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binntho

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Re: "Stupid" Questions :o
« Reply #2600 on: September 10, 2019, 06:31:38 PM »
If the Lake Agassiz outburst cooled that area down rapidly, then the temps from the ice cores will show that.

How does that theory explain the rapidly rising (proxy) temperatures referred to in the video?

The ice core from the Greenland glacier collects snow that fell in the past. The snow, as with all precipitation, comes from evaporation some where else.

In the case of the Greenland glacier, the evaporates that form the snow are mostly from the surface of the North Atlantic Ocean south of Greenland, more or less where the cold blob has been hovering these last years.

The surface temperature of the ocean affects the proportion of oxygen isotopes in the evaporated water. So the proportion of oxygen isotopes is a proxy for the surface temperature where the water evaporated. The ice core is measured for the oxygen isotope ratio as a proxy for the surface temperatures of the Northen Atlantic.

Any and all proper publications that I have read that discuss the Greenland Ice Cores make this very clear - so I'm surprised every time somebody starts claiming that the Greenland ice cores somehow show global temperatures - they can be a good proxy, but one that is very vulnerable to anomalies in the Northern Atlantic.

Generally this can be taken as a fairly good proxy for global temperatures, with the caveat that the Northern hemisphere can and does fluctuate more than the middle latitudes.

But the lake Agassiz burstthrough (and similar events) have the potential to stop the AMOC and dump lots of cold water into the North Atlantic, causing a "mega cold blob".

So now the evaporates are from an anomalously cold area of ocean, and what's more, an area that has cooled down extremely rapidly. The oxygen isotope ratio reflects this.

In short: Greenland ice cores tell us what the surface temperatures were in the North Atlantic. As the recent cold blob in exactly that area shows, future palaeometeorologists(!) might well be fooled into thinking that the earth had not really been warming that much in the 2010's, since the proxy they are using is primarily sensitive to surface temperatures in the North Atlantic which is having a mega cold blob causing the oxygen isotope ratio in the evaporates that eventually snow down on the glacier to reflect the temperatures of the ocean surface where they evaporated ... don't know how to make this any clearer.

It has nothing to do with Greenland temperatures!!!!!!!!
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Jim Hunt

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Re: "Stupid" Questions :o
« Reply #2601 on: September 10, 2019, 08:51:53 PM »
Don't know how to make this any clearer.

You don't need to. I got the "cold blob" message the first time around. Thanks for the expanded explanation, but you still haven't answered my very own "stupid question".

What in your view caused the extremely rapid rise in (proxy) temperature mentioned by Jim White? The AMOC suddenly started up again?
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binntho

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Re: "Stupid" Questions :o
« Reply #2602 on: September 10, 2019, 09:00:31 PM »
Don't know how to make this any clearer.

You don't need to. I got the "cold blob" message the first time around. Thanks for the expanded explanation, but you still haven't answered my very own "stupid question".

What in your view caused the extremely rapid rise in (proxy) temperature mentioned by Jim White? The AMOC suddenly started up again?

I didn't watch the video (haven't got the attention span) but I'm familiar with the thing and I can see that I've been talking about sudden drops rather than spikes. A total brain fart as we used to say in my salad days.

Perhaps it was the AMOC starting up, perhaps it was something else that drew in proportionally more humidity from elsewhere and thus skewing the proxies for a while. I don't know.

The ice cores do not measure Greenland temperatures at all (increadibly common mistake) and are a somewhat unreliable proxy for global temperatures. If the ice core says that temps rise by 1 degree per year for 5 years (and does it twice?) then it's obviously showing something other than global temperatures.

The difference between the LGM at it's coldest and the Holocene maximum is somewhere around 8 degrees. The forcings needed to go from one to the other over a few thousand years are massive (and surprisingly badly understood), but there is simply no forcing that can cause a 1 degree global temperature rise, let alone do it several years in a row.
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Archimid

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Re: "Stupid" Questions :o
« Reply #2603 on: September 11, 2019, 12:06:37 AM »
Variability of Arctic sea-ice cover at decadal to millennial scales: the proxy records

http://www.pastglobalchanges.org/products/latest/11511-variability-of-arctic-sea-ice-cover-at-decadal-to-millennial-scales-the-proxy-records

Quote
Despite limitations, the marine data provide clues on sea-ice cover variations with time windows ranging from decades to centuries, thus yielding smoothed records. At the scale of the Holocene, proxy-data suggest limited variations in general, with likely resilient perennial sea ice in the central Arctic Ocean, but greater variations in the seasonal sea ice as expressed in terms of spring sea-ice concentration (Sha et al. 2014) or number of months of sea ice (de Vernal et al. 2013b) in the Arctic and subarctic seas which are within the limits of winter sea ice. In other words, the variability of sea-ice cover as reconstructed from marine proxies illustrates more the seasonality of its extent and concentration than the actual changes in the Arctic-wide extent of sea ice. The amplitude of local changes during the mid- and late Holocene seems to be mostly comprised within the range of interannual variations as recorded during the last decades.

From the link:




Edit: Missed the link, thanks for pointing it out.
« Last Edit: September 11, 2019, 12:15:58 PM by Archimid »
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binntho

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Re: "Stupid" Questions :o
« Reply #2604 on: September 11, 2019, 06:31:22 AM »
Variability of Arctic sea-ice cover at decadal to millennial scales: the proxy records

Quote
Despite limitations, the marine data provide clues on sea-ice cover variations with time windows ranging from decades to centuries, thus yielding smoothed records. At the scale of the Holocene, proxy-data suggest limited variations in general, with likely resilient perennial sea ice in the central Arctic Ocean, but greater variations in the seasonal sea ice as expressed in terms of spring sea-ice concentration (Sha et al. 2014) or number of months of sea ice (de Vernal et al. 2013b) in the Arctic and subarctic seas which are within the limits of winter sea ice. In other words, the variability of sea-ice cover as reconstructed from marine proxies illustrates more the seasonality of its extent and concentration than the actual changes in the Arctic-wide extent of sea ice. The amplitude of local changes during the mid- and late Holocene seems to be mostly comprised within the range of interannual variations as recorded during the last decades.

From the link:

You forgot the link Archimid, it looks like an interesting publication. But the quoted text, although in favour of perennial ice, is not conclusive.

because a thing is eloquently expressed it should not be taken to be as necessarily true
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KiwiGriff

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Re: "Stupid" Questions :o
« Reply #2605 on: September 11, 2019, 07:39:06 AM »
Google is your friend. ;)

link for Variability of Arctic sea-ice cover at decadal to millennial scales: the proxy records.

http://www.pastglobalchanges.org/products/latest/11511-variability-of-arctic-sea-ice-cover-at-decadal-to-millennial-scales-the-proxy-records





binntho

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Re: "Stupid" Questions :o
« Reply #2606 on: September 11, 2019, 08:58:41 AM »
Google is your friend. ;)

link for Variability of Arctic sea-ice cover at decadal to millennial scales: the proxy records.

http://www.pastglobalchanges.org/products/latest/11511-variability-of-arctic-sea-ice-cover-at-decadal-to-millennial-scales-the-proxy-records

Thans KiwiGriff. The article only adds to the uncertainty of the proxies they use. To my mind, the presence of wave ridges along the north shores of Greenland and the CAA are conclusive evidence of an Arctic Ocean sea ice cover that would be well under the 1MKm2 needed to qualify as a BOE (i.e. slightly less than 1/3 of what was left in 2012).

And per my personal conviction, I don't believe that a 1Mkm2 piece of ice floating at the North Pole surrounded by water has any realistic life expectancy.
because a thing is eloquently expressed it should not be taken to be as necessarily true
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Hopen Times

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Re: "Stupid" Questions :o
« Reply #2607 on: September 11, 2019, 11:37:31 AM »
It has nothing to do with Greenland temperatures!!!!!!!!

I am not sure if the University of Copenhagen agrees with you:
Quote
Under which conditions did the water evaporate, and how much cooling did the vapour experience on its way to the ice cap before forming the precipitation that ended up as the layers in the ice cap?
http://www.iceandclimate.nbi.ku.dk/research/past_atmos/past_temperature_moisture/

Quote
Every time precipitation forms, the air mass will become more depleted in heavy isotopes. In the language of physics, fractionation takes place. During cold conditions (e.g. during winter or in a cold climatic period), the air masses arriving in Greenland have cooled more on the way, thereby having formed more precipitation and the remaining vapor is therefore more depleted in heavy isotopes (corresponding to lower δ18O vales).
http://www.iceandclimate.nbi.ku.dk/research/past_atmos/past_temperature_moisture/fractionation_and_temperature/

Quote
From analyses of the isotopic composition of Greenland ice cores it is possible to obtain a record of past Greenland climate reaching more than 100,000 years back in time. ... But the isotopes also tell about the climatic conditions in the areas from which the moisture source originates.
http://www.iceandclimate.nbi.ku.dk/research/past_atmos/past_temperature_moisture/

As I understand University of Copenhagen, Greenland ice cores reflects both the temperature in the the areas from which the moisture source originates and the temperature the vapour experienced on its way travelling, over both sea and ice. 

This is not my field, so I am very open for that there is something I am missing here.

Edit: More on the same topic.
Quote
So while the individual δ18O and δD records tell about local temperatures, small differences between the two records tell about moisture source temperatures.
http://www.iceandclimate.nbi.ku.dk/research/past_atmos/past_temperature_moisture/isotopes_reveal/
« Last Edit: September 11, 2019, 01:09:09 PM by Hopen Times »

binntho

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Re: "Stupid" Questions :o
« Reply #2608 on: September 11, 2019, 01:47:32 PM »
It has nothing to do with Greenland temperatures!!!!!!!!

I am not sure if the University of Copenhagen agrees with you:

As I understand University of Copenhagen, Greenland ice cores reflects both the temperature in the the areas from which the moisture source originates and the temperature the vapour experienced on its way travelling, over both sea and ice. 

This is not my field, so I am very open for that there is something I am missing here.

You are right, I was way to categorical in my denials above. This is what happens when you think you remember things correctly ("Never trust memory" I was taught in High School, and I usually try not to ...)

And the plot deepens, I found this:

Quote from: https://www.clim-past.net/9/2525/2013/cp-9-2525-2013.pdf
To sum up, all the results derived either from borehole paleothermometry or from isotopic anomalies significantly underestimate temperature changes in central Greenland, thus seriously challenging the conventional isotopic approach.

where the point was that the traditional oxygen isotope approach showed what seemed to be way too large fluctuations, but a closer look showed that they were in fact bigger than they seemed! And amazingly enough, the difference between LGM and present is a full 25 degrees centigrades (but where? At the top of the ice shield it seems)

But I think I can definitely claim the following: This is not what happens to global temperatures, and thus the value of the Greenland cores as a proxy for global changes becomes somewhat doubtful.

So Jim Hunt : I didn't know the answer when I tried the first time, I know even less now!

But back to the original point: Everyone can go and look at graphs of estimated global temperatures between the last glacial and the Holocene and see that the difference on a global scale is around 6 - 8 degrees Centigrade. And according to Greenland ice cores there is a very fast rise at the end of the Younger Dryas / beginning of the Holocene, near vertical at 10 degrees.

But ice cores from Vostok do not show the Younger Dryas event! They show a change in temperatures of perhaps 10 degrees from the LGM at ~26,0000 ky to the the Holocene proper at ~14,000, in two distinct steps, the later of which was pretty steep at 4 degrees in perhaps 1200 years, or a surprisingly rapid 0.3 degrees / century.



Deep sea sediments from the Pacific and Indian oceans (i.e. mid latitude) show a much smaller difference between LMG and Holocene, perhaps as little as 2 or 3 degrees, and no Younger Dryas event.



After some searching I managed to find a paper on a subject that I find quite interesting, i.e. the Holocene temperature conundrum which has a very good graph of the warming at the end of the last ice age:



This graph shows a max difference of 5 degrees and even if it misses out on the LGM, the real warming only began at the ~17,000 ka so no harm done. And from this graph I am unable to maintain that temps might have risen at anywhere close to our current rate of 1.2 degrees per century. The fastest seems to be just over 1 degree in just under 1000 years, or at least 10 times slower than today.
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Jim Hunt

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Re: "Stupid" Questions :o
« Reply #2609 on: September 11, 2019, 03:23:03 PM »
But ice cores from Vostok do not show the Younger Dryas event!

However the original question we are endeavouring to answer was about the Arctic, not the Antarctic? Paraphrasing somewhat:

Quote
Was there, or was there not, a BOE [at the Holocene maximum]?

Jim White is from the University of Colorado's Institute of Arctic and Alpine Research

https://www.researchgate.net/profile/James_White16

Here's a 1989 paper of his with Willi Dansgaard and Sigfus Johnsen:

https://www.tandfonline.com/doi/pdf/10.3402/tellusb.v41i4.15100

which concludes that:

Quote
We present evidence that, in contrast to low elevation stations, the high elevation areas of the Greenland ice sheet receive precipitation, which mainly originates from subtropical moisture sources, under present as well as under glacial conditions.

which I guess we're all agreed on now? In the video Jim states that:

Quote
We (i.e. including Dansgaard and Johnsen) also noted that deuterium excess, which is an indication of ocean conditions, probably sea ice out in the North Atlantic, changed even faster than that.

Their 1989 paper also states that:

Quote
In the search for an explanatory mechanism behind the abrupt climatic shifts, Broecker (1987) points out that in the present ocean circulation system, cold and salty water sinks in the North Atlantic Ocean, from where it is transported southward by deep Ocean currents, via the southern hemisphere oceans, and then northward to the North Pacific Ocean, where some of it upwells. This deep water transport is compensated by surface currents, e.g., the warm North
Atlantic Current, a shut-down of which would cool the adjacent lands by 6-8°C. Conversely, reestablishing the present circulation would result in 6-8°C warming. If this were the immediate cause of the abrupt 𝛿 shifts under glacial conditions, it might also "explain" the drastic, temporary 10‰ drop in 𝛿 at the end of the Eemian interglacial (Dansgaard et al., 1972)

However thus far my limited trawl of the literature hasn't revealed any further insight into a possible "Holocene [Arctic] blue ocean event".

« Last Edit: September 11, 2019, 03:34:42 PM by Jim Hunt »
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wallen

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Re: "Stupid" Questions :o
« Reply #2610 on: September 14, 2019, 09:00:50 AM »
Could some please explain why recent images of the North pole on Worldview, are very bright, with an almost yellowish tinge.
                                     Thanks.

blumenkraft

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Re: "Stupid" Questions :o
« Reply #2611 on: September 14, 2019, 09:23:18 AM »
I would say this is due to the low solar altitude, Wallen.

Happy to be corrected on this.
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Jim Hunt

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Re: "Stupid" Questions :o
« Reply #2612 on: September 14, 2019, 11:26:04 AM »
I would say this is due to the low solar altitude, Wallen.

Spot on I would say. The North Pole on Worldview from September 16th 2018

https://go.nasa.gov/301mtDT

Switch to this year and you can see the winter "pole hole" appearing as we speak.
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slow wing

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Re: "Stupid" Questions :o
« Reply #2613 on: September 15, 2019, 08:35:18 AM »
"The 2019 melting season", Reply #6567
... with melt potentially continuing through this next week given the heat anomalies ... last years min was on 21 Sep!


Three questions I have been wondering about that relate to this melt season:

1) Are the yearly extent minima getting later?

2) Has the Arctic basin been carrying more moisture in the atmosphere at this time of year than in past decades? (Iirc there was an identified step change relating to an extreme weather event in December 2016, was it the 27th? Also, there is more open water in recent years. So this question could include a part 2b: why?)

3) If 'yes' to both 1 & 2, could 2 be at least partially the reason for 1 due to increased moisture in the atmosphere over Arctic basin retarding the loss of heat by long wave radiation?


Have any scientists been watching this and can answer one or more of those questions? Thanks.

oren

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Re: "Stupid" Questions :o
« Reply #2614 on: September 15, 2019, 09:01:07 AM »
1) The date of minima is not showing a drift either earlier or later.
2) I don't know. But I think the event you refer to was in Dec 2015.

Hopen Times

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Re: "Stupid" Questions :o
« Reply #2615 on: September 16, 2019, 08:29:33 PM »
Asking for a friend about analysing ice cores:
"Just wandering if there have been years when it was so warm so the layers of some years now are missing. Would we know that and how would we find the temperature of these years? I mean we would not find the temperatures of 2012 in Greenland ice core 200 years from now. Have there been similar periods in the past?"

blumenkraft

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Re: "Stupid" Questions :o
« Reply #2616 on: September 16, 2019, 08:56:09 PM »
You can see gaps in the core when you compare it to other cores.

Meaning, you might not see 2012 in a Greenland core, but you see it in a Himalayan or Antarctic core. And then the gap itself becomes a data point. You know this year was a melting year in Greenland but not in Alpine areas for example.

Not a scientist though, just a laymen's explanation.
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SteveMDFP

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Re: "Stupid" Questions :o
« Reply #2617 on: September 16, 2019, 09:07:54 PM »
Asking for a friend about analysing ice cores:
"Just wandering if there have been years when it was so warm so the layers of some years now are missing. Would we know that and how would we find the temperature of these years? I mean we would not find the temperatures of 2012 in Greenland ice core 200 years from now. Have there been similar periods in the past?"

Melting events don't just disappear a layer or two of the ice cores, they leave distinctive melt layers.  Thus,

"Furthermore, this melting event on July 30 also sets the record for the preceding century. Prior to 2012, melt layers at summit have been absent since 1889, and only appear again 680 years earlier."

See:
At summit: The highest temperatures in the past 12 years
http://nsidc.org/greenland-today/


Tom_Mazanec

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Re: "Stupid" Questions :o
« Reply #2618 on: September 16, 2019, 10:17:11 PM »
So the last melt was 1209, back in the Medieval Warm Spell?
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SteveMDFP

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Re: "Stupid" Questions :o
« Reply #2619 on: September 16, 2019, 10:32:49 PM »
So the last melt was 1209, back in the Medieval Warm Spell?

The MWP had more than one greenland surface melt episode:

The extreme melt across the Greenland ice sheet in 2012
https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2012GL053611

"From the same core, Alley and Anandakrishnan [1995]studied melt layers from the upper 1565 m of the GISP2 core over a time period of 10,000 years. However, the frequency of melt occurrence varies widely in time as identified by ice layers in ice cores. Prior to the 19th‐century event, another significant melt event occurred about 680 years earlier [Meese et al., 1994] preceded by several events in the Medieval Warm Period (a.k.a. the Medieval Climatic Anomaly). Melt occurred once in about 250 years from 1000 to 4000 BP (referenced to 1950) and once in about 82 years from 5000 BP to 8500 BP according to Alley and Anandakrishnan [1995]. These significant melt events are widely sporadic in different periods of the Holocene, clearly exhibiting their non‐stationary behavior. Thus, a single average value of melt frequency is not necessarily applicable to represent climate change at a given time period in the past, the present, or the future."

Earlier in the paper, the distinctive appearance of melt episodes in the ice core is described.

Hopen Times

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Re: "Stupid" Questions :o
« Reply #2620 on: September 17, 2019, 10:50:59 AM »
Thank you!!

SirLurkALot

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Re: "Stupid" Questions :o
« Reply #2621 on: September 17, 2019, 09:59:59 PM »
Just looking at Daily Average Arctic Sea Ice Thickness graph from PIOMAS.
So I get that momentum, and bottom melt cause
the minimum thickness for most years to be usually around mid October,
unlike extent, where minimum occurs a month earlier.
What I don't get is why there is a local minimum of thickness around
August, then a  'local maximum' of thickness around
mid/end September, which falls off steeply again to the global minimum.
I'd have expected any new ice formed after the extent minimum to be very thin, and
so cause the average thickness to also decrease.
Can someone put me straight on what the mechanism is for 
thickness graphs to have these double dips and peaks?
Thanks.
http://psc.apl.uw.edu/wordpress/wp-content/uploads/schweiger/ice_volume/Bpiomas_plot_daily_heff.2sst.png

oren

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Re: "Stupid" Questions :o
« Reply #2622 on: September 17, 2019, 10:54:44 PM »
October minimum is easy, it's due to refreeze start, lots of thin new ice takes average down. This should take place after area (not extent) minimum.
August minimum is more difficult, but I think it's due to the distribution of thicknesses in the model. When area is lost, the thinnest ice is gone. At some point the very thick ice is the bulk of the volume, and then average starts going up. Wipneus posts an internal distribution graph from time to time, you can check that graph to see if this explanation makes sense.

philopek

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Re: "Stupid" Questions :o
« Reply #2623 on: September 18, 2019, 01:24:52 AM »
October minimum is easy, it's due to refreeze start, lots of thin new ice takes average down. This should take place after area (not extent) minimum.
August minimum is more difficult, but I think it's due to the distribution of thicknesses in the model. When area is lost, the thinnest ice is gone. At some point the very thick ice is the bulk of the volume, and then average starts going up. Wipneus posts an internal distribution graph from time to time, you can check that graph to see if this explanation makes sense.

I started to reply to him and came to the conclusion that it won't be comprehensive enough and that this would be a perfect task for Oren.

My thought was exactly that certainly you would chime in, hence i know my "Pappenheimer's" that's a compliment just to make sure it's understood that way ;)

binntho

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Re: "Stupid" Questions :o
« Reply #2624 on: September 18, 2019, 04:09:25 AM »
Asking for a friend about analysing ice cores:
"Just wandering if there have been years when it was so warm so the layers of some years now are missing. Would we know that and how would we find the temperature of these years? I mean we would not find the temperatures of 2012 in Greenland ice core 200 years from now. Have there been similar periods in the past?"

Occasional (and ever more frequent) melting events on the high glacier come nowhere near to being able to melt away the previous winter's accumulated snowfall. So 2012's snow is still very much up there.

If summer melting ever manages to melt all the new snow from the top of the Greenland glacier it would be because 1) Temps have gone up tens of degrees Centigrade, or more likely, that ongoing negative ice balance has so reduced the height of the central glacier that it has fallen below the (by then significantly raised) equilibrium line below which all accumulated snow melts.

Once that happens, total disappearance of the ice sheet will be within a few tens of years.
because a thing is eloquently expressed it should not be taken to be as necessarily true
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binntho

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Re: "Stupid" Questions :o
« Reply #2625 on: September 18, 2019, 12:46:24 PM »
As kindly suggested I apply to those of you who 'get it' here: Why should there be any connection between ocean depth and surface ice. The assumption that deep water in the CAB should somehow protect the ice keeps popping up, but why should that be the case?
because a thing is eloquently expressed it should not be taken to be as necessarily true
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SirLurkALot

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Re: "Stupid" Questions :o
« Reply #2626 on: September 18, 2019, 02:31:14 PM »
October minimum is easy, it's due to refreeze start, lots of thin new ice takes average down. This should take place after area (not extent) minimum.
August minimum is more difficult, but I think it's due to the distribution of thicknesses in the model. When area is lost, the thinnest ice is gone. At some point the very thick ice is the bulk of the volume, and then average starts going up. Wipneus posts an internal distribution graph from time to time, you can check that graph to see if this explanation makes sense.
Ok, thanks Oren.

oren

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Re: "Stupid" Questions :o
« Reply #2627 on: September 18, 2019, 03:44:19 PM »
As kindly suggested I apply to those of you who 'get it' here: Why should there be any connection between ocean depth and surface ice. The assumption that deep water in the CAB should somehow protect the ice keeps popping up, but why should that be the case?
It ain't necessarily so.
But the physical reasoning behind it is that salty warm water sink below cold freshwater. This is happening along the Barents/CAB border with the incoming current from the Atlantic, A-Team used to post a lot about this back in 2016(?). And also with the incoming Pacific water, as I recall they hug the coast of Alaska to the right and sink in the Beaufort.

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Re: "Stupid" Questions :o
« Reply #2628 on: September 18, 2019, 04:40:56 PM »
that salty warm water sink below cold freshwater.

May i add, that salty warm water sinks below cold freshwater because it's cooling down on its way north but it's still saltier (denser) than the Arctic ocean surface water and therefore falls down. Despite the cooling down, it is still a little warmer and takes that heat with it.

(for how i understand it)
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Re: "Stupid" Questions :o
« Reply #2629 on: September 18, 2019, 04:57:26 PM »
I think you're right blumenkraft. 'it' is not alone but surrounded by other 'it's. There's safety in numbers. Keep warm  ;) :)
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Re: "Stupid" Questions :o
« Reply #2630 on: September 18, 2019, 05:02:58 PM »
As kindly suggested I apply to those of you who 'get it' here: Why should there be any connection between ocean depth and surface ice. The assumption that deep water in the CAB should somehow protect the ice keeps popping up, but why should that be the case?
Whereas the shelves will support wave action once a pressure waves passes the edge of the shelf it dissipates into water which can be orders of magnitude deeper.

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Re: "Stupid" Questions :o
« Reply #2631 on: September 19, 2019, 05:02:19 AM »
As kindly suggested I apply to those of you who 'get it' here: Why should there be any connection between ocean depth and surface ice. The assumption that deep water in the CAB should somehow protect the ice keeps popping up, but why should that be the case?

I'm still waiting to hear from someone who "gets it". I am seeing a lot of talk about how warm salty water can sink under cold fresh water - well of course, if the circumstances are right. And I'd venture to suggest that we could all have written all the answers I've seen so far (except the one from johnm33 which I didn't really understand - how do shelves support wave action? What pressure waves?)

Except for johnm33's not-reallly-an-answer, none of the others have anything to do with bathymetry. They do not answer the question: Why should the ice in the CAB be protected by deep waters?

The reason why I'm pursuing this is that somebody on another thread posted something along the lines of the 100m+ depths in the CAB being a refuge for the ice because warm water will fall over the shelf edges and sink down into the deep.

This is obviously not logical. Warm water does not sink, other things being equal, and when the warm water reaches the Arctic, we all know that it can sink for various reasons, none of which has anything to do with the depth of the ocean.

The bathymetrY question is still unanswered. Pehaps it should perhaps be split into two questions:

1) The Siberian and Alaskan shelves vs. the deep ocean = does ice melt faster over shallower waters? Is there an invisible boundary where bottom melt dynamics change because of increased depth? Sounds reasonable, but why?

2) Incoming warm surface waters from the Atlantic do not sink unless surface conditions are right (lots of fresh water) or because it cools enough to start sinking anyway. (Which reminds me that many fear a slowdown of the AMOC because the warm surface waters will mix with fresh water and stop sinking ...) = but none of this has anything to do with ocean depth! So is there a mechanism that would stop surface currents from flowing out over the CAB and thus protecting the ice there from incoming warm currents?
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Re: "Stupid" Questions :o
« Reply #2632 on: September 19, 2019, 07:48:36 AM »
2) Incoming warm surface waters from the Atlantic do not sink unless surface conditions are right (lots of fresh water) or because it cools enough to start sinking anyway. (Which reminds me that many fear a slowdown of the AMOC because the warm surface waters will mix with fresh water and stop sinking ...) = but none of this has anything to do with ocean depth! So is there a mechanism that would stop surface currents from flowing out over the CAB and thus protecting the ice there from incoming warm currents?
you were given a perfectly good answer that you did not follow up on. Atlantic waters do sink, and they do so more or less at the shelf break - no surprise there, as they can't sink before that. This will continue as long as the CAB surface is fresh - and it is fresh because of the freezing and melting processes. Ergo, the bathymetry plays a very important role in the region.
If the CAB were to magically mix and become salty, the incoming Atlantic water might stop sinking, and might continue to maintain the CAB in its salty state. But for that to happen the current semi-stable equilibrium needs to break.
A-Team posted about this many times in the past, including some research that showed that the fresh water front was shifting backward slowly, IIRC. And tons of animations showing the ice edge and the shelf break and the relation between the two. Someone with more time and more willingness to help could find it for you - but then again you could find it too.
In some other areas of the Arctic, bathymetry plays a much smaller role - it really depends on the specific geography. The Beaufort is deep and melts early, the ESS is shallow and melts late. But that is no reason to ignore the logic in those regions where it does matter.

Here's some random image showing the situation more or less.



Figure 1. Currents in the Northern Norway, Fram Strait, Barents Sea, and Arctic Ocean (AO) region. The warm currents dominated by Atlantic Water are marked in red, for example the North Atlantic Current (NAC), and West Spitsbergen Current (WSC). The cold Arctic Water currents are in blue, for example the East Greenland Current (EGC). In the Lofoten/Vesterålen region the NAC touches the North Norwegian shelf and forms a strong slope current.

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Re: "Stupid" Questions :o
« Reply #2633 on: September 19, 2019, 10:58:24 AM »
However a wave is generated it is a visible sign of a pressure wave passing through the water. So in 20m of water that [1m?]wave may have enough energy to mix recently melted water inhibiting refreeze. That same pressure wave moving into 200m deep water will barely cause a [10cm?] ripple. On the shelves once a certain, differing, threshold of melt has passed wave action will mix the water around the ice, over the deep ocean the meltwater will move to the surface or as close as it can get thus allowing the ice to 'repair' itself with easy to freeze freshwater.
 Incoming Atlantic waters are already denser, more saline, than the surface waters of the Arctic, which is why their currents follow the channels into Barentz, and why they fall into the Eurasian basin.

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Re: "Stupid" Questions :o
« Reply #2634 on: September 19, 2019, 02:46:39 PM »
A simple break down:

1. When sea ice is melting, there is a supply of cold fresh water.

2. The opposite of cold fresh water is warmer saltier water.

3. Fresh water tends to float on denser saltier water.

4 Supply of cold fresh water from melting is next to ice, in correct layer, so doesn't need to move up or down, so doesn't cause mixing.

5. If the water depth is large, this creates mechanism for separating warmth from the ice.

6. If water depth is shallow, warmth can't sink far.

7. If depth is shallow, waves tend to have more effect mixing the shallow water. (7b So separating into layers doesn't work as well.)

binntho, perhaps you could help by indicating which of these statements you dispute and/or don't follow.

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Re: "Stupid" Questions :o
« Reply #2635 on: September 19, 2019, 04:47:12 PM »
1. Only with multi-year ice if I understand correctly. Melting first year ice gives saline water, not fresh water. Correct me if I'm wrong please.
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Re: "Stupid" Questions :o
« Reply #2636 on: September 19, 2019, 05:36:43 PM »
1. Only with multi-year ice if I understand correctly. Melting first year ice gives saline water, not fresh water. Correct me if I'm wrong please.

Melting MYI is fresher than melting FYI. But both are going to be fresher than Arctic sea water (edit even in top 50m mixed layer) that is not immediately from melt water or river water. Correct me if I'm wrong please.

(Edit 2: The more freeze thaw cycles, the fresher the ice as salt gets pushed out by both melt and freeze processes. But just a single freeze will produce fresher ice than the sea water it comes from. Perhaps also saltier if rapidly frozen just once but still fresher than water it came from.)

Yes a pocket of brine can find its way out of FYI and be salty and generally sink. Perhaps I am rather excluding that from what I am referring to as melt water.

« Last Edit: September 19, 2019, 05:54:31 PM by crandles »

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Re: "Stupid" Questions :o
« Reply #2637 on: September 19, 2019, 08:29:09 PM »
As kindly suggested I apply to those of you who 'get it' here: Why should there be any connection between ocean depth and surface ice. The assumption that deep water in the CAB should somehow protect the ice keeps popping up, but why should that be the case?
I don't really 'get it' being ocean dynamics complicated even for oceanographers but I am going to give my simplified two cents.

- There is a mixed layer, top 50 m. This layer is called mixed because, thanks to the action on the surface by winds, waves, etc., the mechanical input is able to mix differences in temperature and salinity by induced turbulence. It is strong enough to keep stratified layers from forming. Curiously the mixed layer has an increased salinity in most oceans except in the Arctic Ocean, which mixed layer is much fresher than at higher depths. The mixed layer ends by an abrupt salinity increase called halocline.

What makes the water of Arctic ocean mixed layer "fresh" and cold relatively? I think it's rivers, and the fact that the halocline comes before the increase of temperature, deeper under the halocline. So thanks to this strong stratification layer, the heat from beneath won't reach the mixed layer, staying relatively cold, and relatively fresh. I think there's a physical explanation for the halocline coming at lower depth than the temperature increase from deep waters, but I don't remember it. If it was not the case, there would not be Arctic ice, probably.

- Currents are entering the Arctic from Bering Strait bring saltier warmer water from the Pacific (not as salty as Atlantic water).

- As these currents push their way along the shallow shelves of Chukchi, ESS, and Alaskan Coast, they encounter ice and surrounding water with much fresher water. There is some mixing between these currents and the marginal zones with broken ice, thanks to the weather and to the current eddies themselves. Since the depths are relatively small around 50 m, the currents are constrained and there is time for direct interaction with the ice and surrounding water.

- These currents reach the continental shelves and (although slightly diluted due to the mixing they have encountered in the long distance from the Pacific) they sink because their density is higher than surrounding Arctic Ocean water and suddenly the 50 m bottom is gone. They surely tended to sink in the shelf as well, but again, since the depth is relatively small, the currents are constrained, are affected by mixing, and transport heat to the Arctic ice. But once they fall to 200, 300m, below the halocline, this heat will not affect the Arctic ice (at least immediately).

- What happens with the Atlantic Currents? The depths at Barents sea are actually more varied, I think it is deeper in general (and I wonder if that is what causes that some years the ice in the Barents side persists for longer). Also the Atlantic currents are extremely massive compared to Bering inflow. But anyway, as soon as they reach the depths beyond Svalbard and FJL, these currents sink if they didn't sink before.

What happens at depth is beyond my understanding.

PS. Wikipedia page of the Arctic brings some interesting facts...
« Last Edit: September 19, 2019, 08:46:48 PM by sailor »
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Re: "Stupid" Questions :o
« Reply #2638 on: September 19, 2019, 09:47:18 PM »
I don't really 'get it' being ocean dynamics complicated even for oceanographers but I am going to give my simplified two cents.

My compliments, a perfect way to reply to condescending undertones that tell everyone else how stupid they are without providing what you just provided, knowledge and insight, simplified ;) ;) ;) but comprehensive and accurate.

Perhaps one could ad surface melt in summer to the reasons for less salinity at the surface or top layer.

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Re: "Stupid" Questions :o
« Reply #2639 on: September 19, 2019, 10:27:19 PM »
It may be a good idea to look at temperature and salinity data from buoys. Pacific and Atlantic sides have quite different profiles but the idea is the same. Water density follows salinity much more closely than temperature (at arctic ocean temps).
Ocean depth makes a difference, notably on the atlantic side, maybe due to the higher latitude and drift. Beaufort/CAB is deep, but often melts, perhaps due to shallow, low salinity warming. ESS is shallow but melts late, perhaps due to near surface permafrost.

itp110, beaufort, a while ago ...click to run
itp116, nth of greenland, more recently.

I ran a lot density gifs but they are quite similar to salinity
https://forum.arctic-sea-ice.net/index.php/topic,2417.msg212911.html#msg212911
« Last Edit: September 19, 2019, 10:36:19 PM by uniquorn »

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Re: "Stupid" Questions :o
« Reply #2640 on: September 20, 2019, 12:07:33 AM »
It may be a good idea to look at temperature and salinity data from buoys. Pacific and Atlantic sides have quite different profiles but the idea is the same. Water density follows salinity much more closely than temperature (at arctic ocean temps).
Ocean depth makes a difference, notably on the atlantic side, maybe due to the higher latitude and drift. Beaufort/CAB is deep, but often melts, perhaps due to shallow, low salinity warming. ESS is shallow but melts late, perhaps due to near surface permafrost.

Uniquorn (or anybody) maybe you know why the halocline is closer to surface than the temperature increase, saving the Arctic ice from the heat? (and that would sort of respond Binntho’s question, since that insulation is only possible over deep enough waters)
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Re: "Stupid" Questions :o
« Reply #2641 on: September 20, 2019, 01:50:41 AM »
<snip>Can anyone recommend a temp/salinity profile contours tutorial?
knowledgeable oceanologists reading this forum appear reluctant to engage in such a tricky topic ;)(I'm not one)
Attempts to show data, if even looked at, may not be conclusive


I suppose mercator chose 34m and 92m depth for a reason. It's not that deep.

why the halocline is closer to surface than the temperature increase, saving the Arctic ice from the heat?

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Re: "Stupid" Questions :o
« Reply #2642 on: September 20, 2019, 07:39:00 PM »
As kindly suggested I apply to those of you who 'get it' here: Why should there be any connection between ocean depth and surface ice. The assumption that deep water in the CAB should somehow protect the ice keeps popping up, but why should that be the case?
...
- There is a mixed layer, top 50 m. This layer is called mixed because, thanks to the action on the surface by winds, waves, etc., the mechanical input is able to mix differences in temperature and salinity by induced turbulence. It is strong enough to keep stratified layers from forming. Curiously the mixed layer has an increased salinity in most oceans except in the Arctic Ocean, which mixed layer is much fresher than at higher depths. The mixed layer ends by an abrupt salinity increase called halocline.

What makes the water of Arctic ocean mixed layer "fresh" and cold relatively? I think it's rivers, and the fact that the halocline comes before the increase of temperature, deeper under the halocline. So thanks to this strong stratification layer, the heat from beneath won't reach the mixed layer, staying relatively cold, and relatively fresh. I think there's a physical explanation for the halocline coming at lower depth than the temperature increase from deep waters, but I don't remember it. If it was not the case, there would not be Arctic ice, probably.
...
PS. Wikipedia page of the Arctic brings some interesting facts...

Thanks for that explanation. As Uniquorn points out, it is not as "idealized" as what you explain or the halocline/thermocline description in Wikipedia, but it seems THE factor: given the conditions of the Arctic Ocean, the halocline exists wherever the ocean is DEEP, inhibits mass and heat transport from the SUNK Atlantic and Pacific waters beneath, BUT the protective effect of the halocline has no room in SHALLOW shelves (peripheral seas of the Arctic proper). Temperature changes happen mostly UNDER the halocline, which helps BIG TIME the survival of the CAB in summer.

I think it is a rational explanation linking DEEP waters and SURVIVING ice.
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RoxTheGeologist

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Re: "Stupid" Questions :o
« Reply #2643 on: September 20, 2019, 09:49:36 PM »
As kindly suggested I apply to those of you who 'get it' here: Why should there be any connection between ocean depth and surface ice. The assumption that deep water in the CAB should somehow protect the ice keeps popping up, but why should that be the case?
...
- There is a mixed layer, top 50 m. This layer is called mixed because, thanks to the action on the surface by winds, waves, etc., the mechanical input is able to mix differences in temperature and salinity by induced turbulence. It is strong enough to keep stratified layers from forming. Curiously the mixed layer has an increased salinity in most oceans except in the Arctic Ocean, which mixed layer is much fresher than at higher depths. The mixed layer ends by an abrupt salinity increase called halocline.

What makes the water of Arctic ocean mixed layer "fresh" and cold relatively? I think it's rivers, and the fact that the halocline comes before the increase of temperature, deeper under the halocline. So thanks to this strong stratification layer, the heat from beneath won't reach the mixed layer, staying relatively cold, and relatively fresh. I think there's a physical explanation for the halocline coming at lower depth than the temperature increase from deep waters, but I don't remember it. If it was not the case, there would not be Arctic ice, probably.
...
PS. Wikipedia page of the Arctic brings some interesting facts...

Thanks for that explanation. As Uniquorn points out, it is not as "idealized" as what you explain or the halocline/thermocline description in Wikipedia, but it seems THE factor: given the conditions of the Arctic Ocean, the halocline exists wherever the ocean is DEEP, inhibits mass and heat transport from the SUNK Atlantic and Pacific waters beneath, BUT the protective effect of the halocline has no room in SHALLOW shelves (peripheral seas of the Arctic proper). Temperature changes happen mostly UNDER the halocline, which helps BIG TIME the survival of the CAB in summer.

I think it is a rational explanation linking DEEP waters and SURVIVING ice.

The relationship between sea ice and bathymetry is well understood, particularly on the Atlantic side of the ocean. The warm salty waters from the Atlantic sink below the fresher Arctic waters from the Atlantic waters in under the Nansen basin. On the Pacific side the warmer Pacific waters in the Chukchi sea form the deeper waters under the Beaufort Gyre. The ice edge closely tracks the edge of the continental shelf in the summer on the Atlantic side of the Arctic.

The Freshwater cap on the Arctic is replenished by freshwater from melting ice and from the rivers, (I think about 50/50 from what I have read. The Siberian shallow seas are freshened because of the distance from the oceans and the big rivers that drain onto the shelf.

The mixed layer depth varies seasonally. In the summer it becomes shallow, there is little mixing and lots of input of freshwater causing stratification. In the winter as freezing starts the formation of ice expels dense brine that causes convection in the upper layers, and the mixed layer deepens, perhaps all the way to the halocline.

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Re: "Stupid" Questions :o
« Reply #2644 on: September 20, 2019, 11:14:49 PM »
Looking at whoi itp110 7m-50m it would certainly seem to be a tale of two parts. Here is the first, over deeper water but also largely in high(ish) concentration ice from 2018, day264 to 2019, day120 (at location -134.8350  73.6623N)
Some incomplete profiles. All over deep water but the halocline appears to get deeper, possibly due to the location relative to the ocean gyre or some other reason, maybe part2 will confirm that.
edit: corrected colour labels, added location in wasted space.
« Last Edit: September 21, 2019, 12:49:27 PM by uniquorn »

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Re: "Stupid" Questions :o
« Reply #2645 on: September 21, 2019, 12:19:43 PM »
Looking at whoi itp110 7m-50m it would certainly seem to be a tale of two parts.
Excuse me uniquorn what does each color line represent? It's not completely clear.
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uniquorn

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Re: "Stupid" Questions :o
« Reply #2646 on: September 21, 2019, 01:38:09 PM »
Excuse me uniquorn what does each color line represent? It's not completely clear.
Overlaying does make it confusing, especially as the colours were initially labelled incorrectly, but it does make it easier to compare the depth of the halocline and thermocline which was the challenge set by sailor. Data is here https://www.whoi.edu/page.do?pid=163197
density green, temperature purple, salinity red
temp    -1.8 to 0.6C
salinity  27.5 to 31.2
density 1021.5 to 1025kg/m^3
For part2 looking at depth 7m-80m but keeping the scales the same as part1 for comparison. There are many more missing data days within this range, probably due to higher drift speed, fading battery and/or more turbulence later in the melting season.
I'm not sure that there is much value in attempting to separate halocline and thermocline based on this one example. It's a shame that the battery failed before reaching shallower water.
Hopefully this is helpful to the discussion. I am also a poster who finds it easier to communicate with images rather than text.



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Re: "Stupid" Questions :o
« Reply #2647 on: September 21, 2019, 03:58:44 PM »
Thanks for this Uniquorn. First impression, the itp116 seems more textbook-like being in the Atlantic side. itp110 data also show a consistent halocline  close in depth but steeper than the thermocline. The picture becomes messed up in part two, probably but not only because of sun-heated water away from the ice pack and closer to Alaskan Coast.
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Re: "Stupid" Questions :o
« Reply #2648 on: September 21, 2019, 05:10:58 PM »
So what are the chances for ITP116 ending up in Nares Strait?

That would be awesome!  ;D
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Re: "Stupid" Questions :o
« Reply #2649 on: September 26, 2019, 07:16:40 PM »
Here's one I could have put in the Oil & Gas thread, but just in case it's stupid, I'll put it here.
Does extracting oil and gas from underground cause subsidence? For example, is the area around the Persian Gulf sinking a millimeter or two a year, exacerbating SLR?
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