Imagine this. In its latest report, the IPCC has predicted up to 3 meters of sea level rise by the end of this century. But “climate sceptics” websites were quick to reveal a few problems (or “tricks”, as they called it).
First, although the temperature scenarios of IPCC project a maximum warming of 6.4 ºC (Table SPM3), the upper limit of sea level rise has been computed assuming a warming of 7.6 ºC. Second, the IPCC chose to compute sea level rise up to the year 2105 rather than 2100 – just to add that extra bit of alarmism. Worse, the IPCC report shows that over the past 40 years, sea level has in fact risen 50% less than predicted by its models – yet these same models are used uncorrected to predict the future! And finally, the future projections assume a massive ice sheet decay which is rather at odds with past ice sheet behaviour.
Some scientists within IPCC warned early that all this could lead to a credibility problem, but the IPCC decided to go ahead anyway.
Now, the blogosphere and their great media amplifiers are up in arms. Heads must roll!
Unthinkable? Indeed. I am convinced that IPCC would never have done this.
The North Sea (see Stefan’s photostream on Flickr)
But here is what actually did happen.
In its latest report, the IPCC has predicted up to 59 cm of sea level rise by the end of this century. But realclimate soon revealed a few problems.
First, although the temperature scenarios of IPCC project a maximum warming of 6.4 ºC (Table SPM3), the upper limit of sea level rise has been computed for a warming of only 5.2 ºC – which reduced the estimate by about 15 cm. Second, the IPCC chose to compute sea level rise up to the year 2095 rather than 2100 – just to cut off another 5 cm. Worse, the IPCC report shows that over the past 40 years, sea level has in fact risen 50% more than predicted by its models – yet these same models are used uncorrected to predict the future! And finally, the future projections assume that the Antarctic ice sheet gains mass, thus lowering sea level, rather at odds with past ice sheet behaviour.**
Some scientists within IPCC warned early that all this could lead to a credibility problem, but the IPCC decided to go ahead anyway.
Nobody cared about this.
I mention this because there is a lesson in it. IPCC would never have published an implausibly high 3 meter upper limit like this, but it did not hesitate with the implausibly low 59 cm. That is because within the IPCC culture, being “alarmist” is bad and being “conservative” (i.e. underestimating the potential severity of things) is good.
Note that this culture is the opposite of “erring on the safe side” (assuming it is better to have overestimated the problem and made the transition to a low-carbon society a little earlier than needed, rather than to have underestimated it and sunk coastal cities and entire island nations). Just to avoid any misunderstandings here: I am squarely against exaggerating climate change to “err on the safe side”. I am deeply convinced that scientists must avoid erring on any side, they must always give the most balanced assessment they are capable of (and that is why I have often spoken up against “alarmist” exaggeration of climate science, see e.g. here and here).
Why do I find this IPCC problem far worse than the Himalaya error? Because it is not a slip-up by a Working Group 2 author who failed to properly follow procedures and cited an unreliable source. Rather, this is the result of intensive deliberations by Working Group 1 climate experts. Unlike the Himalaya mistake, this is one of the central predictions of IPCC, prominently discussed in the Summary for Policy Makers. What went wrong in this case needs to be carefully looked at when considering future improvements to the IPCC process.
And let’s see whether we learn another lesson here, this time about society and the media. Will this evidence for an underestimation of the climate problem by IPCC, presented by an IPCC lead author who studies sea level, be just as widely reported and discussed as, say, faulty claims by a blogger about “Amazongate”?
p.s. Recent sea level results. A number of broadly based assessments have appeared since the last IPCC report, which all conclude that global sea level rise by the year 2100 could exceed one meter: The assessment of the Dutch Delta Commission, the Synthesis Report of the Copenhagen Climate Congress, the Copenhagen Diagnosis report as well as the SCAR report on Antarctic Climate Change. This is also the conclusion of a number of recent peer-reviewed papers: Rahmstorf 2007, Horton et al. 2008, Pfeffer et al. 2008, Grinsted et al. 2009, Vermeer and Rahmstorf 2009, Jevrejeva et al. 2010 (in press with GRL). The notable exception – Siddall et al. 2009 – was withdrawn by its authors after we revealed numerical errors on Realclimate. This is a good example of self-correction in science (in stark contrast with the climate sceptics’ practice of endlessly perpetuating false information). Rather bizarrely, Fox News managed to turn this into the headline “More Questions About Validity of Global Warming Theory“.
** About the numbers stated above. Regarding the actual IPCC AR4 numbers, adjust the IPCC upper estimate of 59 cm by adding 15 cm to make it apply to 6.4 ºC warming (not just 5.2 ºC) and 5 cm to make it go up to 2100 (not just 2095). That gives you 79 cm. Add 50% to adjust for the underestimation of past sea level rise and you get 119 cm.
For the hypothetical case at the start of this post, just introduce similar errors in the other direction. Let’s add 31 cm by going up to 7.6 ºC and the year 2105 (in fact that is “conservative” but it gives a nice round number, 150 cm). Now assume you have a model compared to which actual sea level is rising 50% slower (rather 50% faster): now you’re at the 3 meters mentioned above. For details, see The IPCC sea level numbers.
Man the dykes: the general theory of the blogoshere predicts that within 24 hours, talk radiologists will shamelessly chop off this article’s first two words , and tell the world :
“the IPCC has predicted up to 3 meters of sea level rise by the end of this century. But “climate sceptics” websites were quick to reveal a few problems (or “tricks” :
First, although the temperature scenarios of IPCC project a maximum warming of 6.4 ºC ( just to add that extra bit of alarmism… the IPCC report shows that over the past 40 years, sea level has in fact risen 50% less than predicted by its models – yet these same models are used uncorrected to predict the future! …
Some scientists within IPCC warned early that all this could lead to a credibility problem”
To disinformation artistes disposed to declare misplaced commas ” fatal flaws” any attempt at irony is a godsend.
For a reality check on this dismal hypothesis, just turn the dial to talk radio next week
Sorry if this is not on the exact topic of the present blogpost, but I was wondering if someone here could recommend a clear, point-by-point critique of the climate chapter in Levitt & Dubner’s “Superfreakonomics”?
Raymond Pierrehumbert mentions in his blogpost from 29 Oct. 2009 that “there have been many detailed dissections of everything that is wrong with the treatment of climate” there, so I thought someone with a competent background here might recommend one or two in particular…
Of course IPCC underestimation for sea level rise won’t be widely reported and disseminated within the media. The very idea of accurate reporting in the media is a joke. We actually have to depend on first sources to be able to actually get any reliable information about climate change. When we go to second or third sources (third being the media reporting on bloggers, etc), we find ourselves lost, torn, completely misled. But first sources are extremely difficult to digest for the regular public, very few will spend hours of their free time reading scientific reports, and verifying what they say is true. People would prefer to sit back and listen to those whose disinformation fits within their ideology.
orangejuice (52) — Joe Romm, on his ClimateProgress (listed on the sidebar), did a thorough disection, in several parts.
Target Atmospheric CO2: Where Should Humanity Aim? by Hansen et al. (2008) provides a sobering look at sea level and CO2 concentrations. The last time Antarctica was ice-free, sea levels were 120m (~400 feet) higher than today. CO2 concentrations were estimated to be 425±75 ppm at that time. Today’s values are already “in the zone”.
Stefan or Gavin,
When you are talking about a sea level rise of one meter, are you speaking of world oceans? The volume of ice needed to create a one meter rise would be quite high.
If the area of the oceans is 361×10^6 km^2 and it rose 1 meter, the volume of water would be 3.61 × 10^14 m^3.
Change the units to miles, and we have 86,609 cubic miles of water.
86 thousand cubic miles is a lot of water. I’m not saying it couldn’t happen, but we are talking about a LOT of extra water.
Does ice melt linearly? I wish you guys would post more formulas.
David Benson, thank you for the pointer.
“Most of the current global land ice mass is located in the Antarctic and Greenland ice sheets (table 1). Complete melting of these ice sheets could lead to a sea-level rise of about 80 meters, whereas melting of all other glaciers could lead to a sea-level rise of only one-half meter.” from
http://pubs.usgs.gov/fs/fs2-00/
RE- Comment by EL — 11 March 2010 @ 9:49 PM:
Water expands when it warms.
Steve
Mr. EL wrote on the 11th of March 2010 at 9:49 PM:
—
1 meter SLR=86,609 cubic miles of water by 2100
—
this is 870 cu mi per year
we already have on the order of 122 cu. mi. coming off Greenland/Antarctica per year
currently the political class is betting that it not increase before they get diselected, and the financial class is betting the same does not happen before they retire
do you feel lucky ? i dont
sidd
You’d think policy-makers and people concerned about life on planet earth would be focused like a razor on the high end predictions, and consider the IPCC rather conservative in its claims. They’d be shrugging off the “it isn’t as bad as the IPCC claims on the Himalayan glaciers,” and honing in on “the IPCC isn’t giving a full account of sea rise because of uncertainties regarding the mechanics and other factors; what might it really be?”
Like when they’re planning a bridge, do they figure building it to tolerate the weight (a) during light traffic conditions, (b) during average traffic conditions, or (c) for a rush hour when a caravan of tractor-trailers carrying full loads of lead are bumper-to-bumper on the bridge?
Or, confronted with a sign that says “bridge out” re a broken bridge over a very deep canyon, does one (assuming a non-sucidal person), (a) accelerate (which is what we’re doing by increasing our GHG emissions), (b) maintain the same speed, or (c) come to a stop and find another route?
However, even the low range figures of projected harms from AGW, even earlier IPCC reports, even what science knew back in 1990, before studies had reached .05 on AGW, even then the indication was that we should do everything possible as quickly as possible to reduce our GHGs down by at least 60 or 70% within 10 to 20 years, and then use the savings from that for possible future adaptations.
What’s going to get people off their behinds, or rather keep them on their behinds so they don’t go around emitting GHGs?
#56 EL
Yes, a lot of extra water. 361,000 Km^3 in fact.
Currently it is estimated that the Antarctic is losing about 246 Km^3 per year, and Greenland about 286 Km^3 per year. A total of about 532 Km^3 per year.
http://www.agu.org/pubs/crossref/2009/2009GL040222.shtml
Still a long way to go but the evidence is that the process has sped up over the last few years and fits a quadratic trend better than a linear trend.
Charlie H wrote: “There’s 6 billion people intensely interested in continuous economic growth”
And if wishes were horses we’d all be knee-deep in horse manure.
There are a lot of people intensely interested in achieving continuous bliss through continuous heroin use.
They probably have a better shot at success than people who imagine that we can sustain “continuous economic growth” for a population of 6 billion humans through continuous business-as-usual consumption of fossil fuels.
Of course, what continued business-as-usual consumption of fossil fuels can achieve is trillions of dollars in profits for the fossil fuel corporations in the decades until (1) economically recoverable reserves are exhausted and (2) the resulting unmitigated anthropogenic global warming brings a rather gruesome end to the lives of the vast majority of those six billion people.
But that’s a small price to pay for “continuous economic growth” for the “top one percent”, who expect to command the wealth, power and resources needed to survive the AGW catastrophe, and who, after all, have no real need for the surplus population anyway.
55
Scott A Mandia says: “The last time Antarctica was ice-free, sea levels were 120m (~400 feet) higher than today. CO2 concentrations were estimated to be 425±75 ppm at that time.”
But wasnt that pre the continent drifting over the pole? As i understand it ice started accumulating on Antarctica 45million years ago(approx, top o head figure) With this ice age(not talking interglacial/glacial.. but ice house/hot house) began 2.5 million years ago… but basically the ice sheet was caused by the location of the continents. Rather than atmospheric make up at the time.
The timing of sea level rise is the hardest thing to predict and it isn’t really that important. When Greenland melts, sea level will go up 7 meters. Does it matter if it is 100, 200 or 300 years? Is putting most of Florida under water ok if it is 200 years in the future?
David B. Benson – I never realized there was that much ice.
“Man the dykes: the general theory of the blogoshere predicts that within 24 hours, talk radiologists will shamelessly chop off this article’s first two words , and tell the world : …
If Russell Seitz is a skeptic, he’s the only one I like. That is so accurate!
And David Benson, great work over at Dot Earth. Alas, anything there is a wasted effort. Revkin has the people, and the view, he wants dominating his blog. As with most papers these days, it has an active conservative action program firmly in place for comment threads.
Re David Benson’s USGS link @ http://pubs.usgs.gov/fs/fs2-00/ , keep in mind that the last time atmospheric CO2 was at 387 ppmv there was virtually no permanent ice in the Arctic and there was less ice in the Antarctic than there currently is. So that’s virtually all 6.55 meters from Greenland, plus virtually all .46 meters from the Antarctic Peninsula, plus most of the 8.06 meters from the West Antarctic ice sheet.
Not by 2100, maybe not by 2200 or even 2300, but if we stay at the current level, let alone go higher, it will happen.
Count on it.
56: Yes it is a lot of water/ice, but it represents slightly over 1% of the glacial ice in the world. Losing 1% of the ice in a century does not sound like a very extraordinary thing.
Yet another “gate” is about to make the rounds.
He seems to think that GISTemp uses CRU data in its temperature analysis. AFIAK, it uses GHCN.v2_mean, USHCN.v2 and SCART to cover Antartica. I would like to see what Jim Doyle’s original question was. It seems from the answers to have been something about US regional temps, but I can’t really tell and don’t want to wade through 200+ pages of email to see what it was, if indeed it is even in there.
Just a heads up.
“Who controls the past controls the future. Who controls the present controls the past.” (George Orwell.) So perhaps a historical perspective is justified.
The 10-year rate of rise estimated by the Jason/Topex satellites has been around 3.3 mm/year, almost the double the 20th century average. On the other hand the global warming from 1910 to 1945 was almost identical to the 1975 to 2005 warming in both rate and magnitude. It also was followed by a period of higher than average rates of sea level rise. The 10-year rate of rise in the 1950s (average of Church et al and Jerejeva et al estimates) was around 3.2 mm/year, sensibly identical to the present level rise. (http://www.climatedata.info/Impacts/Impacts/sealevels.html)
The fact that current rates of rise have been experienced in the past after similar temperature increases does not of course invalidate the predictions for the future perhaps it does justify the caution shown by the IPCC.
EL says: 11 March 2010 at 9:49 PM
Don’t forget about thermal expansion.
Scott A Mandia re:#55
Two questions!
When did sea level rise to 120 meters above today’s stand?
[Response: Above? It was 120 meters below today at the Last Glacial Maximum, about 20,000 years ago, and about 70 meters above today in the high-CO2 greenhouse climate before continental ice sheets started to form about 40 million years ago.]
Is there a correlation between sea level and atmospheric CO2 concentration in the recent past(latest Quaternary) other than over the last century?
[Response: Sure, a very close correlation over the Quaternary because of the well-known correlation of CO2 concentration with the glacial cycles that dominated the Quaternary, and which come with about 120 m amplitude in sea level due to the waxing and waning of huge ice sheets. -stefan]
I find it hard to understand why it is OT to mention that some of the IPCC scenarios are unrealistic (like Giles did in #1)? Have a look at this
http://www.tsl.uu.se/uhdsg/Publications/IPCC_article.pdf
very fresh article about Peak Oil/Coal. It has everything to do with sea level rise (as well as other climate projection for this century)!
Any discussion of sea level changes should take into account local subsidence and emergence of the land mass. Very often apparent rises in sea level are in fact due to land subsidence, often due to extraction of water from underlying aquifers.
If rises in sea level were really global, and land subsidence and emergence were not a factor, then we would see the same rate and degree of sea level rise at all coastal points. The fact that we see quite wide variations is surely telling us something.
[Response: This effect is of course taken into account in sea level studies. Your latter point is not correct. Even sea level proper can show regional variations, regardless of land movement. You see this in the satellite data; it is pictured and discussed in the IPCC report and a host of papers. -stefan]
“Re Gilles @36: “OK but don’t forget that in order to reach 5-6 °C, we need a fossil fuel consumption continuously increasing up more to three times the current…”Or for the current and committed warming to cause the release of just a portion of the methane currently locked in clathrate ices and the CO2 currently locked in permafrost tundra and bogs.”
Yes, another scene in the movie. Read the previous thread about methane.
“Just ask yourself what the mean surface temp was the last time atmospheric CO2 was at 387 ppmv, oh, about 15 mya in the middle miocene.”
Several degrees higher , which only proves that the average temperature is by no means a single valued function of CO2 concentration, which is not surprising since the average temperature is not a meaningful measurement of anything physical (it is neither the enthalpy, nor the effective temperature, nor anything else than an average temperature). The radiative balance of Earth can be influenced by other things than the average temperature : ocean and atmosphere circulation, fraction of deserts, forests, ice coverage, influencing cloud coverage, and so on… so basically the comparison with numerical values in the distant past is not accurate enough to draw any conclusion.
Sorry back to my first post and the comment :
“Your logic is flawed, because data of the past century show how the rate of sea level rise increases in proportion with temperature ….But the most optimistic scenarios have warming stopped at about 2 ºC above preindustrial, i.e. two to three times the current warming, which would imply roughly that the rate of sea level rise also doubles or triples.”
Maybe I don’t understand correctly, but the equation of your paper : dH/dt = a(T-To) is obviously non physical since it describes a indefinitely rising sea level even if temperature has stabilized above To ! (and adding a dT/dt term doesn’t help of course). The only meaningful linear equation I can imagine is a relaxation one dH/dt = -a(H-Ho(T)) where Ho(T) is some equilibrium sea level at the temperature T. Of course if H and Ho(T) rises with a approximate linear rate , in first approximation, you will find an approximate linear law comparable to yours , but extrapolation of this law is spurious since the real relaxation equation produces a plateauing of H to the equilibrium value , which is not the case of your equation (there is obviously no equilibrium value in yours !).
[Response: How about reading my paper? It explains all this and even illustrates it with a graph (Fig. 1). -stefan]
EL #57: the rate at which ice melts in big ice sheets is pretty complex as it depends on effects like whether the ice is likely to break up, whether it can move a short distance and land on water and what it is grounded on. The latent heat of melting ice is a well known formula, as is the energy needed to raise its temperature to melting point. I don’t recall exact numbers but on that basis simply increasing energy flows by a few W/m2 would take thousands of years to melt the bigger ice sheets. But the fact that for example the West Antarctic Ice Sheet has a large fraction grounded below sea level means that this is not necessarily a relevant calculation. All it would take to lose much of this grounded below sea level ice sheet much faster than the rate of melting would imply is for water to find its way in substantial quantity under the ice and speed its flow to sea.
So short answer: there isn’t a short answer.
If you’re interested in seeing what the ice in the Southern Ocean and the Weddell Sea near the Antarctic Peninsula looked like in 2009, I’ve put up some 56 shots of icebergs, sea ice and their inhabitants here.
Antarctic Icebergs
http://earthlightimagery.com/gallery.php?gid=49
Even if you looked before I guarantee you’ll find new images.
Tim
Stefan, If I understand you correctly you seem to consider 59cm SLR implausibly low, for 2095, where can we find a more plalusibly proyection, and a global index to compare both?
[Response: Read the p.s. of the post. ]
Re Gilles @36: “OK but don’t forget that in order to reach 5-6 °C, we need a fossil fuel consumption continuously increasing up more to three times the current…”
Nope. We could have various other things that achieve similar effects, including unexpected positive feedbacks, large increases in non-fossil-fuel based emissions (more then 50% of my country’s emissions are not from fossil fuels – and our per-capita emissions are among the highest in the world), spikes in fossil fuel usage followed by declines rather than constant increase, etc.
But I certainly agree that 6 degrees of global warming isn’t an immediate civilisation killer. It probably only means 3 degrees of warming in some areas. Of course, it also probably means average temperatures 9 degrees higher in some areas – but I never much liked the US’s Southern States anyway.
Hey Guys, take a look at the wilkins ice shelf..it’s about to completely break up. I’ve been following http://www.esa.int/esaEO/SEMWZS5DHNF_index_0.html
every day for the last year..and since the ice bridge collapsed last year it’s been pretty stable until now. Deep fissures are now apprearing to the bottom left and right of the time lapse images.
Take a look specifically at frame three of the animation and tell me what you think.
“Response: How about reading my paper? It explains all this and even illustrates it with a graph (Fig. 1). -stefan”
If I hadn’t read it, I would not know your equation. I repeat : your equation is a linear approximation that will be always correct at the beginning, because almost any differential equation can be expanded and cut at first order linear approximation, but is obviously spurious and doesn’t give the correct behavior on the long term. So “calibrating” it in the current period and extrapolating it will produce spurious behavior.
[Response: Hint: the paper introduces the equation with the sentence [emphasis added]: “The initial rate of rise is expected to be proportional to the temperature increase” and then shortly afterwards states: “The equilibration time scale is expected to be on the order of millennia. Even if the exact shape of the time evolution H(t) is not known, we can approximate it by assuming a linear increase in the early phase; the long time scales of the relevant processes give us hope that this linear approximation may be valid for a few centuries.” I was cautious in applying it only to one century, after calibrating it for a 120-year period. I also tested how well this holds up using climate model output. We have a paper submitted looking at longer time scales (multi-century), where of course we do take into account that there is a finite equilibration time scale involved. -stefan]
Did anyone see yesterday’s MacPaper? USA Today repeated all the lies about how the CRU hack revealed that scientists had concealed data and conspired to keep out skeptics.
Gilles, read the 2009 paper. Your complaint above in #78 is about the equation from the earlier paper–the very issue the 2009 paper addresses. I had to reread the 2009 a few times myself just now. Recommended.
Reahrding #74 FHSIV:
Stefan, thanks for the correction. I should have looked out my window here on Long Island and realized that I was not under a huge ice sheet! Doh!
Obviously, the 120m is the amplitude and not the “above today” value.
Sean :”Nope. We could have various other things that achieve similar effects, including unexpected positive feedbacks, large increases in non-fossil-fuel based emissions (more then 50% of my country’s emissions are not from fossil fuels – and our per-capita emissions are among the highest in the world), spikes in fossil fuel usage followed by declines rather than constant increase, etc.”
Sean, either you believe in scenarios from the SRES, or not. I just remind the hypothesis at the basis of these scenarios. If you imagine things very different from what is described in AR4, then you agree with me, that they do not encompass the whole possible stories, but then we should discuss their plausibility from the beginning. Taking numbers computed by these scenarios is then worthless, you can also imagine 10 or 20°C degrees as well.
86 Hank
I read the 2009 paper, and I already addressed that adding a dT/dt term (eq 2 : dH/dt = a(T-To)+bdT/dt ) does not help removing the spurious behavior of a linear increase of sea level toward infinity even if the temperature has stabilized, which is obviously impossible. That’s pretty simple to see on the equation, isn’t it ?
Comment from Stefan at my previous contribution (#38)
“At the beginning of the 20th Century sea level rose at a rate of about 1 mm/yr, and after 0.8 ºC global warming this rate has roughly tripled, now standing at about 3 mm/year. –stefan “
Stefan, you are right that around 1900 the rate of increase in sea level was very low (there was even a short episode of decreasing sea level), but briefly afterwards it increased rapidly, and around 1915 the highest rate of the last century was observed. For a broader perspective see the discussion on Climatedata (especially Fig.1). Link: http://www.climatedata.info/Impacts/Impacts/sealevels.html
Remarkably, there was also a strong increase of sea level around 1950, AFTER the 1910-1940 period when temperature increased at a similar rate as in 1975-1998. Over the last century or so the rate of rise has fluctuated from -20 mm/decade up to 40 mm/decade. The total increase since 1880 has been around 250 mm. And overall the yearly trend has remained about the same during the last century, despite the occurrence of periods when temperature increased strongly and a long period in between when temperature remained the same. So the evidence since around 1890 does not at all support a direct (or even linear) relationship between temperature and sea level.
[Response: You are looking at different time scales. If you look at short periods, the rate of sea level rise does indeed fluctuate wildly up and down, as you say. That happens with any noisy time series that you take a derivative of. I thus doubt whether these fluctuations are real or just artifacts of imperfect data coverage. This noise then drowns out the relationship between sea level and temperature that is clearly demonstrated in our papers for longer periods. Have you even looked at the papers before criticising? -stefan]
“70
Thomas says:
11 March 2010 at 11:09 PM
Losing 1% of the ice in a century does not sound like a very extraordinary thing.”
Really?
Because that would indicate that you expect the Greenland Ice Sheet to be only 10,000 years old…
(oops, typo…)
[edit – PO is OT]
Gilles, please. Gavin’s asked you nicely to stop with the peak oil stuff.
If you’ll make the time to read Stefan’s paper here, the 2009 one, you’ll get a clue why your hobbyhorse is way inappropriate here: even if your group is right, much of the problem is at _this_ end of the time span.
Good ideas: putting off burning fossil fuel and possibly finding there isn’t that much to burn later
Bad idea: burning what we have as fast as we are regardless of the future, and that’s a bad idea even if we run out sooner than expected _because_ problem is rate of change. It’s _early_fast_burning_ we need to stop now.
Rate of change and timing of change.
Re Gilles @77: “Read the previous thread about methane.”
I did, perhaps you missed the words “just a portion of”?
“which only proves that the average temperature is by no means a single valued function of CO2 concentration”
Which no one has asserted. Never the less, continued paleoclimate research shows that the correlation between atmospheric CO2 and global average temperature continues to get stronger. The miocene is no longer the exception it once was, and now even the ordovician is not looking so anomalous.
The past can never be an exact analogue for the present and future because not all factors and conditions will be duplicated, but Richard Alley’s assertion that CO2 is the control knob is looking stronger and stronger.
Jim: ““which only proves that the average temperature is by no means a single valued function of CO2 concentration”
Which no one has asserted. ”
Ergo:
http://en.wikipedia.org/wiki/Straw_man
Scott A Mandia #88
So, sea level was 70 meters higher than today at a point 40 mya. 70 meters relative to what? The shape and positions of the continents are a little different than in the Eocene. Have you considered tectonic changes to the volume of the oceanic basins over this time? or have you assumed that this variable has remained constant. This would be a defensible assumption for the Late Quaternary, but not as far back as the Eocene. And, how is this relevant to a discussion of possible changes of a fraction of a meter over the next century?
The approximatley 6 meter higher stand above today’s level during latest Pleistocene is a more credible basis for discussion and comparison.
Can you give me a reference or a link for the “well-known correlation of CO2 concentration with the glacial cycles that dominated the Quaternary”. What came first, the chicken or the egg? Are you suggesting that the glaciation in the Quaternary has been contolled by CO2 concentration?
[Response: Quaternary glaciations are driven by orbital cycles; CO2 acts as an amplifying feedback and “globaliser” (without it you can’t get such cold glacials, nor would the northern and southern hemispheres freeze in sync). A detailed discussion of the lead/lag relationship between CO2 and temperature in Antarctica (which I presume is what you are referring to) is provided by Ganopolski and Roche 2009. -Stefan]
“The equilibration time scale is expected to be on the order of millennia.”
OK, then do you agree that the linear problem is degenerated following the ratio of sensitivity (dHeq/dT) to equilibrium timescale, since only the ratio of the two determines the initial growth rate. So your hypothesis that the equilibration timescale is “very long” (on the order of millennia) is only useful to justify the linear acceleration rate. However, this has a strong consequence on the asymptotic value, because the actual value at a given time t is of the order of the equilibrium value multiplied by t / teq (hence the quadratic time evolution). So what you’re claiming is that the 1 m sea level rise observed in 100 years is actually a 10 m equilibrium value (which is perfectly compatible of course with the fact that your curves keep growing in 2100 without any sign of slowing, and will continue during a millenium or so).
If you’re right, I would say that we’re heading anyway to a several meters sea level rise in the next millenium whatever we do, even by cutting completely our emissions just now, since the 0.7 °C (and hence a 3 meter rise) is already there, the sea will rise during one millenium in any case. So we’d better start to move away from the coasts , or at least to plan a gradual move , and we could as well use as much fossil fuels we want to do that – it’s just a question of how high we should rebuilt our cities !
“Gilles, please. Gavin’s asked you nicely to stop with the peak oil stuff.
Good ideas: putting off burning fossil fuel and possibly finding there isn’t that much to burn later
Bad idea: burning what we have as fast as we are regardless of the future, and that’s a bad idea even if we run out sooner than expected _because_ problem is rate of change. It’s _early_fast_burning_ we need to stop now.
”
You’re right, peak oil is immaterial with Stefan’s hypothesis. Actually the amount of fossil fuels we burn is immaterial as well, since the sea will continue to rise at some mm/yr during one millenium, inexorably and whatever we burn. So don’t care about fossil fuels : just move high enough , while house on heights are still cheap !
“So, sea level was 70 meters higher than today at a point 40 mya. 70 meters relative to what? ”
Than today.
You even said so in that section.