How high and fast will sea levels rise? An important piece (PDF) by Stefan Rahmstorf in Science concludes:
A rise of over 1 m by 2100 for strong warming scenarios cannot be ruled out, because all that such a rise would require is that the linear relation of the rate of sea-level rise and temperature, which was found to be valid in the 20th century, remains valid in the 21st century.
These scenarios, which are really nothing more than business-as-usual emissions plus amplifying carbon-cycle feedbacks, would give us sea level rising at 6 inches a decade in 2100. In such an inundated world, "adaptation" is almost meaningless term.
And this isn't even the worst case scenario, because ice sheet dynamics are clearly non-linear, as NASA's James Hansen makes clear in a new article (PDF).
But didn't the UN's Intergovernmental Panel on Climate Change just lower their projections for sea level rise in the recently-released Fourth Assessment Report (AR4)? No. That mistaken view was the result of a lot of misreporting by the media. Rahmstorf clears up the confusion in a lengthy post on Realclimate, which concludes:
The main conclusion of this analysis is that sea level uncertainty is not smaller now than it was at the time of the TAR [Third Assessment Report], and that quoting the 18-59 cm range of sea level rise, as many media articles have done, is not telling the full story. 59 cm is unfortunately not the "worst case". It does not include the full ice sheet uncertainty, which could add 20 cm or even more. It does not cover the full "likely" temperature range given in the AR4 (up to 6.4 degrees C) -- correcting for that could again roughly add 20 cm. It does not account for the fact that past sea level rise is underestimated by the models for reasons that are unclear. Considering these issues, a sea level rise exceeding one metre can in my view by no means ruled out.
The subject is a complicated one, and the IPCC has not done a good job of clearing up the confusion. But everyone needs to become knowledgeable on this potentially devastating climate impact.
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Comments View as Flat
Steve Bloom Posted 6:15 am
30 Mar 2007
A possibility of disaster
Stefan's analysis is actully quite conservative (as I think he would agree). This statement (from two days ago) from leading glaciologists regarding the vulnerable West Antarctic Ice Sheet (WAIS) is a watershed. The key point:
"Our understanding of ice-sheet flow suggests the possibility that too much melting beneath ice shelves will lead to 'runaway' thinning of the grounded ice sheet. Current understanding is too limited to know whether, when, or how rapidly this might happen, but discussions at the meeting included the possibility of several feet of sea-level rise over a few centuries from changes in this region."
While stronger than any similar past "consensus" statement from glaciologists, that phrasing is still rather elliptical in that discussion at the meeting probably included much more extreme scenarios than several feet over a few centuries. Note, BTW, that the first signer (Richard Alley) on that statement is the very same IPCC lead author who just a couple of months ago was reticent (see Hansen's quote of him) about saying any such thing (in an IPCC context, anyway).
Reading Hansen's piece very slightly between the lines, I think he believes that the possibility of a WAIS collapse occurring in a matter of decades cannot be excluded, and if so even he's being "reticent." I suspect many of the glaciologists believe that to be the case as well. I think we can expect to see the NAS panel called for by Hansen created very soon, so hopefully at the conclusion of that process (by next year) the glaciologists will be willing to say what needs to be said.
(Just a quick note for those who don't follow this stuff closely: The WAIS is the only one of the three major ice sheets that is both grounded below sea level and substantially open to the sea. If all of the WAIS ice floats off the bottom, the result would be about 20 feet of sea level rise. Note that the ice doesn't need to actually melt for this to happen.)
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tico89 Posted 1:38 pm
30 Mar 2007
It would be nice...
...if the IPCC had been more clear on its predictions for sea level rise, seeing as generally deniers pick up on this as the fundamental flaw in the GW argument, and go on about how 'alarmists' are upset that the IPCC report wasn't 'catastrophic' enough.
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caniscandida Posted 8:45 pm
30 Mar 2007
"adaptation"
That is an interesting, and needless to say, troubling suggestion, that the rate of sea-level rise will be so much greater than the policy-makers anticipated, and so will make "adaptation" a "meaningless term."
One can imagine a scenario in which much expense is laid out for decent, reasonable adaptationist efforts in the next few decades, but then toward the end of the century, even all that impressive work is overwhelmed and rendered obsolete.
Chickens are our cousins! So are other sensitive animals! Enough is enough! No more factory farms!
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WWAGD?! Posted 3:31 am
31 Mar 2007
Offshore Property
If people were smart they'd start buying up flood plains and offshore property -- maybe even as deep as 12 meters below sea level.
Once the permafrost melts, more water will be absorbed by the ground and there will be more water vapour in the atmosphere.
Therefore the sea levels will fall precipitously.
The Texeme Construct offers international text memetics construction and textcasting services. http://www.you-read-it-here-first.com
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Zarkov Posted 7:32 pm
31 Mar 2007
Peace
The problem is not a precipitous raising of the sea level, this will not occur because the melted ice weight lifted of the Earth will allow global expansion to generally account for the small amount of fresh water inflow into the sea.
However a fresh water crisis is rapidly unfolding, especially in agriculture and in drinking water.
The rise of the thirst level will shock everyone.
And even before you know it your fresh water stocks will become toxic algal soups.
You will not win unless you clean up your act and get the facts straight. Y'all are being lied to deceived and wasted..... by bastard psychopaths... and you are all too apathetic (they have poisoned you) to complain or even to think of your children.
It all in the book, out soon
omegafour.com
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WWAGD?! Posted 9:31 pm
31 Mar 2007
Fresh Water
Fresh water will be more abundant because higher temperatures will keep more water as vapor and there will be more frequent and wide spread rain, that will help desert lands start to bloom.
The sea will recede (a) because of more absorption and, yes, I think you are right (b) possible expansion of the earth's crust. We have recently discovered a vast "underground sea" beneath China...clearly water can exist not only on the surface, but inside the Earth as well. This capacity would increase during a time of global warming.
City planners are wasting too much time on "ice packs". We don't need ice packs if there is sufficient year round fresh rainfall to fill our reservoirs. Plus, I think the water quality will be much better.
The Texeme Construct offers international text memetics construction and textcasting services. http://www.you-read-it-here-first.com
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amazingdrx Posted 1:10 am
01 Apr 2007
Exponential
"ice sheet dynamics are clearly non-linear"
Ice melts at an exponentially increasing rate. Nice to see one scientist finally noticed that! Now maybe Hansen could calculate how that affects methane emissions from melting permafrost and methan hydrate ice in the sea bed. Since methane is 20 times more disastrous as a GHG than CO2.
When will he be fired by a 23 year old bushwacker political appointee from a fundamentalist university?
http://amazngdrx.blogharbor.com/blog
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