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General Global Warming / Climate Change Discussion
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| Watsisname | Date: Thursday, 24.10.2013, 23:49 | Message # 61 |
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| Quote Watsisname (  ) ...we are highly confident that the state of the arctic now is unprecedented in the last thousand+ years.
Thanks to recent research, that statement can now be updated to say that recent arctic warming is unprecedented in the last 44,000 years.
Scientific American article
To address a few outstanding points:
Quote However, if the IPCC figure is so smoothed that the fluctuations in Frolov mostly disappear, they can't at the same time show a rapid increase around 2000 reflecting the recent warming, because it remains to be seen whether this is a real trend or simply a fluctuation as in the 20's and 30's.
Your logic sounds persuasive, but it does not follow. The entire temperature regime has been shifted upwards; including the variability. (You'll recall I was pointing out how the figures show that the 21st century temperature is projected to surpass 20th century temperature even including the variability). The fact that the last few decades of warming show up despite the smoothing tells you it is not simply variability that is causing it.
We also know beyond investigation of the raw temperature data that the current warming can't be explained by natural variability; we understand fairly well the relevant atmospheric dynamics, and you can also look at the reconstructions via proxy, as in the study above.
With respect to the (excellent) gif showing the ice flowing out of the arctic:
Yep, I've seen the study associated with that as well; gyre's are fascinating things.  What this tells you is that a given slab of sea ice doesn't remain in the arctic forever, but instead there is (or would be, if global warming was not at play) some equilibrium between the rate of new ice formation that survives each year's thaw and the rate of ice loss by mechanical outflow. So there's also some maximum age for the arctic ice (I don't know what it is and it's probably not easy to determine; maybe a few decades). But you can also clearly see that the total amount of multi-year ice is decreasing, both in response to warming temperatures and changes in the ice transport out of the arctic, the latter of which is also affected by the warming.
For more information I can refer you here.
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| midtskogen | Date: Friday, 25.10.2013, 08:54 | Message # 62 |
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| Quote Watsisname ( ) Thanks to recent research, that statement can now be updated to say that recent arctic warming is unprecedented in the last 44,000 years.
That would be a gross extrapolation. First, the findings don't say that the warming is unprecedented in that period. It says that the summertime temperature level is unprecedented. Of course, the transition from an ice age to an interglacial period sees more warming than we've recently seen. That is, the rapid change such as seen during the 90's and 00's, and during the 20's if we choose not to smooth it out, is not unprecedented.
As for whether the Arctic warmth, as an absolute figure, is unprecedented, you can't conclude that from some receding glaciers on Baffin island. The Arctic is big and the histories differ. For Scandinavia we have different clues. Receding snow and glaciers in Jotunheimen now reveal old artifacts (clothes, arrows, etc), between 1500 to 5500 years old, obviously meaning that these objects haven't or hardly haven't been exposed for all these years. Or put another way, it was likely warmer at that time. We also know that the vegetation was different if you go back a few thousand years. The treeline was up to 400 metres higher than today, and coastal/lowland vegetation was much more varied than today. I don't think any of this is disputed. We must not forget that the land has risen, but temperature must account for the most. It should not be surprising since the summer sun was warmer at that time. It's also generally agreed on that nearly all of Norway's glaciers disappeared after the last ice age. The greatest warmth was around 6000 to 8000 years ago. At that time the northern coast of Greenland was ice free in summer for extended periods. The whole Arctic ocean may have been more or less ice free in summer.
Even Svalbard has been much less glaciated since the last ice age, or even relatively recently. Plants found beneath today's glaciers (in melting tunnels forming in summer) suggest that it was warmer, or at least much less ice, in the medieval period.
I think you have a lot of evidence against you if you think that the Arctic in general couldn't have been warmer than today (in the summer, for which we have the best clues) for extended periods during the Holocene.
Edit: English article rather than Norwegian on the northern Greenland topic.
Edit 2: The Wikipedia article on the Holocene optimum mentions on a study that of 140 sites examined in the western Arctic found 120 clearly warmer than present. Some ancient moss on Baffin Island isn't going to send most papers on the Holocene optimum to the landfill. The study is interesting. Not because it shows that the Holocene optimum had colder summers than today (it hadn't, strongly suggested by evidence and theorised solar radiation), but because it shows moss older than the current interglacial having been preserved (one way or another) through the Holocene optimum. It should be noted that 106 of 110 locations probed show that they were ice free 5000 years ago. The remaining four are the exceptions. It's a sad sign for science that this instead of being seen as "wow, could patches of ice have survived through the entire Holocene optimum on Baffin island?" gets presented as "the WHOLE Arctic has never been warmer in 700 5000 44,000 125,000 years !!! We have PROOF!!!!!111".
NIL DIFFICILE VOLENTI
Edited by midtskogen - Friday, 25.10.2013, 19:30 |
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| Watsisname | Date: Saturday, 26.10.2013, 02:51 | Message # 63 |
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| I appreciate your trying to correct what you perceive as an error on my part, but please note that I am very well aware of the Holocene thermal maximum (HTM here on) and the literature surrounding it. I said the recent arctic warming is unprecedented. I did not say the arctic annual temperatures are unprecedented, which at a first glance of the literature one will find that during the HTM temperatures were higher than the 20th century average by a few degrees C. Instead what is being regarded as unprecedented is the character of the present warming.
The study finds that the Canadian summertime temperature is unmatched in at least the last 44,000 years. Think about that for a moment. It means that even during the peak of the HTM the summer temperatures don’t compare with those of today, and it even extends this record further, by about a factor of 4. It also says that ~2.7°C of cooling over the last 5000 years has been overcome by the current warming of only the last century.
Thus the thing that you label as rapid change is the very thing that is so remarkable. The current spell of anthropic global warming has reversed millennia of natural climate change and has brought the arctic to conditions comparable to or exceeding those of the HTM.
Now let’s look at some of the literature in more detail. You produced a study by Humlum that regards Svalbard glacial growth in the late Holocene, which in turn suggests, quote, “it was warmer, or at least much less ice, in the medieval period.” You can pretty safely dismiss the former proposition. Studies of Svalbard lake sediments find that the glacial growth was likely due to increased winter precipitation, not colder temperatures. This circumstance is not very related to the HTM, which came much earlier.
Looking at the HTM itself, let’s examine a few of the most recent articles:
Kaufman et. al (2004) is a little dated now, but is regarded as a landmark study and earning over 300 citations. Across 140 sites in the western arctic they found clear evidence of warmer than present temperatures, with quantitative estimates averaging ~1.6°C warmer than the 20th century average. (Note that since the temperatures are rising throughout the 20th century and especially recently, the arctic annual temperature is even closer presently and will completely exceed the HTM rapidly under most emissions scenarios. Under high emissions scenarios an increase of 5 to 10 degrees Celsius is likely.) The peak forcing was about ten to twelve thousand years ago, but the climate response had a significant spatial and temporal asymmetry due to the cooling effect of the Laurentide Ice Sheet. (This explains some of the at-first-glance weird results from more localized HTM studies). It should also be noted that current warming is not balanced by such an effect.
Now let’s look at changes in sea ice. You provided an article suggesting the arctic may have been mostly ice-free ~6000 years ago, to explain the formation of apparently wave-affected coastlines. That appears extremely unlikely. The wave features do suggest open water for that area, but unless similar features dating to that same time period can be found across wide expanses of the arctic, then it does not indicate mostly-ice-free conditions.
But we do have alternative evidence to weigh in on this matter: Vernal et. al (2013) did some incredible work with reconstructing Holocene sea ice coverage through the use of dinocysts, and produce time-series for multiple locations going back about 10,000 years. They find that some areas appear to be very sensitive to climate changes and exhibit large variations and a minimum ice extent corresponding to the HTM (though remember this peak happens at different times for different regions). Other regions show very little variation, such as the Canadian arctic which maintained high ice density throughout the entire interval. So a mostly ice-free arctic during the Holocene is not supported by evidence at this time.
The above study is also not the first to examine this; they have an extensive list of references to similar papers discussing Holocene ice extent and the relevant atmospheric and oceanic changes. A common conclusion is that the current conditions are indeed unprecedented throughout the entire Holocene.
Lastly I would highly recommend the study by Renssen (2012), which explores the global characterization of the HTM through extensive models. The findings are quite similar to those gleaned from physical data.
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| midtskogen | Date: Saturday, 26.10.2013, 07:22 | Message # 64 |
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| Quote Watsisname ( ) The study finds that the Canadian summertime temperature is unmatched in at least the last 44,000 years. Think about that for a moment. It means that even during the peak of the HTM the summer temperatures don’t compare with those of today, and it even extends this record further, by about a factor of 4. It also says that ~2.7°C of cooling over the last 5000 years has been overcome by the current warming of only the last century.
Actually, what it confirms is that Baffin island was more or less ice free for extended periods of time in the early Holocene and it suggests that a few areas of ice survived (since it's paywalled I don't know if it discusses alternatives, such as the moss having becoming exposed (freeze dried or whatever) after the last ice age but survived the elements until the later cooling). It doesn't follow that the current warming is unprecedented for a few reasons. Let's forget that were comparing apples and oranges here (warmth and warming). Then the most obvious problem with your reasoning is that you can have as rapid warming as anyone wishes, as long as it didn't last. It takes time to melt glaciers. Many decades or a few centuries, so there are plenty opportunities for much more rapid warming followed by cooling if it didn't had time to melt of everything. In fact, the more rapid warming and subsequent cooling, the more likely it is that it didn't melt off anything significant. So such exposed vegetation can't prove "unprecedented warming". Let's say that the Arctic will soon cool again (as Humlum would argue). Then, in the distant future it would warm again, but this time actually slower and Holocene optimum vegetation began to reappear (either exposed today or not yet exposed). A future version of you would then scream "unprecedented warming!", wouldn't he?
Quote Watsisname ( ) Now let’s look at some of the literature in more detail. You produced a study by Humlum that regards Svalbard glacial growth in the late Holocene, which in turn suggests, quote, “it was warmer, or at least much less ice, in the medieval period.” You can pretty safely dismiss the former proposition. Studies of Svalbard lake sediments find that the glacial growth was likely due to increased winter precipitation, not colder temperatures. This circumstance is not very related to the HTM, which came much earlier.
Glaciation advance or retreat depends on not only temperature changes, but also precipitation and how the temperature and precipitation changes relates to the seasons, so this isn't as simple as sometimes portrayed. But, you know, that's not an argument that you can pick at your convenience. Because of this we can possibly have had warming periods more rapid than the current one during the later Holocene, but the glaciers on Baffin island or whereever didn't retreat much because of increased precipitation.
Having cleared up that you actually spoke of unprecedented warming, not warmth, I'm not sure we need to dig more into the Holocene optimum? But:
Quote Watsisname ( ) That appears extremely unlikely. The wave features do suggest open water for that area, but unless similar features dating to that same time period can be found across wide expanses of the arctic, then it does not indicate mostly-ice-free conditions.
Do you have evidence that the currents were different during all that time? Currently, the ice gets pushed against the high latitude land of the western Arctic until it gets pushed out of through the Fram straight. Even if the currents were different, wouldn't that rather trap the ice more than today?
"Unprecedented" is always a claim hard to prove, and I think scientists need to think a bit less of themselves as being in the centre of action. Interestingly, Baffin island was the smoking gun for the coming ice age according to that Gifford Miller a few decades ago. The following video is worth a watch. The science has changed, but not how things are communicated (such as the use of the word "unprecedented"). Miller appears at about 5:30 into the video.
NIL DIFFICILE VOLENTI
Edited by midtskogen - Saturday, 26.10.2013, 07:24 |
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| Watsisname | Date: Saturday, 26.10.2013, 08:24 | Message # 65 |
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| Quote midtskogen ( ) Having cleared up that you actually spoke of unprecedented warming, not warmth, I'm not sure we need to dig more into the Holocene optimum? But:
Well you could have very easily saved both of us a few thousand words by reading what I wrote exactly as I wrote it. But if you don't have anything to add about the research I have been providing, then sure, we can end the discussion of the HTM here.
Added:
Quote Do you have evidence that the currents were different during all that time? Currently, the ice gets pushed against the high latitude land of the western Arctic until it gets pushed out of through the Fram straight. Even if the currents were different, wouldn't that rather trap the ice more than today?
Relevance or importance? What you quoted was me describing that evidence of wave-affected coastline is not evidence of a mostly ice-free arctic unless you have widely spatially separated instances of these formations all dating to the same period. The best evidence we have right now indicates that many regions had comparable sea ice extents as they do today, and even those that were strongly affected by the HTM were not affected simultaneously. Thus I do not find the conclusion that the arctic was mostly ice-free ~6,000 years ago to be very credible, regardless of what the knowledge or lack thereof of what the currents were doing.
Quote Let's say that the Arctic will soon cool again (as Humlum would argue). Then, in the distant future it would warm again, but this time actually slower and Holocene optimum vegetation began to reappear (either exposed today or not yet exposed). A future version of you would then scream "unprecedented warming!", wouldn't he?
Do you believe your scenario to be likely to be realized? Since I'm unsure of exactly what you mean, may I ask if you are proposing:
(a) natural variability manages to temporarily overcome the continued enhanced forcing due to human activity, causing a reduction of arctic temperature for a couple years or decades.
(b) same as (a), but the effect lasts for more than the standard climatological period of 30 years.
© the current warming of the arctic is itself due to natural variability which may soon switch phase, rather than being primarily human-driven.
If (a), then this scenario is completely possible and does not change the fact that the warming is unprecedented.
If (b), then the scenario is at odds with the best models and understanding that we have today. Recall that the models are adamant that under moderate or high emissions scenarios, the arctic through the 21st century will warm to levels that bring it completely above those of the previous century, even with the variability considered, and this is consistent with the already observed changes. I know of no kind of natural variability that we could expect to undo the warming for a long period, but feel free to propose something if you like.
If ©, then the scenario is contrary to well established science, and I would be unable to take it seriously unless it came with a very powerful refutation of that science.
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| midtskogen | Date: Saturday, 26.10.2013, 17:56 | Message # 66 |
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| Quote Watsisname ( ) Well you could have very easily saved both of us a few thousand words by reading what I wrote exactly as I wrote it. But if you don't have anything to add about the research I have been providing, then sure, we can end the discussion of the HTM here.
I have comments, but seeing that they weren't extremely relevant to the discussion whether Baffin island moss is proof of unprecedented warming, I was just trying to save us a few thousand more words.
I picked the vegetation under the Longyearbreen glacier since it has similarities with the Baffin island research, and because many know about these finds (tourists are guided through these tunnels every winter and the glacier is one of the main routes out of Longyearbyen). It's one piece of the picture. So are the sediments of Kongressvatnet. Neither doesn't alone say much of the climate of Svalbard, even less of the entire Arctic. Longyearbreen is in the desert part of Svalbard (~200 mm/y) and may not be very representative for the more glaciated parts of Svalbard. And Kongressvatnet is much more exposed to the ocean, meaning that it has nearly no summertime variation. Isfjord radio on the same peninsula has these monthly means for July:
The temperature rarely departs by more than 1C from the long term mean. A flatline temperature proxy is really what we should expect anyway.
Quote Watsisname ( ) Relevance or importance?
Ice gets pushed along the northern coast and drains out where that coast turns southward. If you have a container and there's nothing next to its drain, the container must be pretty empty, right? If you want to know whether the Arctic ocean is pretty much ice free, that coast is the place to look.
We don't know for sure that the Arctic ocean was ice free, but it seems probably to me that for a period of at least a couple of thousand years it was regularly ice free (navigable) during late summer, though I also think there were rapid changes even in that period, as has been in the Arctic in recent centuries, too brief to show up in the indirect evidence. It fits the general evidence. A warm Scandinavia. No or very few glaciers in Svalbard apart from Nordaustlandet (which was the accepted knowledge before the more recent warming hysteria, and there might have been attempts to change that view). Etc.
Quote Watsisname ( ) Do you believe your scenario to be likely to be realized? Since I'm unsure of exactly what you mean, may I ask if you are proposing:
It doesn't matter, since that was just an example of conditions that make your conclusion (proof of unprecedented warming) false. My point is, let's say that the temperature surged 10 degrees around 500BC for 30 years then cooled again, we couldn't tell today from some random moss, since the warming wouldn't melt off every glacier and moss that got exposed would to some extent be covered again only to rediscovered in modern times. It doesn't matter if my scenario is unlikely, the same way that you can't argue that the temperature didn't spike like that around 500BC since there is no evidence for it. Then you would be assuming what you want to prove.
Need to go afk. I might make some additions later tonight.
EDIT:
To address your question on whether the Arctic is likely to cool again: First, my personal interpretation of the temperature data so far is that there seems to be a significant natural variability, quite possibly a cycle, at least 60 years in length perhaps more likely 70 years. The two last warming periods are well documented. Earlier accounts suggest it's a recurring event, but we have no evidence that it's a permanent cycle, and I've seen no convincing explanation for it. On top of this cycle there seems to be a slower warming during the 20th century when we recognise the cycle. And the amplitude of the natural cycle clearly surpass the 20th century warming, probably around 2x, possibly 3x. That warming nicely mirrors the general global warming, slightly amplified as expected. I find this pretty obvious looking at the available data, and it surprises me if any die hard climate model believers doubt it as it nicely explains the recent rapid warming that models failed to predict.
The likely future?: If it really is a repeating cycle, we should expect temperatures to drop again. I don't think we have sufficient evidence to say that the cycle will repeat, but it seems slightly more likely that it will than it wont. Even if we read the historical accounts with the right glasses, all we can make out is 4-5 cycles and that's not much. If global temperatures continue to rise, the next bottom of the cycle will not be as low as in the 60's. And we could see a renewed race for an ice free north pole in the 2060's.
NIL DIFFICILE VOLENTI
Edited by midtskogen - Saturday, 26.10.2013, 19:13 |
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| Watsisname | Date: Saturday, 26.10.2013, 19:10 | Message # 67 |
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| Quote midtskogen ( ) Ice gets pushed along the northern coast and drains out where that coast turns southward. If you have a container and there's nothing next to its drain, the container must be pretty empty, right? If you want to know whether the Arctic ocean is pretty much ice free, that coast is the place to look.
If your reasoning is correct, that the lack of ice along that coast necessarily leads to a draining of the entire arctic (which does not follow at all; you still have an equilibrium solution between the rate of new ice formation and ice loss by mechanical outflow, which is not necessarily zero), then you should expect to see these wave features throughout the entire arctic and dating back to the same time. That would be one of the best ways to observationally check the validity of this argument, and it does not require knowledge of ocean currents at the time which may forever be unknowable.
But another way to check it is to look at the sea ice reconstructions for multiple arctic regions, which is exactly what was done by Vernal et. al, which I have already showed you. The data show that the arctic was not mostly ice free at any particular moment in time, indeed many regions maintained high ice density throughout and the timing of thinnest ice shows a strong asymmetry from one hemisphere to the other (particularly by the presence of the LIS, as also described in several of the papers). Thus, by empirical data, an ice free arctic 6000 years ago appears extremely unlikely.
Quote It doesn't matter, since that was just an example of conditions that make your conclusion (proof of unprecedented warming) false.
Quote My point is, let's say that the temperature surged 10 degrees around 500BC for 30 years then cooled again, we couldn't tell today from some random moss, since the warming wouldn't melt off every glacier and moss that got exposed would to some extent be covered again only to rediscovered in modern times. It doesn't matter if my scenario is unlikely, the same way that you can't argue that the temperature didn't spike like that around 500BC since there is no evidence for it. Then you would be assuming what you want to prove.
A 30 year temperature spike of 10 degrees C over the entire region defies any natural explanation and it would most definitely leave behind evidence. At the very least, it would leave evidence in tree rings, ice cores, and varves. But if such an event really did happen, then it would be unprecedented if it was the first and only time warming of that nature had happened. Afterall, that's what unprecedented means. Since we have no evidence of such an event unfolding, nor have any plausible reason to expect it to have despite a lack of evidence, then your hypothetical scenario holds no weight over the currently observed reality, which is that the arctic, and indeed the whole planet, is undergoing unprecedented warming.
I'm absolutely astounded by the way that you shared a video of Leonard Nimoy talking about the next ice age and completely fail to understand the significance of it. If it were not for human-caused global warming, we would indeed be going into a new ice age, because that is the natural progression of the climate system due to the orbital and obliquity forcings. We've discussed this in some detail many times on this forum, including the snowball earth thread. This progression into the next iceage would take place gradually and over a period of thousands of years, just as can be seen by looking at the Vostok ice core records and extending the pattern forward in time.
There are a lot of people out there who hear 'we're heading toward a new ice age!!!' and fail to comprehend the timescales involved. It should be an object lesson in learning to take what you hear from popular media and then compare with what is actually being said by the specialists in the field.
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| midtskogen | Date: Saturday, 26.10.2013, 20:03 | Message # 68 |
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| Quote Watsisname ( ) At the very least, it would leave evidence in tree rings, ice cores, and varves.
Then you missed the fallacy even though I stated it explicitly. If this (intentionally) exaggerated event did happen, it could be missed by the moss, right? Then the moss alone can't rule it out. You need something else (lack of evidence in tree rings, ice cores etc). The moss is simply another piece of evidence along with other hints (which may all not point in the same direction), nothing more.
Quote Watsisname ( ) I'm absolutely astounded by the way that you shared a video of Leonard Nimoy talking about the next ice age and completely fail to understand the significance of it. If it were not for global warming, we would indeed be going into a new ice age, because that is the natural progression of the climate system due to the orbital and obliquity forcings.
I know about that (except that the ice age may be much further away to have been stalled by global warming), of course. But did you fail to see how recent weather and apparent climate changes were used to back it up? How again Baffin island was ground zero ("interest bias"?)? How the message was communicated? The point was not to say "science can't decide, so why listen" if that is what you think. I think the world needs to be reminded once in a while that weather and climate (observable in a person's lifetime) are ever changing, and in the Arctic very so (how many times will we let it surprise us?). While recent events might fit the story that someone wants to sell, it's not necessarily a connection. That applies no matter what kind of climate you're predicting.
If I live into the latter part of this century, I want to know who made the most accurate predictions, and learn whether their predictions where correct for the right reasons.
NIL DIFFICILE VOLENTI
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| Watsisname | Date: Sunday, 27.10.2013, 01:34 | Message # 69 |
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| Quote Then you missed the fallacy even though I stated it explicitly. If this (intentionally) exaggerated event did happen, it could be missed by the moss, right? Then the moss alone can't rule it out. You need something else (lack of evidence in tree rings, ice cores etc). The moss is simply another piece of evidence along with other hints (which may all not point in the same direction), nothing more.
Yes, you're basically repeating what I just explained to you. So, um, please tell me again what fallacy I am apparently missing? Why did you originally posit a lack of evidence to your hypothetical scenario and now you acknowledge that it should leave powerful evidence? In fact why are you espousing an intentionally exaggerated and hypothetical scenario as a means of refuting what we know from real world observations in the first place? You're basically trying to say that we can't call the current warming period unprecedented because maybe there were similar periods in the past, yet we don't have evidence for it, yet there should be evidence.
I'm sorry midtskogen, but you're simply not making a strong or coherent argument here. You're arguing against data and yet you can't deal with it from a standpoint of data, rather you make contrived scenarios and appeals to misunderstood science such as the presentation of the next ice age by people who are not experts in the field...
May I kindly suggest that you pause to reflect for a moment on what you desire to accomplish with this conversation and how to best formulate your posts to achieve that goal? Because this current track is not getting either of us any closer to enlightenment.
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| midtskogen | Date: Sunday, 27.10.2013, 06:14 | Message # 70 |
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| Simply put, your argument is a modus ponens construction: Q → P, Q ⊢ P where Q="ancient Baffin island moss gets exposed" and P="modern Arctic warming is unprecedented". That is a valid argument, but P is only as valid as Q → P or Q. The validity of Q is not in question here, only Q → P. I explained under which circumstances that does not hold. Your response basically was, yes, but we know P from other evidence therefore Q → P must be true. Then you've already decided on the conclusion, so what interest could Q then have?
Can I ask you to reflect for a moment that you took four small locations on Baffin island to represent the whole Arctic, and disregarded the 106 other locations (still only on Baffin island) showing the contrary (a few thousand years as in your original statement, not 44,000+)? Is that how you normally would do science?
And it's still not entirely clear to me if you speak of unprecedented warming or unprecedented warmth (you originally spoke of the "state"), or both. Warming implies that you also claim that the change from ice age to interglacial was a less dramatic warming in the Arctic than what we've already experienced recently. I find that hard to take seriously.
EDIT: Returning to the issue of N coast of Greenland as an indicator for near ice free conditions in the Arctic Ocean, I rarely search abstracts for the single purpose to find quotable sentences because of the bias that involves, but here goes:
Predictions of the rapidly decreasing sea ice in the Arctic Ocean generally point to this area [Northern Greenland coastline] as the last to become ice free in summer.
I also stumbled across these on the way:
Ice free NW passage not unprecedented
Driftwood evidence
More driftwood
It's not perfectly clear either what the "state of the Arctic" includes, something like September ice extent is surely something very visual. Here's the latest 30 year normal (1981-2010 median) I could find (purple line):
If I understand you right, you would claim that we can with high confidence say that there hasn't been a single 30 year period during the Holocene that has had less September ice [than the purple line]. If we ignore the N Greenland evidence, even the unlikely becomes likely given enough time, and the Holocene is a long time. In any case you've set the bar high in what you attempt to demonstrate. Even if you have some supporting evidence, it's hard to prove that you haven't missed a single 30 year period.
NIL DIFFICILE VOLENTI
Edited by midtskogen - Sunday, 27.10.2013, 09:23 |
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| Watsisname | Date: Sunday, 27.10.2013, 12:27 | Message # 71 |
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| It is a good thing I never made such an argument then; you only incorrectly perceived it that way. And if you examine post #63, you will find that I explained the significance of Miller et. al, why I was posting that particular study, and also put it in context with additional literature about the Holocene climate history of the entire Arctic. If you require further elucidation:
Quote midtskogen ( ) And it's still not entirely clear to me if you speak of unprecedented warming or unprecedented warmth (you originally spoke of the "state"), or both.
Oh, well let's see. I have never used the word 'warmth' anywhere in this thread, nor have I ever suggested that Arctic annual temperatures now are warmer than anytime in the Holocene, because they aren't, and I went into quite some detail on this matter. So I am sorry but I do not understand why you are confused; I think I have been pretty clear throughout.
Anyway, what is most unprecedented with this current warming is the rapidity. Think dT/dt. We've reversed millenia of natural climate changes and we've done so on much shorter timescales. The 'state' of the arctic, or the 'character of warming' are indeed vague terms, but I believe you need only try to read them in context to understand them.
Quote
Warming implies that you also claim that the change from ice age to interglacial was a less dramatic warming in the Arctic than what we've already experienced recently. I find that hard to take seriously.
Come now, haven't we discussed climate change enough already for you to realize that I understand the comparison from previous climate changes to this one fairly well? The change from ice age to interglacial was absolutely more dramatic in terms of total change in temperature. Indeed the global temperature change from a typical Milankovitch-cycle ice age to an interglacial outmatches the change we're seeing now with AGW by about a factor of 5 (N.B. we can, however, exceed that in the next century or so given high emissions scenarios).
Your most recent sources are again fairly easily explained by the asymmetry of the HTM and described in the literature (sorry so much of it is paywalled, but there's not much I can do about that.) The basic idea from the literature is that many areas of the Arctic did indeed have low ice, but not everywhere at once, nor everywhere integrated over the entire HTM event. The greatest reduction in ice cover seems to occur about 5 to 7 thousand years ago and this is consistent with many of the observations you've linked. It's absolutely possible the whole Arctic became mostly ice free during that time but I am not convinced that that is the best explanation at this time. This is like high-obliquity vs. snowball earth as the explanation for the cryogenian conditions; the former scenario is possible but not favored. Feel free to search for more compelling evidence though, it's great stuff. Again, time series of sea ice differing from Vernal et. al, or geological formations indicative of extensive ice-free conditions all over the Arctic and all dating to the same time would be very powerful!
Let's actually take a moment to suppose the Arctic was mostly ice free at one time. Would you agree that the character of the current warming, a return to similar conditions on a timescale of centuries, vastly different then that of the HTM, which took millenia? That's what we call unprecedented here, because nowhere in the geologic record do we know of such a great change happening so rapidly.
Quote If I understand you right, you would claim that we can with high confidence say that there hasn't been a single 30 year period during the Holocene that has had less September ice [than the purple line].
No, I claim that if the temperature over the entire arctic region were 10°C higher than today for a 30 year period some time around 500BC (your scenario), then we would see obvious evidence for it in a variety of data (ice cores, tree rings and varves being excellent objects to study for this purpose).
Edit: Sorry, I misunderstood the basis of your question, I think. A level of sea ice extent equal or lesser than that is certainly possible given what we know about the intensity and duration of the HTM, but the timing asymmetry doesn't make it easy to figure out, nor does the spatial/temporal resolution of current sea ice reconstructions. So I don't know and do not claim either way.
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| midtskogen | Date: Sunday, 27.10.2013, 15:26 | Message # 72 |
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Star Engineer
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Norway
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| Quote Watsisname ( ) But the conclusion P is determined not merely by Q, but by {Q}, with Q adding to this set.
Ok. That's basically what I wrote in 68. But here's where we differ: I would agree to the conclusion P if finds in {Q} had shown the same thing (pre-Holocene vegetation), but it's to my knowledge only seen in Q, and actually in just 3.6% of Q.
Quote Watsisname ( ) Oh, well let's see. I have never used the word 'warmth' anywhere in this thread, nor have I ever suggested that Arctic annual temperatures now are warmer than anytime in the Holocene, because they aren't, and I went into quite some detail on this matter. So I am sorry but I do not understand why you are confused; I think I have been pretty clear throughout.
"State" is what you wrote. I would usually associate a "state" with a level rather than a transition, though in the proper context we could of course speak of a change, second derivative and nth derivative as a state. So I asked. The evidence you used speaks more about a level, though, "warmth".
Quote Watsisname ( ) he change from ice age to interglacial was absolutely more dramatic in terms of total change in temperature. Indeed the global temperature change from a typical Milankovitch-cycle ice age to an interglacial outmatches the change we're seeing now with AGW by about a factor of 5
Precisely. So your position is that nowhere in that transition the dT/dt was higher (using 30 year means) than now?
Well, how rapid were the changes before the Holocene? I suppose it's a topic still being discussed. I checked some Greenland ice core data (downloaded here). I then computed the running 30 year mean:
The temperature proxy goes up and down a lot. For instance, around 14700 there is a 7.8C warming from -43.8 to -36.0 in a century reaching nearly 11C/century rate at its peak increase. These are all numbers using the 30 year mean. In the 117 century BP we can find a change in the 30 year mean of 9C/century. The sampling resolution poses an accuracy problem here, but it gives a rough idea. We have not measured anything like this in the past century. Does it explain my disbelief that you actually meant warming?
Quote Watsisname ( ) Let's actually take a moment to suppose the Arctic was mostly ice free at one time. Would you agree that the character of the current warming, a return to similar conditions on a timescale of centuries, vastly different then that of the HTM, which took millenia?
The sea didn't open up until some time into the Holocene, long after the rapid changes at the end of the ice age. So yes, probably, if you include a projected scenario, an ice free Arctic Ocean, something not yet observed, and imit what you compare against as you say (not including ice age changes).
EDIT: I just recalled that I recently saw an attempt to explain the cycle. I haven't read it, though.
EDIT2: Since I don't have the Prolov data to make 30 year means, I made such a plot from Svalbard airport (78N15E) available at eklima.met.no:
As in Prolov, the cycle clearly appears here with an amiplitude roughly 2x the underlying century trend. So far the previous warming (around the 20's) was more dramatic than the current warming, but we don't know yet how long the current warming will last, so it's too early to call whether it will be unprecedented (in a century timescale) or not. Since I worked on this, the current warming has overtaken the previous peak, but that was expected. I have some issues with this homogenised series, though. Measurements began in 1975 and most of it is made up from other places in western Spitsbergen ranging from a few km away to several tens of km away, or as far away as Greenland. Nearly half of the reconstruction uses data from Longyearbyen about 4 km away, so those parts are probably not very far off, but it's situated in a different microclimate. The airport is exposed to Isfjorden which is frequently open even in winter, while Longyearbyen is exposed to the frequent eastern wintertime winds traveling through the valleys from the interior. The overlap with that series is only two years, which doesn't give a very clear picture of how temperatures at the two sites correlate. I tried to replicate the homogenisation some years ago (and older version of it, though) and found some problems. I also discussed it briefly with Humlum, who interestingly had a 10 year private record taken only 200m away from the site shut down in 1977 offering better data for finding the correlations since the overlap was now 12 years, but he had not worked on it. He sent me his dataset, but unfortunately, I never finished this project. All I can say is that the uncertainty of the reconstruction is not insignificant. The homogenisation is likely the best we can hope for, though, but other reconstructions with a slightly weaker long term trend will work equally well. A final note is that even if this cycle is continuously repeating, we know little whether the amplitude remains roughly the same, which complicates finding the exact long term trend.
NIL DIFFICILE VOLENTI
Edited by midtskogen - Sunday, 27.10.2013, 21:00 |
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| Watsisname | Date: Monday, 28.10.2013, 02:22 | Message # 73 |
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Galaxy Architect
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| Well of course, many regions melted out sometime during the HTM so you do not expect to see pre-Holocene vegetation everywhere. The fact that you find it at all is impressive because it means regions are melting now which had remained frozen through the entire period. It is not that these regions were going to melt now anyway, either; the study finds that several thousand years of cooling since the HTM have been undone by this current warming.
Quote Precisely. So your position is that nowhere in that transition the dT/dt was higher (using 30 year means) than now?
No. You most certainly can find higher dT/dt, especially if you use such fine temporal resolution or a data from a single location. Only someone who doesn't know the first thing about climate science would be mystified by this. Similarly and as you pointed out, the Svalbard airport data shows a trend from 1910 to 1940 more than twice the rate of that globally during the same interval. Pretty bad extrapolation, right?
The Gisp2 ice core data are really good of course (and I'm sure Svalbard Airport data are excellent, too), and tell us a lot of interesting stuff about climate changes through the Holocene. Likewise the Svalbard Airport data show the signal of global warming fairly well. But don't presume these delta-T's can be directly extrapolated over a broad region and simultaneously; to do such is to totally neglect local and even regional phenomenon which are very important and are even discussed in this literature I've provided you with. You have brought up a lot of great information about the HTM, but remember that was a climate change driven by orbital/obliquity forcing that took place gradually and over a timescale of millenia, and whose effects were not realized everywhere at once, even in just the Arctic.
Whereas current AGW is being driven by a change in radiative forcing that is at least an order of magnitude more rapid, and despite your repeated suggestions that maybe it will stop soon, the weight of scientific knowledge is that it will not for as long as humans continue to enhance the radiative forcing. Indeed the planet will continue to warm for some time, though to much lesser degree, if we follow zero emissions, simply because of the thermal inertia of the system.
Since you are evidently very deeply interested in the Arctic's Holocene history, it might be worth investing in Kaufman et. al's study of the HTM and regional Holocene temperature as gleaned by examination of data from sites across all over the Arctic. It's a pretty spectacular paper, compiling the work of hundreds of studies spanning several decades.
With respect to your last segment, please remember that humans have been altering the thermodynamics of the Earth since before 1900. So you're looking at both natural variability and AGW together over the whole interval there; you can't just dismiss the first half as being all NV. For an example of how to disentangle the two, refer back to Foster & Rahmstorf (2011), posted on page one.
Edit: Whoops, fixed a silly word repetition.
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| midtskogen | Date: Monday, 28.10.2013, 09:40 | Message # 74 |
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Star Engineer
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| Quote Watsisname ( ) so you do not expect to see pre-Holocene vegetation everywhere.
No, but you would expect to see both, pre-Holocene and Holocene optimum, in many places.
Quote Watsisname ( ) No. You most certainly can find higher dT/dt, especially if you use such fine temporal resolution or a data from a single location.
Even if you carefully choose the temporal resolution that best fits your message, I think you'll find it very hard to find a higher modern dT/dt, given that you use the same resolution then and now. If you use a higher temporal resolution both the modern warming and its warming rate become less severe.
If I use a 60y mean for the Gisp2, I still get a couple of examples showing warming rates of 8C/century, way over a 1.1C/century trend in the 60y mean found in Svalbard data (see below). To smooth the Gisp2 data sufficiently to get below 5C/century trends, I need to move up to 300 years and above, and if you do that to modern temperatures, the AGW signal gets pretty lost. Sorry.
Quote Watsisname ( ) Similarly and as you pointed out, the Svalbard airport data shows a trend from 1910 to 1940 more than twice the rate of that globally during the same interval.
Nono. Well, yes, more, but my 2x was a comparison between the amplitude of the multi-decadal cycle against the long term local trend over a century (The exact factor will of course depend on the smoothing used. 30y gives about 2x, but using a 30y average for a 60y cycle mutes the amplitude, so it seems best to say at least 2x).
If you compare the 1910 to 1940 30y trend against the 30y global trend of the same period (e.g. 30y HadCRUT4), it's more like 7x (and 8x if I chose 1905-1945 instead). That's precisely why I warn against interpreting the Arctic warming of the past decades without an understanding of a possible multi-decadal cycle. If you look at the rate of the 30y mean in the 20's and 30's, it's approaching 7C/century.
Suppose that this cycle is real and natural. Then using a 60 year mean seems just right to make out the underlying trends. For Svalbard I then get -6.8C in 1914 and -5.6C in 1983, which is a 1.1C/century warming. 60y HadCRUT4 gives me a 0.6C/century trend for the same period (-0.28645 and 0.132 in 1914 and 1983 respectively). Looks like a polar amplification of nearly 2x here. But since these things depend the temporal resolution, years picked and sites used, things can be juggled to show slightly different results.
Quote Watsisname ( ) you can't just dismiss the first half as being all NV.
I didn't. The long term trend that I was looking for included that period.
EDIT: Looking for more data on the Arctic 60-70 year cycle, I checked the climate trend (30y) of the other Arctic station available at eklima.met.no, Jan Mayen. It looks like this:
It looks like the early 20th century rise here came earlier and levelled out, the peak ends at the same time as in Svalbard. The amplitude is smaller, probably due to the proximity to the ocean. The long term trend seems harder to work out (it looks flat, but the series is too short to tell).
While most speak of a 60 year cycle, my feeling is that it's rather around 70 (possibly varying slightly), and therefore I think Humlum and Solheims predictions of an imminent Arctic freeze will fail (besides that I think their belief in the solar link is stronger than data can support). I just found that Michael Mann describes it as a 70 year cycle.
Judith Curry has posted comments on the Baffin Island paper. She mentions also a paper speaking of the early 20th century warming as "unprecedented".
NIL DIFFICILE VOLENTI
Edited by midtskogen - Monday, 28.10.2013, 20:03 |
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| midtskogen | Date: Tuesday, 29.10.2013, 10:21 | Message # 75 |
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Star Engineer
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| I tried to find more station data to learn more about the cycle and early 20th century Arctic warming, but the trouble is that hardly any continuous records exist exceeding 100 years. I checked GISS. I picked the longest series I could find, Nuuk and Reykjavik, plus Ostrov Dikson which was the longest I could find in the eastern Arctic, just to get some degree of geographic spread. I plotted both raw and adjusted data, since I have no clue what the adjustments are or a way to judge them (note how the adjustments for Nuuk and Reykjavik are reversed). Again I'm using the 30y running mean which is the agreed way to catch climatic trends. Here's what I got:
This adds to the pattern seen in the Jan Mayen and Svalbard plots. Ok, it's just 5 location and the Arctic is big, but there's something in there which seems hard to explain with AGW. None of these three latest show whether this pattern existed in the 19th century, but we have some indications that it did, though the amplitude might be uncertain.
I think there is a long term trend that could match AGW, but these graphs aren't really to helpful in determining it, since it's totally dwarfed by this ~70y cycle.
How the IPCC has been able to pretty much remove the early 20th century Arctic warming is still a mystery to me. I don't think I've cherrypicked anything here, apart from picking the longest records, which obviously is necessary to determine the existence of a 70y cycle. I've used the entire records and the agreed 30y mean. It makes me wonder if the IPCC muted the pattern and made the current Arctic warming "unprecedented" by changing the degree of smoothing along the way (the older or more uncertain the data, the more smoothing) - which most certainly will produce a hockey stick no matter the data, or by modelling the missing data after the global trend. But this is just speculation.
All these graphs also suggest that the Arctic is not headed into an imminent freeze as predicted by Humlum and Solheim. I think we shall give it another decade.
NIL DIFFICILE VOLENTI
Edited by midtskogen - Tuesday, 29.10.2013, 10:33 |
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