Yet another must-read by James Hansen

On 'scientific reticence' and sea-level rise

Posted by Joseph Romm (Guest Contributor) at 4:01 PM on 25 May 2007

Read more about: climate | climate science | climate change impacts | James Hansen

Sea level rise of 5 meters in one century? Even if most scientists will not say so publicly, that catastrophe is a real possibility, according to the director of NASA's Goddard Institute Of Space Studies.

It may seem like I single Hansen out for recommended reading. But that's only because he:

is the nation's top climatologist
writes prolifically
speaks with unusually bluntness for a scientist
has been more right than just about any climate scientist

He has written a terrific piece for the open-access Environmental Research Letters on "Scientific Reticence and Sea Level Rise":

I suggest that a "scientific reticence" is inhibiting the communication of a threat of a potentially large sea level rise. Delay is dangerous because of system inertias that could create a situation with future sea level changes out of our control. I argue for calling together a panel of scientific leaders to hear evidence and issue a prompt plain-written report on current understanding of the sea level change issue.

I could not agree more. In researching my book Hell and High Water, many leading climate scientists spoke to me candidly off the record that they share Hansen's fear. Fortunately, more and more are speaking out.

Hansen is especially concerned that sea level rise is nonlinear:

Rahmstorf (2007) has noted that if one uses the observed sea level rise of the past century to calibrate a linear projection of future sea level, BAU warming will lead to a sea level rise of the order of one meter in the present century. This is a useful observation, as it indicates that the sea level change would be substantial even without the nonlinear collapse of an ice sheet. However, this approach cannot be taken as a realistic way of projecting the likely sea level rise under BAU forcing. The linear approximation fits the past sea level change well for the past century only because the two terms contributing significantly to sea level rise were (1) thermal expansion of ocean water and (2) melting of alpine glaciers.

Under BAU [business as usual] forcing in the 21st century, the sea level rise surely will be dominated by a third term: (3) ice sheet disintegration. This third term was small until the past few years, but it is has at least doubled in the past decade and is now close to 1 mm/year, based on the gravity satellite measurements discussed above. As a quantitative example, let us say that the ice sheet contribution is 1 cm for the decade 2005–15 and that it doubles each decade until the West Antarctic ice sheet is largely depleted. That time constant yields a sea level rise of the order of 5 m this century. Of course I cannot prove that my choice of a ten-year doubling time for nonlinear response is accurate, but I am confident that it provides a far better estimate than a linear response for the ice sheet component of sea level rise under BAU forcing.

An important point is that the nonlinear response could easily run out of control, because of positive feedbacks and system inertias. Ocean warming and thus melting of ice shelves will continue after growth of the forcing stops, because the ocean response time is long and the temperature at depth is far from equilibrium for current forcing. Ice sheets also have inertia and are far from equilibrium: and as ice sheets disintegrate their surface moves lower, where it is warmer, subjecting the ice to additional melt. There is also inertia in energy systems: even if it is decided that changes must be made, it may require decades to replace infrastructure.

Feedbacks and inertia and the very real threat of catastrophic sea level rise mean the time to act is now!

This post was created for ClimateProgress.org, a project of the Center for American Progress Action Fund.

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5 Comments | Post a Comment

Another argument against jets

Reading this excellent post, what occurred to me as I read about 1 mm/yr sea level increase is how pitifully small that sounds to people who can't comprehend how huge the world is and what a great big honking huge change we're talking about.

To do ANYTHING that changes the entire world by even a little bit is to do something enormous.

What popped into my head when I read the post was a very sharp sense memory of traveling on open ocean for days and days and seeing NOTHING but sea. Travelling without jets gives you an indelible sense of how vast is the world, which is what enables you to appreciate just how serious something is, even if it sounds tiny, if it's a worldwide effect.

I don't think most people who travel by jet have a good sense of this. I wish everyone currently flying around would take the Empire Builder or Southwest Chief a few times, so they really come to appreciate how big the American west is; and that they would take a ship across the ocean rather than fly, so they could really grasp, at a gut level, how extraordinarily enormous anything must be to cause even the tiniest measurable change in sea level.

It's a paradox of human psychology--you'd think that if the world seemed small that we'd realize better that we need to take care of our "global village." But that doesn't seem to be the way of it--instead, jet travel seems to create a kind of amnesia that convinces those who do it that there's nothing that man can't do with his machines; something about roaring around at 400 knots makes the world very small and, at the same time, seemingly too big to be affected by what humans do. But it is affected by what humans do, very much so. I think we need people to spend a lot more time moving through the world more slowly in order to appreciate the magnitude of what we're doing.

The 5% Project

by JMG at 4:35 PM on 25 May 2007

Very good post

JMG is like what you wrote and Joseph did a bang-up job on such a complex subject made so simple - it is really a 1-2-3 punch.

It was synchronous because I wanted to blog about how glacial and arctic sea ice melt could COOL the oceans in certain places.

But where does the meltwater go? Freshwater would float on top, since its density of 1000 kg/m3 is lighter than saltwater at 1020-1030 kg/m3.

However, ice can be formed from saltwater and in this case it would probably sink. It's a fascinating science because the pancake floes and ice shelf is actually a mixture of freshwater, saltwater, and any detritus trapped in the stuff.

Bear with me, but an article called "Climate History Rewritten: Arctic Ice" (2006 abstracts, no author cited) over at Brown University says the artic ice shield is about 45 million years old and the study findings make some very important conclusions about the role of CO2 in global warming.

In terms the geologic history of the Earth, the artic ocean froze in a mere moment. It could melt just as fast, although maybe a litle longer because of some latent heat issues.

I agree it is scary, and definitely non-linear.
/sammie

Onward through the fog

by Sam Wells at 6:54 PM on 25 May 2007

Volcanic Melting at edge of ross ice sheet

I have been tracking imagery of the ross ice sheet since 1994.

In Sept 2006, I put up a terrible page with a few images.

I have been motivated to mention this here because of the most recent imagery.

Right now it is almost winter down there, and -30 on the ross ice sheet, but many areas are above zero, and grey meltwater stains are visble along a 600 mile stretch of the transantarctic mountains.

This page shows evidence of a previous torrential outflow out of the 50 mile wide swath next to Ross island from septmber 2006. Later images show what appear to be pumice swirls..

I have emailed many people about this, and I get nonanswers or no reply. As if no one is supposed to say anything.

In latest imagery, there is a 2nd, far bigger..

http://www.lermanet.com/antarcticmelt/index.htm

I sincerely hope i am wrong about what I see in these images. Especially the most recent Sat Imagery HERE: http://amrc.ssec.wisc.edu/ice_images/icebergs/ross/2007/R ...
The same image above with 5% detail enhancement is on my own antarctic melt page above.

I gained a bit of notoriety for noticing things in imagery once before that made the Washington Post back in 2000, The Man With No head http://www.lermanet.com/nohead.htm, however I sincerely hope I am wrong about what I see this time.

Regards
Arnie Lerma

by ArnieLerma at 10:06 PM on 25 May 2007
[ Parent ]

Sea Level is Falling

Sea levels are falling in major oceans worldwide including the Arctic and Indian Oceans.

My model predicts there will be a calamitous drop in the Pacific Ocean during this century...and that will be a good thing.

by jabailo at 8:46 AM on 26 May 2007

Scariest policy alert of article...

Quoting Hansen: "Important decisions are being made now and in the near future. An example is the large number of new efforts to make liquid fuels from coal, and a resurgence of plans for energy-intensive `cooking' of tar-shale mountains to squeeze out liquid hydrocarbon fuels. These are just the sort of actions needed to preserve a BAU greenhouse gas path indefinitely. "

Hansen's predictions that we could control global warming by stopping coal use, even with oil use, are predicated on these policies not happening, but Obama came out for coal-to-liquids and the phrase "Canadian tar sands" is thrown around like the businessman who whispered "Plastics" to Dustin Hoffmann in the movie "The Graduate".

by Jon Rynn at 9:12 AM on 26 May 2007

ADVERTISING POLICY

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