The recent post that points how Prof. Maslin of College of London has rationalized not only the bigoted use of "denier" but has conflated his politics with climate science is further evidence that few of the climate obsessed are able to actually debate the issue at all. So ATTP, EM, etc. really have given us a sandbox demonstration of this in action, albeit with better manners than the good Prof..

and Then There's Physics
Sorry about the delay in responding, had a hospital appointment for knee work yesterday afternoon.

Are you in agreement with the acceleration figure you quoted?

Apart from the chart not showing any clear sign of continuous acceleration over the ~150 years of rising levels; it is more like a steady increase with periods of greater and lower rates. Their data ends in 2002.

I think that they have fallen into the trap of a taking a small fluctuation and used that as a rate for the next century, as we've seen many times this is a mistake. The current decadal (up to 2002) rate of increase being similar that of the 1950s and 1880s.

Sandy,
My understanding is that the average rate over the last 100 years or so is between 1.5 and 1.7mm/yr and that today it is just over 3mm/yr. So, faster today than in the past and an acceleration of around 0.001mm/yr/yr seems okay, but maybe a bit less than I was expecting.

I agree, though, that it hasn't been some kind of steady increase. However, I believe one can associate the other faster periods as also being periods where there was an increasing external forcing and hence faster warming, and so I think the increased rate is consistent with a combination of increased thermal expansion and some ice sheet melt. The rate sea level rise is also consistent with the expected planetary energy imbalance.

@attp

Perhaps it would be a useful exercise for somebody to bring the figures up to date. The referenced paper stops in 2002. and we've had a further 12 years of observation of both sealevel and temperature since then.

Such an exercise would either help to support, or to eliminate your suppositions about what is going on, n'est-ce pas? It does not look to be too challenging task for anybody with a careers worth of formal academic research experience such as yourself.

Faites vos jeux messieurs, mesdames!

ATTP
So why is the current situation different from those in the past where similar rates of increase and accelerations are evident in the data? As you have said predicting into the future from the (recent) past is not a sensible. Finally what makes the recently terminated period of warming different from the external forcings of the past, that is being attributable to human activity?

Sandy,

So why is the current situation different from those in the past where similar rates of increase and accelerations are evident in the data?

Well, in some of the past periods, the change in external forcing and the resulting warming were similar in magnitude to today. However, if you consider - for example - the 1940s, about half (maybe a little more) of the change in external forcing was due to increased solar insolation, and the other half was mainly anthropogenic. Today, we have a slight reduction in solar TSI and most of the increase in external forcing is anthropogenic.

Therefore, even in those earlier periods we can associate the increased rate of sea level rise with increased energy going into oceans producing thermal expansion. It's the same basic physics as we're applying to today.

If we consider the future, then how we warm will depend on our chosen emission pathway. If we continue to increase our emissions we would expect to warm at an increasing rate (and here I mean overall, rather than surface only). Therefore, we can estimate the rate at which energy will go into the oceans and hence how much thermal expansion will take place. We can also estimate the amount of ice sheet melt and hence how this will contribute to sea level rise. There are clearly uncertainties, but if we expect our warming to accelerate (which it will if we continue to increase our emissions) then we'd expect sea level rise to also accelerate.

Mike,
Okay, add "and if our understanding of radiative physics is correct" after the word "emissions".

@ATTP

H'mm

Surely the problem is that when we check the *quantitative* 'understanding of radiative physics', by putting numbers into a climate model and comparing the observations with predictions, it is apparent that - as part of the climate system as a whole - you do not get the right answers. The system does not behave as predicted. And nobody knows why.

At a qualitative level, I'm reasonably sure it is possible to handwave and say that as emissions go up so will sealevel. But Arrhenius came to that insight 107 years ago. All the discussion since has been about trying to put some numbers into his theory. And at the moment we don't really know.

What we can say *from observations* is that the rate of sea level rise goes up and down. The worst case (around 1950 and around 2000) is about 3.4 mm/annum.

Without any better argument than a purely qualitative 'its based on radiative physics', I see no reason not to use that rate as our worst case starting point. Sea level change is such a slow and gradual process that even if we're wrong by 1 mm/year, it'll only make 3 inches difference in a century. Which is neither here nor there in its consequences.

The connection between radiative physics and slr is not well established. There is no Xppm ^+ in CO2 = Y^+ in SLR.
The threat of slr to civilization is not well established much less well defined:
Any SLR? Some SLR, how much? Over what period of time? What about subsidence? Flood/ocean management (levees, dams, dikes, dredging, land fill, etc.)
The inability of those supporting the proposition to even define, much less defend the proposition after they years of high level promotion of the slr issue is telling.

hunter,
The connection between radiative physics and the planetary energy imbalance is well understood (within the limits of uncertainty about feedbacks). The connection between the planetary energy imbalance and how much of that energy goes into the ocean is also well understood (within the uncertainties about diffusion into the deeper parts of the ocean). the relationship between energy and thermal expansion is well understood. Hence, we can do calculations that tell us something about how much sea level rise if we follow a particular emission pathway.

' Hence, we can do calculations that tell us something about how much sea level rise if we follow a particular emission pathway.'

Please show where we can see these calculations and can assess their track record of making successful predictions.

I'd also be interested in what exactly you mean by 'something' in the sentence above.

Latimer,
Sorry, I'm not about to do a physics lesson. I believe EM did a basic calculation on another thread and you can go and read some papers if you wish.

The word "something" was simply there to indicate uncertainty. We can't do a precise calculation, but we can do one that takes uncertainties into account and gives us a range.

Latimer Alder

I really think this quibbling about precise trivial slr stats by two super-annuated pedants is absurd. Civilisation will adapt. There was an excellent ad in the FT a couple of years ago on behalf of a Dutch civil engineering company pointing this out and also pointing out that it had the skills to protect us.

It seems to me that the way to protect ourselves against future threats is to become prosperous so that Dutch expertise can be bought. For example, countries with well-built storm shelters suffer far less in typhoons and hurricanes than do poor countries with primitive protection.

Where sea level rise could be a civilisation-threatening phenomenon is following some sort of unpredictable Black Swan event such as a super-volcano erupting under the Antarctic (I have no idea whether or not that is a plausible scenario and, physics teachers, I do not wish to know!)

In either case, to be resilient it is better to be rich than poor. It follows that we should stop destroying our society with "green" policies.

@ATTP

Thank you for your reply.

But I fear you may have misunderstood my request. I don't need a physics lesson.

I was asking to see an example of the calculations you say can be done that lead from an emissions scenario to sealevel rise.

I know that you are not alone in believing that these calculations are significant - both as pieces of science and for the future of humanity. It is surely reasonable to assume that they are easily available and that you have studied them. Pleass guide us all to them so that we may understand the method and check the predictive skill.

As to Entropic's calcualtions they were fine indeed, clearly explained and easy to understand. An object lesson in how to do such work. But what they were doing is the inverse of my request. They started with actual observations and worked backwards to hypothesise about how much a radiative imbalance there must be to create the observed rise.

But ypur claim is the opposite. That we can start with a CO2 emissions scenario and work forward to a sealevel rise. Conceptually EM calculated from A to B. The calculations you discuss are from C to B to A. Different things. I note that these shoudl be pretty easy to check...we know historically what SLR has been. And we know the emissions scenarios in place. It cannot be hard to plug in one and to check agreement with the other. Should be an interesting exercise. No doubt plenty of researchers have published on the topic to demonstrate the robustness of the current theories?

BTW I note that your answers here frequently state 'or you could read some papers' in reply to the more complex questions. It would help those of us who are not professional academics greatly if you'd give a hint as to which you think is relevant in each case. Thanks

ATTP,
Thermal expansion plays a tiny role in the slr required for anything close to dangerous.
Your simplistic approach betrays a lack of understanding of the topic.
The slr required for anything close to a problemtaic slr scenario relies on massive melting of land based ice.
Thermal expansion is, even inthe alarmist view, only 40-50% of total slr. And since ocean warming is not a linear process- it is not going to boil, despite the kooky ideas of Hansen, for example- so what is required is a lot of melt.
Those meltings are not taking place as needed.

hunter,
I said nothing about dangerous. If you think my explanation is wrong, feel free to point out where. If you think I was trying to explain why sea level rise would be dangerous, then you're wrong - that isn't what I was trying to do.

HsroldW,

Are you saying that you oppose the motion?

Well, I was actually trying - and clearly failing - to get involved in that actual topic. FWIW, I think sea level rise is not areal threat in the sense it will always be slow enough that we can respond. There are more serious issues (like ocean acidification - and Latimer, I don't care if you think you can't use acidification for an alkaline) and extreme warming.

However, I don't think that the possibility that 100s of millions of people might have to move and that cities that exist today may not in the future, is a good thing. I just don't think that sea level rise is, by itself, a real threat (at least, not in some existential sense).

Harold,
Yes, that might be a good idea. A rare success, of sorts :-)

Excellent.

We all agree

Sea level rise is not a threat to civilisation.

Entropic's motion has failed.