Sea Level Rise and Social Cost of Carbon

[jai mitchell]

Now that we have determined that the likely contribution to sea level rise from WAIS will be 1 meter or so:  http://news.sciencemag.org/climate/2014/05/west-antarctic-ice-sheet-collapsing

and the previous AR5 projection says that the Antarctic contribution was supposed to be about 5 cm

 

What will be the real sea level rise by 2100 under RCP 6.0 now?

1 meter?
2 meters?
3 meters?

Since the DICE model used to determine the costs of climate change only projects 1 meter of sea level rise



and it now looks like we will have 2.5 to 3.5 meters of sea level rise.  What is the new social cost of carbon?  is it now double what it would be without this new information?

[crandles]

AR5 says

For the period 2081–2100, compared to 1986–2005, global mean sea level
rise is likely (medium confidence) to be in the 5–95% range of process-based models, which give ... 0.33–0.62 m for RCP6.0

(Edit that is all sources not just Antarctica.)


Hmm 1.2m over 500 years instead of 5cm by 2100 could be an increase of 20cm or perhaps more likely less if some acceleration is assumed.

or we could take the 200 of the 200-500 years and then there is up to a 55cm increase as a result of the item linked.

So my calcs come to almost anything up to 55cm which leaves me a bit puzzled as to where your increase from 0.33–0.62 m to 3.5 m comes from.

Of course your "What will be the real sea level rise by 2100 under RCP 6.0 now?" requires finding all the other errors and updates to research since AR5 deadline.

[jai mitchell]

Sorry I should have updated:

the current WAIS projections are 1 meter by 2100 and 3 meters by 2200  just from the WAIS.

all of the levels reported in the first calculation was 2100.

Another thing to consider regarding the social cost of carbon is the discounting mechanism.  Since sea level rise was previously expected in the latter half of the century for any real impact, the (very large) impacts were discounted by almost 45% in real dollars.

now that increase is supposed to happen in 20 years.  which should increase the effect on the social cost of carbon by 300% for the sea level component of the costs of climate change (per ton of co2)

It is likely now that the current SCC is already underestimated by at least 30%

[AbruptSLR]

jai,

As we are currently following, and have been following for at least 30-yrs, RCP 8.5, I am not sure why you present RCP 6 as your basis for discussion.  RCP 6 assumes relatively low levels of methane emissions, and with Barrow and Mauna Loa (and every other monitoring station in the world) indicating accelerating methane emissions into the atmosphere, it seems to me that RCP 8.5 is much more justified as a basis for discussion, and at a minimum, should not be ignored in any meaningful discussion about SLR to the end of the century, and beyond.  I know that you are aware of the discussions on this topic in the Antarctic folder, but I am citing it here for those who have not yet looked at that folder.

Best,
ASLR

[jai mitchell]

Thanks SLR

Yes, I am aware.  I also am aware that for the purposes of realistic projections, the RCP 8.5 will not possibly be maintained.  If we want to understand real potential sea level rise, then the RCP 6.0 is the most likely candidate for actual emissions.

this is because we will experience a catastrophic global economic collapse sometime around 2050 if we attempt to maintain the RCP 8.5 scenario.

I believe that, with aggressive mitigation, the carbon-cycle feedbacks will mimic the RCP 6.0 (but it may be closer to RCP 8.5 as you say, depending on clathrates)

[AbruptSLR]

jai,

Thanks for your response, and I guess that we will both need to wait to see what anthropogenic greenhouse gases are (or are not) emitted in the coming years.  But that said, we should not forget the following factors that have little to do with anthropogenic GHG emissions after 2050: (a) RCP 6.0 also assumes an ESS (Earth System Sensitivity) of about 3.0 degrees C this century; which may well be too low; (b) The most likely sources of accelerated methane emissions this century are from northern/tropical wetlands and from fracking, not from clathrates; and (c) as SLR is most closely related to the temperature of the ocean, and as the most significant changes in ocean temperature take about 50-years to manifest after the GHG emissions (due to thermal inertia), even if societal GHG emissions drop dramatically by 2050, the SLR to 2100 will still follow the RCP8.5 scenario for at least 50-yrs after your postulated drop in societal GHG emissions.

Obviously, I do not have a crystal ball, but I prefer to follow the Precautionary Principle rather than to make overly optimistic assumptions.

Best,
ASLR

[wili]

I agree that none of us has a perfect crystal ball, except that we can be pretty damn sure that the future will be hotter, no matter what the pathway.

I know of a number of people who have been counting on peak oil, global economic collapse, or other bottlenecks to suddenly stop the juggernaut of global industrial civilization and its predations. Those predictions have so far not come to fruition, and so I find I no longer count on them to slow down global warming.

Even if/when collapse comes, there is no guarantee that it will greatly slow down un-sequestering of buried carbon. Power struggles will surely ever more fiercely center around control over whatever source of such carbon are left, no matter how dirty or expensive to exploit. And the emphasis will be on exploiting them as quickly as possible before the other side(s) have a chance to do so, no matter how inefficient or bad for GW those methods are.

Modern wars are waged and won with massive use of energy, and the wars will (and mostly have been) about getting control of those ff sources. You don't really need an economy beyond a war economy to keep extracting enormous quantities of ffs. And the ability to wage war will take priority more and more over every other part of the economy.

Anyway, that is (part of) my dark vision of how things are likely to play out in the last days of the naked ape/ homo necans--no salvation in collapse, just increasingly nasty, universally destructive and globally polluting wars. 

Have a nice day.

[AbruptSLR]

The following linked article by Forbes encourages more fracking in Europe due to both the Ukrainian situation and the new $400 Billion gas deal diverting more Siberian gas to China:

http://www.forbes.com/sites/christopherhelman/2014/05/21/china-russia-gas-deal-should-unleash-a-euro-fracking-revolution/

This shows how political tension may drive more fossil fuel consumption.

[Laurent]

An other problem with Sea level rise but because of Dams this time...Ouuffff it is not AGW....

Life-Giving Deltas Starved by Dams
http://www.huffingtonpost.com/peter-bosshard/lifegiving-deltas-starved_b_5380336.html?utm_hp_ref=green&ir=Green

[Ned W]

OK, maybe I missed something obvious, but I don't see what Jai is basing this on:

the current WAIS projections are 1 meter by 2100 and 3 meters by 2200  just from the WAIS.

The new paper by Joughin, Smith, and Medley says that SLR from Thwaites -- one of the largest sources in WAIS -- will be "moderate (<0.25 mm per year at sea level) over the 21st century".  That is expected to rise to 1mm/year sometime between 2200 and 2900. 

So Thwaites would produce something like 2.2cm of sea level rise by 2100.  And, again, Thwaites is among the larger sources in WAIS.

I understand that Eric Rignot and others may think that Joughin's model is underestimating the rate of ice loss.  But even if you double or triple that 2.2cm to account for this alleged underestimation, it's less than 10cm SLR from Thwaites.  Of course there is more from PIG and other sources.  But that much more?

I am seeing a lot of very large numbers for SLR being tossed around the forums.  But I don't see what they're based on.  Is this "1 meter from WAIS by 2100" coming from an actual study, or is it just speculation?

[AbruptSLR]

Ned W,

I do not know where jai's numbers for WAIS SLR contribution by 2100 came from; however the linked NRC study on Abrupt Climate Change (with a free pdf), contains the following quotes clearly indicating that a collapse of WAIS this century is plausible:


http://serppas.org/Files/Climate/NAS.Abrupt%20Impacts%20of%20Climate%20Change.Anticipating%20Suprises.pdf

"An abrupt slide of the vast West Antarctic Ice Sheet into the ocean would suddenly sink coasts worldwide under 10 to 13 feet (3 to 4 meters) of water. The report rates the risk of this calamity as "unknown" although probably low for this century.
"Unknown means we should be studying this question intently, not pretending it isn't there," White says."
…..
"However, a large part of the West Antarctic Ice Sheet (WAIS), representing 3-4 m of potential sea-level rise, is capable of flowing rapidly into deep ocean basins. Because the full suite of physical processes occurring where ice meets ocean is not included in comprehensive icesheet models, it remains possible that future rates of sea-level rise from the WAIS are underestimated, perhaps substantially. Improved understanding of key physical processes and inclusion of them in models, together with improved projections of changes in the surrounding ocean, are required to notably reduce uncertainties and to better quantify worst-case scenarios. Because large uncertainties remain, the Committee judges an abrupt change in the WAIS within this century to be plausible, with an unknown although probably low probability."

Best,
ASLR

[Ned W]

Thanks.  I've read that report already.  It is pretty vague on the timeframe, magnitude, mechanisms, and likelihood for sea level rise from WAIS, not surprisingly I guess since it's more than a decade old now. 

I guess I will wait to see if Jai has a source for the "1m by 2100" figure, and if not, I guess I'll have to look into it myself.

[AbruptSLR]

Ned W,

I do not know if you bothered to click on the link that I provided, but it leads to a 2013 report (not one that is more than a decade old).

Best,
ASLR

[Ned W]

I'm temporarily dealing with a slow connection here, and wasn't able to open the link iin anything resembling a timely fashion.  From glancing at the link I mistakenly thought it was pointing at the 2002 NAS report ("inevitable surprises") rather than the 2013 report ("anticipating surprises").  Sorry about the confusion.

In any case, I'm looking for something along the lines of what Jai was referring to (and others here who have made similar statements).  That is, what is currently considered the *best estimate* for SLR from WAIS by 2100?  Worst-case scenarios are interesting too, but it's important to be clear about the distinction between the two.

[Ned W]

I wonder if some people are  being confused by the press coverage of the new paper by Rignot et al.  For example, this:

http://www.nasa.gov/jpl/news/antarctic-ice-sheet-20140512/

Rignot said this new study suggests sea level rise projections for this century should lean toward the high-end of the IPCC range.

which is described as 98 cm, very close to Jai's "1 meter".

But that's total SLR by 2100, not just the portion from WAIS.

[crandles]

http://www.bbc.co.uk/news/science-environment-27381010

seems to be suggesting 1.2m from 6 big ice streams in West Antarctic in 200-500 years.

That links to
http://onlinelibrary.wiley.com/doi/10.1002/2014GL060140/abstract

and the 7mb pdf seems freely available:
http://onlinelibrary.wiley.com/doi/10.1002/2014GL060140/pdf

but I don't think the 1.2m and 200-500 years figures are in that paper. Don't know if this 'background information' may have been provided in press briefing.

[jai mitchell]

In the press briefing Rignot confirmed that the 6 WAIS glaciers studied will yield an IPCC maximum projection value of 98cm  BASED ON CURRENT LOSS RATE PROJECTIONS.

this does not include the increases in total west AND east Antarctic mass loss in the warming scenarios produced by RCP 8.5 emissions.

When the Filcher-Ronne gives way it will produce an additional 4.5 mm per year of sea level rise.

http://www.awi.de/en/news/press_releases/detail/item/climate_scientists_discover_new_weak_point_of_the_antarctic_ice_sheet/?cHash=9308ad709f71d96e875d5c332f9b5078

In addition, when the arctic sea ice is gone (in the next 10 years or so) the regional summer temperatures are going to experience a non-linear increase, jumping by over 5C

this will greatly exacerbate Greenland's ablation, leading to rapidly lower altitudes of ice sheets and exponential warming.

I expect that the 2100 sea level rise will be closer to 2M  Based on these factors.

And in the event of a more catastrophic collapse scenario?

well, we know that 24 feet in less than 1,000 years is possible, under NORMAL MILANKOVICH DRIVEN INTERGLACIALS.

[Ned W]

Rignot's comment about SLR being near the IPCC's upper range (98cm) includes all sources of SLR, not just WAIS.  If you believe that other non-WAIS sources of SLR (Greenland, etc.)will be greater, that still doesn't turn Rignot's 98cm into an appropriate number to cite for the WAIS-specific SLR.  WAIS is only a fraction of that 98cm.  Not the whole thing.

[crandles]

In the press briefing Rignot confirmed that the 6 WAIS glaciers studied will yield an IPCC maximum projection value of 98cm  BASED ON CURRENT LOSS RATE PROJECTIONS.

Is anyone able to rule out this taking 200 or more years?

[Ned W]

If you mean 98cm from WAIS alone, then it's almost certainly post 2100.  If you mean 98cm from all sources, then it seems to me you can't rule out either "by 2100" OR "well after 2100" ... Either one is possible.  (Edit:  but even for all sources 98cm by 2100 is on the high side of likely).

For the past 20 years, SLR has been quite linear at approx. 3.5 mm/yr.  By 2100 that would yield 30cm of SLR total.  So 98cm by 2100 would require a fairly rapid acceleration of current trend (more than tripling).  Possible?  Sure.  Probable?  I don't think so, but YMMV..

[wili]

I seem to have posted this on the wrong thread. Apologies to mods. Please delete which ever seems more inappropriate:

The Intergovernmental Panel on Climate Change in August warned of a three-foot sea level rise by 2100. But with new insight into melting glaciers in West Antarctica, that increase must be revised to at least seven feet

http://america.aljazeera.com/articles/2014/5/18/greenland-ice-melt.html

And that's not counting the increase in Greenland ice melt over previous projections discussed in the article--so add another couple feet, at least, from that source, and you get...


at least 9 feet (3+ meters) of sea level rise by the end of the century.

Most of that will come in the second half of the century, but I would think we could expect a meter by mid-century, 2050, and a half meter well before that, in about 20 years, say 2035.

On that last point, keep in mind that a half meter sea level rise increases probability of coastal flooding be 100 to 1000 times.

http://www.huffingtonpost.com/2014/05/12/west-antarctic-ice-sheet-melting_n_5310679.html
(toward the end of the video)

If you have ocean side property, sell it soon. In spite of recent legislative shenanigans, it will not be possible to get any kind of insurance on those properties, government or otherwise, in a very few months to years. And after that, they will be washing away at record rates.

...

Similarly:

http://www.climatecentral.org/news/antarctic-ice-collapse-food-supply-17481


Antarctic Ice Collapse Could Devastate Global Food Supply

The report, due to be released at a high-level conference in Washington, DC on Thursday, is the first to factor in the effects of the slow-motion collapse of the Western Antarctica ice sheet on future food security.

Two independent studies last week warned the retreat of the Western Antarctica ice sheet was unstoppable – and could lead to sea-level rise of up to 4 meters (13 feet) over the coming centuries.

Those rising seas would displace millions of people from low-lying coastal areas - and wipe out rice-growing areas across Asia, Gerald Nelson, a University of Illinois economist and author of Thurday's report, said.

"That sea-level rise would take out half of Bangladesh and mostly wipe out productive rice regions in Vietnam," Nelson told The Guardian. "It would have a major effect on Egyptian agricultural areas."

The projected levels of sea-level rise, due to the retreat of ice in West Antarctica, pose a far greater threat to future food supply even than that envisaged in the United Nations' IPCC report in March, Nelson said.

"A sea level rise of 3 meters (10 feet) over the next 100 years is much more likely than the IPCC thought possible," the report said.

[jai mitchell]

If you mean 98cm from WAIS alone, then it's almost certainly post 2100.  If you mean 98cm from all sources, then it seems to me you can't rule out either "by 2100" OR "well after 2100" ... Either one is possible.  (Edit:  but even for all sources 98cm by 2100 is on the high side of likely).

For the past 20 years, SLR has been quite linear at approx. 3.5 mm/yr.  By 2100 that would yield 30cm of SLR total.  So 98cm by 2100 would require a fairly rapid acceleration of current trend (more than tripling).  Possible?  Sure.  Probable?  I don't think so, but YMMV..

We are experiencing a doubling of WAIS contribution rates every 4-7 years.  This will continue through 2040.

current contributions are .45mm per year Antarctica Total.

by 2040 under RCP 8.5 emissions this will become 4mm per year for a total contribution of 4.5cm from WAIS

between 2040 and 2070 the average WAIS contribution will be 5.5mm/year for a total contribution overt this period of 16.5cm.

In 2070 the filcher-ronne will collapse, leading to an additional 4.5 mm/year average contribution from 2070-2100.  This yields the last 3 decades average WAIS contribution of 30cm

for a total WAIS contribution of 50 cm by 2100. 

notice I did not include PIG?

[crandles]

Table 13.5 of AR5 for SLR by 2100 in m says Antarctic Ice Sheet SMB is negative for all scenarios. For RCP 6 –0.02 [–0.05 to –0.01]

SRES A1B RCP2.6 RCP4.5 RCP6.0 RCP8.5
Antarctic ice-sheet SMBc –0.03 [–0.06 to –0.01] –0.02 [–0.04 to –0.00] –0.02 [–0.05 to –0.01] –0.02 [–0.05 to –0.01] –0.04 [–0.07 to –0.01]

Rapid dynamics are +0.07 regardless of scenario:

Antarctic ice-sheet
rapid dynamics
0.07 [–0.01 to 0.16] 0.07 [–0.01 to 0.16] 0.07 [–0.01 to 0.16] 0.07 [–0.01 to 0.16] 0.07 [–0.01 to 0.16]

Only the collapse of the marine-based sectors of the Antarctic ice sheet, if initiated, could cause GMSL to rise substantially above the likely range during the 21st century. This potential
additional contribution cannot be precisely quantified but there is medium confidence that it would not exceed several tenths of a meter of sea level rise.

In the multicentennial projections, Antarctic becomes more negative as you go further into the future.

-.02+.07=+.05 as Jai gave earlier. There may be other changes since AR5 but...

Jai, are you sure you expect this negative SMB contribution to double every 4-7 years? (That would have quite a different effect to what you are saying.)

(Edits: TBH I think data out since AR5 may have changed the negative SMB contribution from -.02 to possibly positive. Jai also said "doubling of WAIS contribution rates every 4-7 years" not doubling SMB contribution but I couldn't resist and there was a hint of SMB rather than rapid dynamics in the "notice I did not include PIG".)

I think the chances of initiating a collapse of marine based sectors has been increased substantially (if not already started) by Rignot et al. Excited media may not have realised that from initiation of collapse to a 1m rise in SL is quite likely a 200+ year process. I don't see any reason to think that there is much if any change to

"This potential additional contribution cannot be precisely quantified but there is medium confidence that it would not exceed several tenths of a meter of sea level rise" [by 2100]

[Ned W]

The Intergovernmental Panel on Climate Change in August warned of a three-foot sea level rise by 2100. But with new insight into melting glaciers in West Antarctica, that increase must be revised to at least seven feet

http://america.aljazeera.com/articles/2014/5/18/greenland-ice-melt.html

That sentence appears to be speculation by the Al Jazeera reporter, not anything from the Rignot or Joughin papers that the reporter is citing as the source of the "new insight".  It looks like a case of the reporter misunderstanding the time-frame involved.

Again, let's look at the two new papers about WAIS that sparked all this attention this month:

* Rignot's paper doesn't attempt to quantify expected melt by 2100, but in his explanatory remarks he has made it clear that he expects total SLR from all sources by 2100 to be near the upper end of the IPCC AR5 range, i.e. around 98cm.  Of that, WAIS's contribution would presumably be a few tenths of a meter.

* Joughin's paper predicts a total of 2.2cm SLR from Thwaites, one of the largest sources of ice in West Antarctica.  I haven't seen Joughin extrapolate that to WAIS as a whole, but I do not think there's much likelihood of WAIS's total being more than a few tenths of a meter if Thwaites's contribution is 2.2cm.

For comparison, Little et al 2013 suggested an upper bound of around 20cm SLR from all of WAIS by 2100 (99th percentile). 

Back to wili...

And that's not counting the increase in Greenland ice melt over previous projections discussed in the article--so add another couple feet, at least, from that source, and you get...


at least 9 feet (3+ meters) of sea level rise by the end of the century.
Most of that will come in the second half of the century, but I would think we could expect a meter by mid-century, 2050, and a half meter well before that, in about 20 years, say 2035.

That also seems to be pure speculation.  The new paper by Morlighem does not actually quantify how much SLR is likely from Greenland at any particular timeframe in the future.  Other recent papers give estimates by 2100 of a couple tenths of a meter (e.g. Pfeffer et al. 2008) or less (e.g., Howard et al. 2014). 

Once more back to wili:

Similarly:

http://www.climatecentral.org/news/antarctic-ice-collapse-food-supply-17481


Antarctic Ice Collapse Could Devastate Global Food Supply

The report, due to be released at a high-level conference in Washington, DC on Thursday, is the first to factor in the effects of the slow-motion collapse of the Western Antarctica ice sheet on future food security.

Two independent studies last week warned the retreat of the Western Antarctica ice sheet was unstoppable – and could lead to sea-level rise of up to 4 meters (13 feet) over the coming centuries.

Those rising seas would displace millions of people from low-lying coastal areas - and wipe out rice-growing areas across Asia, Gerald Nelson, a University of Illinois economist and author of Thurday's report, said.

"That sea-level rise would take out half of Bangladesh and mostly wipe out productive rice regions in Vietnam," Nelson told The Guardian. "It would have a major effect on Egyptian agricultural areas."

The projected levels of sea-level rise, due to the retreat of ice in West Antarctica, pose a far greater threat to future food supply even than that envisaged in the United Nations' IPCC report in March, Nelson said.

"A sea level rise of 3 meters (10 feet) over the next 100 years is much more likely than the IPCC thought possible," the report said.

That's a bit of a mess, and the key part of it appears to be wrong.  (This is why it's important to go to the actual scientific literature, not rely on the general media....)

First, "up to 4 meters (13 feet)" refers to a multi-century time frame, not by 2100.

Second, the phrase you quote in bold ("A sea level rise of 3 meters (10 feet) over the next 100 years is much more likely than the IPCC thought possible") does not actually appear anywhere in the report itself.  I don't know if it's a mistake by ClimateCentral, or what.  But the report they are referring to (available online here) doesn't say that.  It only cites the IPCC range of 28 to 98cm total SLR by 2100.  There is no mention of "3 meters" over the next 100 years anywhere ... unsurprisingly, since that is well outside the range of what is supported by the scientific literature.

[Ned W]

We are experiencing a doubling of WAIS contribution rates every 4-7 years.  This will continue through 2040.

current contributions are .45mm per year Antarctica Total.

by 2040 under RCP 8.5 emissions this will become 4mm per year for a total contribution of 4.5cm from WAIS

between 2040 and 2070 the average WAIS contribution will be 5.5mm/year for a total contribution overt this period of 16.5cm.

In 2070 the filcher-ronne will collapse, leading to an additional 4.5 mm/year average contribution from 2070-2100.  This yields the last 3 decades average WAIS contribution of 30cm

for a total WAIS contribution of 50 cm by 2100. 

notice I did not include PIG?

I asked if you had a source for the "1 meter from WAIS" claim.  Your reply is to list a bunch of other numbers with no sources either.  How is that helpful?

Also, I'm not sure what you mean by this:

the average WAIS contribution will be 5.5mm/year for a total contribution overt this period of 16.5cm.   [...]

notice I did not include PIG?

PIG drains the WAIS.  If you quote a number for the total contribution from WAIS then you are including PIG.

[Ned W]

I think the chances of initiating a collapse of marine based sectors has been increased substantially (if not already started) by Rignot et al. Excited media may not have realised that from initiation of collapse to a 1m rise in SL is quite likely a 200+ year process. I don't see any reason to think that there is much if any change to

"This potential additional contribution cannot be precisely quantified but there is medium confidence that it would not exceed several tenths of a meter of sea level rise" [by 2100]

That is my understanding as well. 

I do think the long-term (multi-century to millennium) outcome is likely to include several meters of SLR from WAIS and Greenland.  But the 21st century forecast is quite different.  For now, it seems to be less than 2 m total SLR, of which a few tenths of a meter are from WAIS.

[Lennart van der Linde]

About 2m by 2100 and 9m by 2300 seems to be the worst-case in the peer-reviewed literature, as illustrated by the attached figure 3b from Rohling et al. 2013:
http://www.nature.com/srep/2013/131212/srep03461/full/srep03461.html

The expert elicitation by Horton et al. 2013 shows that about 33% of the experts think the worst-case could be 2m or more by 2100 and 5m or more by 2300, as shown in their figure 2:
https://marine.rutgers.edu/pubs/private/HortonQSR_2013.pdf

Rohling et al also say that at 400 ppm less than 9m in the long run is unlikely, 24m the best estimate, and more than 31m still a 17% probability.

[Ned W]

In 2070 the filcher-ronne will collapse, leading to an additional 4.5 mm/year average contribution from 2070-2100.  This yields the last 3 decades average WAIS contribution of 30cm

Melting of the ice shelf doesn't directly raise sea level since it's already floating.  Instead, it reduces the backpressure on the glaciers feeding the shelf (not all of which come from WAIS, by the way -- much of the ice flowing into the shelf is from East Antarctica).  Those glaciers may then increase their velocity, which does raise sea level as more ice crosses the grounding line.

The figure from Hellmer at AWI, of "4.4 mm/year" sea level rise, is not instantaneous.  It's what you would get once the glaciers flowing into the Weddell Sea had time to fully respond to the change in pressure.  Would that take decades, or centuries?  Hellmer et al. don't try to speculate, at least not anywhere that I've seen.  Their actual paper is about basal melt of the shelf itself, not quantifying the resulting change in velocity above the grounding line.

Reducing this to "the ice shelf disappears in 2070 and sea level begins rising by 4.4 mm/year immediately" does not seem accurate, in my understanding (I could be wrong).

[Shared Humanity]

About 2m by 2100 and 9m by 2300 seems to be the worst-case in the peer-reviewed literature, as illustrated by the attached figure 3b from Rohling et al. 2013:
http://www.nature.com/srep/2013/131212/srep03461/full/srep03461.html

The expert elicitation by Horton et al. 2013 shows that about 33% of the experts think the worst-case could be 2m or more by 2100 and 5m or more by 2300, as shown in their figure 2:
https://marine.rutgers.edu/pubs/private/HortonQSR_2013.pdf

Rohling et al also say that at 400 ppm less than 9m in the long run is unlikely, 24m the best estimate, and more than 31m still a 17% probability.

I am not as informed as most here and would normally post this in the stupid questions thread but since it is relevant.......

Given that current level of atmospheric CO2 is 400ppm....

http://www.esrl.noaa.gov/gmd/ccgg/trends/

........and the long term growth trends in CO2 emissions (see CO2 graph) which is a direct result of our industrial economy which shows no signs of reducing, anytime soon, its consumption of fossil fuels (see growth in coal consumption graph) does anyone here actually believe that 400ppm is likely?

Given that this level is ridiculously low (my opinion), what impact should an exponentially accelerating level of atmospheric CO2 mean for these sea level rise projections?

And please don't answer based on IPCC proposals regarding acceptable levels of CO2. Any significant reductions in the accelerated use of fossil fuels before 2050 is a fantasy.

I do not want to derail this thread so, if you want to review forum discussions of coal use and trends, you can find it here.......

http://forum.arctic-sea-ice.net/index.php/topic,347.0.html

[Ned W]

what impact should an exponentially accelerating level of atmospheric CO2 mean for these sea level rise projections?

It increases the likelihood that much of the land ice will end up in the ocean, though that process will still take a long time. 

And it increases the amount of SLR from thermal expansion of the oceans.

[Laurent]

I do not see any confort using the models that we have now for sea level rise purpose. In the past we had around 4 cm of sea level rise per year around 14.000 years ago...so we have to expect that minimum very soon and certainly much more since what we have done never existed before. And please do not mention the CO2 level since it is the combined green house gazes that are important...so around 480 ppm of CO2 eq right now...(http://www.esrl.noaa.gov/gmd/aggi/aggi.html)
In the recent past (holocene) the relationship between CO2 temp and SLR was linear why don't use that linear relationship to calculate the SLR knowing it is the CO2 that is leading nowadays ?

[Lennart van der Linde]

SH,
I think Rohling et al., and also Jim Hansen, strongly suggest that we will be melting all the ice on the planet, unless we manage to stay or return below 500 ppm in time. See for example the attached fgure 1 from Rohling et al, also linked here:
http://www.nature.com/srep/2013/131212/srep03461/fig_tab/srep03461_F1.html

If we go above 500 ppm for too long, slow carbon and albedo feedbacks will probably take over and bring us to 800 ppm and more, which would melt all the remaing ice. Hansen seems to be even more pessimistic on this point than Rohling.

Only very strong mitigation will probably prevent all the ice from melting, since otherwise the momentum of anthropogenic climate forcing will grow so strong that slower feedbacks will finish the job no matter what we would try to stop it.

[crandles]

Since the title mentions "social cost of carbon",

http://www.forbes.com/sites/timworstall/2014/05/13/if-antarctic-melting-has-passed-the-point-of-no-return-we-should-do-less-about-climate-change-not-more/

was heavily criticised for not taking timing into account. (eg see Daniel Nazar comment on page 3)

However, if you look at the numbers I quoted from AR5

SRES A1B RCP2.6 RCP4.5 RCP6.0 RCP8.5
Antarctic ice-sheet SMBc –0.03 [–0.06 to –0.01] –0.02 [–0.04 to –0.00] –0.02 [–0.05 to –0.01] –0.02 [–0.05 to –0.01] –0.04 [–0.07 to –0.01]
Antarctic ice-sheet
rapid dynamics
0.07 [–0.01 to 0.16] 0.07 [–0.01 to 0.16] 0.07 [–0.01 to 0.16] 0.07 [–0.01 to 0.16] 0.07 [–0.01 to 0.16]

the rapid dynamics in particular do not change much or at all with scenario!

So perhaps that scuppers that heavy criticism?

If so, then the concluding paragraph

It is only if continuing emissions are going to lead to something more, something else possibly worse, happening that there’s any economic case at all for limiting them. As it happens I think that there are worse things that might happen and that there is a very good case indeed for limiting future emissions. But this finding, that West Antarctica is going to melt no matter what just isn’t a valid reason to limit future emissions. The damage is already done, see?

becomes a lot harder to criticise.

So the effect of the Rignot et al study is to reduce the social cost of carbon! this is because the main effect is to move costs from possible consequences with possible changes of timing bucket into an already incurred with no chance of changing the timing bucket. The bucket it is moved to is one which should be ignored for calculating relevant social costs of carbon.

I doubt this is perfectly true, I suspect we might be able to have a tiny effect on the timing of this event unfolding but I cannot see much difference between tiny effect and no effect on timing.

That is not a conclusion I want to come to but if that is the way it is then it should be reported as it is.

[Ned W]

So by that reasoning, the SLR from the loss of WAIS (and presumably Greenland as well?), and the resulting sinking coasts ... would be seen as a ... (ghastly pun coming) ... sunk cost?

Of course, it would be nice to not lose all the ice on EAIS too.  And thermal expansion keeps going in lockstep with temperature.  And there are all the non-SLR impacts of climate change.

[jai mitchell]

That is not how the Integrated Assessment Models operate.  They have damage-loss functions that are determined using regional value computations under sea level rise scenarios.  They run multiple iterations to get an average result.

The damage loss functions are heavily discounted so that damages that occur in the next 3 decades, while being identical in physical effect, are 3X the value of the same type of damage that occurs at the end of 2080.  This is the effect of discounting.

Now that we know that the rate of mass loss will continue to double, over the next several decades, radically increasing the timing of the sea level rise, moving the models from damage-loss values typically expected in 2100 to damage loss values occurring in 2050.

This will easily double the social cost of carbon in the Integrated Assessment model runs.

[crandles]

So by that reasoning, the SLR from the loss of WAIS (and presumably Greenland as well?), and the resulting sinking coasts ... would be seen as a ... (ghastly pun coming) ... sunk cost?

Of course, it would be nice to not lose all the ice on EAIS too.  And thermal expansion keeps going in lockstep with temperature.  And there are all the non-SLR impacts of climate change.

groan.

Absolutely, lots of other things will happen and they do make a case for more action. The article does throw in that sentence:

As it happens I think that there are worse things that might happen and that there is a very good case indeed for limiting future emissions.

but only at the end which I think is a bit wrong, people with denier leanings will see the article as confirming their opinions and stop reading before they get there or think too much about it. So I think that should have been stated much more prominently much earlier.

[wili]

Thanks all for discussions about slr figures.

LvvL wrote:

About 2m by 2100 and 9m by 2300 seems to be the worst-case in the peer-reviewed literature, as illustrated by the attached figure 3b from Rohling et al. 2013:
http://www.nature.com/srep/2013/131212/srep03461/full/srep03461.html

The expert elicitation by Horton et al. 2013 shows that about 33% of the experts think the worst-case could be 2m or more by 2100 and 5m or more by 2300, as shown in their figure 2:
https://marine.rutgers.edu/pubs/private/HortonQSR_2013.pdf

Rohling et al also say that at 400 ppm less than 9m in the long run is unlikely, 24m the best estimate, and more than 31m still a 17% probability.

(My bold.)

But the "2m or more by 2100" was before the recent news about WAIS and GIS. I understand that the main point of the papers is that they show that long term significant sea level rise now seems to be locked in. But they also seem to indicate some increase in our estimation of slr from these sources in the coming decades. It is unfortunate that they are not clearer about how much additional slr that might be. But whatever addition we have to "2m or more by 2100" pushes us ever closer to about 3 meters, which would sink considerably more cities and land than 2 meters.

It seems at this point that we only have speculation, though, at this point on these crucial issues...speculation all too easily colored by wishful thinking on the one hand and sensationalism on the other. (I'm sure people may see me as at the latter end of that spectrum, but it does seem important to know what the worst case possible scenarios are, even if their possibility may be remote, as Richard Alley has stressed repeatedly.)

[jai mitchell]

has anyone here seen a contour map of expected average summer temperatures of Antarctica, in 2080 under RCP 6.0 scenario and an ECS of 4.5 C per 2XCO2?

It would look similar to this one:



except all of the dark red would be turned to orange.

This means that in the summer there are melt ponds in low-lying Antarctic regions.  This would be a late 2080-2090 effect. 

However, the summer weddell sea ice will be long (long) gone by then.

Yes, I understand the ronne shelf/buttress won't be instantaneous, The 4.5mm is an average value over a period of time.  by 2090, combining the loss of sea ice and shelf-grounding with surface warming and increased plasticity these shelves will experience rapid and catastrophic collapse.

I believe that the Eemian analogy recorded by Blachon et. al here: ftp://ftp.soest.hawaii.edu/coastal/Coastal%20Geology%20Class%20GG420/Blanchon%205e%20reef%202009.pdf

is the only real analogy we have in the paleo record. 

The author states that, under the correct conditions, a 5cm per year SLR for 50 years is feasible.

From Joe Romm
http://thinkprogress.org/climate/2009/04/15/203960/nature-sea-level-rise-global-warming-reefs/

In other words, the Nature study says that during the last interglacial (the Eemian) evidence now suggests sea levels rose 20 inches per decade for five straight decades — a roughly 8-foot rise in a half century.

Now, this means that under normal Milankovtich-driven warming cycles, we will reach a tipping point on those glaciers.  We understand now what that will look like. 

A long-drawn slow melting of the region until grounding lines retreat to the point of no return (now observed).  Except, this time we will see the 1 mile high glacier cliffs buttressing up against a warm water shoreline within only about 100 years.

-----------
late edit question:  what feedback response scenario is potentially able to cause a "sudden and catastrophic" warming of the  West Antarctic Sea Surface temperatures  in 2050?

[jai mitchell]

http://eesc.ldeo.columbia.edu/courses/w4937/Readings/Kennet.Stott.1991.pdf

Abrupt deep sea warming, Palaeoceanographic Changes and Benthic Extinctions at the end of the Paleocene

Kennett & Stott

The oceanographic changes associated with the excursion were clearly broad and complex, and seem to reflect a transient state between fundamentally different modes of ocean circulation.

[Lennart van der Linde]

On the SLR-cost of carbon: I would think that while the WAIS is disintegrating the EAIS will also start losing more and more ice, and (much) earlier than previously thought probable. So the costs would indeed rise along with faster and higher SLR.

[AbruptSLR]

As most people posting on this topic have already reviewed the Antarctic folder, which has extensively discussed the possible SLR contribution of both the WAIS, and the EAIS, by 2100; I will not bother to repeat those discussions here.  Nevertheless, I would like to note that the Antarctic folder cites a considerable amount of evidence that a significant portion of the WAIS became ungrounded/collapsed during the Eemian, and my favorite paper on this topic is the following by O'Leary et al (2013), which shows that around 119 to 120 kya RSLR in Western Australia jump up over 6m in less than 1,000 years (see linked and attached figure/caption):

O'Leary, M.J., Hearty, P.J., Thompson, W.G., Raymo, M.E., Mitrovica, J.X., and Webster, J.M., (2013), "Ice sheet collapse following a prolonged period of stable sea level during the last interglacial", Nature Geoscience;  doi:10.1038/ngeo1890.

http://www.nature.com/ngeo/journal/v6/n9/fig_tab/ngeo1890_F3.html

Caption for the linked and attached figure is: "A geomorphically defined palaeoMSL datum of +2.5 m 120 kyr ago (Fig. 1c) anchors a predicted relative sea-level curve at Red Bluff, which includes a GIA signal based on the test calculation (see Methods) plus the following ESL history: ESL jumps from 0 to 3.4 m between 127.5 kyr and 127 kyr ago and remains at this level until 120 kyr ago; and 120 kyr ago, ESL jumps ~ 6 m over 1 kyr. Dashed green line is an inferred sea-level curve based on a minimum coral palaeodepth (solid bar above circle) of 0.4 m below palaeoMSL. This palaeodepth calculation is applicable only to highest in situ corals, as corals of the same age found at lower elevations will have a known water depth of at least up to the height of the coral above it. Arrows indicate potential for greater palaeodepth range."

While this paper does not make it clear how much of this RSLR came from the WAIS, and how much faster than 1,000 yrs did it occur over; the researchers are working hard to address these questions and are making progress as indicated in the following recent paper:

Rovere, A., M. E. Raymo, J. X. Mitrovica, P. J. Hearty, M. J. O'Leary, and J. D. Inglis. 2014. “The Mid-Pliocene sea-level conundrum: Glacial isostasy, eustasy and dynamic topography.” Earth and Planetary Science Letters 387: 27-33

My general point is that paleo-evidence indicates that marine ice sheets and marine terminating glaciers appear to be less stable than commonly assumed by most researchers, so no one reading this thread should be too surprised when AR6 has higher SLR projections than AR5; not because this risk of SLR is increasing that fast, but because the more we learn the more we acknowledge the risks that are already dialed into the Earth systems.

[crandles]

That is not how the Integrated Assessment Models operate.  They have damage-loss functions that are determined using regional value computations under sea level rise scenarios.  They run multiple iterations to get an average result.

The damage loss functions are heavily discounted so that damages that occur in the next 3 decades, while being identical in physical effect, are 3X the value of the same type of damage that occurs at the end of 2080.  This is the effect of discounting.

...

This will easily double the social cost of carbon in the Integrated Assessment model runs.

If you discount then the discount rate to use is often the dominant variable that needs to be tied down to reduce the uncertainty.


"not how the Integrated Assessment Models operate" might depend on how you interpret the results. The damage loss functions don't take account of what are sunk costs. However I suggest the appropriate way for politicians to view the results is not to look at how high the damage loss function arrives at but to look at the difference between the damage loss result for one scenario against another to see how much effort should be put into ensuring we head for one scenario vs another. If politicians do that then they are effectively treating the sunk costs as not relevant.

[AbruptSLR]

As a follow-up to my last post, while crandles cites that as many marine ice sheets and marine terminating are already past their tipping point that responsibility for the trillions of dollars of damaged caused by this SLR (whether sooner or later) has moved from the fossil fuel industry to either the insurance companies, or to any owners who cannot get insurance, because even though there were numerous warnings by researchers over 30-years ago that we were nearing this tipping point, that the group/tribal consensus had not yet acknowledged the tipping point, this observation ignores several points including:
(1) As Super Storm Sandy demonstrated, just a few inches of storm surge over-topping can cause hundreds of billions of dollars of losses to one major port city for one event alone.  As all the major port cities around the world are partly at sea level, and as climate change will increase the frequency and magnitude of storm surge events which are added on top of RSLR; cutting back now on fossil fuel emissions will clearly reduce inundation damage no matter what eustic sea level does.
(2) Due to the non-linear nature of the rate of SLR a little bit of prevention now will likely buy a lot of time in the future to implement adaptive flood defense systems.
(3) As others have noted some tidewater glaciers have not yet passed their tipping points yet, so cutting back on fossil fuel emissions sooner rather than later will help everybody.

[Shared Humanity]

Reading above comments, it would seem there is a near consensus that increasing levels of CO2 in this century will definitely increase long term slr but have little impact in this century due to lags in the response of the ice.

NOAA currently shows a 2 ppm average increase in atmospheric CO2 per year in the last 15 years. If we are to assume this rate of increase continues into the future, then we will be at 500 ppm by 2065 and 570 ppm by the end of the century. Most likely 500 ppm for 2065 is a low estimate as the annual contribution to atmospheric CO2 has actually been growing. Between 1980 and 2000 CO2 grew 1.5 ppm per year. I would expect this increase will continue at least until 2050 as the developing nations continue along a fairly rapid growth trajectory. I would think we shall hit 500 ppm closer to mid century.

This is where I get lost. Can these increases in atmospheric CO2 actually have no impact this century on ice melting and slr?

[crandles]

Reading above comments, it would seem there is a near consensus that increasing levels of CO2 in this century will definitely increase long term slr but have little impact in this century due to lags in the response of the ice.

I wouldn't put it like that. Much of the discussion above is about Rignot et al saying 6 West Antartic ice streams are irreversibly collapsing. That in isolation does not respond much to rising GHG levels per IPCC AR5.

However looking at other lines in that table:

Thermal expansion varies from 0.14 [0.10 to 0.18] to 0.27 [0.21 to 0.33]
Glaciersa vary from  0.10 [0.04 to 0.16]  to 0.16 [0.09 to 0.23]
Greenland ice-sheet SMBb 0.03 [0.01 to 0.07] to 0.07 [0.03 to 0.16]
Greenland ice-sheet rapid dynamics 0.04 [0.01 to 0.06] to 0.05 [0.02 to 0.07]
Land water storage doesn't vary per scenario 0.04 [–0.01 to 0.09]

gives totals (inc Antarctica) from 0.40 [0.26 to 0.55] to 0.63 [0.45 to 0.82]

63cm is more than a 50% increase over 40cm. That is not a negligible difference though RCP 8.5 to RCP 2.6 is a big difference in scenario. Most of the difference is going to be after the end of the century with only a small part of the difference towards the end of this century.

[Ned W]

This is where I get lost. Can these increases in atmospheric CO2 actually have no impact this century on ice melting and slr?

It does have an impact, mainly on the fraction of SLR from thermal expansion and ice sheet surface melt, because those have a shorter response time.  Discharge of ice from marine glaciers is slower to respond so changes in CO2 at the decadal time scale don't show up as much.

Edit:  crandles has the numbers.  Going from a low-co2 to high-co2 scenario increases SLR by a couple of tenths of a meter in 2100, which is exactly what I would have guessed.

The likelihood of SLR much greater than 1 meter by 2100 is small, IMHO.

[Ned W]

Wili in #36:

What you're doing is taking (a) the worst case scenario, from (b) the individuals at the uppermost end of the range, and then (c) adding in a bunch of additional increase on speculation.

One could do the same in the opposite direction -- taking the best case scenario, from only the most optimistic individuals, and then subtract off a bit more on the assumption that they're still over-estimating reality. 

Neither of those is a good way to think about likely outcomes.

Now, you may be just doing this as a thought-experiment to see what the real worst-case scenario would be.  But the danger is that you, and others here, will begin to internalize that worst-case scenario as if it were the expected outcome ... And thus the estimate creeps upward, from under 1 m to 1 m, then 2 m, and then 3 m ... And people gradually lose touch with what most scientists think is likely. 

[crandles]

It does have an impact, mainly on the fraction of SLR from thermal expansion and ice sheet surface melt, because those have a shorter response time.  Discharge of ice from marine glaciers is slower to respond so changes in CO2 at the decadal time scale don't show up as much.

Temperatures don't change in response to current GHG emissions for ~3 decades SMB can begin to take effect from then though if main effect on Antarctica is not from surface melting but from warm water on underside of ice then the heat has to mix into the oceans. I would have thought it would take quite a while for heat to mix down into oceans to cause much thermal expansion so I am a little surprised you put that first.

My previous post said "[Ice streams collapsing] in isolation does not respond much to rising GHG levels"

But of course it isn't in isolation!

GHG levels will cause further SMB and thermal expansion. This SLR will presumably affect rate of collapse by changing what ice is below sea level hence more buoyancy reducing friction and more ice volume underwater. I guess that has a relatively short response timescale to get some of the effect but the full effect takes as long as the longest response timescale.

[Ned W]

Gotta put something first, right?  SMB is small, and ice discharge is slow.  What else is there?

Also, Both thermal expansion of oceans and marine ice sheet instability need heating of the ocean.  But as the ocean warms TE happens more or less instantaneously while MISI follows some unknown time scale that probably isn't instantaneous.

[wili]

Antarctica's ice collapse threatens metres of sea level rise within decades

   

Scientists know that if Antarctica's ice sheets and glaciers collapse, sea levels could rise 5 metres. But the idea that it will take 200 years to happen is based on a linear model, writes Dady Cherry. In fact, the process is exponential - and could take place 'within decades'.

    The acceleration is driven, among other things, by an accelerated warming of the atmosphere and sea surface, continued expansion of the ozone hole, strengthening of currents that bring greater masses of warm waters from the tropics to Antarctica, weakening of the ice shelves due to accelerated melting of the surface ice, weakening of the attachment of the ice below sea level due to an accelerated erosion, and decreasing reflectivity of the Earth.

West Antarctic ice sheet could raise sea levels 5m 'within decades'

Rignot blames carbon emissions, which have tripled since the Kyoto Protocol, for the current state of affairs, and he categorically says that the collapse of the ice cover from "the Amundsen sea sector of West Antarctica [is] unstoppable, with major consequences - it will mean that sea levels will rise one metre [more than 3 feet] worldwide.

"What's more, its disappearance will likely trigger the collapse of the rest of the West Antarctic ice sheet, which comes with a sea level rise of between three and five metres [10 to more than 16 feet]. Such an event will displace millions of people worldwide."

The sea-level rise of 10 to 16 feet will come in decades, rather than 200 years. It will submerge essentially every port city in the world, including Guangzhou, Mumbai, Shanghai, Ho Chi Minh City, Kolkata, Osaka-Kobe, Alexandria, New York, New Orleans, Miami, and indeed all of South Florida.

This will likely displace over 300 million people, many of them in countries that have equated development with movement of the majority of their populations to low-elevation coastal zones in port cities.

Again, most of the rapid slr seems to be speculation of the author. But he doesn't seem to be the only one making these speculations.

http://www.theecologist.org/News/news_analysis/2404476/antarcticas_ice_collapse_threatens_metres_of_sea_level_rise_within_decades.html

Thanks to Graeme at POForums for this link.