sea level rise - measured how, exactly?

These might help answer your question:

The projected range from AR5 is 0.26 m (lower bound of low emission scenario) to 0.98 m (upper bound of high emission scenario). The current rate is in excess of 0.3 m/century and likely accelerating. Sea level rise currently is roughly equal parts steric (expansion due to added heat) and mass (ice sheet melt). The greatest part of the uncertainty is the latter and there is research published since AR5 that suggests the rate of ice sheet loss is on the high end of projections and perhaps higher than the high end.

Welcome to 1988 when the IPCC was organized to look at these hard questions and summarize the best available understanding.

As a brief overview for those who might not understand the process, the IPCC assessment reports are three volumes compiled by three working groups of specialists in relevant disciplines.

"The Physical Science Basis" - The Working Group I contribution provides a comprehensive assessment of the physical science basis of climate change. The report includes a detailed assessment of climate change observations throughout the climate system; dedicated chapters on sea level change, biogeochemical cycles, clouds and aerosols, and regional climate phenomena; extensive information from models, including near-term and long-term climate projections; and a new comprehensive atlas of global and regional climate projections for 35 regions of the world.

"Impacts, Adaptations, and Vulnerability" - The Working Group II contribution considers the vulnerability and exposure of human and natural systems, the observed impacts and future risks of climate change, and the potential for and limits to adaptation. The chapters of the report assess risks and opportunities for societies, economies, and ecosystems around the world.

"Mitigation of Climate Change" - The Working Group III contribution assesses the options for mitigating climate change and their underlying technological, economic and institutional requirements. It transparently lays out risks, uncertainty and ethical foundations of climate change mitigation policies on the global, national and sub-national level, investigates mitigation measures for all major sectors and assesses investment and finance issues.

No Way wrote:These might help answer your question:

http://web.mit.edu/globalchange/www/MITJPSPGC_Rpt156.pdfhttp://www.ipcc.ch/ipccreports/tar/wg2/index.php?idp=298

Thanks, great resources. Reaffirms my decision to pose the question(s) on Letsrun. The IPCC report doesn't converse and answer simple queries easily.

(1) I guess the snark is a comment on my basic ignorance. Fair comment I suppose. If we are going to bring up 1988, then I suppose it's also fair to make a general comment about the strength of the "predictions" in the IPCC reports, and point out the marked difference between the consensus predictions and actual temperature anomaly from 1997-present.

(2) Thanks for that overview, I will admit to not knowing that.

No Way wrote:These might help answer your question:

...

http://www.ipcc.ch/ipccreports/tar/wg2/index.php?idp=298

It's hard to pull a clear answer out of those resources, but one illustrative example the IPCC summary includes is the following:

"For a 0.5-m sea-level rise, the damage cost without countermeasures in Japan would be about US$3.4 billion yr-1, based on the comparison of the utility level between no sea-level rise and a 0.5-m sea-level rise without countermeasures."

As Citizen Runner pointed out, 0.5 m is "about" what we expect to 2010, so let's say that's a cost experienced in about 85 years, by 127 million residents of Japan.

That's about $27/person per year, when the sea level rise is about 0.5 m.

Is that a catastrophic loss to bear? Doesn't feel like it.

There's another more relevant example:

"Neumann et al. (2000) have estimated that a 0.5-m sea-level rise by 2100 could cause cumulative impacts to U.S. coastal property of US$20 billion to US$150 billion and that more extensive damage could result if climate change increases storm frequency or intensity."

Given a population of 318 million, that's an annulaized per capita cost of about $0.75 to $5.50. Catastrophic loss? You tell me..

Apologies to anybody if I've done the math wrong, sometimes arithmetic is not my strong suit.

If I've done the math right.... the numbers look big when presented without context, but not so big when presented with context. Happy to take arguments that my choice of context is flawed. It could be...

the shill wrote:

Apologies to anybody if I've done the math wrong, sometimes arithmetic is not my strong suit.

If I've done the math right.... the numbers look big when presented without context, but not so big when presented with context. Happy to take arguments that my choice of context is flawed. It could be...

Your shtick has gotten really old, dude. Get a new line of work.

"Oh, I really don't know much. Oh, math is not my strong suit. Oh, I'm ashamed to admit... Oh, I'm just curious..."

Seriously, get a new shtick. Or a new job. Or just stop altogether. You are way, WAY too transparent and annoying.

What the What? wrote:Seriously, get a new shtick. Or a new job. Or just stop altogether. You are way, WAY too transparent and annoying.

Hey, I'm owning all that, I'm "the shill" right?

Don't get me wrong, I think I'm pretty smart, but I recognize there's a lot in this topic I don't know or understand, and I may be making mistakes in my logic. One of things I enjoy about discussing this here is I get to "hear myself" when I say something stupid and then realize and accept and own my mistakes. Reading the 1500 page IPCC report in quiet contemplation doesn't provide the opportunity to float trial baloons and have them shot down.

On that note, my last post released a trial baloon. Can you shoot it down instead of calling me out for what my username plainly admits?

And let the record reflect that I have not been sworn and my testimony here may contain irony in place of truth:

the shill wrote:... my username plainly admits?

On my weekend trail run with my single friend who will tolerate discussions about climate change, it dawned on me that most people equate absolute belief in / acceptance of AGW as equivalent to being pro-environment, and any hint of skepticism, healthy or not, big or tiny, meaning pro-development/business/etc at the expense of the environment. In my own case nothing could be further from the truth. In the same way that lack of religion (or opposition to the idea of religion) doesn't imply a lack of "intrinsically good" beliefs and values.

the shill wrote:

(2) Overlaying two plots is OF COURSE naive. It's a quick and crude way of comparing two sets of data and looking for similarities or patterns.

(3) I didn't "expect them to move in concert" but I admit I am surprised by the nearly complete absence of similarity at any scale shorter than the century scale.

If you look at the variation in the sea level rise data, you can see there is very little short term variation compared to the century scale, so why would you expect any correlation with 12 month moving average of temperature which shows variation at 3-4 year time scale?

The 12 month moving average of temperature shows a lot of variation at all time scales above about 3 years.

dingle wrote:If you look at the variation in the sea level rise data, you can see there is very little short term variation compared to the century scale, so why would you expect any correlation with 12 month moving average of temperature which shows variation at 3-4 year time scale?

That's not really correct. The plot of sea level change I provided earlier was smoothed. Here are a couple of example US tide gauges with trends also plotted:

There is quite a lot of short term variability. There is not very significant decadal variability from the overall trend, mind you. I find that a little puzzling frankly. In the 1970s, when global temperatures were in a lengthly slight decline, and there was local readvance of mountain glaciers, one might expect sea level to drop for both steric and water balance reasons, but it did not.

No Way wrote:

Anyway, 8 inches itself may not be a lot in many places..

says it is.

the shill wrote:In the 1970s, when global temperatures were in a lengthly slight decline, and there was local readvance of mountain glaciers, one might expect sea level to drop for both steric and water balance reasons, but it did not.

And my implied question, then, is, what are the causal factors that influence sea level? Clearly global temperature alone is not the sole (or even most important?) factor. I think the correlation between sea level and DJIA may be stronger than that with global T anomaly.

For those familiar with the IPCC work, has anybody modelling sea level forecasts used their model to accurately hindcast actual sea levels? I'm pretty sure this has not been well done for the global T anomaly.

While you're running numbers, try a low lying third world country (Bangladesh is the classic example) would be interesting, particularly if impact cost were normalized to average income level.

One of the more interesting moral aspects of climate change is that the most severe negative costs are predictably born by people who aren't us and most of the cost of mitigation is born by us.

A few points

1) Sea level rise doesn't stop in 2100 even though most of the charts do. Even if there were zero net greenhouse gas emissions at that point we'd expect the greenhouse gases to take centuries to return to "normal", steric sea level rise will continue at essentially the same rate throughout that period and ice mass would continue along some unpredictable path.

2) Impact cost of sea level rise is not linear, that is, 1 meter rise is more than twice as expensive as 0.5 meters and it's not out of the question that we get there by 2100.

3) Sea level rise is obviously not the only impact (it's probably the easiest to quantify) of global warming.

Citizen Runner wrote:While you're running numbers, try a low lying third world country (Bangladesh is the classic example) would be interesting, particularly if impact cost were normalized to average income level.

Yeah that would be interesting, but I don't know how to generate the consequence numbers.

It is a truism in my line of work that most of the people affected by potential natural hazards (whether or not potentially exacerbated by anthropogenic influence, including AGW) tend to be poor, with relatively low means to invest in mitigation.

Thinking out loud, I wonder what is the relative value of potential (hypothetical?) AGW-sea level-related losses, measured in human life, environmental impact, loss of productive ground, infrsatructure damage or some other meaningful measure, in comparison with ACTUAL losses associated with other natural hazards that are unrelated to AGW, AGW-sea level rise or other AGW effects? Here I think specifically about major earthquakes (and associated secondary and tertiary hazards, like landslides, liquefaction, tsunami, etc), significant volcanic eruptions, major rainfall events (and associated flooding), tornadoes, tropical storms, and so on.

It's common for the news media to link these things (e.g. AGW is causing more frequent flooding, is responsble for Hurricane Sandy damage to Manhattan, etc) even when there is either no clear link or clearly no link. My instinct (and practical experience with "regular old run of the mill" natural hazards) tells me the projected AGW-sea level change impacts are likely to be dwarfed by "regular" natural hazards by many orders of magnitude. But I don't KNOW this to be the case...

As a partial answer to my own question, here is an interesting article about US weather and climate disasters from 1980 to 2014:

https://www.ncdc.noaa.gov/billions/

Key quote: "Found here are the weather and climate events that have had the greatest economic impact from 1980 to 2014. The U.S. has sustained 178 weather and climate disasters since 1980 where overall damages/costs reached or exceeded $1 billion (including CPI adjustment to 2014). The total cost of these 178 events exceeds $1 trillion."

$1 trillion over 34 years is about $29 billion per year for US-only "weather disasters" exceeding $1B each. That's already an order of magnitude bigger than the projected sea level rise-related costs, and does not consider non-weather related natural hazard losses.

Steric sea level is a function of the heat content so it would more or less be proportional to the integral of the surface temperature above equilibrium. It wouldn't be directly correlated with the surface air temperature. The month to year scale global average fluctuations are due to mass moving between the seas and land.

There are regional sea level variations due to prevailing wind patterns, regional water temperatures, and salinity as discussed in article I linked at the beginning of the thread.

It would be pretty strange if that wasn't done unless one starts with the assumption that people doing this were morons. The difficulty with hindcasting is that going back in time relevant source data becomes unavailable or unreliable. Aerosol levels in particular are not well constrained. One can put in plausible levels to get a reasonable match between model and observations but there's obviously uncertainty when imperfectly known parameters are put into an imperfect model producing some level of correlation with imperfect observations.

Citizen Runner wrote:The difficulty with hindcasting is that going back in time relevant source data becomes unavailable or unreliable.

And of course forecasting is LESS difficult than hindcasting because one is less constrained by not knowing the unknowns...

Sorry, cheap shot I know, couldn't resist. :-)