Sea Level Rise and Social Cost of Carbon

[AbruptSLR]

The link leads to an article indicating that the rate of SLR over the past two decades was faster than previously realized:

http://www.theguardian.com/environment/2015/may/11/sea-level-rise-accelerated-over-the-past-two-decades-research-finds

[Lennart van der Linde]

From the Guardian article ALSR linked:
"Watson’s team found that the record of sea level rise during the early 1990s was too high. The error gave the illusion of the rate of sea level rise decreasing by 0.058 mm/year2 between 1993 and 2014, when in reality it accelerated by between 0.041 and 0.058 mm/year2... The IPCC’s landmark report in 2013 found the sea had risen on average by 3.2 mm per year since 1993. Waston’s study found the rate was slightly slower, between 2.6 and 2.9 mm per year."

So the acceleration of SLR was faster than previously thought, but the average rate of SLR itself was somewhat slower than earlier estimates, according to this research.

[AbruptSLR]

So the acceleration of SLR was faster than previously thought, but the average rate of SLR itself was somewhat slower than earlier estimates, according to this research.

Here is a link to the paper where even White & Church are admitting that over the past 10-years SLR contributions from ice sheets are causing global mean sea level rise rates to accelerate (faster than previously thought):

Christopher S. Watson, Neil J. White, John A. Church, Matt A. King, Reed J. Burgette & Benoit Legresy (2015), "Unabated global mean sea-level rise over the satellite altimeter era ", Nature Climate Change, doi:10.1038/nclimate2635


http://www.nature.com/nclimate/journal/vaop/ncurrent/full/nclimate2635.html


Abstract: "The rate of global mean sea-level (GMSL) rise has been suggested to be lower for the past decade compared with the preceding decade as a result of natural variability, with an average rate of rise since 1993 of +3.2 ± 0.4 mm yr−1. However, satellite-based GMSL estimates do not include an allowance for potential instrumental drifts (bias drift). Here, we report improved bias drift estimates for individual altimeter missions from a refined estimation approach that incorporates new Global Positioning System (GPS) estimates of vertical land movement (VLM). In contrast to previous results, we identify significant non-zero systematic drifts that are satellite-specific, most notably affecting the first 6 years of the GMSL record. Applying the bias drift corrections has two implications. First, the GMSL rate (1993 to mid-2014) is systematically reduced to between +2.6 ± 0.4 mm yr−1 and +2.9 ± 0.4 mm yr−1, depending on the choice of VLM applied. These rates are in closer agreement with the rate derived from the sum of the observed contributions GMSL estimated from a comprehensive network of tide gauges with GPS-based VLM applied and reprocessed ERS-2/Envisat altimetry. Second, in contrast to the previously reported slowing in the rate during the past two decades, our corrected GMSL data set indicates an acceleration in sea-level rise (independent of the VLM used), which is of opposite sign to previous estimates and comparable to the accelerated loss of ice from Greenland and to recent projections, and larger than the twentieth-century acceleration."

See also:

http://thinkprogress.org/climate/2015/05/12/3657633/study-sea-level-rise-accelerating/

[Lennart van der Linde]

ASLR,

The abstract of Watson et al 2015 says:
"In contrast to previous results, we identify significant non-zero systematic drifts that are satellite-specific, most notably affecting the first 6 years of the GMSL record. Applying the bias drift corrections has two implications. First, the GMSL rate (1993 to mid-2014) is systematically reduced to between +2.6 ± 0.4 mm yr−1 and +2.9 ± 0.4 mm yr−1, depending on the choice of VLM applied."

The Climate Progress news article says:
"Using the newly recalibrated data, the researchers found that sea level rise between 1993 and 1999 — the earliest segment of satellite data — was overstated. According to satellite data, over that six-year period, global sea level rose 3.2 milimeters (about .12 inches) per year; using Watson’s recalibrated data, sea levels probably rose closer to between 2.6 to 2.9 mm (about .1 to .11 inches) per year."

It seems this is not correct, since the abstract says: "the GMSL rate (1993 to mid-2014) is systematically reduced to between +2.6 ± 0.4 mm yr−1 and +2.9 ± 0.4 mm yr−1".

So Watson et al are talking about 2.6-2.9 mm/yr for 1993-2014, not only for 1993-1999. Or am I misunderstanding something?

[AbruptSLR]

ASLR,

The abstract of Watson et al 2015 says:
"In contrast to previous results, we identify significant non-zero systematic drifts that are satellite-specific, most notably affecting the first 6 years of the GMSL record. Applying the bias drift corrections has two implications. First, the GMSL rate (1993 to mid-2014) is systematically reduced to between +2.6 ± 0.4 mm yr−1 and +2.9 ± 0.4 mm yr−1, depending on the choice of VLM applied."

The Climate Progress news article says:
"Using the newly recalibrated data, the researchers found that sea level rise between 1993 and 1999 — the earliest segment of satellite data — was overstated. According to satellite data, over that six-year period, global sea level rose 3.2 milimeters (about .12 inches) per year; using Watson’s recalibrated data, sea levels probably rose closer to between 2.6 to 2.9 mm (about .1 to .11 inches) per year."

It seems this is not correct, since the abstract says: "the GMSL rate (1993 to mid-2014) is systematically reduced to between +2.6 ± 0.4 mm yr−1 and +2.9 ± 0.4 mm yr−1".

So Watson et al are talking about 2.6-2.9 mm/yr for 1993-2014, not only for 1993-1999. Or am I misunderstanding something?

Lennart,

You need to be very careful when using averaged numbers such as the average from 1993 to 2014, as they can mask acceleration trend in the data as noted in the following quote from the Watson et al 2015 abstract:

Extract: "... Second, in contrast to the previously reported slowing in the rate during the past two decades, our corrected GMSL data set indicates an acceleration in sea-level rise (independent of the VLM used), which is of opposite sign to previous estimates and comparable to the accelerated loss of ice from Greenland and to recent projections, and larger than the twentieth-century acceleration."

Best,
ASLR

[Lennart van der Linde]

ASLR,
Yes, they're talking about more acceleration than previously thought, but slower total SLR over 1993-2014 than previously thought. So logically average SLR over say 1993-2003 should be less than over 2003-2014 and than over the whole period 1993-2014. The question is how much SLR they estimate over the last decade. Since their estimated acceleration is about 0.05 mm/yr2 over the whole period, total acceleration should be about 1 mm over this 20-yrs period. So I would estimate average SLR around 1993 to have been about 2.1-2.4 mm/yr and around 2014 about 3.1-3.4 mm/yr.

[AbruptSLR]

Lennart,

Also see the following extract that helps to elaborate on this matter, but be aware that as Church is a co-author this paper likely errs on the side of least drama:

http://www.straitstimes.com/news/world/more-world-stories/story/sea-level-rise-accelerating-earths-ice-sheets-melt-say-scientist

Extract: "The new study, published in the journal Nature Climate Change, takes land movement into account, along with an important statistical tweak - hourly data from a network of tide gauges deployed around the world's oceans. It finds that the overall rate of sea level rise between 1993 and mid-2014 is between 2.6 and 2.9 mm per year, with a margin of error of plus or minus 0.4 mm. The bad news is that the first six years of the satellite data - 1993 to 1999 - is the period that is most affected by these corrections. For those six years, estimates have to be scaled down by 0.9-1.5 mm a year. That mean in more recent years the rate of sea-level rise has actually increased rather than declined, according to the paper, led by Christopher Watson of the University of Tasmania, Australia. The acceleration "is higher than the observed twentieth-century acceleration but in reasonable agreement with an accelerating contribution from the Greenland and West Antarctic ice sheets over this period", the team said."

[AbruptSLR]

Lennart,

I re-post your Reply #341 below:

"Some indications that SLR may have been accelerating over the past few years:
http://onlinelibrary.wiley.com/doi/10.1002/2015GL063902/abstract?utm_content=buffer63d49&utm_medium=social&utm_source=twitter.com&utm_campaign=buffer

"The global mean sea level (GMSL) was reported to have dropped 5 mm due to the 2010/11 La Niña and have recovered in one year. With longer observations, it is shown that the GMSL went further up to a total amount of 11.6 mm by the end of 2012, excluding the 3.0 mm/yr background trend. A reconciled sea level budget, based on observations by Argo project, altimeter and gravity satellites, reveals that the true GMSL rise has been masked by ENSO-related fluctuations and its rate has increased since 2010. After extracting the influence of land water storage, it is shown that the GMSL have been rising at a rate of 4.4 ± 0.5 mm/yr for more than three years, due to an increase in the rate of both land ice loss and steric change.""

Therefore, we all need to remember that GMSL dropped 5m due to the 2010/2011 La Nina, are impacting Watson et al 2015 numbers; while GMSL has "... been rising at a rate of 4.4 +/- 0.5 mm/yr for more than three years now; and in this current El Nino year GMSL is jumping up still high.  We all need to be very careful with using SLR rate values that do not consider the influence of the coming 20, or so, years of positive PDO; and the likely accelerating contribution from ice sheets (which the AR5 panel on SLR that Church chaired underestimated).

Best,
ASLR

[Lennart van der Linde]

The link leads to an article indicating that the rate of SLR over the past two decades was faster than previously realized:

ASLR,
My first reaction to your original post on this matter was to the part in bold (but I forgot to point this out, so maybe that was not so clear). Watson et al 2015 say the rate of SLR of the past two decades was slower, not faster, than previously realized. They also say the acceleration over this period was faster than previoulsy thought. And this doesn't exclude the possibility that over 2010-2012 the rate of SLR and acceleration was even faster than in the years before. A correction for the influence of El Nino en La Nina on the numbers of Watson et al 2015 (and IPCC) seems useful, but how much that would change the average over 1993-2014 does not seem obvious to me.

[sidd]

Watson(2015) is a carefully done paper. As to acceleration:

" the previously reported deceleration[1] , estimated here as −0.057 ± 0.058 mm/yr/yr (over 1993–2014), becomes an acceleration of +0.041 ± 0.058 mm/yr/yr "

The previously reported deceleration is from a paper by Cazenave last year.

Watson et al. go on to note:

"Neither of these is significantly different from zero, however, the revised estimate is significantly different from the earlier estimate derived from data unadjusted for the effects of bias drift."

and

"Our computed acceleration is higher than the observed twentieth-century acceleration[2,8,23] but in reasonable agreement with an accelerating contribution from the Greenland and West Antarctic ice sheets over this period[2,24] , and the Intergovernmental Panel on Climate Change projections[2,10] of acceleration in sea-level rise during the early decades of the twenty-first century of about +0.07 mm/yr/yr ."

The numbers in brackets are references.

My takeaway is that the satellite record so far cannot definitely ascribe nonzero acceleration, and that OHC is still a major player in SLR. Once ice sheet melt takes off, the acceleration will become unmistakable, and it will be clearly too late to forestall eventual SLR rates of 1 meter every score of years. One might speculate that the recently observed mass waste acceleration in west antarctica (or Greenland) with a doubling time of a decade will dominate SLR in the future. With current contribution of about 1/3 mm/yr to SLR from WAIS out of the total observed 3mm/yr, naive extrapolation  shows WAIS waste dominating in 30-40 years. Greenland seems to be contributing around a mm/yr right now, so a decadal doubling there would give more than cm/yr by midcentury. And after that, a deluge comparable to MWP1A.

sidd

[AbruptSLR]

To me it is clear that as Church is Chairman of the IPCC SLR committee, that any paper that he co-authors must err on the side of least drama.  Therefore, I lean more towards sidd's rough assessment above than to Watson et al 2015 use of limited historical SLR data to characterize ice sheet contributions to global mean sea level rise.

However, I point out that sidd's use of the average WAIS SLR contribution of about 1/3 mm/yr; does not fully illustrate our true risks, as the attached GOCE measurement of SLR contribution from the Amundsen Sea Sector alone was 0.51mm/yr averaged from November 2009 to June 2012 (which includes the major 2010/11 La Nina event), see the attached image & the linked article.

http://www.esa.int/Our_Activities/Observing_the_Earth/GOCE/GOCE_reveals_gravity_dip_from_ice_loss

The point that I am trying to make is that by talking about averaged data, we underestimate the future risks of SLR contribution from such exponentially degrading areas as the Amundsen Sea Sector (& I give Pollard et al 2015's assessment of this risk much more credence than some short-term tide gauge record gathered predominately during the last negative PDO cycle).

Edit: I forgot to note that the GOCE estimated SLR contribution form the Amundsen Sea Sector, by eventually need to be increased by up to 40% in order to correct for the GIA (glacial isostatic adjustment); which is currently being measured in this sector.

[Michael Hauber]

Just for fun, the current rate of 2.6ymm/year, and acceleration of 0.04 mm/year gives an increase to 6.6 mm/year and a 46cm total sea level rise for the next century.  If we assume that the acceleration is exponential (i.e. 0.04/2.6 % compound growth) this gives a rate of 11.8mm/year in 100 years, and a total of 61 cm of sea level rise.

We need more acceleration than is being currently observed to get anything above 1 meter for the next century.  If I remember right a faster exponential growth on just the ice sheet portion of the current melt as Hansen calculated could get us to 7 meters in a hundred years.

 

[sidd]

"We need more acceleration than is being currently observed ..."

Precisely. And I claim

1) the acceleration from WAIS and GIS is not visible yet inSLR
2) When it is, doom is nigh.

sidd

[AbruptSLR]

"We need more acceleration than is being currently observed ..."

Precisely. And I claim

1) the acceleration from WAIS and GIS is not visible yet inSLR
2) When it is, doom is nigh.

sidd

I concur with sidd that policy makers who over-emphasize the importance of the past couple of decades of observed record will likely be in for a big surprise when the highly non-linear positive SLR feedbacks (such as PIG, Thwaites, Jakobshaven etc) accelerate rapidly while the largely linear negative SLR feedbacks (such as episodic atmospheric river driven snow fall in Antarctica or La Nina driven rainfall in the tropical land areas) accelerate slowly.  The only justification for MH-type of projections is if one has a high tolerance for transferring risk to others; by thinking that in a zero-sum game that you can do alright at the expense of others.

[Lennart van der Linde]

Also see this comparison of collapsing ice sheets with avalanches:
http://johnenglander.net/sea-level-rise-blog/inability-predict-slr-similar-avalanche-problem

"The most common question about sea level rise is 'how high will it rise by when.' It surprises many to learn that there is no way to predict that answer with any certainty. Also many mistakenly believe that projections for three or six feet are really the worst case scenario, which they are definitely not.

One of the ways that I explain our inability to predict when catastophic sea level rise (SLR) could happen, is to use avalanches as an example. (The recent tragedy in Nepal makes this very poignant.)

Many of us have been in areas of heavy snow and been told there is the "potential for an avalanche." Yet there is absolutely no way to predict if or when an avalanche could occur. It could start in 3 minutes or 3 weeks, or never. There is simply no way to model the complex dynamics of melting heavy snowmass to know when the structure will hit a critical point of failure.

A slightly different metaphor is an earthquake. In spite of thousands of earthquakes to study, and putting sensors on known fault lines, we cannot predict an earthquake. Last summer for example, in the San Francisco Bay Area, seismologists were proud that they were able to issue a 10 second warning of a significant earthquake allowing some people to get out of elevators or buildings. There is simply no way to predict how the pressures on the tectonic plates will suddenly shift.

The ice sheets in Greenland and Antarctica are similar.  They are two or three miles thick. Like a potential avalanche there is no way to model exactly when they will collapse.  When they collapse we will get many feet of SLR, in fact, eventually we will get tens of feet of SLR. Because scientists cannot predict whether that will happen by the year 2100, or in the following century, that potential is generally omitted from the SLR projections. Scientists need to be able to cite objective data, based on measurements that can be verified. The collapse of the glaciers and two great ice sheets do not follow that.

We need to explain this phenomenon better. People, communities, companies, and governments need to understand that we are going to get tens of feet of sea level rise sometime in the next few centuries. In the second half of this century we could start to see catastropic SLR.  Now is the time to do strategic planning. One way to explain the misleading or misunderstood limitations about rising sea level may be mountain avalanches -- though that is of course very counterintuitive."

[AbruptSLR]

Also see this comparison of collapsing ice sheets with avalanches:
http://johnenglander.net/sea-level-rise-blog/inability-predict-slr-similar-avalanche-problem

Lennart,

Thanks for the link to the John Englander website:

http://johnenglander.net/

Englander seems to have a lot of very reasonable things to say about SLR in the numerous posts on his blog site.

I hope that efforts like efforts like the 10-yr ACME program will identify the true SLR risks before large-scale cliff failure and hydrofracturing calving events become common in marine glaciers in both the GIS and the AIS:

http://climatemodeling.science.energy.gov/sites/default/files/publications/acme-project-strategy-plan.pdf

http://climatemodeling.science.energy.gov/

http://crf.sandia.gov/acme-climate-modeling-powered-by-doe-supercomputers-tamed-by-uncertainty-quantification/

Best,
ASLR

[Martin Gisser]

Also see this comparison of collapsing ice sheets with avalanches:
http://johnenglander.net/sea-level-rise-blog/inability-predict-slr-similar-avalanche-problem

I hope I misunderstood  this article... He seems to tell that SLR from ice sheet collapse cannot be predicted by comparing this to the problem of predicting when an avalanche or earth quake gets loose. That looks totally wrong to me: The collapse will not come sudden, like a house collapsing due to an earth quake. No, the collapse is already happening! (E.g. Rignot et al found WAIS collapse now is even irreversible). But it is happening in slow motion.

The avalanche metaphor seems quite apt, but only when taken in slow motion. (I'm no ice sheet expert and wanted to ask for this today somewhere on the forum - so I searched for the key word "exponential" and thus came here. )

The ice sheet "avalanche" is already rolling upon us, meanwhile, accumulating in mass, growing more exponentially than linearly. (+). Taking a conservative estimate of 10y doubling time of melt rate and taking just Greenland, then we get 3.5-7 meters SLR by 2100, as Hansen said long time ago. (Now imagine that it looks more like 5y doubling time - the avalanche then growing monstrously bigger and faster. I hear it roaring...)

Problem with extrapolating exponential trends is of course the growing error margin (E.g.: Is it half of Greenland by 2100 or all of it?). But that doesn't mean prediction is impossible -  you just have to get rid of the common image of a linear scale of numbers. (Maybe play with an ancient mechanical slide rule calculator. Every pre-calc math student should have one.)

Albert Bartlett's famous dictum:

The greatest shortcoming of the human race is our inability to understand the exponential function.

(Well, methinks that's due to the cultural dominance of left brain hemisphere thinking, which only can do linear bean counting (however complex it may be) but fails at holistic systems grasp. Grasping exponential stuff (and its vagaries in a finite real world) is more for the right hemisphere. But that's for a different thread...)

--------------------
(+) Edit, P.S.:
There are general systems thinking reasons for preferring exponential over linear. (A bit more detail in my 2009 comment here.) Me dunno know more. And Hansen said the same. Meanwhile, my impression is that it's almost consensus amongst ice sheet experts to assume exponential decay (and monstrous SLR as a corollary) - drawing from their expert intuition about the concrete physical system at hand.

[AbruptSLR]

Also see this comparison of collapsing ice sheets with avalanches:
http://johnenglander.net/sea-level-rise-blog/inability-predict-slr-similar-avalanche-problem

I hope I misunderstood  this article... He seems to tell that SLR from ice sheet collapse cannot be predicted by comparing this to the problem of predicting when an avalanche or earth quake gets loose. That looks totally wrong to me: The collapse will not come sudden, like a house collapsing due to an earth quake. No, the collapse is already happening! (E.g. Rignot et al found WAIS collapse now is even irreversible). But it is happening in slow motion.

If you want to know more about this topic you may wish to review the following reference and the following linked threads in the Antarctic folder:

Pollard, D., R.M. DeConto and R.B. Alley (2015) "Potential Antarctic Ice Sheet retreat driven by hydrofracturing and ice cliff failure", Earth Plan. Sci. Lett., 412, 112-121

http://www.sciencedirect.com/science/article/pii/S0012821X14007961

http://forum.arctic-sea-ice.net/index.php/topic,130.150.html

http://forum.arctic-sea-ice.net/index.php/topic,263.100.html#lastPost

[AbruptSLR]

With a hat tip to Lennart from the WAIS Collapse thread in the Antarctic folder, the linked reference (with a free access pdf) shows that assuming both cliff failure, and melt-driven hydrofracturing, active the WAIS could contribute from 2m to 3m to SLR by 2100 (note that almost all of my posts in the Antarctic folder support this approximation), per the attached image and associated caption:

Pollard, D., DeConto, R.M. and Alley, R.B., (2015), "Potential Antarctic Ice Sheet retreat driven by hydrofracturing and ice cliff failure", Earth and Planetary Science Letters, Volume 412, 15 February 2015, Pages 112–121, doi:10.1016/j.epsl.2014.12.035

http://www.sciencedirect.com/science/article/pii/S0012821X14007961



Abstract: "Geological data indicate that global mean sea level has fluctuated on 103 to 106 yr time scales during the last ∼25 million years, at times reaching 20 m or more above modern. If correct, this implies substantial variations in the size of the East Antarctic Ice Sheet (EAIS). However, most climate and ice sheet models have not been able to simulate significant EAIS retreat from continental size, given that atmospheric CO2 levels were relatively low throughout this period. Here, we use a continental ice sheet model to show that mechanisms based on recent observations and analysis have the potential to resolve this model–data conflict. In response to atmospheric and ocean temperatures typical of past warm periods, floating ice shelves may be drastically reduced or removed completely by increased oceanic melting, and by hydrofracturing due to surface melt draining into crevasses. Ice at deep grounding lines may be weakened by hydrofracturing and reduced buttressing, and may fail structurally if stresses exceed the ice yield strength, producing rapid retreat. Incorporating these mechanisms in our ice-sheet model accelerates the expected collapse of the West Antarctic Ice Sheet to decadal time scales, and also causes retreat into major East Antarctic subglacial basins, producing ∼17 m global sea-level rise within a few thousand years. The mechanisms are highly parameterized and should be tested by further process studies. But if accurate, they offer one explanation for past sea-level high stands, and suggest that Antarctica may be more vulnerable to warm climates than in most previous studies."

Caption: "Global mean equivalent sea level rise in warm-climate simulations. Time series of global mean sea level rise above modern are shown, implied by reduced Antarctic ice volumes. The calculation takes into account the lesser effect of melting ice that is originally grounded below sea level. Cyan: with neither cliff failure nor melt-driven hydrofracturing active. Blue: with cliff failure active. Green: with melt-driven hydrofracturing active. Red: with both these mechanisms active."

Edit: I note that the values given in the attached image are for a simple Pliocene-like warming scenario, and not for any RCP or SRES pathways.

Martin,

I also reproduce Reply #250 here & I noted that if Abrupt Sea Level Rise, ASLR, occurs faster than society can respond, then the analogy with a slow moving avalanche seem apropos.

ASLR

[Martin Gisser]

If you want to know more about this topic you may wish to review the following reference and the following linked threads in the Antarctic folder:

Pollard, D., R.M. DeConto and R.B. Alley (2015) "Potential Antarctic Ice Sheet retreat driven by hydrofracturing and ice cliff failure", Earth Plan. Sci. Lett., 412, 112-121

http://www.sciencedirect.com/science/article/pii/S0012821X14007961

http://forum.arctic-sea-ice.net/index.php/topic,130.150.html

http://forum.arctic-sea-ice.net/index.php/topic,263.100.html#lastPost

Thanks!
But methinks that doesn't change my criticism of Englander's article: Pollard et al just explain a mechanism by which the avalanche accumulates momentum even faster. There is not one point of failure (and then there goes the avalanche or tumbles the building) - but lots of calving and sliding away at many ends, adding/averaging up to a rather smooth process. A quite possibly exponential one (e.g. due to feedback by lowering elevation of ice sheets or e.g. widening of calving fronts, etc.). When much of the ice is gone (e.g. perhaps half - here's the rub perhaps) things might slow down and get linear and finally equilibrate.

Pollard et al:

Incorporating these mechanisms in our ice-sheet model accelerates the expected collapse of the West Antarctic Ice Sheet to decadal time scales, and also causes retreat into major East Antarctic subglacial basins, producing ∼17 m global sea-level rise within a few thousand years. The mechanisms are highly parameterized and should be tested by further process studies. But if accurate, they offer one explanation for past sea-level high stands, and suggest that Antarctica may be more vulnerable to warm climates than in most previous studies.

That doesn't change my exponential-qualitative data driven impression much. (Luckily the EAIS looks still a millenium away...) Except I now tend more toward a 5y doubling time. And thus I'm now more sure that I will see some of the monstrosity of things to come within my own life time.  (But it doesn't change the monstrosity of mankind's ecocide cum genosuicide cum econocide if SLR hits 4m by 2050 or by 2100.)


-------------
P.S.: Last Edit done, then noted your post right above

[Martin Gisser]

Regarding the avalanche metaphor, I'd say to the society: "Better run now and fast and don't gaze at the funny snow movement up the mountain! We don't know how large it will get and when or if it will hit us and how deep we could get buried. And forget about the fat stupid uncle."

[Michael Hauber]

"We need more acceleration than is being currently observed ..."

Precisely. And I claim

1) the acceleration from WAIS and GIS is not visible yet inSLR
2) When it is, doom is nigh.

sidd

I concur with sidd that policy makers who over-emphasize the importance of the past couple of decades of observed record will likely be in for a big surprise when the highly non-linear positive SLR feedbacks (such as PIG, Thwaites, Jakobshaven etc) accelerate rapidly while the largely linear negative SLR feedbacks (such as episodic atmospheric river driven snow fall in Antarctica or La Nina driven rainfall in the tropical land areas) accelerate slowly.  The only justification for MH-type of projections is if one has a high tolerance for transferring risk to others; by thinking that in a zero-sum game that you can do alright at the expense of others.

You brought up the Church paper claiming that it showed sea level rise was faster than previously thought.  When it was pointed out to you that the paper reduced the sea level rise from 3.2 to 2.6 you said that was missing the point because it found that there was now an acceleration.  I showed how much sea level rise the acceleration rate from the paper you originally promoted would actually cause in the next century and you talk about MH-type projections.

[AbruptSLR]

"We need more acceleration than is being currently observed ..."

Precisely. And I claim

1) the acceleration from WAIS and GIS is not visible yet inSLR
2) When it is, doom is nigh.

sidd

I concur with sidd that policy makers who over-emphasize the importance of the past couple of decades of observed record will likely be in for a big surprise when the highly non-linear positive SLR feedbacks (such as PIG, Thwaites, Jakobshaven etc) accelerate rapidly while the largely linear negative SLR feedbacks (such as episodic atmospheric river driven snow fall in Antarctica or La Nina driven rainfall in the tropical land areas) accelerate slowly.  The only justification for MH-type of projections is if one has a high tolerance for transferring risk to others; by thinking that in a zero-sum game that you can do alright at the expense of others.

You brought up the Church paper claiming that it showed sea level rise was faster than previously thought.  When it was pointed out to you that the paper reduced the sea level rise from 3.2 to 2.6 you said that was missing the point because it found that there was now an acceleration.  I showed how much sea level rise the acceleration rate from the paper you originally promoted would actually cause in the next century and you talk about MH-type projections.

Per the linked article (& associated extract) if the rate of sea level rise from 1993 to 1999 was slower than previously thought, but if estimates of current sea level remains essentially unchanged; then the rate of sea level rise from 1999 to now must have accelerated faster than previously thought; which implies that the SLR contributions from ice sheets is accelerating; which is the key point of the Watson et al 2015 paper.


http://www.straitstimes.com/news/world/more-world-stories/story/sea-level-rise-accelerating-earths-ice-sheets-melt-say-scientist

Extract: "The new study, published in the journal Nature Climate Change, takes land movement into account, along with an important statistical tweak - hourly data from a network of tide gauges deployed around the world's oceans. It finds that the overall rate of sea level rise between 1993 and mid-2014 is between 2.6 and 2.9 mm per year, with a margin of error of plus or minus 0.4 mm. The bad news is that the first six years of the satellite data - 1993 to 1999 - is the period that is most affected by these corrections. For those six years, estimates have to be scaled down by 0.9-1.5 mm a year. That mean in more recent years the rate of sea-level rise has actually increased rather than declined, according to the paper, led by Christopher Watson of the University of Tasmania, Australia. The acceleration "is higher than the observed twentieth-century acceleration but in reasonable agreement with an accelerating contribution from the Greenland and West Antarctic ice sheets over this period", the team said."

[jai mitchell]

I showed how much sea level rise the acceleration rate from the paper you originally promoted would actually cause in the next century

   I don't know why I bother coming here when I can just as easily gather lots of other disinformation about climate sciences from watts up with that. . .

are you then claiming that sea level rise will not continue to accelerate in a warming world?  really???

 

[Michael Hauber]

I showed how much sea level rise the acceleration rate from the paper you originally promoted would actually cause in the next century

   I don't know why I bother coming here when I can just as easily gather lots of other disinformation about climate sciences from watts up with that. . .

are you then claiming that sea level rise will not continue to accelerate in a warming world?  really???

 

I am pointing out that the acceleration reported in the paper ASLR quoted is only enough to give about a meter of sea level rise of 1 meter in the next hundred years. 

I've already said that other sources such as Hansen can give a higher sea level rise such as 7 meters (although his analysis is highly speculative extrapolation of 'what if the ice sheet melt keeps doubling throughout the century'), and I have no problem with the chart ASLR posted earlier which shows 5 meters over the next 200 years.

[Sigmetnow]

@billmckibben: Kivalina--Arctic village imperiled by climate change--needs $ to build a road to its new school. Donations welcome.
http://storm-swan.wix.com/relocatekivalina

[Shared Humanity]

From the Guardian article ALSR linked:
"Watson’s team found that the record of sea level rise during the early 1990s was too high. The error gave the illusion of the rate of sea level rise decreasing by 0.058 mm/year2 between 1993 and 2014, when in reality it accelerated by between 0.041 and 0.058 mm/year2... The IPCC’s landmark report in 2013 found the sea had risen on average by 3.2 mm per year since 1993. Waston’s study found the rate was slightly slower, between 2.6 and 2.9 mm per year."

So the acceleration of SLR was faster than previously thought, but the average rate of SLR itself was somewhat slower than earlier estimates, according to this research.

I am trying not to comment often on these threads as I do not understand much of the science (I do visit every day and read almost every thread.) but this discovery is frightening to me. The acceleration of SLR is far more important than the average rate in the same period.

SLR is simply the best, the most accurate aggregate measure of what is happening in the cryosphere. Every study I have read here has shown acceleration in the melt of ice. Glaciers are speeding up and thinning faster. Greenland mass loss is accelerating. Previously stable glaciers are beginning to show signs of deterioration. The WAIS mass loss is accelerating. Specific ice shelves and glaciers defending the WAIS are thinning and speeding up at an accelerating rate. Ice caps previously considered stable (Northeast Greenland and the EAIS) are now exhibiting signs of  accelerating melt and increasing mass loss. Given this, SLR cannot do anything but accelerate and I expect this acceleration to continue in a warming world as this rise captures, in aggregate, the increasing melt across the planet.

I cannot imagine any argument that would convince me that a linear or near linear increase in SLR is what we should expect through this century. Given this acceleration in SLR, the only conclusion that can be drawn is that a doubling rate of growth in SLR is a reality. We should expect that the SLR rate will exhibit an exponential trend. The only question.......what is that doubling rate and where will we end up at the end of the century? My fear is that Hansen is more correct than the current projections of the various models.

(Graph taken from Church 2008)

[Shared Humanity]

In August of 2012, the North Carolina legislature passed a law that required all state planning agencies to only use historical SLR and ignore science that shows that the rise in sea levels will accelerate.

http://abcnews.go.com/US/north-carolina-bans-latest-science-rising-sea-level/story?id=16913782

Specific language of the legislation.....

"These rates shall only be determined using historical data, and these data shall be limited to the time period following the year 1900. Rates of seas-level rise may be extrapolated linearly …"

They calculate the average rate of SLR from 1900 and then use this linear rate to predict future SLR. This is ignorant and laughable.

[Shared Humanity]

With regards to the doubling rate, this can be hard to calculate given the difficulty in measuring accurately small increases in SLR in an environment where ocean levels have a natural variation. I expect that, within a decade, we should have a much better sense of the doubling rate and it will not be pretty.

[Shared Humanity]

Just for fun, the current rate of 2.6ymm/year, and acceleration of 0.04 mm/year gives an increase to 6.6 mm/year and a 46cm total sea level rise for the next century.  If we assume that the acceleration is exponential (i.e. 0.04/2.6 % compound growth) this gives a rate of 11.8mm/year in 100 years, and a total of 61 cm of sea level rise.

We need more acceleration than is being currently observed to get anything above 1 meter for the next century.  If I remember right a faster exponential growth on just the ice sheet portion of the current melt as Hansen calculated could get us to 7 meters in a hundred years.

I may be missing something or misunderstanding how compounding works but how exactly did you arrive at the 2.6% compound growth which suggests a 27 year doubling rate.

From a comment by ASLR above...

Also see the following extract that helps to elaborate on this matter, but be aware that as Church is a co-author this paper likely errs on the side of least drama:

http://www.straitstimes.com/news/world/more-world-stories/story/sea-level-rise-accelerating-earths-ice-sheets-melt-say-scientist

Extract: "The new study, published in the journal Nature Climate Change, takes land movement into account, along with an important statistical tweak - hourly data from a network of tide gauges deployed around the world's oceans. It finds that the overall rate of sea level rise between 1993 and mid-2014 is between 2.6 and 2.9 mm per year, with a margin of error of plus or minus 0.4 mm. The bad news is that the first six years of the satellite data - 1993 to 1999 - is the period that is most affected by these corrections. For those six years, estimates have to be scaled down by 0.9-1.5 mm a year. That mean in more recent years the rate of sea-level rise has actually increased rather than declined, according to the paper, led by Christopher Watson of the University of Tasmania, Australia. The acceleration "is higher than the observed twentieth-century acceleration but in reasonable agreement with an accelerating contribution from the Greenland and West Antarctic ice sheets over this period", the team said."

And from another post by ASLR above...

Lennart,

I re-post your Reply #341 below:

"Some indications that SLR may have been accelerating over the past few years:
http://onlinelibrary.wiley.com/doi/10.1002/2015GL063902/abstract?utm_content=buffer63d49&utm_medium=social&utm_source=twitter.com&utm_campaign=buffer

"The global mean sea level (GMSL) was reported to have dropped 5 mm due to the 2010/11 La Niña and have recovered in one year. With longer observations, it is shown that the GMSL went further up to a total amount of 11.6 mm by the end of 2012, excluding the 3.0 mm/yr background trend. A reconciled sea level budget, based on observations by Argo project, altimeter and gravity satellites, reveals that the true GMSL rise has been masked by ENSO-related fluctuations and its rate has increased since 2010. After extracting the influence of land water storage, it is shown that the GMSL have been rising at a rate of 4.4 ± 0.5 mm/yr for more than three years, due to an increase in the rate of both land ice loss and steric change.""

Therefore, we all need to remember that GMSL dropped 5m due to the 2010/2011 La Nina, are impacting Watson et al 2015 numbers; while GMSL has "... been rising at a rate of 4.4 +/- 0.5 mm/yr for more than three years now; and in this current El Nino year GMSL is jumping up still high.  We all need to be very careful with using SLR rate values that do not consider the influence of the coming 20, or so, years of positive PDO; and the likely accelerating contribution from ice sheets (which the AR5 panel on SLR that Church chaired underestimated).

Since you gave no link to support this 2.6% figure and since we cannot be certain what the true compound rate of growth is, I thought I would also speculate but draw on the linked articles.

The first article suggests that the rate of growth from 1993 to 1999 is 1.2 mm per year. (I know. I am using the mid point with no recognition of error but I'm speculating, right?) This article also states that the average rate of increase for the period between 1993 to 2014 is 2.75. (Yes, again the midpoint.) Meanwhile, the second article calculates the annual rise in sea level is 4.4 mm per year for the most recent 3 years. (Please don't make me point out that I have again used the midpoint. Oh damn! I've already done it.) Purely speculative of course, but these measurements suggest a doubling rate of 10 years. A 7% growth rate compounded for the rest of the century, means that in the last decade of this century, SLR will be 1126 mm per year.

Do I believe that SLR will be more than a meter per year by the end of the century? No. Do I believe the doubling rate is 27 years as you suggest? No. Mine is grossly over estimated and yours is grossly underestimated.

[sidd]

Re: SLR in 2100

1m/yr by century's end stretches credibility, but 1m/20yr was seen in MWP1A, lasting  for five centuries. That's 50mm/yr,  4 doublings or a factor of 16 away. Two score years, say around midcentury.

[Shared Humanity]

Re: SLR in 2100

1m/yr by century's end stretches credibility, but 1m/20yr was seen in MWP1A, lasting  for five centuries. That's 50mm/yr,  4 doublings or a factor of 16 away. Two score years, say around midcentury.

Absolutely. There is no way 1m/yr could happen.

I suppose the only point my post makes is how silly it is to take compound rate of growth and extrapolate it out to the end of the century to conclude we are fine (MH) or screwed (me).This is entirely different than observing that we are currently experiencing an exponential growth in SLR and concluding that this trend will continue for some time as I think it will. What is flawed in my analysis is not so much my suggestion that we are currently seeing a doubling every 10 years but that this doubling would continue until 2100. Obviously, some powerful negative feedbacks would show up (the disappearance of sea terminating glaciers and ice shelves etc.)

[wili]

"silly ... to ... extrapolate"

If a bit of mathematical humor may be allowed at this point:

[Lennart van der Linde]

Recent lecture by Richard Alley, including remarks on Pollard et al 2015 and Applegate et al 2014 on potentially very fast ice loss from WAIS and GIS:


Thanks to Colorado Bob for posting this over at the ASIB.

[Laurent]

Growing climate change threat to Britain's historic coastline
http://www.telegraph.co.uk/news/earth/environment/climatechange/11655087/Growing-climate-change-threat-to-Britains-historic-coastline.html

[anotheramethyst]

math humor??!!!

5 out of 4 people have trouble with fractions.

there are 10 kinds of people in this world, those who understand binary and those who don't.

sorry, continue.

[Lennart van der Linde]

Rignot on ice sheet models and Hansen's 5m by 2100 thought experiment:
http://climatestate.com/2015/06/09/eric-rignot-observations-suggest-that-ice-sheets-and-glaciers-can-change-faster-sooner-and-in-a-stronger-way-than-anticipated/

"Machens: Hansen (2007), assumed an ice sheet contribution of 1 cm for the decade 2005–15, with a potential ten year doubling time for sea-level rise, based on a nonlinear ice sheet response, which would yield 5 m this century. Considering past sea level sometimes rose quickly, jumps associated with catastrophic ice-sheet collapses, Hansen appears plausible. Thus, are we getting closer to modeling ice sheet dynamics in a nonlinear fashion?

Rignot: Jim’s calculations are back of the envelope calculations that do not include any ice physics. That ice sheet loss will proceed in a non linear fashion is certainly a given but from there on a whole variety of scenarios are possible, and we do not have the tools in hand to answer that question. We need fully coupled ice sheet/ocean/sea ice/atmosphere models and we do not have them now. 5 m this century is hard to conceive, because even a speed up of all glaciers in Antarctica and Greenland by a factor 10 would not get us there in time. But I would rather hear Jim’s upper bounds being discussed than the overly conservative scenarios from existing, poorly skilled numerical models."

[AbruptSLR]

I thought that I would post this in this thread even though  it is cited already in other threads, as it indicates that we could be headed to more than 6m of eustatic SLR:

A. Dutton, A. E. Carlson, A. J. Long, G. A. Milne, P. U. Clark, R. Deconto, B. P. Horton, S. Rahmstorf, M. E. Raymo. Sea-level rise due to polar ice-sheet mass loss during past warm periods. Science, 2015 DOI: 10.1126/science.aaa4019

http://www.sciencemag.org/content/349/6244/aaa4019

Abstract: "Interdisciplinary studies of geologic archives have ushered in a new era of deciphering magnitudes, rates, and sources of sea-level rise from polar ice-sheet loss during past warm periods. Accounting for glacial isostatic processes helps to reconcile spatial variability in peak sea level during marine isotope stages 5e and 11, when the global mean reached 6 to 9 meters and 6 to 13 meters higher than present, respectively. Dynamic topography introduces large uncertainties on longer time scales, precluding robust sea-level estimates for intervals such as the Pliocene. Present climate is warming to a level associated with significant polar ice-sheet loss in the past. Here, we outline advances and challenges involved in constraining ice-sheet sensitivity to climate change with use of paleo–sea level records."

Caption for the attached figure: "Peak global mean temperature, atmospheric CO2, maximum global mean sea level (GMSL), and source(s) of meltwater.
Light blue shading indicates uncertainty of GMSL maximum. Red pie charts over Greenland and Antarctica denote fraction (not location) of ice retreat."


See also:
http://www.climatecentral.org/news/sea-levels-rise-20-feet-19211
&
http://www.washingtonpost.com/news/energy-environment/wp/2015/07/09/why-the-earths-past-has-scientists-so-worried-about-sea-level-rise/
Extract: " As a result, he thinks that currently, the mid-Pliocene is a better analogy for where we could be headed, given the comparable carbon dioxide levels. “In the Pliocene, global temperatures 1 – 2 °C warmer than present came with at least 6 m of rise,” Rahmstorf wrote. Thus, while we may not currently be committed to raising seas as much as occurred in these past periods, if we don’t get global warming under control, that could change."

[Lennart van der Linde]

New paper by Rignot et al on depth of Greenland fjords, implying faster potential ice melt and SLR:
http://blogs.agu.org/geospace/2015/07/15/greenlands-fjords-are-far-deeper-than-previously-thought-and-glaciers-will-melt-faster-researchers-find/#.VaadhJ2OWMI.twitter

[Sigmetnow]

WaPo on the Greenland fjords study:

The shape and depth of fjords have big implications for the ice sheet, which has been melting both from the top and the bottom and contains 20 feet of potential sea level rise in total. Warm air erodes ice above the water, but warmer waters — which reside at deep levels in some parts of the polar regions — undercut glaciers and melt ice from below. “As they melt faster, they can slide out to sea,” said Eric Rignot, leader researcher and a glaciologist at the University of California at Irvine.

Deeper fjords means there are “a lot more places where the warm water, subsurface water, can reach the glaciers,” Rignot said. Shallow fjords don’t pose as much of a threat.

On average, the fjords in this region are about 200 to 300 meters deeper than previously thought in some areas, he added. Glaciers undercut by warm water can melt twice as fast as those in colder waters, all other things being equal.

http://www.washingtonpost.com/news/energy-environment/wp/2015/07/17/the-troubling-reason-why-greenland-may-melt-faster-than-expected/

[Lennart van der Linde]

On the new paper by Hansen et al coming out this week:
http://www.thedailybeast.com/articles/2015/07/20/climate-seer-james-hansen-issues-his-direst-forecast-yet.html

Apparently warning for 3m of SLR by 2100...

[jai mitchell]

James Hansen:  3.2 meters of sea level rise by 2100

http://www.thedailybeast.com/articles/2015/07/20/climate-seer-james-hansen-issues-his-direst-forecast-yet.html

This apocalyptic scenario illustrates why the goal of limiting temperature rise to 2 degrees Celsius is not the safe “guardrail” most politicians and media coverage imply it is, argue Hansen and 16 colleagues in a blockbuster study they are publishing this week in the peer-reviewed journal Atmospheric Physics and Chemistry. On the contrary, a 2 C future would be “highly dangerous.”

If Hansen is right—and he has been right, sooner, about the big issues in climate science longer than anyone—the implications are vast and profound.

[AbruptSLR]

Here is another link about the new Hansen paper with much the same information:

http://www.rtcc.org/2015/07/20/hansen-2c-warming-will-raise-sea-level-several-metres/

Extract: "Hansen: 2C warming will raise sea level several metres -
Scientists warn feedback effects will melt polar ice faster than thought, causing “highly dangerous” impacts this century"

[Lennart van der Linde]

So it appears this paper is not peer-reviewed before publication... (in contrast to what the news-article by Mark Hertsgaard suggested).

[Laurent]

If the purpose is to claim that we are facing a greater threat than expected...then ok, good. But if it is to say we are aiming at 3 meters of SLR then I disagree ! Why don't we have figures explaining things just like these two ?  Assuming that we can absorb carbon (globally) is just non sense for the moment.
There is two point, one is the 400 ppm of  CO2 and the other one is 485 ppm of CO2 eq where we are now. At the end of the century if everything goes well meaning we keep the pace at 3 ppm of CO2 eq per year, we will be at 800 ppm of CO2...well off the charts...
I am not a scientist so if you have something more precise and with references, I would be very glad.
(I assume that in the past the CO2 eq was not very different than the CO2)

[Lennart van der Linde]

More on the new Hansen paper in this excellent Washington Post article:
http://www.washingtonpost.com/news/energy-environment/wp/2015/07/20/the-worlds-most-famous-climate-scientist-just-outlined-an-alarming-scenario-for-our-planets-future/

The peer review has begun, sort of...

[AbruptSLR]

I thought that the following quotes from the new Hansen et al (2015) paper (per the linked Washington Post article provided by Lennart) was worth highlighting.  They point-out that ice mass loss from the GIS, the WAIS and the Totten/Aurora basins are all growing nonlinearly with doubling times of about 10 years; which if continued could result in several (as in over three) meters of SLR by 2065. 

http://www.washingtonpost.com/news/energy-environment/wp/2015/07/20/the-worlds-most-famous-climate-scientist-just-outlined-an-alarming-scenario-for-our-planets-future/

Extract: " “Ice mass losses from Greenland, West Antarctica and Totten/Aurora basin in East Antarctica are growing nonlinearly with doubling times of order 10 years,” notes the study. Elsewhere, it notes that “Doubling times of 10, 20 or 40 years yield sea level rise of several meters in 50, 100 or 200 years.”"

I imagine that any such projection of over 3m of SLR by 2065 must be a fat-tailed upper limit of the PDF comparable to the attached figure from the 2014 paper by Jevrejeva, Grinsted & Moore:

Jevrejeva, Grinsted, Moore (2014), Upper limit for sea level projections by 2100, Environ. Res. Lett. 9 104008 doi:10.1088/1748-9326/9/10/104008

[Lennart van der Linde]

Scientific American had a short interview with Hansen as well:
http://www.scientificamerican.com/article/fossil-fuels-must-be-phased-out-to-avoid-drowned-coastlines/

It's time we can read the paper ourselves...

[Lennart van der Linde]

One more news article on Hansen et al:
http://insideclimatenews.org/news/21072015/new-study-says-even-2-degrees-warming-highly-dangerous

[Lennart van der Linde]

Climate Cenrtral on Hansen et al:
http://www.climatecentral.org/news/dire-climate-warning-questions-19268

And Science Insider:
http://news.sciencemag.org/climate/2015/07/climate-researcher-blasts-global-warming-target-highly-dangerous