« Second storm | Main | Are scientists conservative about sea ice? »

Comments

Feed You can follow this conversation by subscribing to the comment feed for this post.

TenneyNaumer

In the case of the ESAS in the Laptev Sea region, the subsea permafrost is only 53 m deep, according to Shakhova, and its temperature is above -1.0 C. Methane plumes that rise to the surface are a combination of methanogenesis, from the decomposing ex-permafrost, and thermogenesis from the melting methane hydrates below the subsea permafrost.

See this video interview of Shakhova (with Semiletov in the background) by Nick Breeze:

http://vimeo.com/71177231

Jai Mitchell

Terry,

Just wanted to be clear, the 53 meter deep surface of the ESAS seafloor is actually sediment, not permafrost. This is the same sediment that she is speaking about in the opening statement that is not a barrier to released methane.

jonthed

I still don't understand this mentality of obsessing over what is 'most likely' to happen, and refusing to take the 'less likely' scenarios into account when deciding how seriously we should view our current situation, particularly when some of those less likely scenarios result in global catastrophe.

Same as the IPCC emissions scenario projections. The fact that 8C warming is even on the table surely should mean we take the most aggressive reductions path possible. Not just carry on BAU and think 'well it could only be 2C'.

Ned Ward

I get as annoyed as anyone else when I see "skeptics" (a) pointing out the uncertainty in a forecast, and then (b) assuming that the outcome will be off by that much in the preferred direction.

It's like saying "My household budget appears to be in the red by 100€, plus or minus 350€, so it's possible that I'm actually saving 250€ each month and have nothing to worry about." Er, yeah, but it's also possible that you're losing 450 euros each month, Mr/Ms Wishful Thinking.

But I don't really see that happening around here; the people who are arguing against the idea of an imminent "time bomb" or year-round ice-free Arctic Ocean or whatever seem (to me) mostly to be doing so on the basis of reasoning, not just "hope for the best".

Ned Ward

jonthed writes: Same as the IPCC emissions scenario projections. The fact that 8C warming is even on the table [...]

Just noting that as far as those projections are concerned, 8C isn't really "on the table" this century (IPCC mostly doesn't look at longer timescales).

Most likely is 2C to 3C by 2100, though it could be below 2 or over 4. Of course it will be higher on land and in the Arctic, lower over the oceans and in the tropics.

http://www.ipcc.ch/publications_and_data/ar4/wg1/en/figure-spm-5.html

I do think it's worth undertaking major efforts to limit emissions anyway. It's got to happen sooner or later.

Jai Mitchell

with regard to 8C not "on the table"

The current review of the AR5 is ongoing and the unpublished data has been leaked. To see what the current views are regarding Projections of future sea ice extent, AMOC declines, temperature projections and methane releases being modeled, you can go here:

http://www.stopgreensuicide.com/Ch12_long-term_WG1AR5_SOD_Ch12_All_Final.pdf

Takeaways:
1. Sea ice extent anomalies in the models are underestimating sea ice loss by at least 25 years and by a mean of 35 years. figure 12.28

effects--significantly underestimates albedo feedback rates for this period. Also affects methane emission scenarios.


2. Only the RCP 8.5 model incorporates a methane emission scenario even close to what is currently happening in the cryosphere with increased sea ice extent collapse. See worst case scenario based on Siberian wetland emission (note: models does not expect permafrost or ESAS emissions to increase significantly, so even this worst case scenario is likely to be somewhat below actual) http://acmg.seas.harvard.edu/presentations/IGC6/talks/WedC_SourcesC_holmes_christopher_2_mac.pdf See Page 8.

3. Holmes et. al 2013 (see: http://www.atmos-chem-phys.net/13/285/2013/acp-13-285-2013.pdf )

has determined that the CH4 forcing is 32X more than CO2 on a 100 year scale this is 50% more than the 25X as currently held in AR5 models)

in addition, they significantly underestimate CH4 emissions which impacts both forcing and CH4 lifetime rates.

"Uncertainty in 2100 methane abundance is 10% based on the processes we have assessed here, which include a simple treatment of natural methane emissions."

P 298

and

"The scenario specifies future anthropogenic methane emissions and we assume natural emissions could change ±20% by 2100 due to climate feedbacks, which is about twice the change in wetland emissions since the preindustrial era (Houweling et al., 2000)."

Page 295

These two quotes show that their estimation does not include significant increases in cryosphere originated CH4 emissions and that their models significantly raise the warming potential from even a smaller increase in emissions by 50%.

in summary,

1. The AR5 RCP8.5 emission scenario does not include the current effects on the cryosphere due to sea ice extent retreat.

2. The omission produces a summer season overestimation of albedo by over 35% during the next 35 years. Leading to artificially cooler NH temperatures during this time.

3. The SIE omission also causes an underestimation of permafrost degradation and therefore underestimates CH4 emissions (even without the potential increase from the ESAS) through 2100.

4. The AR5 also significantly underestimates the warming potential from CH4 at 25X CO2 equivalent on a 100 year scale. Holmes et al has 32X as the correct value with an underestimated emissions scenario that will go up if the emissions are larger. This 100 year potential is based on oxidation rates by tropospheric OH. The primary reason for the increase in warming potential of CH4 is due to depletion of Ozone, causing persistence of CH4 to go from 12 years to over 20. An increased emission scenario that includes Permafrost and ESAS emissions will additionally increase the warming potential of the emitted methane.

5. Under these lower methane emission scenarios the RCP8.5 in the AR5 review indicates a potential warming by 2100 of 4.8C with a 90% confidence interval range of 3.25C to 7.45C (See: http://www.stopgreensuicide.com/Ch12_long-term_WG1AR5_SOD_Ch12_All_Final.pdf ) Figure 12.40

Jai Mitchell

response got caught in the spam bucket.

[released now; N.]

TenneyNaumer

@ Jai, thanks for clarifying that.

btw, I am Tenney not "Terry."

Apocalypse4Real

To help monitor current and future emissions from the beginning of 2013, methanetracker.org has added a new set of reports that breakdown methane averages between three ranges 1750-1850, 1850-1950 and 1950+ ppb on a global basis.

Currently the forest fires in Siberia, Canada and Alaska are quite apparent.

Please register and have an opportunity to track changes as we go through the rest of the melt season and into the fall, methane release in the Arctic Ocean becomes more apparent.

GeoffBeacon

Dolomin

I did thank you for your 0.5 w/m2 comment but forgot to press the "Post" button. You helped me find a different way of looking at the "local heating from methane" issue. I have asked this before and you have been the first to help.

1)A radiative forcing of 0.5 w/m2 is due to a 1 ppmbv increase in methane concentration since the industrial revolution.

2) 1 ppmbv is about 1 cm of pure methane in the atmospheric column above the place beneath.

Do you know at what "depth" of methane would this effect deserve consideration?

GeoffBeacon

Tenny,

Thanks for the link to Shakhova's scary video. I've logged on the "good videos wanted" section on the forum.

Jai,

Is it us or "the scientists" that are living in an alternative reality?

I remember Aberfan.

I remember box girder bridges.

I remember when continents stood still - except for that nutter, Alfred Wegener.

Allen W. McDonnell

Dorlomin asked for a definition of Hothouse climate so after giving it some thought I came up with one of my own.
Hothouse climate [to me] is when the year around weather never decreases below 0 C degrees as the yearly average in a polar hemisphere of the Earth.
I think it is necessary to specify it refers to a polar hemisphere because Paleoclimate data demonstrates that the northern hemisphere remained ice free year around as recently as 2.5-2.8 Mya based on the recently published Lake El'gygytgyn core data. Up until that time the northern hemisphere was in a permanent thaw situation instead of the permafrost climate that existed there for the last 2.5 Million years. During the period from 28 Mya to present we are certain Antarctica has had a large quantity of ice sheet coverage, so clearly the southern hemisphere was not in the Hothouse climate regime. We have evidence of periodic Antarctic ice going as far back as 34 Mya. If you pause and think about that for a minute you will see that Antarctica went through a series of freezes and retreats similar to the Canada/Scandinavia/Siberia glaciations of the last 2.8 Million years in the Northern Hemisphere. Perhaps if Humans had not come along when we did the North would have gone into a permanent freeze in a few million more years as global CO2 levels gradually declined from weathering in the Himalaya's and other mountain regions.

In any case if the Arctic continental shelf methane all burps out over the next century or so it will be just a blip on the graph of all the warning gasses humans have added to the planet since the beginning of Agriculture. If enough comes out at once to take up all the OH radicals in the atmosphere the Ozone layer will backstop the situation as the methane gradually rises into the stratosphere.

wili

Perhaps. But what happens when it hits the stratosphere, exactly?

Klon Jay

Does anyone know if this is a big fire in the heat-wave area, or just gray clouds? More fires are supposed to warm the permafrost by darkening the soil, leading to more methane release.

http://www.arctic.io/observations/8/2013-07-29/7-N65.795685-E64.526969/Russia-Yamalo-Nenets-Autonomous%20Okrug

Klon Jay

I thought I was looking at todays image, but that was yesterday. I think it is massive fires.
http://www.arctic.io/observations/8/2013-07-30/7-N64.531009-E60.03906/Russia-Khanty-Mansi-Autonomous%20Okrug

Jai Mitchell

@Allen W. McDonnell

you said,

"In any case if the Arctic continental shelf methane all burps out over the next century or so it will be just a blip on the graph of all the warning gasses humans have added to the planet since the beginning of Agriculture."

Please see: http://www.elic.ucl.ac.be/repomodx/users/thierry/articles/2004_Renssen_et_al_Pal.pdf

in this paper they modeled a 1500Gt release of methane over 100 years.

There is currently about 5 Gt of methane in the atmosphere.

under this scenario they showed a 1C increase in temperature in the first 25 years or so and a gradual increase after that.

wili

And there is also this more recent paper on the effect of terrestrial methane release:

http://www.skepticalscience.com/Macdougall.html

It both come out together, at the same time that other feedbacks kick in while other sinks stop absorbing CO2 and start emitting it, it will be quite a bit more than a "blip."

wili

Sorry, that should say: "methane release from terrestrial permafrost"

TenneyNaumer

@ Geoff You're welcome. btw, I am Tenney, not "Tenny."

Climate Changes

Uni Bremen graph today shows many areas with low concentration surrounding the CAB. A severe drop in extent expected soon?

Jai Mitchell

Igor Semiletov Responds to Gavin Schmidt (and others)

http://www.theecologist.org/News/news_analysis/2017089/arctic_methane_catastrophe_scenario_is_based_on_new_empirical_observations.html

The problem is that these reservations are based on outdated assumptions that sea floor released methane would not make it into the atmosphere - but all the new fieldwork on the levels of methane being released above the ESAS shows this assumption is just empirically wrong.

Atmospheric methane levels in the Arctic are currently at new record highs, averaging about 1900 parts per billion, 70 parts per billion higher than the global average. NASA researchers have found local methane plumes as large as 150 kilometres across - far higher than previously anticipated.

Dr Gavin Schmidt, climate modeller at NASA, was also cited claiming lack of evidence from ice cores of previous catastrophic methane pulses in the Earth's history in the Early Holocene or Eamian, when Arctic temperatures were warmer than today. But the blanket references to the past may well be irrelevant. In the Early Holocene, the ESAS was not an underwater shelf but a frozen landmass, illustrating the pointlessness of this past analogy with contemporary conditions.

Dr Schmidt also overlooked other issues - such as new research showing that the warm, Eamian interglacial period some 130,000 years ago should not be used as a model for today's climate due to fundamental differences in the development of the Arctic ocean. Ice core methane records are also too short to reach back to the entire Cenozoic - another reason suggesting lack of past evidence is no basis for present complacency; and even Prof Archer himself recognises that ice cores will not necessarily capture a past catastrophic methane release due to fern diffusion.

Climate Changes

@Jai

Kevin McKinney picked this up on the Guardian. "fern diffusion" should be "firn diffusion" :)

Jai Mitchell

Thanks CC.

The closing statement by Dr. Semiletov is especially valid to this discussion and deserves an additional repost:

"Wadhams thus describes the previous research dismissing the methane threat by Rupple and others as "rendered obsolete by the Semiletov/Shakhova field experiments - the seeing - and the mechanism described above."

So far, cutting edge peer-reviewed research on the link between Arctic permafrost melt and methane release has received no attention from these critics. Indeed, their offhand dismissals are based on ignoring the potential implications of the specific empirical evidence on the ESAS emerging over the last few years, which challenges the assumptions of conventional modelling."

Allen McDonnell

My statement about the arctic shelf methane releasing being nothing but a blip appears to have not been clear in context. What I mean is, releasing the arctic shelf methane will not have a long enough duration sustained warming effect to warm deeper waters and release the bulk of methane clathrates. So long as the vast deep and intermediate ocean stay cold enough those clathrates will stay stable.

It is not great news that the shelf clathrates could be breaking down, but it isn't doom to the 12th order either.

Apocalypse4Real

Jai,

Thanks for finding Semelitov's comments, very helpful.

Climate Changes

For the last 5 years or so, just north of Severnaya Zemlya and just above the Gakkel Ridge, an area develops were the ice melts fairly quickly. A polynya would be the right term but I understand that there is volcanic activity on the ridge underneath and therefore heat must be released causing this? To me it appears that this polynya follows the direction of the ridge for about 300km and this year is particularly obvious already. Looked up on CT and the further back in time the less obvious it is and the nearest to the September min it appears. Prior to 2006 is hard to see it as the ice was much thicker and I guess the warmer water would have had more of a job to break through. In anycase any extra warming cannot be too good for temperatures on the East Siberian Seas.

Jai Mitchell

Thank you back A4R

so much good work going on here, I had to add my .02

wili

Jai and A4R, I believe the words quoted were not those of Semiletov but of the author of the piece, Ahmed--just to be clear.

Semiletov and Shakhova were mentioned a bit later in the article.

Neven
For the last 5 years or so, just north of Severnaya Zemlya and just above the Gakkel Ridge, an area develops were the ice melts fairly quickly. A polynya would be the right term but I understand that there is volcanic activity on the ridge underneath and therefore heat must be released causing this? To me it appears that this polynya follows the direction of the ridge for about 300km and this year is particularly obvious already.

CC, over here on the ASIB we like to call that phenomenon the Laptev Bite. Or do we call it the Laptev Hole?

Anyway, someone suggested a couple of weeks ago that we call it the Laptev Gobble this year. :-)

Robert S

Another lurker, surfacing...

As someone who has built lots and lots of ecosystem finance models, I have to say that the sort of global cost analysis modelling contained in the Nature paper is usually essentially meaningless. It makes for a good headline, but doesn't really tell us anything, since the economics are wholly peripheral to the problem.

The real measure here is a much grimmer one : how many additional human deaths will result from loss of agricultural production, etc. I was working on ecosystem carbon issues in Southern Africa recently, and even the slightest disruption of food production would have catastrophic consequences, especially if the money of the developed world is sucking the reserves dry... as it inevitably will. Impact transference down economic gradients will result in another whole realm of non-linear/dragon king events.

Following this blog makes it only more evident to me that global warming mitigation is no longer the issue. It's now all about adaptation...

Climate Changes

"CC, over here on the ASIB we like to call that phenomenon the Laptev Bite. Or do we call it the Laptev Hole?

Anyway, someone suggested a couple of weeks ago that we call it the Laptev Gobble this year. :-)"

Oh aye, I've found the Gobble references on the ASI Forum and a thread about the Laptev Bite on ASI back in 2011, thank you :).

I don't see however any mention of the volcanic activity on the Gekkel Ridge as its cause? Comments about its origin refer to an influx of warmer Atlantic waters but as the ice gets weaker year on year it appears more obvious that thermals from the ridge could possibly be the cause. In 2001, 2007 & 2011 expeditions found volcanic activity at the ridge greater than previously thought. My guess would be that the Gobble (xD) will be a yearly feature (and perhaps a permament one in the future) as the ice above the ridge is far too thin.

Kate

This image shows smoke being fed into the latest circulation around the basin. Not sure how this will affect the ice
and not sure if the link will work, but think Russian coast!

http://earthdata.nasa.gov/labs/worldview/?map=-1893024,-360448,3349856,3321856&products=baselayers,!MODIS_Aqua_CorrectedReflectance_TrueColor,MODIS_Terra_CorrectedReflectance_TrueColor~overlays,arctic_coastlines_3413&time=2013-08-01&switch=arctic

Apocalypse4Real

The high temperatures and fires in Siberia and North America are beginning to increase CH4 levels in the upper troposphere. See the new images from the METOP 2 IASI satellite I posted in the ASIF permafrost section.

http://forum.arctic-sea-ice.net/index.php/board,20.0.html

Concentrations at some layers are as high as 2276 ppb CH4.

Climate Changes

Bremen Uni map today shows the Laptev Bite more than doubled in length and still running along the direction of the Gakkel ridge (maybe call it Gakkel Bite?). Reading literature (papers, etc) about it I find that there are two fields of opinion. One that argues that the volcanic activity in 1999 is responsible for the Arctic ice decrease seen in recent years(something I disagree with) and another that states that given the depth at which the hydrothermal vents and volcanos are situated within the ridge (2 to 3 thousand meters) it would be impossible to melt such a vast area of ice.

I'd have agreed with the second view 10 years ago when the ice above the ridge was thick but now that the ice is thinner it appears that the activity in the ridge is affecting the water column above so much that it shows on the ice as the Bite. It has been noticed that, for the last 5 years, the Bite has become a regular to the melt season. what effect this 'new' source of heat has in terms of mixing layers? Can the volcanic activity become another 'time bomb' now that the thick ice that kept the heat at bay is gone?

Lewis Cleverdon

Neven wrote:
"We see the drastic changes in the Arctic, we know there's around 1500 Gt of methane in the Arctic Ocean's seabed, and so it's quite legitimate to think about worst case scenarios, in this case a rapid release of just 3% of those methane stores."

An aspect of the Archer-Wadhams debate that Ned and others here have yet to assimilate is that a 50Gt CH4 bomb (~3.3% of ESAS stock) is not the threshold for a terminal impact.

A mere 1Gt CH4 annual output (0.067% of ESAS stock) poses a terminal threat in its consequences. Over the critical 20yr timeframe its CO2e of 105Gts would impose an additional warming equal to roughly a quadrupling of present anthro-CO2 outputs. While the CO2e of CH4 does decline by year 100 to around 23, an annual 1.0Gt CH4/yr output would mean that what happens 100 years hence would no longer be of any concern to humans.

To put that 1.0Gt/yr output into perspective, it equates to about 10 new China's-worth of emissions, continuing for an open ended period. Its impact on the six other already-accelerating interactive mega-feedbacks
-(of Water Vapour, Albedo Loss, Microbial Peat Decay, Permafrost Melt, Forest Combustion and Soil Desiccation)
would, undoubtedly, be profoundly destabilizing.

Ned's notion that 1C of anthro-warming plus 0.2C of clathrate-CH4 warming then generates only 0.04C of subsequent clathrate warming, not only massively understates the ratio of anthro to clathrate warming potentials at 5 : 1, it also ignores both the direct and timelagged feedback-interaction warmings, that are now driven not by 1.0C but by 1.2C.

Morever, given that most of the combined feedback warming must go into the oceans, whose waters then circulate though the Arctic including over the ESAS, it seems scarcely credible to propose that a clathrate output would be constrained to just 1.0Gt CH4/yr.

While the belief in an effective resolution of AGW by Emissions Control alone is already patently delusional for reasons of physics, not politics, the scale of the potential feedback warming driven by 1.0Gt CH4/yr is beyond the viable control capacity of any Albedo Restoration technology that I've heard of. It is for this reason that it can fairly be described as a 'terminal impact'.

Regards,

Lewis

wili

A4R, your link just connects to the methane threads over at the forum. Could you provide a link to a more specific site?

wili

Here's a link to a Shakhova video on the subject. (Semiletov seems to be off camera making occasional contributions.)

https://www.youtube.com/watch?v=kx1Jxk6kjbQ

Kate

I had a quick look at the SST anomaly figures at Wunderground. Very high anomaly around GL

http://www.wunderground.com/tropical/

Apocalypse4Real

wili,

Here is the updated link. I added in August 1st images as well.

http://forum.arctic-sea-ice.net/index.php/topic,479.0.html

A4R

www.google.com/accounts/o8/id?id=AItOawn4S99JJRLrNfgA838BLqx0pzoN7lqRBgI

Looks like the sea ice melt has stalled.

Twemoran

Lewis
I'm in agreement with your 20 year time frame. What happens afterward won't have much impact on civilization since civilization will not survive those decades.
Terry

Susan Anderson

Tenney Naumer with two e's ... but that's not why I'm here. Just found this nice image of wildfire smoke vortex, and have an additional question. There are ongoing volcanic eruptions in Alaska (and one in Siberia as well if I remember correctly but that one hasn't made as much news). Is that big enough to have a damping effect.

This is just an update of other news coming in from that region:

http://www.theatlanticcities.com/neighborhoods/2013/07/giant-vortex-wildfire-smoke-appears-over-russia/6374/
"A Giant Vortex of Wildfire Smoke Is Hovering Over Russia"

EO volcanoes:
http://earthobservatory.nasa.gov/IOTD/view.php?id=81751

OK, answering own query, I see words "low level" here:

"The Alaska Volcano Observatory (AVO) originally detected an eruption at Veniamanof on June 13, 2013. On July 25, AVO reported volcanic tremors, high surface temperatures, and nighttime glow. These signals indicated 'an ongoing low-level eruption characterized by intermittent effusion of lava and emission of minor amounts of ash and steam.'"
Russian (most recent appears to be February):
http://earthobservatory.nasa.gov/IOTD/view.php?id=80226

Ned Ward

Lewis Cleverdon writes: Ned's notion that 1C of anthro-warming plus 0.2C of clathrate-CH4 warming then generates only 0.04C of subsequent clathrate warming [...]

You're referring to a comment of mine from back on the first page of this thread. It was purely a thought experiment, in response to a previous commenter's mistaken idea that a methane feedback would necessarily lead to runaway warming.

In fact there are many positive feedbacks in the climate system, and they don't lead to runaway warming. My comment was explaining the reason for that, which in my experience many people find counterintuitive. This argument used to come up repeatedly over at Skeptical Science, leading eventually to the posting of this handy explanation.

wili

Thanks for the link, AR4.

And for yours, Ned.

I do think 'runaway' is used in different ways by different people, and that is unfortunate and leads to needless disagreement.

Most arguing against the possibility of 'runaway' (including the otherwise-helpful SS article) are arguing against a runaway to Venusian conditions.

But most people who I have seen express a concern about 'runaway' seem to be defining it as the point when enough tipping points have been reached that, even if all further emissions of GHGs from human sources were completely halted at once, increase in levels of GHGs in the atmosphere would continue for some time, just from the action of the feedbacks.

I believe Hansen has a discussion of these various definitions in a recent article, but don't have time to track it down right now.

Chu seems to be using that second definition in this video.

http://www.youtube.com/watch?v=oHqKxWvcBdg

wili

Early in this now-long thread, it was claimed that early holocene temperatures were warmer in the Arctic than today. It was never shown, though, that it was warmer specifically in the area we are talking about--the ESAS.

Also, during the same period, the sea level was steadily rising--that is the warming was slow enough that the melting of ice caps and glaciers didn't have the long time-lag that we see from the very rapid warming today.

http://www.sciencedirect.com/science/article/pii/S0277379111001211

Besides temperature, pressure and salinity are two of the other major conditions for permafrost and hydrate stability. But at that time, the pressure would have been steadily increasing, and the salinity decreasing.

So even if the ESAS has been warmer than it is now in the holocene (a claim yet to be fully supported), other factors would have contributed to help stabilize the hydrates.

We can only hope (for the purpose of these issues at least) that sea level rise and freshening of Arctic waters from GIS melt happen quickly enough to deepen and freshen the shallow ESAS waters where so much methane resides before it starts explosively emitting methane, whether from permafrost, from hydrate, or from the large pools of highly pressurized pure methane gas below.

Ned Ward

Early in this now-long thread, it was claimed that early holocene temperatures were warmer in the Arctic than today. It was never shown, though, that it was warmer specifically in the area we are talking about--the ESAS.

First of all, there are good a priori reasons to expect that it was warmer in this region during the early to mid Holocene. Due to Milankovich geometry summer insolation in the Arctic was much higher than now, and other sites elsewhere in the Arctic are certainly believed to have had higher temperatures at that time.

Paleoclimate data from the eastern Russian Arctic seem to follow this pattern.

For example, Andreev et al 2004 examined pollen records from the Taymyr peninsula, at the western end of the region you're referring to:

"TVII [i.e., reconstructed temperatures] were slightly warmer than today during the Allerød and 2–3°C colder during the Younger Dryas and became 0.5–1.5°C warmer than present again in the early Preboreal; two sharp decreases in TVII to the modern value occurred at about 9600 and 8500 yr BP; and after TVII fluctuated between 1.5 and 3.5°C above modern values."

Andreev and Klimanov 2000 looked at pollen from seven locations across Arctic Russia. In general, they found a similar pattern of mid-Holocene warmth. The easternmost of their sites (Kazach'e) is closest to the ESAS. The warmest temperatures there (2C warmer than today) occurred at around 6000-4500 BP.

Further east, at Lake El’gygytgyn, Melles et al 2012 report that the peak Holocene warmth was 1C to 2C above present temperatures. They also note that previous interglacials were substantially warmer (they refer to MIS 11c and 31 as "super-interglacials; with temperatures 4C to 5C above the peak Holocene temps, or 5C to 7C above current temperatures).

It's worth keeping in mind that these are land temperatures. I don't think there are a lot of paleo reconstructions of temperatures in the East Siberian sea. Melles et al. 2012 notes that climate models suggest that past temperature changes in the Arctic Ocean in general would likely have been much smaller than those on the surrounding lands (see fig. 4).

Sources:

Andreev, A. A., and V. A. Klimanov. "Quantitative Holocene climatic reconstruction from Arctic Russia." Journal of Paleolimnology 24.1 (2000): 81-91.

A.A. Andreev, P.E. Tarasov, V.A. Klimanov, M. Melles, O.M. Lisitsyna, H.-W. Hubberten, Vegetation and climate changes around the Lama Lake, Taymyr Peninsula, Russia during the Late Pleistocene and Holocene, Quaternary International, Volume 122, Issue 1, 2004, Pages 69-84.

Melles, Martin, et al. "2.8 million years of Arctic climate change from Lake El’gygytgyn, NE Russia." science 337.6092 (2012): 315-320.

Ned Ward

I do think there's a good chance that 21st century temperatures in the Russian Arctic will approach or surpass those from earlier in the Holocene.

But as far as "methane time bombs" go, I think the absence of a "bomb" during previous interglacials -- including what Melles et al 2012 refer to as the "super-interglacials" -- argues against the likelihood of a "bomb" going off any time soon. The Arctic was *very* warm for long periods during previous interglacials, at some points warm enough for long enough to melt most or all of the Greenland ice cap. That's a lot of heat! But no "bomb" went off.

Ned Ward

Chris Colose has an excellent post about methane at Skeptical Science:

Toward Improved Discussions of Methane & Climate

Some participants in this site have already commented over there, but others might not have seen it yet.

In general, I agree with Chris's perspective on this issue. I think Arctic methane is a real but second-tier concern as an element of the terrestrial carbon feedback. I don't think there is any prospect of near-future "catastrophic" release of methane.

wili

Wow. Thanks for the very detailed response about heating.

I do still wonder whether those earlier, slower warmings allowed for slr to keep ahead of warming, providing enough pressure to keep hydrates intact, even as temperatures warmed.

I see that the phase boundary curve is flattest at the shallowest depths--that is, the shallow hydrates we are talking about would need the least amount of additional meters of water (and the pressure they provide) to make up for the added temps.

http://pubs.usgs.gov/of/1996/of96-272/fig8.html

But I can't get precise quantities from that graph at that detail, and I'm too damn lazy to do the maths.

Apocalypse4Real

An excellent article in today's Guardian on the recent research supporting potential large releases of CH4 in the Arctic.

http://www.theguardian.com/environment/earth-insight/2013/aug/05/7-facts-need-to-know-arctic-methane-time-bomb

Allen McDonnell

@Ned
While there re strong proxies for higher peak temperatures in the past there is a second indicator whis is often inored. Duration. The last interglacial before the current on for example was warmer than the Holocene, however it was quite short. The Holocene has already lasted over twice as long as the Eemian did 125,000 years ago. Less time means less total mpact, like baking a loaf of bread at 350 for 20 min instead of 340 for 40 min. You just can't get the same results that way.

Ned Ward

Well, other interglacials saw periods of warmth that lasted longer, such as MIS 11 (during which Greenland ice sheet and WAIS pretty much entirely disappeared). Could a methane "bomb" survive through enough warming to melt all the ice in Greenland, but then explode now when we've not even managed to melt 0.5% of that ice?

Jai Mitchell

Ned,

It seems you are comparing two seperate things.

1. MIS 11 which was, at most 3-4C warmer in the arctic than current pre-industrial (and so, very much similar to todays environment)

http://dosbat.blogspot.com/2012/12/lake-elgygytgyn-and-arctic-warming.html

http://www.whoi.edu/cms/files/rohling10epsl_72104.pdf

2. MIS 11 was much longer in duration at these temperatures.

http://www.clim-past.net/9/1467/2013/cp-9-1467-2013.pdf

3. compare that to today when we are looking at the potential for an additional 6-14C arctic warming over the next 5 decades.

This is arguably a completely distinct event compared with previous interglacials.


Even so, the evidence currently indicates that subsea methane clathrates HAVE been released during these interglacials.

http://www.pnas.org/content/101/25/9187.long

Here we document evidence that two massive methane releases from clathrate dissociation, of amplitude two to three times larger than those inferred in the Santa Barbara Basin, occurred during the last glacial episode in the western Pacific.

Ned Ward

Jai writes: "MIS 11 was much longer in duration at these temperatures."

Yes. In the comment immediately preceding mine, Allen McDonnell had suggested that "duration" was the determining factor that had prevented a methane time bomb from going off during the Eemian interglacial, which he suggested was too short. So I pointed out that MIS 11 was a much longer interglacial.

Apparently I'm being criticized by some for focusing on duration of warming rather than peak temperatures, and by others for focusing on peak temperatures rather than duration of warming.

:-)

Again, the total warming during MIS 11 was great enough to melt most or all of the Greenland ice sheet plus the West Antarctic ice sheet, with sea levels on the order of 10-20 meters above today's. That is a lot of warming, sustained for a very long time. I don't think there's any sign of a catastrophic 50-gigaton release of methane during MIS 11.

Jai continues: "we are looking at the potential for an additional 6-14C arctic warming over the next 5 decades"

Source?

IPCC WGI chapter 11 (fig. 11.18) says approx. 3-6C for the Arctic by ~2060s. Where do you get 6-14C?

Jai concludes with: "Even so, the evidence currently indicates that subsea methane clathrates HAVE been released during these interglacials."

That's an interesting paper, though I'm no expert in that area. Taking it on face value, though:

(1) It's not about interglacials (describes events that occurred *during* the last glacial cycle).

(2) There was no 50-gigaton methane release (events they describe were more than two orders of magnitude smaller).

(3) The study area is in deep waters of the tropical Pacific, not a shallow continental shelf in the Arctic.

I'm not sure how that relates to this thread, but it does seem kind of funny that you began your comment by writing "Ned, It seems you are comparing two separate things."

Ned Ward

Again, just to re-emphasize here. I think high-latitude methane sources will contribute to 21st century warming. I think we should keep a close eye on methane fluxes. I think we should start now (25 years ago actually) to reduce CO2 emissions so as to minimize 21st century climate change.

But I don't see justification for portraying a scenario like this as realistic:

Red line is ice core record, blue line is direct measurement up to mid-2013. In other words, actual history up to now.

Green line is imaginary 50 Gton release of CH4 over a single decade.

In the global atmospheric methane record, as of mid-2013, there is no sign of any such thing. CH4 levels are rising, but more slowly than a half-century ago.

Jai Mitchell

Ned,

you said,

"IPCC WGI chapter 11 (fig. 11.18) says approx. 3-6C for the Arctic by ~2060s. Where do you get 6-14C?"

1989-2008 surface trends for the arctic are close to 2C per decade warming.

http://www.researchgate.net/publication/43352154_The_central_role_of_diminishing_sea_ice_in_recent_Arctic_temperature_amplification?ev=pub_cit

This warming was previously caused by normal amplification, the next phase of warming will be primarily caused by loss of sea ice.
http://www.people.fas.harvard.edu/~moore3/Lawrenceetal2008.pdf

This trend is accelerating
http://archive.mrc.org/pdf/WANG-OVERLAND-ARCTIC%20SEA%20ICE%20ESTIMATE.pdf


In fact, I see that the actual trend indicates a step-change in temperature due to total sea ice loss by 2030 of 5C, This additional warming effect will be on top of the 2.5C/decade warming trend that we have previously seen.

I believe that under these scenarios,
https://sites.google.com/site/arctischepinguin/home/piomas
a 6C-14C arctic warming above current numbers to be highly likely with an expected warming of >10C by 2060.

These values are not surface water temperature anomalies for the ESAS which have already been measured to be 7C above normal during the summer melt.

So in the next few decades we are looking at a remarkable shift, on a decadal scale in the temperature regime of a region that has been held below freezing for over 5 thousand years.

Jai Mitchell

addendum

The amplification of Arctic terrestrial surface temperatures by reduced sea-ice extent during the Pliocene


http://www.sciencedirect.com/science/article/pii/S0031018213002265

Figure 5 show annual temperatures >10C for the annual average from today.

Ned Ward

Jai Mitchell writes: "1989-2008 surface trends for the arctic are close to 2C per decade warming."

Actually, the paper that you cite says 0.5 to 1.6C depending on the season, or 1.15C/decade overall.

and then continues: "on top of the 2.5C/decade warming trend that we have previously seen"

How did the past decade's warming go from 1.15C/decade to "close to 2C/decade" to "2.5C/decade" within a couple of paragraphs? You've more than doubled the trend that was reported by the very paper you yourself cited.

Jai Mitchell

Ned,

While the decadal average in the paper was 1.15C over this period. The reason this is low is because the majority of this warming has occurred since 1998.

http://www.wwfblogs.org/climate/sites/default/files/SurfTempAnomaly,64oN-90oN-1880-2010.jpg

The rate of 1.15C/decade is taken from an average of a series that ended 5 years ago. The temperature profile of the arctic is growing exponentially and proportional to sea ice decline. The most recent decade has shown catastrophic sea ice collapse, this is not currently captured in the decadal temperature average of the paper.

https://14adebb0-a-62cb3a1a-s-sites.googlegroups.com/site/arctischepinguin/home/piomas/grf/piomas-trnd6.png

In addition, you failed to respond to the 5C step change when we reach a June 1st 2030 0% sea ice extent.

Even so, do you still think that a 3-6'C by 2060 is even a remote possibility? How does this change your perception of the comparisons between now and the last super interglacial of 400,000ybp when temperatures were close to what they are today for about 15,000 years and leading to the melting of the Greenland ice cap and the West Antarctic Shelf?

The exponential trend of average temperature increase in the arctic will grow even faster when the sea ice is completely gone in early summer.

Boa05att

CLIMATE REPORT: “Is the Unthinkable Now Possible?” With Chris Hope and Peter Wadhams

Tom Bowman talks with economist Chris Hope and oceanographer Peter Wadhams about how rapid changes in the Arctic could have devastating impacts on the rest of the world.

http://tombowman.com/posts/climate-change-is-the-unthinkable-now-possible/

Jai Mitchell

Thank you for that link BOA!

It says that they based their release on a previously published estimate and that the evidence for the potential reality of this release is pending publication from Semiletov and Shakhova in Nature and will be out soon.

LRC

I may be wrong, but it is my understanding that methane in large quantities needs special situations, such as high water table, stagnant water, specific vegetation and microbiology.
If those did not exist during the previous high spells then would the methane be there in large quantities in the first place?

LRC

Hot not high.

Ned Ward

Jai Mitchell writes: "While the decadal average in the paper was 1.15C over this period. The reason this is low is because the majority of this warming has occurred since 1998.

http://www.wwfblogs.org/climate/sites/default/files/SurfTempAnomaly,64oN-90oN-1880-2010.jpg

"The rate of 1.15C/decade is taken from an average of a series that ended 5 years ago. The temperature profile of the arctic is growing exponentially and proportional to sea ice decline. The most recent decade has shown catastrophic sea ice collapse, this is not currently captured in the decadal temperature average of the paper."

===================

I hardly know where to begin here. I apologize for the length of what follows, but so much is wrong or confused in Jai's comment that I don't see a way to keep this short.

(1) You originally said "1989-2008 surface trends for the arctic are close to 2C per decade warming" and then later increased that to "2.5C/decade that we have already seen". The source you gave for that was Screen & Simmonds 2010.

But Screen & Simmonds don't say that. They say 1.15C/decade. May I suggest that if you don't agree with Screen & Simmonds, don't cite them as a source for your claims?

(2) If "the majority of the warming occurred after 1998" that would tend to increase not decrease the magnitude of the trend. I think you may be confused about how trends are calculated, because you keep referring to an "average". The figure that Screen & Simmonds report for 1989-2008 temperature is a trend, not an average. If the decadal average was higher for the later part of that period (which it was) that would tend to increase the trend, not decrease it. So your explanation for why Screen & Simmonds' trend is too low makes no sense.

(3) In fact, Screen & Simmonds' trend is probably too high, as shown by the very graph you link to in the new comment. The graph appears to be a plot of the GISTEMP Land+Ocean temperature index for the Arctic. The version you link to truncates it at 2010, but the full data set through 2012 can be downloaded from NASA.

The trend in GISTEMP's Arctic temperature for 1989-2008 is 0.7C/decade, or only about half of what Screen & Simmonds reported, and just over a quarter of your "2.5C/decade". Since you suggest that the problem with Screen & Simmonds was that their study period ended in 2008, we can extend it through 2012 ... but that decreases the trend slightly (to 0.66C/decade).

(4) When you say "The most recent decade has shown catastrophic sea ice collapse, this is not currently captured in the decadal temperature average of the paper" ... well, the trend over the most recent decade (2003-2012) is even lower (0.48C/decade).

===================

Continuing with Jai Mitchell's comment: "In addition, you failed to respond to the 5C step change when we reach a June 1st 2030 0% sea ice extent."

===================

That's because I haven't seen any justification for a "5C step change" in 2030. I think that's highly improbable.

===================

Jai again: "Even so, do you still think that a 3-6'C by 2060 is even a remote possibility?"

===================

It seems likely to me. It assumes that warming is likely to increase, at a rate that is somewhere between a linear and exponential trend.

Here's the same temperature data you linked to, but extended to the most recent year (2012). Blue line is annual temperature, red line is a LOESS smoothed version, yellow line is a linear trend over the past three decades:

The linear trend is 0.6C/decade (as noted above, the trend for the most recent decade [0.48C/decade] is actually slower than the overall trend).

Extrapolating that 0.6C/decade trend for five decades would give 3C warming by the 2060s.

If one assumes that temperature will increase exponentially, extrapolating that to 2062 would give about 7.5C of warming.

So my expectation (3C to 6C, which also matches the IPCC's projection) suggests that the temperature will increase at a rate that is faster than linear, but slower than exponential.

That said, projecting a past trend in noisy data so far into the future is obviously unreliable. I'm just going through this to show that, yes, 3C to 6C warming in the Arctic over the next five decades is certainly plausible.

===================

Back to Jai Mitchell one last time: "How does this change your perception of the comparisons between now and the last super interglacial of 400,000ybp when temperatures were close to what they are today for about 15,000 years and leading to the melting of the Greenland ice cap and the West Antarctic Shelf?"

===================

I'm not sure what perception of mine is supposed to change. I was the one who originally pointed out here that GIS and WAIS basically melted away completely during MIS 11. If temperatures stay high for the next few millennia, I would expect that to happen again. Am I supposed to change that expectation, and if so, why?

Jai Mitchell

Ned,

You are indeed correct, I misstated the trend. It is 1C or so increase in arctic temperature per decade.

That being said, you post a GISTEMP graph that clearly shows temperatures rising 3'C over the least 30 years and you then say that a 3-6C rise in the next 50 years is plausible? That seems beyond the pale to me. Either you are in denial about what is currently happening in the arctic today or you are a fan of Lindzen who likes to propose wanky theories as to why there won't be a water vapor component to climate sensitivity.

The 5C step change brought about by a June 1st ice free state is in the paper I linked to you. The isothermic ice melt that we are currently experiencing will rapidly collapse in the next few decades leading to a step increase in arctic temperatures.

Your perception is the one that MIS 11 (or even the Eemian interglacial) having not experienced a 50GT methane pulse indicates that the potential for one in the next 50 years is implausible.

MIS 11 temperatures in the arctic were consistent with today's temperatures, we will likely be experiencing temperature increases much larger than the 6C that you hope for over the next 50 years.

Ned Ward

Jai writes: "That being said, you post a GISTEMP graph that clearly shows temperatures rising 3'C over the least 30 years and you then say that a 3-6C rise in the next 50 years is plausible?"

Sorry, but you must not be reading it right. Temperatures have risen about 1.8C over the last 30 years, not 3C. To get 3C of warming you'd need to go back to the 1890s or so.

Ned Ward

"you failed to respond to the 5C step change when we reach a June 1st 2030 0% sea ice extent."

I haven't found that yet, but you've linked to several papers in your comments and maybe I was looking in the wrong place. The closest match I can find is Lawrence et al. 2008, which claims that the NOAA CCSM model often shows "rapid ice loss events" when September sea ice extent drops by a couple million km2 over a few years. They say this results in an increased warming of ~3C in fall or 1.6C annually averaged.

That's the closest I've seen in your links, though it's not 5C and I didn't notice anything about June 1st or 2030.

Ned Ward

Oh, and that 1.6C/decade that Lawrence 2008 found during "RILE"s isn't an addition on top of the warming trend, it is the trend after the RILE. Their model shows an average of 0.46C/decade before the RILE (quite close to this past decade's 0.48C/decade warming!) and 1.6C/decade after.

So if you postulated 2 decades of 0.46C (2010-2030) followed by 3 decades at 1.6C, you'd end up with a total of 5.7C warming over the five decades. Which in fact is within the IPCC's projection of 3 to 6C warming in the Arctic by 2050.

It's also worth noting that this is a model result, and one that according to Lawrence et al. only occurs in 50% of the models. There's no guarantee this will actually happen.

At least, that's my understanding of what they say. I could be missing something.

Ned Ward

"by 2050" should read "by 2060", sorry.

Ned Ward

There's a pretty good article on this topic by Chris Mooney in Mother Jones:

How Much Should You Worry About An Arctic Methane Bomb?

Jai Mitchell

Ned,

Sorry, I thought you were not answering so stopped visiting this thread.

the 5C warming is found here:

http://arxiv.org/pdf/0812.4777.pdf
Nonlinear threshold behavior during the loss of Arctic sea ice

figure 1 shows expected temperature increases of 5C when the arctic is ice free in June.

this is an older paper though, a newer one, though it was designed to show how a tipping point would not necessarily be reached modeled a 10C SST increase during the same ice loss event.

http://www.seas.harvard.edu/climate/seminars/pdfs/Tietsche_GRL_2011.pdf
Recovery mechanisms of Arctic summer sea ice

See figure 2

------------

With regard to the actual topic of this post. The real issue is not air warming it is ocean warming at the shelf and the perilous condition of ESAS sediments and whether or not they

a) contain a high volume of methane

and

b) are starting to release this methane because of ice loss.

I suspect that these questions cannot be answered by anyone except those who are currently studying it and their paper has been accepted for publication but is, as yet, unavailable.

The simple fact that the models and projections STILL have it wrong, that the people involved refuse to use PIOMAS but rather use extent as a predictive tool, and the excessive rate of volume melt indicates that we have already reached a tipping point.

back in 1998, we just didn't realize it.

2007 should not have been a surprise.

Ned Ward

Jai, I feel like I'm chasing unicorns here. You keep citing papers, and then I spend a lot of time reading them and discover that they don't say anything along the lines of what you're claiming.

You first introduced the idea of a "5C step change" in this comment:

"In fact, I see that the actual trend indicates a step-change in temperature due to total sea ice loss by 2030 of 5C, This additional warming effect will be on top of the 2.5C/decade warming trend that we have previously seen." [6 Aug 2013 19:56]

You then reiterated the "5C step change" claim:

"In addition, you failed to respond to the 5C step change when we reach a June 1st 2030 0% sea ice extent." [6 Aug 2013 21:45]

I said I didn't know where that came from. You then replied that it was in a paper that you had linked to:

"The 5C step change brought about by a June 1st ice free state is in the paper I linked to you." [7 Aug 2013 22:06]

So I looked back at the first comment where you mentioned the "5C step change" thing, and there were three papers linked there:

(1) Screen and Simmonds 2010. That paper is about reanalysis data for the 1989-2008 period. It says nothing at all about a 5C step change or an ice-free June 2030.

(2) Wang and Overland 2009. That paper models sea ice retreat over the next century. It doesn't predict an ice-free June in 2030, though it does mention the possibility of a nearly ice free September by the late 2030s. It doesn't refer to a "5C step change" in 2030, though it does mention that IPCC AR4 projects the Arctic to be 5C warmer than baseline in autumn by 2070. Note that that is the total warming, not an additional "step change" on top of the underlying trend.

(3) Lawrence et al. 2008. This paper discusses the simulated rapid loss of ice that occurs in about half of models. It says nothing about June 2030, and nothing about a 5C step change. Figure 1a does show a temperature curve going from "-2" on the left axis to "+3" on the right axis, which could easily be mistaken for a 5C step change ... but only the right axis is temperature, the left axis is sea ice extent in million km2.

When I pointed out that none of the papers you'd linked to supported the "5C step change" concept, you replied:

"the 5C warming is found here [...] figure 1 shows expected temperature increases of 5C when the arctic is ice free in June." [14 Aug 2013 20:13]

That's a new paper, it's not any of the ones you had originally cited. So why did you tell me (in the 7 Aug comment) that the source for the "5C" claim was in one of the papers that you'd already cited?

OK, whatever. So I looked at the new paper (it's a preprint for Eisenman and Wettlaufer 2010). Figure 1 says that a model Arctic Ocean that is ice-free for most of the year will have temperatures in the mixed layer approaching 5C in September. But the annual mean looks like something around 1C, not 5C. I don't know what the current annual mean temperature of the mixed layer is, but it's probably somewhere between -1C to -2C, so this would represent a warming of up to 3C relative to present conditions. Needless to say, this is not "a step change of 5C on top of the existing trend".

At this point I'm pretty much ready to give up. I keep reading the papers you're linking to, and not only do they not say what you claim they do, none of these papers contradicts the regional warming of 3C to 6C by 2060 that I originally proposed, and that you immediately rejected as not remotely possible.

It would prevent a lot of wasted time on other people's behalf if you could just make sure that you're only citing papers that really say what you claim they do.

Ned Ward

Back on the subject of methane.

Jai writes: "The real issue is not air warming it is ocean warming at the shelf and the perilous condition of ESAS sediments and whether or not they a) contain a high volume of methane and b) are starting to release this methane because of ice loss."

(1) A newly discovered source is not the same as a source that is new.

(2) Quite a bit of ice has already been lost since the 1980s. Any new methane flux from the ESAS has not had much effect on the global atmospheric methane concentration, which is not increasing particularly fast.

Jai: "The simple fact that the models and projections STILL have it wrong, that the people involved refuse to use PIOMAS but rather use extent as a predictive tool, and the excessive rate of volume melt indicates that we have already reached a tipping point."

How do you know we've reached a tipping point?

Did you even notice that the paper you just cited a few sentences ago (Eisenman and Wettlaufer 2010) specifically addressed the question of "tipping points"? There's a whole section of the paper dealing with this! If that's too much, the first sentence of their conclusion is written in pretty plain English and is easy to read.

Short version: no, we haven't passed a tipping point and even a seasonally ice-free Arctic can be a stable state.

LRC

My definition of tipping point (I stand corrected if I am wrong): The point that has been reach where returning to previous state is not possible unless an opposite force is applied.
By that definition. If we are heading to a stable state of seasonal ice free Arctic, then we indeed have passed a tipping point. The problem with tipping points is that unless through many previous examples you know what is going to happen, you have no way of knowing when it occurred and once beyond it, how far it will take you until it has reached its new equilibrium. The other problem is that if you go by one tipping point to fast, momentum can then carry you beyond the next unseen tipping point in which case you can get into a situation of a runaway freight train whose stopping point no one can predict.
In comparing environmental changes to previous records, most took far longer to occur and therefore your tipping points were far more controlled. The only examples that we can equate to are when there was a natural world wade catastrophe. In those cases the time line resulted in changes in days, but I believe we are not that far off as we are talking about changes in decades not millennia.

Ned Ward

"My definition of tipping point (I stand corrected if I am wrong): The point that has been reach where returning to previous state is not possible unless an opposite force is applied."

We're probably drifting further and further off topic, but ...

I think the language here is a bit fuzzy. Both of the papers in Jai's last comment specifically say that Arctic sea ice has not passed a tipping point (and will not any time soon).

By tipping point, they mean a point where the system becomes unstable, such that an initial decline in sea ice inevitably leads to further decline and the disappearance of most of the ice. According to the papers Jai cited, that doesn't really happen, or at least not any time soon.

Consider three types of systems:

1. The system resists change.
2. The system changes in proportion to the force applied to it.
3. The system runs away, such that a small force sets in motion a self-sustaining process in which it drifts further and further away from its initial state.

The two papers Jai linked to say that sea ice is an example of type 2 here. A certain warming (or cooling) will cause sea ice to decrease (or increase) to a new equilibrium, at which point the ice loss (or gain) stops. If you then reverse the forcing, the ice will go back to its previous state. The system moves when you apply pressure, and stops moving when you stop applying pressure.

In this way of talking about it, a tipping point would be the point where behavior (3) takes over. For example, people have suggested that there is a tipping point for land ice caps (Greenland and WAIS). A small amount of warming could lead to initial melting of the ice, lowering the altitude of the ice sheet, which in turn leads to further melting, and further lowering. In that case, even if type climate stops warming, the disintegration of the ice sheet becomes self-perpetuating.

But lots of people use the term "tipping point" in different ways, some of them very loose and ambiguous.

LRC

@ Ned: Thanks for the clarification.
If you treat the Arctic in isolation from the rest of the world then I could see that indeed you could argue that the tipping point has not been reached. That argument hs been made about the Antarctic and its ability to sustain its ice sheets. The wind and currents trapping in the cold. Its is more and more been proven the the building heat in the world is still getting to the AIS, and many critical ones are in danger of making a major collapse in the near future.
The reason I bring that example up is that What is going on in the rest of the world, building heat budget, changing wind and ocean currents, will come back and hit the Arctic hard. Just as the loss of Arctic Ice has already changed the jet stream and ocean currents to a small extent.
My previous argument is that even if we were to return to Arctic 'norms', the ice will still be lost in the long run, because the forces built up world wide will still doom the Arctic ice. The only way around it is for a negative feed back of equal strength to counter act that.
To get back to time bombs: something that get little play are the changes happening in the sub Arctic region such as the Boreal forest. In Canada they are being devastated by pests that are no longer getting killed off in the winter because it no longer gets cold enough. That is killing off huge tracts of old growth forest making them ripe for fire. That heats up the land and can farther heat up the land in the High Arctic. When (not if) that dries up you will then get the same fire conditions as are in Siberia.
I am sorry but as far as I can see, no matter how you define tipping point, that has gone long ago it is just a matter of how severe. As far as time bombs, you have man created CO2 that is still exponentially increasing, trapped methane gas being released and I believe will be released exponentially unless the Arctic can be xuddenly cooled by 5C+ over night and the whole sub to high Arctic ready to go up in flames .

Ned Ward

Michael Tobis continues to write about this topic:

Climatifact: Seven Points in Support of Shakhova? Or not?

Ahmed refers in the Twitter exchange to a paper in Rev Geophys, suggesting that Arctic thawing may release in excess of 50 GT of C, a very serious matter, amounting to something like 10% of our remaining margin to a best-guess warming around the best-guess dangerous threshhold of 2 C. This is in keeping with my prior understanding, and make no mistake, it is very bad news – it amounts to more than 50 billion tons MORE of fossil fuel that needs to be left in the ground for a given level of damage.

But Ahmed refers to the paper in support of a very different assertion, that 50 GT of methane would be released. It’s commonly assumed as a rule of thumb that an abrupt methane release is from 20 to 70 times worse per molecule than the same amount of carbon released as CO2. So if true this would be very serious business indeed. 50 billion tons of methane would plausibly be civilization-ending and a massive extinction event. But the paper to which he points triumphantly says nothing of the sort.

So I conclude that he doesn’t really know what he is talking about. Specifically he has already shown that he is confused about the distinction between methane releases and CO2 releases, something that someone on the climate beat ought to be clear about.

THE MAIN ISSUE WITH THE CLATHRATE BOMB SCENARIO

The fact that there’s a lot of methane under the sea floor is not in dispute. The question is whether there is a way to destabilize a whole lot of it at once.

In order to justify this, Shakhova points to a possibility that some clathrates remain in the frozen phase even though they are at an unstable depth. This can occur if they are encased in water ice. A few nodules of this configuration have been identified, ironically because they are a threat to oil rigs, but they have NEVER been observed in the East Siberian sea, and it’s a long way from a few ounces to fifty billion tons. If fifty billion tons of the stuff were distributed just below the sea floor, the scenario proposed would not be wholly implausible. But there is no evidence of anything remotely like that, and no mechanism whereby it might exist.

Anything which does not directly defend the existence of a large deposit of clathrates existing for millennia at pressures where they ought to have long since disintegrated is not a serious defense of the clathrate bomb scenario. And none of Ahmed’s points address this.

Verify your Comment

Previewing your Comment

This is only a preview. Your comment has not yet been posted.

Working...
Your comment could not be posted. Error type:
Your comment has been posted. Post another comment

The letters and numbers you entered did not match the image. Please try again.

As a final step before posting your comment, enter the letters and numbers you see in the image below. This prevents automated programs from posting comments.

Having trouble reading this image? View an alternate.

Working...

Post a comment

Your Information

(Name is required. Email address will not be displayed with the comment.)