/ Rising Sea Levels

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The Ice Doctor - on 11 Jan 2017

I am baffled on this one. Ice expands when frozen, so how will melted icecaps increase sea levels?

Melting glaciers maybe, but icecaps ?

Please explain.....
Post edited at 07:27
2
MG - on 11 Jan 2017
In reply to The Ice Doctor:

The Southern icecap is largely on land
pass and peak - on 11 Jan 2017
In reply to The Ice Doctor:

As is the Greenland ice cap, also as far as I understand there's more potential from a warmer ocean's thermal expansion
wbo - on 11 Jan 2017
In reply to The Ice Doctor: Does UKC ofer the option to change user name?

phizz4 - on 11 Jan 2017
In reply to The Ice Doctor:

Much of the water held as ice in ice caps is on the land, such as Antarctica, so will add to volumes in the oceans when it melts. However, the largest proportion of sea level rise is due to increased ocean temperatures, due to global warming causing thermal expansion of the sea water.
Pesda potato - on 11 Jan 2017
In reply to The Ice Doctor:

as above, but also Ice floats
ianstevens - on 11 Jan 2017
In reply to The Ice Doctor:

As others have pointed out, water stored as ice on land is what causes sea-level rise, not sea ice or the floating sections of marine terminating ice masses. Greenland is mostly on land, and has enough water for 7 m of sea level rise should the whole thing melt (in around 1000 years at current estimates). The East and West Antarctic ice sheets are also mostly on land, but could contribute around 60 m to sea level if melted in their entirety - not that this will happen anytime soon, if at all. We think there has been ice cover of some sort in Antarctica for the past 2 million years. Typical valley glaciers (e.g. the Alps, Patagonia, Himalaya et al.) have very little to contribute, in the order of a few metres. This is for the best as they'e most sensitive to warming.

You may have been inspired to ask this question given the current state and predicted huge calving event of Larsen C? Apologies if I'm wrong, but as I've got going now... This calving event will not DIRECTLY increase sea level. It will result in a huge (2.5x the size of Wales) iceberg, orders of magnitude larger than that which we normally observe. The big issue with this extraordinary calving event is that a similar event preceded the break-up of Larsen B in 2002, and as such some people are worried that Larsen C could be about to undergo the same fate. Again, as ice shelves are essentially floating marine ice, this makes no difference to sea level itself, but begins a feedback loop. After ice shelf removal, back stresses on the (land based) outlet glaciers that feed the ice shelf are removed and they speed up, drawing down ice from the ice sheet to lower elevations where it can melt. Greater volume of melting land based ice = more water into the sea = sea level rise.

In the Northern Hemisphere, sea ice has nothing to do with long term sea level, but obviously has more local impacts (especially on wildlife, arctic people/cultures and shipping) an can influence global radiation reflectivity (albedo). A lower area of sea ice means that a greater proportion of low albedo (i.e. more absorbent) ocean covers the Earth surface, absorbing more energy via solar radiation, and hence contributing further to warming by increasing heat in the oceans. This hasn't really been quantified as far as I am aware, but given that sea ice has an albedo of ~0.7 (i.e, 70% reflectance) and water has an albedo of 0.1, I'd guess this is quite a bit of energy.
RyanOsborne - on 11 Jan 2017
In reply to ianstevens:

In the arctic, most of the primary production (turning energy into organic matter) takes place in sea ice. So less sea ice means less primary production, which means less life in our oceans.

But most importantly and worryingly, with a rise in sea levels, Big Ger's vineyards will have to move to higher ground.
1
blurty - on 11 Jan 2017
In reply to The Ice Doctor:

Interestingly, and counter-intuitively sea level rise has not yet accelerated despite obvious global warming. The rise in sea level remains at a pretty constant 30cm per century with blips for the Little Ice Age and the Medieval Warming.

Once all the ice melts, sea levels will rise around 75m it is thought.
skog on 11 Jan 2017
In reply to The Ice Doctor:

Two people have mentioned it above, but, as I understand it, thermal expansion of the water in the ocean will have a much larger effect than melting of ice from on land.

And melting of ice already floating on the ocean should have no effect, I think (1kg of ice should displace 1kg of water, regardless of the volume of the ice, shouldn't it?)

If I remember correctly, through geological history, both of the above effects can be dwarfed by the increase in sea level caused when the mid-ocean ridges are more active (but that probably isn't something we need to worry about in the short to medium term!)
Postmanpat on 11 Jan 2017
In reply to blurty:

> Interestingly, and counter-intuitively sea level rise has not yet accelerated despite obvious global warming. >

Not so, according to these people, or according to Wilikipedia. The sea level rise is accelerating.

http://oceanservice.noaa.gov/facts/sealevel.html
ianstevens - on 11 Jan 2017
In reply to RyanOsborne:

> In the arctic, most of the primary production (turning energy into organic matter) takes place in sea ice. So less sea ice means less primary production, which means less life in our oceans.

> But most importantly and worryingly, with a rise in sea levels, Big Ger's vineyards will have to move to higher ground.

Increasing amounts in thawing permafrost as well. Whilst I don't know about sea ice specifically, glacial surface microbiology is actually half of my soon to be completed PhD, and whilst there is definately a lot of PP occuring on ice masses the net influence of the microbial communities (i.e. self-regulating, net carbon sequestration from the atmosphere or net carbon release from external mineral sources to the atmosphere) upon carbon cycling is still an area we don't really know huge amounts about. Although as you say, lots of PP. With ice masses we don't really know what happens to "stuff" (cells, ions in solution and debris) in the grand scheme of things - whether it remains on the glacier, enters the subsurface via the hydrological system or exported to the proglacial environment, whether that be marine or terrestrial (probably a nit of each). I guess with sea ice it mostly melts in the summer dumping biological carbon and cell material into the sea seeding ecosystems.

It's never as simple as just water melting is it?
blurty - on 11 Jan 2017
In reply to Postmanpat:

The IPCC remain cautious on this and say that "the acceleration of sea level trend is ‘about as likely as not.’"

There are poorly understood and likely underestimated factors beyond global warming that influence the mean global sea level: Isostatic rebound, under-sea igneous activity (or lack of), human depletion of fossil water reserves, etc.

The IPCC do however project that sea level rise will start to accelerate quite hard, quite soon - a la hockey stick

So far, the rate of sea level rise has been pretty constant (E.g. see the longest, continuously monitored tide gauge below) :

https://tidesandcurrents.noaa.gov/sltrends/sltrends_station.shtml?stnid=8518750

Postmanpat on 11 Jan 2017
In reply to blurty:
> The IPCC remain cautious on this and say that "the acceleration of sea level trend is ‘about as likely as not.’"

>
Which neatly highlights the problem with the climate change debate. We have what one assumes are respectable organisations giving the impression that the facts are very clear
and pretty much beyond debate, in this case that the rise in sea level is accelerating, and another equally respectable organisation saying that facts are not clear and nor are the causes.

As a layman is simply leads to one treating all such prognostications with circumspection ie. sceptically.
Post edited at 12:03
4
Trevers - on 11 Jan 2017
In reply to blurty:

> The IPCC remain cautious on this and say that "the acceleration of sea level trend is ‘about as likely as not.’"

> There are poorly understood and likely underestimated factors beyond global warming that influence the mean global sea level: Isostatic rebound, under-sea igneous activity (or lack of), human depletion of fossil water reserves, etc.

> The IPCC do however project that sea level rise will start to accelerate quite hard, quite soon - a la hockey stick

> So far, the rate of sea level rise has been pretty constant (E.g. see the longest, continuously monitored tide gauge below) :


There are various feedbacks in the system that are likely to start increasing SLR dramatically over coming years and decades. One of the most obvious ones is the Marine Ice Sheet Instability, to which the Pine Island and Thwaites Glaciers in West Antarctica are vulnerable. Put simply, due to the fact that the beds of those glaciers (and much of West Antarctica) are below sea level, once you start their retreat, it kicks off a chain reaction and there's nothing you can do to reverse it.
Trevers - on 11 Jan 2017
In reply to Postmanpat:

> Which neatly highlights the problem with the climate change debate. We have what one assumes are respectable organisations giving the impression that the facts are very clear

> and pretty much beyond debate, in this case that the rise in sea level is accelerating, and another equally respectable organisation saying that facts are not clear and nor are the causes.

> As a layman is simply leads to one treating all such prognostications with circumspection ie. sceptically.

I think the problems are manifold.

The IPCC are rightly cautious and conservative in their projections, because extreme projections that don't come to pass (as happened recently with Arctic sea ice projections by an individual) will inevitably be pounced on by the media, and undermine the credibility of the science in the eyes of the public.

At the same time however, it's equally important that likely worst case scenarios are explored, since these are the ones we need to be planning against and mitigating for.

It's a very easy job for climate deniers, all they have to do is sow the seeds of doubt. Find one incorrect prediction, or a result that appears to be at odds with a very naive understanding of climate change, and take that out of all context. Or confuse the public by suggesting that the reliance on computer models undermines the process of science. When it's pointed out that there's a strong scientific consensus on climate change, spin this as evidence of a whitewashing conspiracy, playing on the public's understanding that science is about scepticism.

There are other problems too, relating to science journalism. Headlines always read "Scientists say...", regardless of who says it, whether it's an individual or an organisation, their level of experience (PhD student or internationally renowned professor). So if one contrary result is reported, the average reader takes that as the "new official position of the scientific community", not just of one individual.

And another problem, of which the BBC is often guilty, is the (generally noble) urge to present balance, which often leads to false balance. For example, in an effort not to be partisan, they may interview a prominent climate denier along with a leading professor of science, setting up a false equivalence in their positions. To the lay public, their viewpoints appear to be equally valid, when in reality the denial side has little to no credibility.

There is still debate in many areas of climate and earth science. There are still processes that are missing from our models, and a great deal of effort is being made to rectify that. But it's not beyond any reasonable doubt that climate change is happening and that it's anthropogenic in origin.
Postmanpat on 11 Jan 2017
In reply to Trevers:
> I think the problems are manifold.

> The IPCC are rightly cautious and conservative in their projections, because extreme projections that don't come to pass (as happened recently with Arctic sea ice projections by an individual) will inevitably be pounced on by the media, and undermine the credibility of the science in the eyes of the public.

> At the same time however, it's equally important that likely worst case scenarios are explored, since these are the ones we need to be planning against and mitigating for.

>
All that you say is no doubt true. But taking this specific example, the NOAA, and other such institutions treat their analysis as "fact" when in reality they know that it is not a "fact". (One infers that it is not a "fact" by the IPCC's description).

I recognise that by acknowledging such things are complex and not cut and dried one might be opening the door to deniers, but by falsifying the level of certainty one implicitly undermines the credibility of not only the rising sea level assertions but wider climate change assertions.

It's bad enough that Gore and other publicists make this error without serious scientific institutions making the same mistake.

Rereading your post you seem to be making the same mistake-ie.lets tell the public it is all clear and factual in order to stop deniers exploiting a chink in our arguments.
All it does is look dishonest.
Post edited at 13:15
3
MG - on 11 Jan 2017
In reply to Postmanpat:
Looking at those two websites they seem pretty compatible to me, noting they use different measurements (one local, one global). Both show long term rises, both give reasons for these rises, both acknowledge the uncertainties. OK, only one shows a increase in rate of sea level rise but this is fairly mild and from a global measurement, not the NY local one. Actually eyeing the NY one, I think it too shows a recent increase anyway - the line is just a linear fit to all the data.

You are also wrong, the uncertainties are acknowledged, for example
"However, it’s uncertain whether that acceleration will continue, driving faster and faster sea level rise, or whether internal glacier and ice sheet dynamics (not to mention natural climate variability) will lead to “pulses” of accelerated melting interrupted by slow downs."

https://www.climate.gov/news-features/understanding-climate/climate-change-global-sea-level

Nothing is being "falsified" - just the conclusions presented in a fairly digestible form. Would you really want error analysis and qualifications of every statement on a public presentation of scientific findings? Anyway, all the sources are cited if you want the detail.
Post edited at 13:31
Postmanpat on 11 Jan 2017
In reply to MG:
Which two sites? I am referring to the NOAA one which headlines

"Is sea level rising?
Yes, sea level is rising at an increasing rate."

and continues "With continued ocean and atmospheric warming, sea levels will likely rise for many centuries at rates higher than that of the current century."

It doesn't really allow for much dispute.


The one you link to, although have a little more nuance, still asserts "Sea level has been rising over the past century, and the rate has increased in recent decades."
Post edited at 13:35
1
MG - on 11 Jan 2017
In reply to Postmanpat:
I thought we were discussing these two
http://oceanservice.noaa.gov/facts/sealevel.html (global measurements)
https://tidesandcurrents.noaa.gov/sltrends/sltrends_station.shtml?stnid=8518750 (New York measurements)

Edit: my link is from the first.
Post edited at 13:35
Postmanpat on 11 Jan 2017
In reply to MG:

I'm discussing the differnece between the NOAA site I linked to (same as your upper one) and the IPCC's suggestion that "the acceleration of sea level trend is ‘about as likely as not.’"


MG - on 11 Jan 2017
In reply to Postmanpat:
Where is that quote from? A very brief google gives this, which suggests an increasing rate (note error bars...)

https://www.ipcc.ch/pdf/unfccc/cop19/3_gregory13sbsta.pdf
Post edited at 14:10
Trevers - on 11 Jan 2017
In reply to Postmanpat:
> Rereading your post you seem to be making the same mistake-ie.lets tell the public it is all clear and factual in order to stop deniers exploiting a chink in our arguments.

> All it does is look dishonest.

I'm trying to say that due to the nature of the reporting of science to the lay public, to some extent scientists are damned if they do and damned if they don't. That's even the influence of climate deniers is thrown into the mix.

What it boils down to is that there needs to be a greater public understanding of the scientific method, uncertainty analysis and how consensus is reached. But also that scientists should be mindful of how their press releases are going to be received by the wider public, and be incredibly careful in their wording. And that the media should exercise some restraint when it comes to choosing their headlines (this last one is wishful thinking I know).

I don't think it means that every news report needs to be mired down with a detailed analysis on the level of certainty on the finding or projection.
Post edited at 14:17
Trevers - on 11 Jan 2017
In reply to Postmanpat:

Agreed with MG. Please point out where that assertion is made. Is it referring to a specific process or overall?
tony on 11 Jan 2017
In reply to Postmanpat:

> I'm discussing the differnece between the NOAA site I linked to (same as your upper one) and the IPCC's suggestion that "the acceleration of sea level trend is ‘about as likely as not.’"

That's not an IPCC suggestion. That a GWPF interpretation of a 2013 paper on Twentieth-Century Global-Mean Sea Level Rise.
Irk the Purist - on 11 Jan 2017
In reply to Postmanpat:

NOAA is American and IPCC is international. The IPCC approach is consistent with a public engagement approach to science and is the more enlightened. It attempts to put across probability, likelihood, risk in a way that doesn't hide the uncertainty of science.

In the UK we have been stung by high profile scientific disasters BSE, MMR etc and they have led to a much more honest and conciliatory approach to communicating scientific ideas.

The slightly outdated NOAA approach may be symptomatic of US culture or it may be a cause. That's a debate for another day.

We live in a post truth world and frankly, it couldn't have come quicker!
Trevers - on 11 Jan 2017
In reply to tony:

> That's not an IPCC suggestion. That a GWPF interpretation of a 2013 paper on Twentieth-Century Global-Mean Sea Level Rise.

Could you link please?
tony on 11 Jan 2017
Trevers - on 11 Jan 2017
In reply to tony:


The GWPF have essentially put words into the mouths of the IPCC. Nowhere was the phrase ‘about as likely as not’ used to refer to GMSLR (global mean sea level rise) acceleration, until that press release.

The paper itself is about reconciling the observed GMSLR over the early 20th century with the estimates of the various contributors to GMSLR, which didn't appear to add up. As you can probably appreciate, that's painstaking work taking data of varying quantity and quality from various sources and making sense of it all.

The paper doesn't claim that GMSLR is not acclerating:
"In the last two decades, the rate of GMSLR has been larger than the twentieth-century time mean, because of increased rates of thermal expansion, glacier mass loss, and ice discharge from both ice sheets"
http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-12-00319.1

I think there's a lesson in this somewhere.
Postmanpat on 11 Jan 2017
In reply to Trevers:

> Agreed with MG. Please point out where that assertion is made. Is it referring to a specific process or overall?

Ask blurty! He's the guy who introduced it!!
Trevers - on 11 Jan 2017
In reply to Postmanpat:

> Ask blurty! He's the guy who introduced it!!

Oh right, sorry for thinking you'd dragged that into this thread! A lesson for me too. If you're interested, I've just debunked the 'about as likely as not' claim.
MG - on 11 Jan 2017
In reply to Postmanpat:

So, to sum up, no one reputable has claimed "as likely as not", the scientific reports are in agreement, aren't falsified and show sea-levels, globally are rising at an increasing rate?
Postmanpat on 11 Jan 2017
In reply to MG:
> So, to sum up, no one reputable has claimed "as likely as not", the scientific reports are in agreement, aren't falsified and show sea-levels, globally are rising at an increasing rate?
>
Yup, if Trever's characterisation of tony's link is correct. Just as I said in my OP!

Having said that, if I'm understanding who is saying what in tony's link, the Gregory report itself is saying that "The reconstructions account for the approximate constancy of the rate of GMSLR during the 20th century, which shows small or no acceleration, despite the increasing anthropogenic forcing."

So at least one reputable report would appear to question whether there has been acceleration. I think......
Post edited at 16:57
Trevers - on 11 Jan 2017
In reply to Postmanpat:

> Yup, if Trever's characterisation of tony's link is correct. Just as I said in my OP!

> Having said that, if I'm understanding who is saying what in tony's link, the Gregory report itself is saying that "The reconstructions account for the approximate constancy of the rate of GMSLR during the 20th century, which shows small or no acceleration, despite the increasing anthropogenic forcing."

> So at least one reputable report would appear to question whether there has been acceleration. I think......

I'm guessing the actual paper itself is behind a paywall for most people here, so I'll lay out what it's saying for people. I'll admit out that I've only read the abstract and conclusions, the detail of methods and results is rather involved and not within my area of expertise.

===================================================================================================
What the paper ISN'T about:

The study doesn't concern itself with warming or GMSLR trends post ~1990. There is little doubt that this is accelerating due to increasing contributions from the ice sheets. It finds no evidence that this isn't the case, agreeing with previous studies, and quoting a study by Church et al (2011) which is widely cited.

==================================================================================================
What the paper IS about:

The paper sets out to reconcile differences between the observations of GMSLR (i.e. checking sea level against an actual height gauge) and the estimates of the three main contributions (loss of ice from glaciers and ice sheets, loss of water from land based storage, and thermal expansion of water already in the oceans). This is set out clearly by the authors:

> "The title of this paper refers to the difficulty of accounting for the magnitude of twentieth-century global mean sea level rise (GMSLR) estimated from the tide gauge records. Previous authors have found observed GMSLR to exceed the sum of the quantified contributions, especially in the early decades of the century, when the influence of anthropogenic climate change was small"

The problem being that calculating estimates for such processes on such a vast scale means taking data from a variety of disparate sources and making a bunch of assumptions. That's already fraught with difficulty and uncertainty, and becomes harder as you go further back in history because technology was less advanced, computerised data storage didn't exist, international standards may not have been in place, and the understanding of climate change as a serious issue was lacking.

For example, ocean measurements were non-existent in the first half of the 20th Century, so atmosphere–ocean general circulation models (AOGCMs) are used to estimate thermal expansion of the oceans. The estimate of this study is higher than previous studies because the authors make an adjustment based on the long term effects of volcanism on ocean heat storage. So the assumptions are updated and the estimates should be more accurate.

The study also finds that early 20th Century GMSLR from glaciers and ice sheets was roughly equivalent to that in the latter half. The authors lay out some possible reasons for this. There's a lot of uncertainty in the contribution from ice sheets (i.e. Antarctica and Greenland), but the contribution from these is almost certainly accelerating today. Due to their continental scale, the ice sheets take longer to respond to climate forcings so there is a lag time.

The overall picture from the paper is that the climate was cooler than it's long term average in the early part of the century, due to volcanic activity and reduced solar irradiance. Therefore part of the trend of warming and increasing GMSLR was due to a rebound from this cooler state, which led into the anthropogenic warming trend we now see.

==================================================================================================
GWPF interpretation:

The GWPF (Global Warming Policy Forum) interpretation is to paint this paper as an estimate of current acceleration trends, which is a highly dishonest reading of it, because it's explicitly not about that, and the authors state so.

The phrase ‘about as likely as not’ was at no point used by either the IPCC or the authors of the study to refer to acceleration trends of the GMSLR. The IPCC report states it is 'likely' that GMSLR rates have accelerated since 1900, which is not at odds with the results of the studies mentioned.

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

I hope that's useful in clearing things up!
Postmanpat on 11 Jan 2017
In reply to Trevers:

Thanks for that, very helpful.
Big Ger - on 11 Jan 2017
In reply to RyanOsborne:

> But most importantly and worryingly, with a rise in sea levels, Big Ger's vineyards will have to move to higher ground.

Don't panic. I think they're already high enough to be safe.


MikeYouCanClimb - on 11 Jan 2017
In reply to Trevers:

> There is little doubt that this is accelerating due to increasing contributions from the ice sheets.

At least in part, the rate of sea-level rise has been explained by a gradual increase in ocean thermal expansion due to rising heat content. The remaining contributions come principally from melting land ice.

Fluctuations are at least partly related to volcanic eruptions and increasing contributions from land ice etc.

It is worth noting that that sea levels will continue to rise for centuries even if greenhouse gases are reduced. Between 1880 and 2009 sea level rose by 210mm.

Church, J.A. & White, N.J. Surv Geophys (2011) 32: 585.
blurty - on 12 Jan 2017
In reply to Postmanpat:


> Ask blurty! He's the guy who introduced it!!

Oh shit - sorry about that. I took the quote from a website without going back to the IPCC site to cross check



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