere already during the following autumn and winter. Once that heat release has cooled the ocean to its freezing temperature, sea ice forms again. Because this ice is initially very thin, the efficient release of heat from the ocean continues for some time, causing a rapid growth of the new sea ice. Much of this ice then survives the following summer, and sea-ice conditions can quickly return to those before the artificial perturbation.
Figure 3: Evolution of September sea-ice extent in coupled climate model simulations. The blue curve shows the evolution of the unperturbed sea-ice extent for the A1B scenario, with the gray shading showing the ensemble spread of three model runs. For the red curves, sea ice was artificially removed at the beginning of June in 1980, 2000, 2020, 2040 and 2060 within the climate model simulations. For all these perturbations, sea-ice extent recovered rapidly to the unperturbed extent. A similar result was found for sea-ice volume.
The finding that the long-term evolution of Arctic sea ice is primarily governed by the prevailing climate conditions implies that the loss of Arctic sea ice can still be slowed down and eventually stopped if an efficient reduction of CO2 emissions were to become reality soon. Last week, however, it became obvious once more how unlikely such scenario is: On 30th August, Exxon announced a deal with Rosneft, the Russian state oil company. As part of this deal, Exxon will invest more than US$2 billion to support Rosneft in the exploitation of oil reserves in the Kara Sea, which is part of the Arctic Ocean north of Siberia. One requirement for the success of this deal: a further retreat of Arctic sea ice. Given that climate model simulations indeed all project such further retreat of Arctic sea ice, it seems that at least to some degree, managers of big oil companies have started to make business decisions based on climate-model simulations. That may be good news. Or not.
This article is in part based on a German article that was published at Klimalounge.
References
- S. Tietsche, D. Notz, J.H. Jungclaus, and J. Marotzke, "Recovery mechanisms of Arctic summer sea ice", Geophysical Research Letters, vol. 38, pp. n/a-n/a, 2011. http://dx.doi.org/10.1029/2010GL045698
OK guys. Having something “like” recaptcha to reduce spam is fine. But now it expects me to type (in the little box) the partial derivative of omega with respect to z. No, I don’t mean its description in words — I mean the partial derivative sign, and the Greek letter omega.
This is ludicrous. You do NOT serve your purpose by making it prohibitively difficult to post comments. It would serve you well to think more highly of your readers — because this kind of obstacle indicates otherwise.
Tad, beyond the satellite or other human observations, sedimentary layers show whether the plankton was of kinds that thrive in open water or under ice.
You’ll find a lot in Scholar; here’s one as an example:
http://europa.agu.org/?uri=/journals/jc/jc0803/2007JC004202/2007JC004202.xml&view=article
Paleo–sea ice conditions of the Amundsen Gulf, Canadian Arctic Archipelago: Implications from the foraminiferal record of the last 200 years
NSIDC has a new report out, but they have not yet declared a new record minimum.
But I did. I have been suspecting it for a while now, but with the latest NSIDC report and the upticks on the IJIS sea ice extent graph, I’m quite certain that the melting season has come to an end and the minimum has been reached in most, if not all data sets.
—
Tamino, I always refresh the captcha (one of very small buttons in the mddile) if I can’t read it. I never saw one of those symbols you mention, but then again, I wouldn’t recognize them (except for the omega of course). :-)
Tad, there is declassified US submarine track data showing Arctic ice thickness and extent that extends the long term decline back to the early 1960s. Late 1960s high-res weather satellite imagery showing the arctic basin is currently being reprocessed, which presumably will do the same.
Tamino: But now it expects me to type (in the little box) the partial derivative of omega…[general annoyance]
So it’s probably not a good idea to implement the full plan in which comments will be earned by actually solving a partial derivative. :-)
(ominous recaptcha: “function rsfInfo,” I kid you not!)
Thanks tamino, Hank, Jim, All
You’ve given me lots of direction for further research as I try to put together some of the pieces of the arctic sea ice picture, and what it means, for myself.
“So it’s probably not a good idea to implement the full plan in which comments will be earned by actually solving a partial derivative. :-)”
Well, it might reduce the scientifically illiterate comments. But as it would rule me out, I’d selfishly vote against–presuming a vote was held, and I got one!
On another topic, Neven’s methodology always works for me, and, like Tamino, I have got some Captchas with arcane symbols. But just hit the little ‘arrows’ icon, and hey presto. . .
Speaking of Captcha, it’s giving me “personnel snacess.” Close enough. . .
NSIDC confirm that Bremen data is high resolution, possibly record minimum for past 8000yrs
http://blogs.nature.com/news/2011/09/arctic_sea_ice_drops_to_record.html
At NSIDC
“Other sea ice data are available from other data providers, using different satellite sensors and sea ice algorithms. For example, data from the University of Bremen indicate that sea ice extent from their algorithm fell below the 2007 minimum. They employ an algorithm that uses high resolution information from the JAXA AMSR-E sensor on the NASA Aqua satellite. This resolution allows small ice and open water features to be detected that are not observed by other products. This year the ice cover is more dispersed than 2007 with many of these small open water areas within the ice pack. While the University of Bremen and other data may show slightly different numbers, all of the data agree that Arctic sea ice is continuing its long-term decline.
.
Tad. you’re in luck.
Patrick Lockerby has just done one of his history of science pieces …. on Arctic warming. There’s an earlier one using historic maps but I didn’t find it just now. http://www.science20.com/chatter_box/brief_history_arctic_warming-82545
91Tad Boyd :
“Would it be fair to say that the low ice extents from 2008-2011 are really the same low ice extent of 2007? I’ve seen reports of a new record low hit this year and I’m trying to determine if this is a new event or if this is really just current state of the 2007 ice loss which NASA attributed to ‘unusual winds’ ‘set up by an unusual pattern of atmospheric pressure that began at the beginning of this century’”
No…
The local small glaciers on Cornwallis Island have disappeared gradually over 2007-2011 till now
where they are mostly all gone leaving very little traces of their existence, like ruins from an ancient city
reminding us of a once upon a time colder period.
Big wind systems have always existed over the Arctic ocean, the term “unusual winds” is nonsense. The more proper term would be consistent winds towards the North Atlantic is better, and is equally not so rare, in fact it is so frequent as to give the sea surface currents. Present day satellite pictures suggest a total lack of cohesion of the Arctic ocean ice pack as compared to decades ago. Lack of old multiyear ice basically ensures a loose pack, free to move wherever the tides, sea current, winds and momentum takes them. I suggest it possible to have far less resulting ice at minima given the right winds, timed again with non conflicting tides, along with the usual sea currents and proper momentum (the big gorilla, massive from consistent long lasting flows). What can be said since 2007 is that summer ice has been spared by really “unusual” winds and timely clouds. If the melt bottomed as contrarians suggest then I would see evidence of that elsewhere, on the flanks of Arctic hills especially.
No 103 Hi Neven, I agree with NSIDC waiting for declaring us at minima. Surface air temperatures over the Arctic ocean must be colder than -11 C, it was detected so by daring scuba divers from France near the Pole, noticing ice bottom 2 meters thick disintegrating or melting when surface temps were -11 C. So I surmise -10 to -15 C weather is needed to start the long freezing season. I checked the -11 C in the Arctic here and it works with open water with last few years freeze-ups. -5 C doesn’t cut it.
#111 Thanks Wayne. That helps to paint a clearer picture. The temperature/ice melt/re-freezing correlation gave me another piece of context to understand the discussion with. (i.e. even though the temps are below freezing, it doesn’t mean the ice is maintaining [or now increasing])
#110 adelady. The link you provided hit the nail square on the head for helping me with the ‘what time period does long term decline’ cover concerning arctic sea ice decline and may be at least a sample of what tamino was referring me to in post 100 about the available data from shipborne observations. This line from ‘A Brief History of Arctic Warming’ that you linked to, appears to support that the long term decline in arctic sea ice may have been in progress at least since 1818.
‘From the reopening of access to Baffin Bay in 1818 and the reopening of the sea route from Kolyma to Bering Strait around 1879, there has been a clear and almost continual change in the behavior of Arctic ice. The rate of that change has accelerated and appears to be accelerating more.’
That is the kind of context (as well as what all of the other posters have directed me to) that I am looking for so I at least have a chance of understanding what news reports, NASA reports, (family members at family gatherings), and other reports are referring to.
Thanks again. I haven’t had a chance to check out all of paths you all have provided but I will keep reading.
Whilst a record low might be interesting, isn’t it more important that we are seeing a 2nd ice extent event in 5 years that is around 4 standard deviations below the 1979-2000 average? I suggest we can now be confident in stating that we are seeing the start of a transition from the stable climate Earth has enjoyed since the end of the last glacial period. The question is whether that transition can be halted.
59. Phil at http://community.nytimes.com/comments/dotearth.blogs.nytimes.com/2011/09/12/the-arctic-ice-watch/?sort=oldest&offset=3
says:
Large Variations in Arctic Sea Ice: Polar Ice Much Less Stable Than Previously Thought, Study Finds
http://www.sciencedaily.com/releases/2011/08/110804141706.htm
which says: “During the so-called Holocene Climate Optimum, from approximately 8000 to 5000 years ago, when the temperatures were somewhat warmer than today, there was significantly less sea ice in the Arctic Ocean, probably less than 50% of the summer 2007 coverage, which was absolutely lowest on record.”
What is going on?
114, Edward Greisch – There was a short discussion of this in the August unforced variations thread.
The high temperatures during the Holocene Climate Optimum were largely associated with greater insolation in the Northern Hemisphere due to orbital mechanics. Temperatures in the Arctic were most likely ‘somewhat warmer’ than today due to the enhanced NH insolation but I think the global average wouldn’t have been much warmer than today, if at all, because the Southern Hemisphere would have experienced decreased insolation over the same period.
re: 113
The extent and area records this year are made worse by the fact that volume this year is a std.dev. less than in 2007. There’s far less ice this year than in 2007.
Paul S, not just the Southern Hemisphere, but also regions closer to the equator: the Serbian Barbecue has several components, and while increased obliquity produces more high-latitude insolation, it does so on the polar areas of both hemispheres. Precession together with orbital eccentricity OTOH would produce more summer insolation on one hemisphere but less on the other, producing the effect you describe.
Milankovic cycles
@ 114, 115: the paper of Funder et al. A 10,000-Year Record of Arctic Ocean Sea-Ice Variability—View from the Beach
has been discussed several places.
Moving ahead just a little we come to Rampal et al., also already discussed but did not get enough attention imho.
RE:117
Hey Martin,
So can vegetation sequestration. It depends on whether the active element/organisms are UV or are Human Species destructive activity sensitive.
I maintain we continue to look at cause and effect via a narrow scope when we likely need to apply a richfield scope. When there are multiple contributors it is very difficult to isolate contributing factors without the ability to “tag” sources. Oxygen isotopes associations help, as do others.
I believe as we improve the richness of the datasets the correlations shall improve. We have a bit further to go yet, if my logic/critical thinking process is right… It requires many years and filled gaps between specialties to advance this science. I hope I get to see the conclusion.
Cheers!
Dave Cooke
#117, Thanks Martin, I thought I might have some of the details wrong after I posted so have been doing a bit more research. Could you explain the ‘Serbian Barbecue’ reference? A google search only brought up, well, Serbian barbecues.
“….throughout the entire satellite record…” yer man writes. Entire? As in “that’s the best meal I’ve eaten in my entire, er, week!”m
Proof of further melting since 2007 can be seen in the NW and NE Arctic passages, clear and wide with sea for a plastic bath tub of a boat to travel. In particular in the Canadian Archipelago, more or less wind neutral because of the many channels and Islands which obstruct the winds from massing ice over its waters.
This again is reflected in its small land glaciers, almost all completely gone. We can see the further melt since 07, difficult to dissociate with mechanical forces as with over the Arctic ocean, but clearly seen from space in the Arctic navigation channels..
“No warming since 1998” meet “only 32 years of satellite data? means nothing!”.
Gotta admit that denialists flat-out cherish consistency …
“Gotta admit that denialists flat-out cherish consistency”
Except when they start trying to explain global warming, in which case they have over 160 inconsistencies ;)
At the risk of beating a dead horse, here’s more proof that the albedo of sea-ice isn’t as large as most people seem to think:
http://i454.photobucket.com/albums/qq268/Know_body/GRENFELL2006T1.jpg
This table is taken from: Grenfell, et al., “Energy and mass-balance observations of the land–ice–ocean–atmosphere system near Barrow, Alaska, USA, November 1999–July 2002”, Annals of Glaciology 44 2006. Notice the reduction in albedo reported for melt ponds and dirty sea-ice. Now consider the impact of large zenith angle at high latitudes on the albedo of the ocean.
I’m still convinced the minimum has been reached for IJIS and NSIDC extent. I’ve compared the two biggest melt years on record:
Final score: 2007 vs 2011
#125–OK. But did you note the figure for open water?
“Serbian barbecue”: Milankovic was a Serb. Kind of an obscure allusion, I guess.
Re: #127 Kevin McKinney mentions the low albedo number given in my reference, comment #125. From the referenced report, we find this comment:
“The final albedo values after the ice had melted are taken to be 0.07 following Pegau and Paulson (2001)”
In other words, the referenced report didn’t actually measure the local open water albedo. I suppose that’s where I have my disagreement. I’ve tried to find the data from that report, which was collected during the SHEBA experiment, but I’ve had no success. I think their data was deleted from the SHEBA site at U Washington. Pegau and Paulson’s experimental setup was rather flaky, if you ask me, as they hung their measurement instruments off the rear of a small skiff floating in a lead, which could not be considered a stable platform and they did not provide any information regarding the weather conditions, such as the amount of overcast or the total insolation…
Hey Mal,
If I do not miss my guess Martin (Re:117), was referencing the Serbian Traps as an example of a complication to observations for hemispherical variances. The point is there are localized variations which can occur; however, eventually they will become fully distributed reducing their local impact; however, impacting the globe at a diminished level.
Cheers!
Dave Cooke
No, it’s Siberian traps. I don’t know where Martin came up with Serbian barbecue, but they are supposed to be very good.
Hey Greg,
Of course you are correct, I simply over looked the differences and replicated the obvious error.
Cheers!
#114 Edward Greisch,
An important preceding paper to read w.r.t. Funder et al is Jakobsson et al 1010. “New insights on Arctic Quaternary climate variability from palaeo-records and numerical modelling.” Their figure 2 shows that relative to current levels (~425W/m^2), 65degN July insolation was around 470W/m^2.
So during the Holocene Thermal Maximum, when the Arctic probably had lower levels of sea ice than now, July 65degN insolation was 10% higher than present.
> Siberian traps
http://siberia2009.wordpress.com/ blogs an expedition collecting rocks.
The Siberia Project Main Page
siberia.mit.edu
Hm, nothing I’ve tried to add for several days has showed up. Boring ya?
Might not be boring.
Pielke Sr attacks SkS out of nowhere
SkS answers back
Pielke returns (sort of)
You can follow updates on ‘SkS answers’ post.
My comment should be in the open thread. Sorry.
“There has not been warming significantly, if at all, since 2003, as most everyone on all sides of the climate issue agree….” (Pielke returns)
#138 Hi Hank, go to my blog, http://eh2r.blogspot.com/, see the Pielke stall in action. By the way, I need goole earth latest 2011 pictures, how to get I wonder?
#138 Hank, Go to http://eh2r.blogspot.com/ and see Pielke’s temperature stall in action. Need to know if it is possible to get summer of 2011 Google Earth pictures as well,
further proof awaits.
I notice that th word “wind” is mentioned seven times here but never in relation to the NASA study about the Arctic ice low in 2007 being caused by the wind
http://www.nasa.gov/vision/earth/lookingatearth/quikscat-20071001.html
Is it different now?
[Response: It wasn’t different then. You are confusing proximate causes with ultimate ones. The wind patterns in 2007 were not exceptional, but they had an outsize effect because there was much less ice. In every year, the specifics of the winds and weather affect the final minimum, but the long term trends are not related to wind changes. – gavin]
Paul S, Mal Adapted got it right: it is an obscure reference to the Milankovic mechanism.
Note to self: don’t invent inside jokes when explaining something. The excuse I have is that during the Apollo Project — yes I’m that old — reference was made to barbecue mode for the thermal management of that spacecraft. Appropriate metaphor, no?
““There has not been warming significantly, if at all, since 2003, as most everyone on all sides of the climate issue agree….” (Pielke returns)”
Funny how the recent period during which it hasn’t been warming significantly keeps getting shorter and shorter. I remember, seems like it was as recently as early this year but maybe it was late last year, when it was “since 1995”.
RE: 141
Hey Martin,
Then congratulations to Mal, though now your point leaves me a bit confused. Granted there is wobble or at least a slight variation in the angle of rotational axis of the Earth in relation to the solar equitorial plane; however, I find myself confused as to how that may cause a difference in either solar insolation or hemispherical warming.
Granted if we are talking of a deviation of 30 degrees I could see your point. But how does 5-7 degrees significantly change global temperatures. Are you suggesting that the angle of inclination varies between 30 and 23 or are you suggesting a dfference of between 30 and 16 degrees? If the latter and we are only 1/2 way towards the terminal value how much warmer could it get? If we are talking of the former then are we approaching the return? So how much does the climate currently change across 5-7 degrees of a temperate zone?
The reason for asking is if wobble influences the GAT then I find the ice core work of Dr. ALLEY and others to be in jeporady, if the global average record rises to a peak, falls away, in a pattern of durable cooling with periodic warm extremes roughly every 100ky, rapidly hitting a peak again, kind of reminds me of a top about to fall over. A wobble of this magnitude I do not believe has been demonstrated as the character of the Earth, unless you are suggesting a rotational inversion of the Earths crust. Of course even then I would wonder if the solar insolation would change much…
Cheers!
Dave Cooke
RE:143
Hey All,
Just to update the accuracy of the last post a bit, the inclination of Earths rotational axis in relation to the solar equitorial plane (obliquity) is between roughly 21 and 24 degrees. As to the orbital variation it appears the value to be approximately 3 million miles between a near circular versus eliptic maximum. Hence a L1 larange satellite at 150km towards the Sun with a photometer / pyrometer should provide a clue as the possible additional insolation. The biggest question is the possible tilt of Earths orbital plane as there are some indications of dust which may be shading Earth a bit at times.
This leaves the question of insolation variation being a participant climate change. As of a few years ago I would have suggested that solar activity variation might account for up to 6 watts variation. Based on the latest data I do not know that this is accurate any longer. If you were to add in CO2s estimated 2.5 watts (Hansen 05) and the orbital variation they might have added up to a 0.3-4% variation in the average insolation reaching the Earth. Whether this is enough to account for a 0.7 deg.C increase in GAT and a possible 7deg. C increase in Arctic air temperatures is an interesting thought, I am just not sure that this is a significant contributor.
Though additional ocean heat, (due to reduced cloud cover and CCN aerosols near the equator or Arctic Circle) being carried far into the Arctic ocean region by ocean currents, evaporation, convection, advectation, all affecting the atmospheric currents with changes in Blocking and Cutoff systems, I believe is supportable. Now if we add in the insolation changes noted earlier it would appear that the combination of multiple contributors may be significant.
The hard part is in the attempt to identify all the various contributors and the weight they add to the mix. Though many may be at loggerheads, I believe there is an element to the many points of view, some more then others. The diffcult thing is trying to make a place for everyone at the table when there are limited place settings. Eventually it will be resolved, I hungerly anticipate that day…
Cheers!
Dave Cooke
Eureka of sorts, especially for contrarians, and also for those pursuing the rate of planetary warming.
I’ve added an old picture of small high Arctic glaciers on Cornwallis Island on my blog, didn’t realize how many of them have vanished over the years, really noticed their disappearance in the last few summer seasons though.
Their melt was slow but steady accelerating within the last few years. Like the last small ice sheets have really no chance.
The key is to take earthsat platforms and count their yearly extinction rate. It would be very practical and extremely convincing for especially skeptical scientists of all stripes! Have a look before you claim a lull in the warming. Evidence by white ice spots, here http://eh2r.blogspot.com/ is proof of heating of the Arctic as predicted, the albedo effect over permafrost lands.
If someone has access to old high res polar orbiting sat pictures similar in resolution to Google Earth, You are it! Go and display, and put to bed the latest skeptics myth in no time.
Re 143 & 4
Hi Dave,
Obliquity does not change solar insolation but it it does change the Earth’s albedo because it moves the Arctic Circle, and influences climate that way. The ellipticity does alter the solar radiation reaching the Earth, and precession determines whether the NH or the SH hemispheres are warmer in summer. When all three cycles coincide to make the Northern Hemishere warm then an interglacial is the result.
HTH,
Cheers, Alastair.
Hey Alistair,
Long time no see/read… The Arctic Circle is an artifical line. A northern pole and a region within 30 degrees of that pole will remain. Hence, globally there is no change in surface insolation.
Cheers!
Dave
Hey Alistair,
BTW, concur wrt progression, currently favoring the SH, and the eliptic. Scratch est. wrt eliptic variation of 3% of the orbit should point to roughly a 7 deg. K variation in ToA insolation potential. If the current ToA value is modified by ghg and wv, the added potential should be significant. Based on the pattern we should be near the warmest period? Suggesting minimum elipticality? The signatures in the land are pointing to this condition.
I guess I am more interested in the change caused by the eliptical variation and the effect on the TSI in watts at the ToA, as opposed to the absolute temperature. Does the potental 3% elipictical mean that the TSI varies between 1367 and 1325w/m^2? If so one would think that the Earth would have to be a ice planet and very likely to fall into “snowball” territory. It would appear on the surface it is only the protection provided by ghg and wv that we do not freeze.
Your thoughts…
Cheers!
Dave
Hi Dave,
The Arctic circle is not artificial. It is the minimum latitude at which you can experience the midnight sun, for want of a better definition. As the obliquity increases the Arctic circle moves south, increasing the size of the Arctic ice cap. Actually it is more complicated than that, but I hope you get the general idea.
Cheers, Alastair.