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John Hartz at 03:13 AM on 22 September 2010A detailed look at Hansen's 1988 projections
@Dana1981 & John Cook: Because it is a poor B&W copy of a color graphic, Figure 2 is virtually worthless to anyone not already familiar with its contents. Suggest that someone track down a color version of this graphic and replace the B&W with it. Although Figure 3 is a color graphic, the colors chosen are pretty much shades of the same basic color. Is it possible to use a different set of colors in this graphic? -
dana1981 at 03:07 AM on 22 September 2010Climate scientists respond to Monckton's misinformation
That list of 21 climate scientists has some very impressive names. It's just too bad they have to waste their time debunking Monckton's nonsense. -
Daniel Bailey at 02:58 AM on 22 September 2010Climate scientists respond to Monckton's misinformation
Long overdue. Thanks! The Yooper -
Joe Blog at 02:55 AM on 22 September 2010A detailed look at Hansen's 1988 projections
dana1981 at 02:02 AM No dana, saying if we change his models assumptions to thus, does not actually make it right, or more accurate... this isnt a rebuttal, but a postmortem. Saying why something is dead dosnt change the fact it is dead. C is the closest scenario to observations in temp, B is the closest in relation to emissions. Now obviously, some of the criticisms cited are pushing the envelope, in how they have chosen to interpret the predictions vrs temp... but so is this one. So what percentage of the temperature anomaly is B from observations? This is relevant. Im not drawing any other conclusion from this, other than Hansen had it wrong in 88. Because he did, you have demonstrated it, it is obvious from a glance at the predictions vrs observations. This dosnt change anything. I still think we are effecting climate through co2 emissions... But Hansen had assumed a higher climate sensitivity than observations. And you have demonstrated this, But then you are claiming it as a rebuttal to criticisms, that have made the exact same observation???? (John Christy) -
Albatross at 02:37 AM on 22 September 2010Climate scientists respond to Monckton's misinformation
This is fantastic news! In fact, it made my day. -
CBDunkerson at 02:36 AM on 22 September 2010A detailed look at Hansen's 1988 projections
dana1981 #41: Are you assuming they actually READ the whole article? It seems pretty clear to me that several of those posting objections have not. Baz #37: I'm not sure which graph you are referring to, but I'd guess the problem is different baseline periods. If the anomaly numbers you are looking at were computed against a different baseline then the graph then you're going to get different values. The relative values should be the same, but the absolute numbers would be shifted by whatever the difference between the baselines is. -
Anne-Marie Blackburn at 02:33 AM on 22 September 2010Climate scientists respond to Monckton's misinformation
I will never understand why Monckton was allowed to testify to the US Congress since it's been clear for some time that he doesn't know what he's talking about. Look forward to reading to the report. -
The contradictory nature of global warming skepticism
Baz writes: I'm not a scientist or in any science field. I'm what Americans call a regular Joe - I'm indicative of the vast majority of people out there (I know because in my job I get to talk to lots of people). Everyone speaks only for her/himself here. You're writing solely on behalf of Baz; you don't speak for "the vast majority" of Americans, let alone for "the vast majority of people." FYI, though, when evaluating how representative your opinion is, you might consider that a large majority of Americans says that the federal government should regulate the release of greenhouse gases from sources like power plants, cars and factories in an effort to reduce global warming. -
A detailed look at Hansen's 1988 projections
Thanks Daniel, but after the Email Episode he stopped replying to my emails! 37. Seriously, anyone? Please excuse my ignorance. -
The contradictory nature of global warming skepticism
Trying again - my last posting was apparently harsher in tone than I had intended. Baz - If you wish to argue from admitted confirmation bias and statistically unsupportable timeframes, just keep in mind that reality is a harsh critic. Hence the focus here on peer reviewed papers, evidence, statistical significance, etc. It's very important to keep in mind the "Average Joe" when discussing topics like climate change - that's one of the reasons for this site. Everyone in the field should be aware of the need to present science clearly and often, so that when policy decisions are made, they can be made in an informed manner. -
dana1981 at 02:02 AM on 22 September 2010A detailed look at Hansen's 1988 projections
I have to say, it's a little irritating how many people can't get past the "it looks like Scenario C" perception. Is the entire rebuttal over their heads? Are they just incapable of seeing anything other than what they want to see? -
CBDunkerson at 01:29 AM on 22 September 2010A detailed look at Hansen's 1988 projections
NETDR #36 writes; "They can’t possibly exactly predict the past exactly without cheating." Yet your prior post objected to their 'failure' to exactly predict the future... down to the month. "The 5 year average for 2009 was .54° C" Actually, 0.55 C based on the URL you provided. Apparently you rounded down. "The 5 year average for Hansen’s prediction is hard to get precisely but it seems to be .9 ° C" Yes, since all of the values from 2005 through 2009 on scenario B are clearly less than 0.9 C (the only one which comes close is 2009) it definitely IS hard to get how you come up with that average. The 'UHI skews temperature records' and 'satellite temperatures are different' bits have been debunked on this site so many times that I can't be bothered. -
Riccardo at 01:20 AM on 22 September 2010Risky Business: Gambling on Climate Sensitivity
adelady, maybe i looked pessimistic while i'm not. What I've tryed to say is that it's a broader cultural problem and consequently broader changes in our societies are required. In this, science alone is not enough. -
Doug Bostrom at 00:58 AM on 22 September 2010A detailed look at Hansen's 1988 projections
...like the horse player who bets on the wrong horse but shows how he could have picked the right one if only. Or one can take the approach of imagining much of the field had never raced, thus concluding one's own pick won. Alternatively, how about ignoring most available data in order to gin up a comfy conclusion? -
Daniel Bailey at 00:42 AM on 22 September 2010A detailed look at Hansen's 1988 projections
Re: Baz (37)"Can someone please explain why the graph shows HadCRUt3 (in pink) dipping well into the 0.5s when the data says it hasn't."
You can try asking Phil Jones. :) The Yooper -
A detailed look at Hansen's 1988 projections
Can someone help me out here? I can't see (by eyeballing) that the actual temps match any of them, even C. However, that's not important to me. Can someone please explain why the graph shows HadCRUt3 (in pink) dipping well into the 0.5s when the data says it hasn't. http://www.cru.uea.ac.uk/cru/data/temperature/hadcrut3gl.txt I know there is obviously a simple explanation! Thanks. -
NETDR at 00:15 AM on 22 September 2010A detailed look at Hansen's 1988 projections
CB Dunkerson [35] If you notice all scenarios start approximately together in 1988. They can’t possibly exactly predict the past exactly without cheating. They were adjusted to converge on the right answer in 1988. [No problem, I would do it that way too.] You complained that the time period I chose for my end point was too short. Let’s go back to 2009 and use a 5 year average. The 5 year average for 1988 was .25 ° C [Anomaly] The 5 year average for 2009 was .54° C The 5 year average for Hansen’s prediction is hard to get precisely but it seems to be .9 ° C http://data.giss.nasa.gov/gistemp/graphs/Fig.A2.txt Let’s do the math. The chart predicts .9 ° C - .25 ° C = .65 Reality is .54 - .25 = .29 Even with uncorrected UHI and other surface station issues. If I had used Satellite data his predictions look worse, because there are no perking lots in space. In my book that is pretty poor performance. His excuses ring hollow to me, it is like the horse player who bets on the wrong horse but shows how he could have picked the right one if only. Everyone “could have” and “should have “. Putting those guesses to work on predicting the future will verify or refute them. Anyone can predict the past. -
muoncounter at 22:43 PM on 21 September 2010Global warming and the unstoppable 1500 year cycle
Just noticed a small typo in the 3rd paragraph: 'rising over 390 ppm' should be 'rising to 390 ppm'. -
Berényi Péter at 22:01 PM on 21 September 2010The significance of past climate change
#86 Berényi Péter at 08:36 AM on 21 September, 2010 If surface temperature is increased by 1%, surface temperature goes up by 0.5°C. That's plain silly. Of course it should read "If surface pressure is increased by 1%, surface temperature goes up by 0.5°C." It is calculated this way: Density of air at ambient pressure is about 1.3 kg/m3. As mass of air above an 1 m2 surface is about 104 kg, a 1% increase implies an additional 100 kg/m2. To get to this value, the air column should be 77 m deeper. With a 6.5°C/km environmental lapse rate it makes the surface 0.5°C warmer. Now, here is this paper. Nature Geoscience 2, 891 - 896 (2009) Published online: 15 November 2009 doi:10.1038/ngeo692 Nitrogen-enhanced greenhouse warming on early Earth Colin Goldblatt, Mark W. Claire, Timothy M. Lenton, Adrian J. Matthews, Andrew J. Watson & Kevin J. Zahnle They hypothesize nitrogen partial pressure during the Archaean was twice as high as it is today and they say there would be 3-5°C warming for N2 doubling. It is much lower than the result given by the first-order approximation above and I just can't see where the huge difference comes from. -
CBDunkerson at 21:52 PM on 21 September 2010A detailed look at Hansen's 1988 projections
NETDR, there are a couple of glaring flaws in your analysis; "From 1988 to present [Aug 2010] the warming has been .53 ° C - .31 ° C = .22 ° C" 0.53 C is the anomaly for JUST August 2010 while 0.31 C is the anomaly for the entire year 1988. Monthly variations are, of course, greater than annual variations. This method is also subject to huge variations depending on the precise timing. If we pick different months, say March 2010 with 0.84 C anomaly minus November 1988 with -0.03 C anomaly we get a +0.87 C increase... MORE than the model predicted. Also, LOOK at the Hansen graph in the URL you posted. The temperature values BEFORE 1988 diverge significantly from the actual temperature record in individual years. For instance, for 1981 scenario B 'predicted' (7 years after the fact) that the anomaly had been roughly double what the actual record showed. From this we can conclude either that Hansen's model was wrong before it was even released... OR we could be remotely logical and realize that these models were never intended to precisely match each and every year... which is the test you are applying. A model is 'accurate' if it matches the long term trend. Picking out individual years (or months) and saying 'the model is off by X% at this moment in time' is meaningless. Through 2005 the model trend lined up with scenarios B & C. Since 2005 it has lined up with scenario C while emissions have actually been just a bit below those assumed for scenario B. Thus, it could be said that the trend isn't matching the model's prediction for our approximate emissions over the past five years... except that is a ridiculously short period of time on which to base a trend. -
NETDR at 20:44 PM on 21 September 2010A detailed look at Hansen's 1988 projections
I think the article is far too forgiving with Dr Hansen. He got it significantly wrong. From 1988 to 2010 his graph shows his predicted warming to be. 1.0 ° C - .31 ° C = 69 ° C From 1988 to present [Aug 2010] the warming has been .53 ° C - .31 ° C = .22 ° C http://cstpr.colorado.edu/prometheus/archives/hansenscenarios.png Giving Hanson the benefit of the doubt and using GISS’s own numbers: http://data.giss.nasa.gov/gistemp/tabledata/GLB.Ts+dSST.txt The earth only warmed 31 % as much as predicted. This is less than scenario “C” which is what was predicted for what would happen with stringent carbon cuts. When the “debate is over” you have all of the answers and are expected to be correct. If he got climate sensitivity wrong that is just an excuse, this means his predictions of 2020 and beyond will be way off track and getting worse each decade. -
Michael Le Page at 20:16 PM on 21 September 2010Risky Business: Gambling on Climate Sensitivity
A few little things that struck me: It seems a little odd to include Royer 2007 in the climate model category, it's a bit of a hybrid but based on past changes in CO2. Also, where does that the top limit for Royer come from? The paper states "GEOCARBSULF simulations cannot exclude the possibility of a high climate sensitivity"? Finally, why not include Lunt 2010 and Pagani 2010? -
adelady at 18:21 PM on 21 September 2010Risky Business: Gambling on Climate Sensitivity
Riccardo "My impression is that our time horizon is pretty near, we're not able (or not willing) to consider long term plans." I really think it's a failure of the imagination. I can speculate about my grandchildren's grandchildren. When people talk about this they don't really visualise it, they just hope that they'll be decent people who'll enjoy life in much the same way we do. In this I'm more with Hansen. I see good possibilities if this generation and the next does the right thing. I see nasty stuff if we and they don't. Of course for them, it'll be just the way the world is. But my generation is not too thrilled about the way our predecessors mucked up our forests and agricultural lands and introduced pests of every kind. I'd hope that our descendants will see that we did our best even though it was too little too late for some things they'll never get to see. -
Glenn Tamblyn at 18:15 PM on 21 September 2010Climate sensitivity is low
A common misconception that people have about Climate Sensitivity is that it is a fixed value over a wide range of climatic conditions. This leads to some quite bizarre 'analyses' in the denialosphere, attempting to show that CS couldn't be that high because that implies that CO2 contributes far too much of the 33 DegC of extra warmth attributed to the Greenhouse Effect. The fallacy they make is projecting the same CS value back through lower and lower CO2 levels and temperature regimes. Climate sensitivity is an idea used to encapsulate how the planet IN A PARTICULAR CONFIGURATION - temperature, distribution of land masses, ocean currents, air movements, ice cover, vegetation patterns etc - will respond to a change in radiative forcing from whatever source - GH Gases, Solar changes, Aerosols. So Climate sensitivity will certainly be different at different times. In fact sensitivity to a warming pressure would likely be different to the sensitivity to a cooling pressure in the same climate. So sensitivity to a warming pressure at the bottom of an ice age would be higher than at the top of the ice age; with ice down to lower latitudes, any retreat of that ice due to temp rise exposes a larger area of land and sea and thus has a bigger effect on albedo than the same distance of retreat when the ice is only at higher latitudes. However given the thickness of the ice sheets, the time lags in responding to the warming will be large as it takes time for the ice to melt away. Conversely sensitivity to a cooling pressure coming out of an inter-glacial is likely to be high since even modest cooling can quickly increase the area and duration of snow fall; 1 metre of snow has much the same albedo as ice sheets kilometers thick. The time lag responding to any such cooling is thus also likely to be quicker. In an Ice free world, CS to a warming pressure might be much lower since Ice based albedo change doesn't occur. Similarly in a world with very low CO2, a Snowball Earth, CS might also be low. If the world is literally covered in ice, modest warming may not be enough to cause any ice melt - going from -18 DegC to - 15 DegC for example may not cause any ice cover reduction. It would only be when enough warming pressure has occurred that ice cover retreat begins that change might be rapid. In effect, CS would change when the climatic conditions change enough. This is also important when considering the oft cited figure of 33 DegC of warming due to the GH effect. The calculation that arrives at this number is based on the Earths current Albedo; that around 30% of sunlight is reflected away and isn't part of the energy balance. However in a world that is -18 DegC ON AVERAGE, Ice Cover would be much greater, more even than an Ice AGe which still has a positive average temp. At minus 18 DegC, ice cover sufficient to cause 50% of sunlight to be reflected is quite conceivable. The calculation for this albedo gives 53 Deg extra warmth: -38 DegC -
The contradictory nature of global warming skepticism
archiesteel. I'm honest! It's a rarity these days. That's why it actually really annoys when someone says I'm a liar or dishonest. No, I'm completely open about my scepticism, my confirmation bias, my 'illogical' choice of 10 years of data. As I tried to point out (and I'm sure I don't need to!) I'm not a scientist or in any science field. I'm what Americans call a regular Joe - I'm indicative of the vast majority of people out there (I know because in my job I get to talk to lots of people). We don't see what you see. Maybe seeing it scientifically is wrong. Sometimes it takes an outsider to see something an expert has been staring at for some time. You might see noise and incomplete data, I might see something entirely different. Give it just a passing thought, at least. If I get time later I'm going to pop back and show you what my experience was like on here. But if I don't get time then, have fun - and stay healthy Archie! -
Riccardo at 17:46 PM on 21 September 2010Risky Business: Gambling on Climate Sensitivity
Apart from the die-hard skeptics, I think that for the general public is not even a gambling. My impression is that our time horizon is pretty near, we're not able (or not willing) to consider long term plans. In this sense we are culturally limited to the financial-style next quarter results. These considerations does not apply just to climate or global resources limitation but even to our everyday life. And it's the prologue for the disaster. -
Bern at 17:14 PM on 21 September 2010Risky Business: Gambling on Climate Sensitivity
I thought the entire article was well written, Graham, thanks. Regarding the above comments on gambling, and stressing the potential disastrous outcomes - I guess it's a fine line to be walked, between over-caution on the one hand, which may lead to complacency, and alarmism on the other, which will of course lead to dismissal by the denialosphere. (Mind you, the skeptic tendency to leave zero space between 'alarmism' and 'nothing to worry about' makes that a particularly difficult task...) If the more pessimistic results from the climate models are at all correct, it's not just gambling - it's more like playing russian roulette, but with nuclear weapons... if you're wrong, it doesn't just affect you, it affects everyone else as well. Sure, it may just be a sub-kiloton tactical nuke, that 'only' takes out your neighbourhood. Then again, it might be the launch code for the world's entire arsenal. The sad bit is that some people look at that problem, and see that it might not be their neighbourhood, but, say, a neighbourhood in Bangladesh, or a low-lying island nation, and they think "Meh, it doesn't affect me" and push the button anyway... -
MattJ at 16:31 PM on 21 September 2010Risky Business: Gambling on Climate Sensitivity
I thought the last sentence was already pretty good. It really doesn't need the "before it is too late" kind of thing huntjanin proposes. In fact, I was pretty pleased with the way it built up carefully to the pivotal and climactic statements, "Even such a small rise would signal many damaging and highly disruptive changes to the environment. In this light, the arguments against mitigation because of climate sensitivity are a form of gambling." That is the essential point of the post: it is a form of gambling, and a particularly foolish one, like that game 'chicken' middle schoolers play -- but on a planetary scale. In fact, if I were to ask to any change at all, it would be right here, rather than at the end: something to make it clear that we are not talking about just any 'gambling', but such a particularly reckless one, one where the odds are not only heavily against us, but the price paid is unimaginably high compared to any other form of gambling. So I might, for example, change "a form of gambling" to "the worst sort of gamble, with planetary disaster for the price of losing." -
huntjanin at 16:05 PM on 21 September 2010Risky Business: Gambling on Climate Sensitivity
Good post but in my opinion it needs a last sentence, along the lines of "remedial measures should therefore be adopted befor it is too late." -
John Chapman at 14:49 PM on 21 September 2010A South American hockey stick
Looking at the link identified in #19 is quite interesting if one takes the time to examine the records from around the globe. Unless I'm mistaken it appears that the mini ice age was widespread and not confined to Europe as sometimes asserted. -
John Chapman at 14:43 PM on 21 September 2010A detailed look at Hansen's 1988 projections
A slightly pedantic point ... in the calculation the input figures are 3 or 4 significnat figures. Please make them two. eg. 389 ppm -> 390, 329 -> 330, 1788 -> 1800. The rounding will not affect the final 2 sig fig result. -
scaddenp at 14:02 PM on 21 September 2010Global warming and the unstoppable 1500 year cycle
GC - how many times have you brought this up here? How many times has it been explained to you that your conclusion is totally faulty (CO2 can be forcing and feedback and you cant make the maths come out any other way)? What is so hard about you understanding this? -
gallopingcamel at 13:46 PM on 21 September 2010Global warming and the unstoppable 1500 year cycle
thingdonta, Your words shine like "...a good deed in a naughty world." Merchant of Venice, (William Shakespeare). 1. OK, climate change is happening. 2. The atmosphere causes average temperatures to be ~33 Kelvin higher than without the atmosphere. Let's call that the "Greenhouse Effect". 3. CO2 has an effect on global temperatures but not enough to to explain the observed variations on any time scale. What thingdonta says is totally vindicated by the Vostok ice core records but just for light relief here is Richard Alley's lesser known ice core data going back only 50,000 years for central Greenland. This data set shows the recent "Hockey Stick" but also the warm period that allowed Vikings to colonize Greenland and the subsequent cold period that destroyed their mini-civilization: http://www.foresight.org/nanodot/?p=3553 For those who are inclined to doubt the Foresight Institute, you can make your own analysis by retrieving the raw data from NOAA: ftp://ftp.ncdc.noaa.gov/pub/data/paleo/icecore/greenland/summit/gisp2/isotopes/gisp2_temp_accum_alley2000.txtModerator Response: #3 is covered in the post CO2 Is Not the Only Driver of Climate.That's where you should discuss it. -
Daniel Bailey at 10:23 AM on 21 September 2010Arctic sea ice has recovered
Stop the presses, this just in: Mayans were right! North Pole to be ice-free (well, except for various edges) September 2012! From Neven's blog. Gimme lemons, I'll make lemonade... The Yooper -
dana1981 at 10:22 AM on 21 September 2010A detailed look at Hansen's 1988 projections
I did like your comment on adding the actual 2010 GHG concentrations to Table 1, Sense Seeker, and have updated the post accordingly. -
dana1981 at 10:08 AM on 21 September 2010Hansen's 1988 prediction was wrong
Also while actual temps are in the range of Scenario C, greenhouse gas emissions have not followed those in that particular projection. It makes more sense to focus on Scenario B, which has been very close to actual emissions, and then determine why the actual temp change has been lower (mainly the climate sensitivity factor difference). -
dana1981 at 10:04 AM on 21 September 2010A detailed look at Hansen's 1988 projections
Sense Seeker - you can't get to a surface temperature change from a GHG change without determining the associated forcing (and knowing the climate sensitivity parameter). I'm a big proponent of 'show your work', so I don't want to skip that step. Personally I think the logical process in the advanced version is reasonably clear, but the intermediate and basic versions are less detailed for those who just want to get the general gist. -
dana1981 at 09:57 AM on 21 September 2010A detailed look at Hansen's 1988 projections
archiesteel - you are correct. Joe Blog, you have missed the point entirely. The point, once again, is that yes, Hansen's model's sensitivity of 4.2°C for 2xCO2 is too high (in the short-term), but it also tells us that 3.4°C for 2xCO2 is approximately right. This sort of inability to see past the conclusion you want to see is exactly what I was talking about - "a common reaction to Hansen's 1988 projections is 'he overestimated the rate of warming, therefore Hansen was wrong'...This is obviously an oversimplified conclusion, and it's important to examine why Hansen's projections didn't match up with the actual surface temperature change. That's what we'll do here..." -
Rob Honeycutt at 09:23 AM on 21 September 2010A detailed look at Hansen's 1988 projections
Joe... You have to bear in mind this is coming from a study done in 1988 and it's an incredibly complex model. Given that Hansen managed to closely predict warming for the following 22 years is astounding. As well, give how much less was known at the time about climate sensitivity it's amazing that he settled on a number that is so close to reality. The scenario C is actually not as close because (I believe) it used more optimistic GHG emissions rates that didn't come to pass. B has the right GHG emissions and is only off on climate sensitivity by 0.8C. It's also impressive that his middle scenario is the closest. It's what you'd be aiming for in a study like this. Think of it this way. What if you had to guess what global temperatures would be 22 years from now. How close could you get? This is essentially Hansen hitting the first ring outside the bulls eye from a very very very long distance. -
Joe Blog at 09:08 AM on 21 September 2010A detailed look at Hansen's 1988 projections
archiesteel Yes, so Hansen was wrong, in his climate sensitivity. It certainly doesn't prove Hansens projections were accurate, or disprove criticisms of his projections, as the article claims to do. -
archiesteel at 09:01 AM on 21 September 2010A detailed look at Hansen's 1988 projections
@Joe Blog: "how can this mean anything other than an overstated climate sensitivity" Isn't that the conclusion of the article, i.e. that Hansen overestimated climate sensitiviy (4.2C instead of 3.4C)? -
Joe Blog at 08:49 AM on 21 September 2010A detailed look at Hansen's 1988 projections
Youve lost me with this analysis... in the top graph, the closest is scenario C to observations... A and B appear to clearly over estimate climate sensitivity... Now B is the closest to observed emissions clearly, But C is the closest to observations, how can this mean anything other than an overstated climate sensitivity? Now it dosnt matter one iota what anyone's opinion is on what the temps "will be" in a decade, all that matters for testing the model is a straight comparison between projected and observations. It may be due -
Berényi Péter at 08:36 AM on 21 September 2010The significance of past climate change
Posted by John Cook on Wednesday, 21 April, 2010 at 19:56 PM Climate changes when it’s forced to change. When our planet suffers an energy imbalance and gains or loses heat, global temperature changes. You mean surface temperature, of course. However, surface temperature depends not only on the heat content of the climate system (atmosphere+hydrosphere+soil), but also on surface pressure (via lapse rate). If surface temperature is increased by 1%, surface temperature goes up by 0.5°C. Therefore while it is true a positive energy imbalance implies surface warming, it does not work in the reverse direction. You can have warming with no net heat energy gain, just by increasing pressure. It has no direct consequences on our present situation, for the volume of atmosphere is pretty stable on historic timescales. However, on geologic timescales the situation is radically different. In the late Carboniferous - early Permian atmospheric oxygen level is assumed to be much higher than today, perhaps as high as 35% per volume. If N2 partial pressure is held constant (at 0.754 atm), it implies an overall atmospheric pressure 24% higher than today. This pressure increase alone would make surface temperatures some 12°C higher. Of course according to the Standard Solar Model luminosity of the Sun was 2-3% lower 300 million years ago than it is today. But it would make surface temperatures only 2°C cooler at most. On the other hand we do know surface temperatures in that epoch were about the same as they are today (with slightly more CO2 in the atmosphere).
We have 10°C unexplained lack of warming here (and a permanent polar ice cap). That's more than we asked for.
The only way out is to assume surface pressure was also about the same as it is today. However, in this case N2 partial pressure must have been about 20% lower than its present value.
As average residence time of N2 in the atmosphere is ~20 million years (due to biological nitrogen fixation) and there is about sixty times more Nitrogen in the crust than in air, it seems to be entirely possible, especially because sequestration of organic detritus was particularly intense in those times.
However, if N2 partial pressure can vary on a multi-million year timescale, we should be extremely cautious in interpreting the paleoclimate record, for as far as I know, there is no reliable reconstruction in the literature of past atmospheric pressure changes so far.
The upshot is that it is rather difficult (or should we say impossible?) to derive climate sensitivity from paleoclimate data while one of the major ingredients is indeterminate. Understanding the nitrogen cycle should be given high priority.
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Rob Honeycutt at 08:34 AM on 21 September 2010The contradictory nature of global warming skepticism
pbjamm.... Science journalist Peter Hadfield (aka PotHoler54) does a really good job of explaining it here. In fact, he has a series of videos on climate change that is really good. Highly recommended. -
Sense Seeker at 08:30 AM on 21 September 2010A detailed look at Hansen's 1988 projections
A night's sleep does help. I can see what you were trying to do. You are comparing the inputs of Hansen's scenario B (translated into forcings) and the actual changes in the input variables (as 'observed' forcings), and then compare Hansen's output (= projected temperatures) with the real output (= realised temperatures). From that you conclude that Hansen's model was 24% too sensitive. It is a pity that the detour via forcings is there, but I guess that is the best way to summarise all different emissions? (I cannot judge that.) You could consider explaining why the translation into forcings is necessary and justified; it was not obvious to me when I first read it. To guide the reader, you could also consider indicating somewhere in the beginning of your explanation what you are going to do, in broad terms. (Determine difference in input values (GHGs) and compare to differences in output (temp) between Hansen's model and reality.) PS: typo "global surface temperature (dF)" should be (dT)? -
Spaceman Spiff at 08:21 AM on 21 September 2010Global warming and the unstoppable 1500 year cycle
@thingadonta: You've just commented on a website dedicated to countering with scientific evidence 121 largely disparate, mostly contradictory, and definitely not unified "arguments" placed against climate science ( http://www.skepticalscience.com/argument.php ) -- often made by the same people. The contrast between that situation and the one found in the present state of climate science that unifies wide-ranging physical phenomena and finds multiply converging lines of evidence is utterly striking. If there is any confusion concerning the state of "skeptical arguments", it's certainly not John Cook's fault. -
hadfield at 08:05 AM on 21 September 2010A South American hockey stick
John, can you correct the mis-spelling of Moberg's name in the article, please.Response: Fixed. You'd think I'd have noticed the correct spelling in the graph :-( -
archiesteel at 08:00 AM on 21 September 2010The contradictory nature of global warming skepticism
@Baz: " I have said before that I display confirmation bias (a perfectly human trait)" So, you recognized you are biased, but will not try to correct that bias? And you wonder why we don't take you seriously? It's human to be biased, but it's rather stupid to continue being in the wrong once your errors have been pointed out to you. -
scaddenp at 07:50 AM on 21 September 2010The contradictory nature of global warming skepticism
"KR. I didn't agree with the 20-30 period at all, I accepted that's what the general consensus of opinion is on this site." Umm, but the 20-30 year period is determined objectively from the statistical study of internal variability. I notice that you have given links to this long ago. The point of doing such studies is to have an objective basis for that "consensus opinion". Can you think of a better way? -
CoalGeologist at 07:36 AM on 21 September 2010The contradictory nature of global warming skepticism
@Baz #314 You have stated:"KR. I didn't agree with the 20-30 period at all, I accepted that's what the general consensus of opinion is on this site. I have said before that I display confirmation bias (a perfectly human trait), but I'm in good company here."
Will you also accept that the reason this is the general consensus on this site is because this is how the term "climate" is defined within the scientific community? Specifically, here is the definition of climate from the AR4 Synthesis Report Glossary:Climate "Climate in a narrow sense is usually defined as the average weather, or more rigorously, as the statistical description in terms of the mean and variability of relevant quantities over a period of time ranging from months to thousands or millions of years. The classical period for averaging these variables is 30 years, as defined by the World Meteorological Organization. The relevant quantities are most often surface variables such as temperature, precipitation and wind. Climate in a wider sense is the state, including a statistical description, of the climate system. In various parts of this report different averaging periods, such as a period of 20 years, are also used.
Scientific dialog is most meaningful when participants are using well-established terminology in a consistent manner. There may be other web sites that would be more amenable to your redefining established terminology to suit your argument. Confirmation bias may be a perfectly human trait, but it is poison to scientific reasoning. I don't know to what degree any other bloggers at this site might be guilty of this offense, but if you, personally, are guilty of it AND aware of it, then you relinquish any credibility to valid scientific reasoning. This site is supposed to be about scientific evidence, not to validating preconceived conclusions.
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