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Ray at 19:57 PM on 31 March 2013Making Sense of Sensitivity … and Keeping It in Perspective
I posted a comment about two hours ago and although it was visible initially it has now been disappeared. Is this due to snippage or should I post again?
Moderator Response: [DB] The moderator on duty at that time deemed it too far off-topic. -
nealjking at 18:45 PM on 31 March 2013Making Sense of Sensitivity … and Keeping It in Perspective
MA Rodger:
I mean the Stefan-Boltzmann formula for total blackbody radiation power is not applicable in the context of the enhanced greenhouse effect.
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nealjking at 16:27 PM on 31 March 2013Making Sense of Sensitivity … and Keeping It in Perspective
ubrew12:
#61: You start off complaining that the author left his point to the end: "But there's a reason for that placement: how many readers make it to the END of such an article?"
#68: Later, you point out that he made his point in his first sentence: "The author made his point in his first sentence."
Which is it?
All I'm pointing out, as I subscriber who reads The Economist every week, is that their articles are frequently written in such a fashion that you need to read to the very end to get the picture.
Does that make it a bit harder to digest their articles? Yes, it does. But they've been in publcation since 1843, so I guess they think they know what they're doing.
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ubrew12 at 15:42 PM on 31 March 2013Making Sense of Sensitivity … and Keeping It in Perspective
nealjking@66 - I think Economist readers are like any other. The author made his point in his first sentence.
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Andy Skuce at 12:19 PM on 31 March 20132013 SkS News Bulletin #5: Alberta Tar Sands and Keystone XL Pipeline
Thanks, Chris & John. The reason I didn't publish it here is that it was a little bit too political and opinionated for Skeptical Science norms.
Michael Tobis and Dan Moutal have a great blog going at Planet 3.0, with a slightly different focus than SkS, with more discussion on sutainable technologies and cultures, but with the same overall goal: promoting understanding and solutions on climate change. I urge all SkS regulars to check it out.
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CraigD at 12:08 PM on 31 March 2013Earth Encounters Giant Speed Bump on the Road to Higher Sea Level
Interesting. I had no idea that La Nina and El Nino had such impact on sea levels. However, I expect that after the Arctic goes ice free in summers after about 2017-2020, the Greenland Ice Sheet melting will accelerate significantly. With the Arctic ice gone the summer sun will warm the Arctic Ocean. The warming of the Arctic Ocean will also accelerate at more ice is lost, and the time of no ice lengthens. With this, the Arctic will warm considerably over its current state. As the Arctic warms, the Arctic Winter Ice Maximum will decrease. Now the big question is how long will it be before the Winter Ice Maximum reaches zero? As the WIM decreases each year, Greenland will melt more and more ice. It is going to get interesting.
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nealjking at 11:47 AM on 31 March 2013Making Sense of Sensitivity … and Keeping It in Perspective
MA Rodger:
I don't believe the equation
ΔF/ΔT = 4σT^3
has much relevance in this context. The blackbody spectral radiation formula is not applicable in the context of the greenhouse effect.
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Rob Painting at 11:43 AM on 31 March 2013Earth Encounters Giant Speed Bump on the Road to Higher Sea Level
Philp Cohen - Duly noted. I think a tweak is all that's required.
Nichol - depending on the time frame under consideration, there can actually be a net gain, or net loss, of moisture from the continents. There doesn't seem to be any long-term trend over multiple decades - See Ngo-Duc (2005) linked to in the blog post - but for any given decade the trend can vary. From 2002-2009 , for instance, there has been a net gain in continental water mass equivalent to a fall in global sea level of around 0.2 mm per year (Jensen [2013]). Not that surprising given the ENSO trend.
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nealjking at 11:39 AM on 31 March 2013Making Sense of Sensitivity … and Keeping It in Perspective
ubrew12:
Articles in The Economist are frequently not designed along the well-known journalistic "upside-down pyramid" approach: It is often the case that you have to read to the end to get the point.
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Treesong2 at 11:03 AM on 31 March 2013Earth Encounters Giant Speed Bump on the Road to Higher Sea Level
Count me as another who misread the title and considers a vivid, memorable metaphor a bad thing if it inclines you to remember a falsehood. The recent rise is a speed bump-up, not a speed bump. Metaphor aside, good piece.
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Tsumetai at 10:52 AM on 31 March 2013Earth Encounters Giant Speed Bump on the Road to Higher Sea Level
Still open to a better metaphor.
Snakes and Ladders. -
John Hartz at 10:35 AM on 31 March 2013To frack or not to frack?
gws:
With all due repect, the title of your OP is all-encompassing with repsect to the upsides and downsides of fracking. Futhermore, there is no other article posted on SkS that addresses fracking and water impacts.
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Nichol at 10:21 AM on 31 March 2013Earth Encounters Giant Speed Bump on the Road to Higher Sea Level
Looks like if there will be more rain, there is an argument for more effort in keeping that water on land, or replenish ground-water reserves. More dams, even more so where water can 'leak away' into underground aquifers. In stead of returning to the oceans. I imagine that in the past such locations for dams have been avoided?
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vrooomie at 08:42 AM on 31 March 2013To frack or not to frack?
"Do any of you know what chemicals go into fracking?"
thanks for asking: here's the ones the industry *admits* to.
http://fracfocus.org/chemical-use/what-chemicals-are-used
Methanol? Formic acid? Potassium hydroxide? Trust your well water to thousands of oil and gas wells going through your aquifer? Not me, not yet.
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David Kirtley at 08:40 AM on 31 March 2013Back from the Dead: Lost Open Mind Posts
I was able to get to a "still missing" tamino post: Oct 5, 2007 Wait for it...
Moderator Response: [DB] Added, thanks! -
MA Rodger at 08:28 AM on 31 March 2013Making Sense of Sensitivity … and Keeping It in Perspective
Shoyemore @63
Your equation is of course mathematically identical to the equation @43.
The question asked (or was it a demand) by elsa about an equation linking ΔCO2 with ΔT first appeared @38 - “Perhaps, since you say that the link between CO2 and temperature is derived from physics, you can tell us what the equation is that links the two and how it is derived?” - itself prompted by the statement @24 - “Both the models and how CO2 affects temperatures are entirely derived from physics.” So the question was a bit presumptious.
The insistence on a single 'equation' kind of rules out addressing the model aspect but the CO2-temperature relationship when shorn of feedbacks can be reduced to that anticipated single equasion. Half of it I rather cheekily presented @57, the half which yields ΔF. From it with the derivative of the Stephan-Boltzman eqn (pretty much a constant for small changes in T) ΔT can be derived.
ΔF/ΔT = 4σT3
This is all such straightforward stuff that usually just the result from it is quoted. A link to point folk at might be good but I cannot say that I know of one.
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nealjking at 08:20 AM on 31 March 2013Making Sense of Sensitivity … and Keeping It in Perspective
ubrew12:
Articles in The Economist are frequently not designed along the well-known journalistic "upside-down pyramid" approach: It is often the case that you have to read to the end to get the point.
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gws at 06:37 AM on 31 March 2013To frack or not to frack?
@10: Who is your comment addressed to?
The post does not address the fracking&water issue and was not intended to. Please take discussions of the water issue to other venues. I know the issues cannot be completely seperated, that this discussion should be not morphing into one not related to the post topic.
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Alexandre at 06:18 AM on 31 March 2013Skeptical Science Firefox Add-on: Send and receive climate info while you browse
I'm having trouble signing in with the Firefox add-on. I type my username and password, click "log in" but nothing happens... Same thing happens with version 12 and 19 of the Firefox. Any suggestions?
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shoyemore at 05:55 AM on 31 March 2013Making Sense of Sensitivity … and Keeping It in Perspective
Elsa, @55
∆T = K Ln(CO2final/CO2initial)"/Ln(2), where Ln(.) is the natural log function.
If you can use Excel, it should be easy for you to download one of the temperature records, and the CO2 Mauna Loa series since 1958.
Plot ∆T since 1959 against the right hand function and come up with a rough estimate for K, or at least the transient K for a non-equilibrium situation.
John Niesen-Gammon has a good post here about this equation.
http://blog.chron.com/climateabyss/2012/10/carbon-dioxide-and-temperature/
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OPatrick at 05:51 AM on 31 March 2013Earth Encounters Giant Speed Bump on the Road to Higher Sea Level
Speedbumps works well for me - a temporary slowing often followed by an aggressive acceleration. In reality there's often a futility to the few speedbumps that get built, they provide a false sense of security and stop people looking at the bundle of measures needed to actually cut traffic speed to a safe level.
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scaddenp at 05:37 AM on 31 March 2013Making Sense of Sensitivity … and Keeping It in Perspective
Sphaerica - Not only are most of Elsa's posts offtopic, but Elsa is persistantly repeating false statements from who knows where, without any supporting evidence. We are replying with papers and links that as far as I can see are being simply ignored. Ignorance is excusable - we are all ignorant of many parts of sciene - but wilful ignorance isn't/ This appears to be sloganeering and I would hope moderators would take a stronger line in demanding substantiation of claim (in the appropriate thread).
Moderator Response: [DB] Indeed, much latitude has been given in the now-vain hope that elsa would have something substantive to offer to support her assertions. Until that new materiel is forthcoming, no further diversions to the OP of this thread will be permitted. -
ubrew12 at 05:03 AM on 31 March 2013Making Sense of Sensitivity … and Keeping It in Perspective
'Location, location, location' Many commenters on this thread have mentioned that the author of the Economist hit-piece somewhat redeems himself by mentioning in the article's last paragraph the potential of a 4 C rise, which is 'hardly reassuring'. But there's a reason for that placement: how many readers make it to the END of such an article?
To recount: "OVER the past 15 years air temperatures at the Earth’s surface have been flat" This is the very first sentence, the one most likely to be read and retained by readers. No provisional, like "of course, in the past 20 years, the surface temperature anomaly has almost doubled". This could literally be the second sentence of his article: why isn't it?
The second section is titled 'The insensitive planet'. If you were just skimming this piece, what message would you take away from that title?
The third section is title 'New Model Army'. This section makes it very clear that there is a 'war going on' between the [possibly communist] IPCC and a 'New Army' of rambunctious young Scientists who are all converging on a sensitivity of 1-2 C. Who will win? Unsure, but we know who is losing: "the chances of climate sensitivity above 4.5°C become vanishingly small"
There's 'obviously' a war going on in the climate science community, so why take action before 'they' resolve it? As the fourth section is titled, there are 'Clouds of Uncertainty' on this whole subject. Could the lack of recent atmospheric heating be due to better ocean heating? The author: "Perhaps it lies in the oceans. But here, too, facts get in the way" and there is a graph of the surface ocean ALSO not heating. Again, if you're skimming this material, THAT'S the graph you're going to see, with its ready-made conclusion: Nope, its not the oceans. Now the author produces the caveat that maybe warming is going into the deep ocean. Or maybe not, since according to the author, that is "obscure".
In the section titled 'Double A-minus', the author directs the reader to sources of natural atmospheric heating, like the recent paper by Tung and Zhou. It should be obvious that the ONLY reason this flawed paper deserves to be singled out is its use of the word 'natural'. That's a very important word to the 'doubt is our product' crowd.
All of this fresh doubt piled on IPCC's 3 C sensitivity leads to this statement, which Rupert Murdoch's 'The Australian' newsmagazine chose to lead off with: "If climate scientists were credit-rating agencies, climate sensitivity would be on negative watch". Because, as we all know from the housing bubble, credit-rating agencies are the gold standard when it comes to understanding value...
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ajki at 04:29 AM on 31 March 20132013 SkS Weekly News Roundup #13
Missing link:
Two key climate change concepts are ‘misunderstood’ [climatecentral.org]
Moderator Response: [JH] Link inserted. Thanks for bringing this to our attention. -
MA Rodger at 03:57 AM on 31 March 2013Making Sense of Sensitivity … and Keeping It in Perspective
The video that dana1981 linked @45 gives us the name of the author of the article - John Parker, Globalisation Editor of The Economist (although in their list of journalists, he is listed as Energy & Environment Editor. This would be a recent appointment as James Astill was for a while from 2011 Energy & Environment Editor ). Parker doesn't seem too fluent with his message in the video & has colleague Oliver Morton riding shotgun for him.
And in the video Parker kicks off again telling us temperatures have plateaued for at leat the last ten years and possibly the last fifteen. This is bonkers. Temperatures, say GISS 5-year average, have 'plateaued' between 2003 and 2010. Yet the creation of that plateau only begins in 2008. Until the 2008 temperature arrives to influence the 5-year average of 2006, the data is wholly consistent with a continuation of the accelerating temperature rise. The plateau or flat or pause or whatever is only 5 years old, going on 6. It is never "possibly fifteen"!!
There is also a further video featuring John Parker from December 2012, this time putting the questions to fellow Economist journos Oliver Morton & Ryan Avant in the aftermath of Doha.
http://www.economist.com/blogs/babbage/2013/03/global-warming-slows-down
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dana1981 at 02:22 AM on 31 March 2013Making Sense of Sensitivity … and Keeping It in Perspective
NIck @54 - see A Glimpse at Our Possible Future Climate, Best to Worst Case Scenarios, which is relevant to the point you're making.
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Paul R Price at 00:30 AM on 31 March 2013Making Sense of Sensitivity … and Keeping It in Perspective
@52 MA Rodger
I have to agree: For the huge majority of general readers, the middle of the roaders, the take-home message of both the article and the video @45 (entitled "Global Warming Slows Down", misleadingly, as shown by the ocean warming) will be that there is less need to worry and therefore less need to act. This is exactly the opposite of the truth but it is the message of the article.
To discuss ECS so deeply in the context of The Economist provides effective distraction from the core problem of policy inaction, something one can be sure many of its readers do not wish to see. The second video interviewee does say that ECS sensitivity discussion might be meaningful if policy had been delivering action but that is not the 'take home', especially when the first interviewee jumps in to say that policy-makers prefer to look at the next decade or decades – as if the future of 2100 is of little concern.
One trouble is that knowledgeable readers can look at the article as relatively balanced compared to so many poor ones generally. Indeed such readers may be gratified that the detail of the science is finally being discussed for a general readership. This can please the knowledgeable and serve to blunt critique from them.
However, by focusing on scientific uncertainty in ECS values, and avoiding discussion of the complete lack of action by policy makers and developed nations, the article's impact on most readers will be to confirm their economic preference to delay action. The policy makers and developed nations, along with major corporations and rich individuals, all comprising the target market of The Economist, will be well pleased with this approach
In the context of economics and the Economist, the ECS discussion is a denialist distraction that works to delay support for action. By discussing scientific 'uncertainty' that translates in many readers mind to 'policy uncertainty', which is code for let's do nothing for now until things are more certainty. This is how 'lukewarmist' denial works in the media to support continued inaction.
Scientists and climate policy experts need to start talking to media about certainty in the sense that media and the public understand. If the minimum ECS is 2ºC and the current path is to at least 3CO2 by 2100 then the experts need to say, "On our current path it is certain that we will reach 6ºC and that will be utterly catastrophic for human civilisation" or "If all emissions stopped then warming would stop". Science experts need to state that the uncertainty they are referring to has nothing to do with policy failures or the urgent need for large-scale mitigation action.
Scientists have to start learning how to communicate definitely in public rather than being led into discussing uncertainty – even though that is in fact their area of expertise!
Paul - www.climie.blogspot.ie
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MA Rodger at 00:10 AM on 31 March 2013Making Sense of Sensitivity … and Keeping It in Perspective
elsa @55
I do not see why you would consider it unhelpful to use a base 2 log. Would you rather increase complication by using a different base? If so, try:-
ΔF = 5.35 In(C/Co) W/sq m
There is no argument about this, even from denialists like Lindzen, Spencer & Christy mentioned above (although to include the Mad March Monckton may be a step too far). Your inability to accept that CO2 can be a cause of significant climatic change would be easier to address if you explained your position on this, rather than us trying to give you a crash course in basic science. The present process here is being so poorly directed because it is being directed by you.
So what is your problem with CO2 being the most significant LLGHG?
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Bob Lacatena at 23:27 PM on 30 March 2013Making Sense of Sensitivity … and Keeping It in Perspective
elsa,
K = climate sensitivity, the degree to which the climate responds to a CO2 forcing or any other forcing. The measure of the forcing of CO2 is 3.7 W/m2, and the value of K in this equation is between 2.0 and 4, with the most likely value being 3 or 3.5.
A lot of people are currently engaged in estimating climate sensitivity using a very wide variety of methods.
Current estimates of climate sensitivity are in the range of 2˚C to 4.5˚C, although based on the way the earth is currently responding to a mere 0.8˚C of warming to date, it seems that even if we luck into a climate sensitivity of 1.6˚C (which is highly unlikely) we will still regret it dearly.
Note: All of your posts are off topic. If you wish to discuss the basics of climate sensitivity (as opposed to the specific issues of climate sensitivity raised by the Economist article), post your comment on one of the two threads linked above. If you wish to ask questions about the physics of CO2, post your question here. Many people will be more than happy to answer your questions and help you to learn more about the science, to correct your misconceptions, however it is important not to clutter the wrong threads with random diversions. -
Paul R Price at 22:56 PM on 30 March 2013Earth Encounters Giant Speed Bump on the Road to Higher Sea Level
'Slumps 'n' Jumps'?
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elsa at 22:47 PM on 30 March 2013Making Sense of Sensitivity … and Keeping It in Perspective
Sphaerica
You say "The relationship between CO2 and temperature is:
∆T = K log2(CO2final/CO2initial)"
Let us examine this. We are looking at what would happen if the concentration of CO2 doubled so I guess CO2 final/CO2 initial = 2
The log to base 2 of 2 = 1
So what you say is that the change in temperature is K
This in unhelpful to say the least. What we need (-snip-) is a value for delta T that we can compare with actual temperatures and concentrations of CO2. So please, what is that equation?Moderator Response: [DB] Off-topic snipped. -
Rob Painting at 22:34 PM on 30 March 2013Earth Encounters Giant Speed Bump on the Road to Higher Sea Level
Ups and downs? Meh...
Still open to a better metaphor.
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Nick Palmer at 22:06 PM on 30 March 2013Making Sense of Sensitivity … and Keeping It in Perspective
Rethinking my post (#39) and gpwayne's (#47), I think we now have a pretty unassailable case against the lukewarmers - the only part of the scepticosphere that still has a leg to stand on.
If +2°C is regarded as dodgy and +4°C is definitely dangerous, then even if Lindzen, Spencer and Christy's (even Monckton's!!!) admitted ~1°C figure is correct, the second doubling to 1120 ppm puts us in trouble. As I pointed out before, if the world thinks that sensitivity is as low as the minority suggest, it makes it far more likely that little or nothing will be done to mitigate, or even stop the growth of, emissions.
The only shred of Lindzen's ideas left to deal with is his contention that although the basic CO2 feedback is ~1°C, he claims there is a negative feedback from clouds based on his work with tropical clouds. Show that, even if that holds for the narrow band in the tropics, the probability is that it does not hold for the majority of the planet, particularly the polar regions, and the remaining scepticosphere case collapses entirely.
That may not be enough to fully convince the voting public who have been relentlessly propagandised by experts. The standard infuriatingly deceptive but dumb denialist memes, that the general public are pretty receptive too, should be handled by large full page press ads in high circuation newspapers with the memes (it's the sun, it's not warming etc) down one side and SKS type rebuttals down the other.
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MA Rodger at 22:03 PM on 30 March 2013Making Sense of Sensitivity … and Keeping It in Perspective
I think it would be easier for elsa to come out from under the bridge and explain why she/he believes that an increase in the insulative properties of the atmosphere will not increase global temperatures. The analogy of wearing a coat on a cold day should be something he/she has experience of, so why would anybody think the atmosphere wouldn't be governed by similar physics?
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Bernard J. at 21:58 PM on 30 March 2013It's not bad
KenD.
Bet on volume rather than area, and you will almost certainly have money in the bank.
And sadly, Sphaerica is correct about time spans and realisations. The only slight point at which I would diverge is that I suspect that the genie's already been out of the bottle for a few years.
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MA Rodger at 21:58 PM on 30 March 2013Making Sense of Sensitivity … and Keeping It in Perspective
I'm a little surprised that my interpretation of this Economist article was considered too harsh by others up thread. For the record, rather than to convince folk, here is my counter-comment.
I think all agree the article is mainly factual although it does kick-off in error (the 15-year flat temperature myth) which is never a good sign. In my view its analysis is straightforwardly denialist all the way down to near the end with but the occasional grudglingly-provided caviat (eg 'if deep oceans are heating, it may help explain things') suggesting otherwise.
The end could perhaps have redeemed it, the end being its conclusion, its take-away message, except it doesn't recap its coverage and pronounce judgement. Rather it goes unsignalled into 'warning mode' in the final two paragraphs, the last being.
Since CO₂ accumulates in the atmosphere, this (ie, 1,500GtC total emissions) could increase temperatures compared with pre-industrial levels by around 2°C even with a lower sensitivity and perhaps nearer to 4°C at the top end of the estimates. Despite all the work on sensitivity, no one really knows how the climate would react if temperatures rose by as much as 4°C. Hardly reassuring.
The numbers used in the first sentence are low (ECS=1.6°C and “at the top end of the estimates” 3.2°C) although for the lower one that was the point. The second sentence comes from nowhere. What is the relevance to work on sensitivity to predicting climate after 4°C of warming? And if “no one really knows,” how come they ran an article on it two years back?
Then the final comment - is it meant to be ambiguous? Depending on its missing noun, it can easily be read to mean anything from 'all climatology is inept' to 'mankind is in deep do-do'.
In the paper version of The Economist, this article is a tight fit onto the page. It is possible it may have suffered some severe editing to get it to fit. Still no excuse though.
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Bernard J. at 21:43 PM on 30 March 2013Making Sense of Sensitivity … and Keeping It in Perspective
Just a heads-up for the commenters in general.
Elsa has a habit of capturing the first post on more than a few threads on various climate-related online fora. I have a strong suspicion that it's not just simple chance...
Beyond that I will not speculate as to motive.
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Glenn Tamblyn at 21:42 PM on 30 March 2013Making Sense of Sensitivity … and Keeping It in Perspective
elsa
The basis for the 3.7 W/M2 per doubling is this paper, cited in the IPCC's AR4. Myhre et al 1998. However, if you want to dig deeper than that you need to start delving into Radiative Transfer science. The Eqn of Radiative Transfer; Line-By-Line, Narrow Band & Broad Band radiative transfer codes; Databases of spectral data such as HiTran and Geisa; the history of the developement of this through the 1950's and 1960's; The particular role the Nimbus 3 satellite played in 1969 in confirming previous observations and so on. Lots of research.
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Bernard J. at 21:40 PM on 30 March 2013Making Sense of Sensitivity … and Keeping It in Perspective
Elsa's education seems to be lamentably lacking in the basic science that demonstrates that CO2 can absorb infrared radiation.
If the scientific literature itself is too challenging, perhaps she might consider a visual proof such Iain Stewart's demonstration, or Pieter Trans' very similar demonstration. These are very simple yet very graphic corroborations of the fact that CO2 is not transparent to infrared.
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bouke at 21:01 PM on 30 March 2013Earth Encounters Giant Speed Bump on the Road to Higher Sea Level
Rob, if you show 100 people a headline "Sea level rise encounters speed bump", and ask them if it means an increase or a decrease in the speed of sea level rise, I'd expect more than 50 of them to choose a decrease. I myself would interpret it that way. In fact, I feel strongly enough about it to make this comment.
So, at least some people interpret the title to mean the opposite of what was intended, which is also not a good thing from a communication point of view.
If you want memorable, how about 'The downs and ups of sea level rise'? That's exactly what happened, and the reversal of 'ups and downs' sure sticks.
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Pierre-Normand at 19:48 PM on 30 March 2013Earth Encounters Giant Speed Bump on the Road to Higher Sea Level
There is no need to use another metaphor, Rob. This metaphor would be just fine if you weren't using it to denote the almost exact opposite (a temporary increase in speed) of its already well established use (a sudden hurdle/a cause of a slowdown). I'd be surprised if any other reader of this thread will have at first understood your title "Earth Encounters Giant Speed Bump on the Road to Higher Sea Level" to designate the fast increase of the last two years, as you intend it to. NASA/JPL also were clearly describing the previous sea level fall -- the pot hole -- as an extreme case of a mere speed bump (mere reduction of a positive trend).
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nealjking at 18:31 PM on 30 March 2013Making Sense of Sensitivity … and Keeping It in Perspective
elsa:
The first-order warming from the enhanced greenhouse effect (EGHE) is due to radiative forcing, and this is derived on the basis of radiative transfer theory. The general idea goes like this:
- The temperature profile of the atmosphere makes it generally cooler as you go higher.
- A beam of radiation that starts at ground level and proceeds upwards to the sky will be roughly at ground temperature at the bottom; its temperature will be reduced along the beam as you proceed upwards, remaining roughly the same as the surrounding greenhouse gas (GHG) at each level. (The local beam temperature is reflected in the spectral density of radiation at that point.)
- When the GHG has become so thin that the remainder of the GHG gas (up to the very top of the atmosphere) has total optical depth of 1 (optical depth = line integral of the coefficient of absorption), the local beam temperature stops tracking the local gas temperature profile, and the beam "escapes".
- So the bottom line is that the radiation of the beam at ground level is characteristic of the ground-level temperature; the radiation of the beam as it escapes the atmosphere is characteristic of the temperature at the altitude at which the GHG optical depth = 1 (as measured from that altitude out into space).
- Because the high-altitude temperature is lower than the ground-level temperature, LESS radiation escapes than started out at the bottom of the beam. That is the mechanism of the greenhouse effect (GHG). In radiative equilibrium, the radiation escaping has to equal the solar radiant energy absorbed by the Earth, so this defines a characteristic temperature at that critical point.
- So now, when extra GHG is added to the atmosphere, it permeates the atmosphere and raises the GHG concentration everywhere; in particular, CO2 gets as high up as 100 km. The result is that the optical depth at every altitude INCREASES, thus the point at which optical depth = 1 moves UPWARD; therefore, the local temperature at this new critical point is cooler, implying that the intensity of escaping radiation is REDUCED. This means that the radiant power lost is NO LONGER in radiative equilibrium with the solar radiation.
- So what happens? The Earth is now absorbing more radiant energy than it is losing, so it warms up. The temperature increase also propagates up through the atmosphere over time, such that the temperature increases at every altitude. When the temperature at the NEW critical point (where optical depth = 1) increases enough to match the original temperature at the OLD critical point (before the extra GHG was added), the escaping radiation will again match the incoming solar radiation. The temperature everywhere will be a bit higher. This is the mechanism of the enhanced greenhouse effect (EGHE).
- This walk-through of the radiative transfer physics of radiative forcing is taken from the textbook Principles of Planetary Climate, by Raymond Pierrehumbert (U. Chicago). There are some additional complexities due to the fact that the the infrared radiation has to be considered as made up of separate spectral bands appropriate to each type of GHG molecule, but this is the basic idea.
- The total magnitude of the warming is determined also by 2nd-order feedback effects that entail the complexity of the cllmate system. But the calculation briefly described above sets the "first step".
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gpwayne at 16:43 PM on 30 March 2013Making Sense of Sensitivity … and Keeping It in Perspective
On the subject of sensitivity: recently, I've considered that, in the context of such discussions, we may be rather missing the point.
Climate sensitivity has, for some time now, been one of the few scientific uncertainties on which sceptics can call to support their position. Their argument has been - roughly - that if sensitivity was low, feedbacks did not materialise or have a significant effect, then climate change would be considerably less of a problem (therefore requiring considerably less spending on the solutions).
What has been under-emphasised in my opinion is the relationship between cause and effect. Predictions of temperature rises for a doubling of CO2 represent a way of calculating how much additional energy may be retained by the ecosystem - oceans, land, air - but climate sensitivity does not tell us how the ecosystem will react, by how much, or when.
I mention this because, from a real-world perspective, the issue is not by how much the temperatures will rise, but what effect any rise will have - and here we are in much less certain territory. Consider the melting ice and the way that weather appears to be showing increases in localised extremes. Both these effects have, until recently, been discussed as effects we might see mid-century, as heat/energy accumulates. These timescales now seem hopelessly inadequate, suffering from the conservatism I believe has materially biased much climate science. (Hardly surprising when you're under attack all the time, of course).
We will, as a matter of retrospective measurement, determine the true value of energy retension for a doubling of CO2. Meanwhile, I hope others might agree that we need to emphasise not so much the theoretical aspect of climate sensitivity, but the dawning realisation that massive - and catastrophic - disruption of the climate may be wrought by as little as a 2 degree increase in temperatures, the same figure touted for so long as a 'safe' limit.
I would also like to add one other point: the homogenization of regional temperature records that give us the 0.8 degree anomaly to date, or the putative figures for future doubling of CO2, also conceal a more disturbing metric. Temperatures do not rise evenly across the globe, and therefore the effects of even the warming to date cannot be understood merely by averaging the change. Local anomalies will be the cause of local effects - the Arctic is a particularly compelling example given the effect its local temperature anomalies of up to 2.28 degrees C (GISS) are already having on N. Hemisphere climate patterns - and I think the actual effects of significant local temperature increases on our lives are being disguised by using the global metric in our discussions.
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gpwayne at 16:13 PM on 30 March 2013Making Sense of Sensitivity … and Keeping It in Perspective
Since one of her few remaining posts on my blog has been quoted in order to demonstrate the historical antecedents of Elsa's inveterate denial, I'll just point out that before my blog she wrote some very strange stuff in the Guardian's CiF, the content of which along with posts on my blog were so irrational that I had to show her the door. Of course, I was accused of censorship etc (corresponding to the victimhood status inherent in all climate change denial) but I mention this now because, as then, her posts are extremely disruptive - which I believe is one purpose of denialist activism, as well as to infer doubt where, in fact, none exists. Is it wise to take such posts seriously?
By the way, if SkS considers this post to be off-topic or in any way inappropriate, please remove it.
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Rob Painting at 16:06 PM on 30 March 2013Earth Encounters Giant Speed Bump on the Road to Higher Sea Level
The obsession with overinterpreting the metaphor is somewhat odd. Figure 1 shows a striking resemblance to an uphill road with a large number of pot holes and speed bumps on it.
BillEveritt - sorry, but your suggested alterations have poor memorability - which is not a good thing from a communication point of view. If you can come up with a better metaphor, I'll consider it when next writing on this topic.
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sidd at 15:00 PM on 30 March 2013New Research Confirms Global Warming Has Accelerated
Balmaseda et al., 2013 has reanalyses of OHC
http://onlinelibrary.wiley.com/doi/10.1002/grl.50382/abstractthe divergences of the traces since 2000 seemed interesting so i plotted the differences
http://membrane.com/sidd/balmaseda-2013.html
when will the Kraken rise ?
sidd
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BillEverett at 13:43 PM on 30 March 2013Earth Encounters Giant Speed Bump on the Road to Higher Sea Level
I have the same problem with the metaphor as Pierre-Normand@6,9 but object more strongly to its use. The purpose of a metaphor is to provide a strong image explaining a reality that may otherwise be unfamiliar. In this case, "sea level rise encounters a speed bump" clearly means that "sea level rise slows down abruptly (and will presumably increase after passing over the speed bump)." In other words, the common implication of the metaphor is opposite to the reality. No metaphor is better than a bad metaphor. In this case, it might be better to replace "pothole" with "(abrupt) slow down" and "speed bump" with "(abrupt) speed up."
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dr_who1379 at 13:09 PM on 30 March 2013February 2013 Arctic Sea Ice Death Spiral Update
It is my understanding that sattelite data overestimate the total ice cover. Ships that have been sent to the arctic by Greenpeace report that at points that the sattelites report total ice cover it is found to be burger bits for miles around. Enough reflection from the burger bits looks from space like solid ice cover: i.e. it is worse that we thought
Moderator Response: [DB] "burger bits" = Bergy Bits. -
dana1981 at 12:44 PM on 30 March 2013Making Sense of Sensitivity … and Keeping It in Perspective
Nick @39 - yes, actually The Economist filmed an interview with the two contributors to this article. One of the points they made was that lower sensitivity might matter if our climate policy was suitable for a world with 3°C sensitivity; however, in reality our policy is woefully inadequate. Thus from a policy perspective, 3°C or 2.5°C or even 2°C sensitivity makes little to no difference. In any case we're not doing nearly enough to mitigate climate change.
As I've said, this article is not written from a denialist perspective. They recognize the problem and that we need to solve it; they've just been convinced by evidence for slightly lower climate sensitivity that really is quite weak.
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Bob Lacatena at 12:43 PM on 30 March 2013Making Sense of Sensitivity … and Keeping It in Perspective
elsa,
...the models are not derived from physics, but from measurements. ... They are fitting (or tuning as you put it) the data to the theory so of course they will appear to work.
False.
Casual readers are asked to please recognize the completley vacuous and programmed nature of Elsa's comments. She seems to merely recite the most childish of climate denial myths, while making no effort to use the power of the Internet to correct her ignorance.
This is the stuff that denial is made of; smoke, pixie dust, ignorance and frustration.
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