Friday
Jul222011
by 
Bishop Hill
Bishop Hill John Droz on sea level
Jul 22, 2011 Climate: WG2 John Droz, writing at WUWT, has a very interesting article on a battle of wits over sea level rise. As I noted after the Cambridge Conference, I have made a mental note to pay more attention to this aspect of the global warming debate. There are some remarkable stories in this area. The conclusions of the paper Droz is writing about are startling enough
To reach the multimeter levels projected for 2100 by RV requires large positive accelerations that are one to two orders of magnitude greater than those yet observed in sea-level data.
The story of the counterarguments from Profs Rahmstorf and Vermeer is rather remarkable too.
Reader Comments (71)
golf charley
I do understand why you think a lot of stuff about future climate change is "scaremongering", I think so too, but in the case of IPCC AR4 sea level rise the projections were much more moderate than Rohmstorf's (with the caveat that they didn't know enough about rapid ice dynamics to include that in the estimates - but as I said earlier, Rahmstorf's estimates are still regarded as extreme).
BTW It's clearly the actual impacts on society that count, and you shouldn't think that scientists who project future changes in the physical system necessarily buy in to what other people say these mean in terms of actual impacts on society, including whether the impacts are best dealt with through adaptation or mitigation.
Richard Betts, thank you for that response.
It seems to me that the actual impacts on society that are observable today, result from policy implementation, rather than actual climate change, and if more scientists had the nerve to echo your views expressed above, we would have fewer people starving to death in the world
ssat
"duck filled hypothesis"
:-)
That little duck interlude with GC, LC and SSAT - very good. Made oi larf, anyway! Pleasant diversion from all the bad news elsewhere.
Thankyou for a Saturday Smile!
Xp
Cinque ports == cinq ports === 5 ports.
xplod
Does that mean you're a retired policeman or that your car has the sort of sound system beloved by chavs?
This sort of thing
@ Peter Walsh Jul 22, 2011 at 7:34 PM. Unfortunately I missed the programme you watched last week. But I liked your synopsis, very interesting. Shall look out for the BBC's repeat. Hope I don't miss it.
The Fifth Assessment Report (AR5) is now underway. A number of workshops and expert meetings, in support of the assessment process, have been held. One in Kuala Lumpur asked the questions about sea level rise.
There is a John Church apperent, if he is the same as mentioned above:
John CHURCH
Antarctic Climate Research Centre and
CSIRO Marine Research
AUSTRALIA
http://www.ipcc.ch/pdf/supporting-material/SLW_WorkshopReport_kuala_lumpur.pdf
Some of the questions raised leave little interpretation that everyone is focussed on a warmimg planet.
2. What are the key uncertainties in predicting Greenland’s contribution to sea level by 2100 for a given regional
warming (e.g., 3°C), and over what time periods could extrapolation of the current rate of mass change be a useful
tool?
3. What parameters and processes need to be known for the theoretical understanding of the calving and basal melting
at marine margins and how well can we predict ice-ocean interface response in a warming climate?
4. What are the key parameters, improvements in process understanding and modelling schemes needed to include ice
stream dynamics in predictive ice sheet models for climate scenarios? Are we expecting a several fold change in ice
velocity of outlet glaciers in a warming climate?
Closely-couples chaotic system, anyone?
Those models are useless.
Lord B, that is the same John Church.
Despite the assurances of Richard Betts, consider the following:
Douglas 1992, Global sea level acceleration: Finds no acceleration, in fact slight deceleration.
Holgate and Woodworth 2004, Evidence for enhanced coastal sea level rise during the 1990s: Sea level rise was largest in the 1950s.
Church and White 2006, A 20th century acceleration in global sea level rise: finds acceleration of sea level.
Holgate 2007, On the decadal rates of sea level change during the twentieth century: Sea level rise greater in first half of 20th century than second.
Woodworth et al 2009, Evidence for the accelerations of sea level on multi-decade and century timescales: finds deceleration in mid-late 20th century.
Houston & Dean 2011: Finds small deceleration.
Watson 2011: Finds weak deceleration.
Now, who could have guessed, which of these authors will be selected to write the relevant chapter for IPCC AR5?
Bias! what Bias....
To the credit of the breakout groups in the Kuala Lumpa workshop, there are many uncertainties stated as reasons not to predict future sea levels but we will see how this gets translated into the final AR5. I'll not be calling in William Hill's on the way home.
This is a nice link on sea level rise. Somehow it got past the moderators at Realclimate.
http://i.minus.com/idFxzI.jpg
Late to this - apologies.
Is not the argument that SLR response to increasing T will be non-linear? Eg abrupt SLR following break-up of WAIS and/or accelerated mass-loss from GIS? Both appear to be losing ice mass.
Hence the apparently high projections for 2100?
Simon Abingdon, re the Swedish program, I think this may already have been repeated. But keep an eye out on BBC3/4. It was part of the "Coast" series.
Incidentally, the Swedish guide, while on top of the hill, cracked a joke, saying that they were standing on what was once the beach!
Rgds
Current sea level rise is very small and if it continues at the same rate is unlikely to be more than mildly inconvenient. However, the geological and paleoclimatic records show that if global average temperature rises as predicted (i.e. 3 deg C for a doubling of CO2) then the rate of sea level rise will accelerate rapidly as the Greenland and Antarctic ice sheets begin to melt.
Unfortunately by the time this process starts it is likely to be too late to do anything about it.
Hopefully satellite pictures of an ice-free arctic - which it now seems likely we will see in the next decade - will be the wake-up call that will send the contrarians scuttling back to the shelter of their tanks.
Scots --
What paleo records support your projection of a rapid acceleration? Can you supply a few papers? And perhaps you could be more quantitative about the rates and durations of your projection.
Paleoclimate records include cases in which sea level rose several meters per century, even though known natural positive forcings are much smaller than the current anthropogenic forcing, implying that ice sheet disintegration can be a highly nonlinear process.
One well-know paper:
Paleoclimate Implications for Human-Made Climate Change - Hansen 2007
Quantification: Hansen suggested the possibility of a 5m rise by 2095
HaroldW
There's a good overview of this here.
References include Rignot & Jacobs (2002); Tarasov & Peltier (2003); Rignot & Kanagaratnam (2006).
BBD - Thanks. I'm familiar with a more recent paper by Rignot, but will read those papers and the post you recommended.
The Hansen article recommended by Scots is slow reading. When it opens with
it is apparent this is not the cool clear voice of reason speaking. Hence one must verify each assertion.BBD -
From your reference:
So while he predicts an eventual increase in sea level of several meters, he's not confident whether this is over a century or a millennium.
Back to the Hansen paper.
HaroldW
You are right to point to the uncertainties - as is the author of the OD review piece. I thought it a fair and honest consideration of the issues which is why I linked to it. And I'm heartened - you are reading the links! Thank you.