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Doug Bostrom at 07:47 AM on 21 May 2010Climate's changed before
Roger, I'm not spotting the tautology. Which part of the physics do you disagree with? -
Rogerthesurf at 07:25 AM on 21 May 2010Climate's changed before
"71.Rogerthesurf at 12:52 PM on 8 April, 2010 "What does past climate change tell us about global warming?" In case you dont know it, your explanation uses the AGW theory to explain the question when the question is really asking for some proof of the AGW theory. Cheers Roger http://www.rogerfromnewzealand.wordpress.com 72.doug_bostrom at 13:53 PM on 8 April, 2010 Rogerthesurf, you'd do better to explain yourself. Failing that, presumably you won't care if your post is deleted? " Sorry your reply did not show up on my "My Comments" page. Thank you for editing my comment (not) However my point is simple. Correct me if I am wrong, but at no point does your explanation discuss the validity of the "Anthropogenic CO2 causes Global Warming" hypothesis. Instead your host of explanations which are all based on the assumption that it (the above hypothesis) is fact, which actually it is not fact but as yet simply an unproven hypothesis. Therefore all your explanations are no better than this unproven hypothesis. I trust that is clear. Cheers Roger I also always post my comments and replies on my other site http://globalwarmingsupporter.wordpress.com where my readers can evaluate my questions and your answers. Check under your url and post title. -
Riccardo at 06:54 AM on 21 May 2010Has the greenhouse effect been falsified?
Berényi Péter, "Fig. 1 can not be produced by actual measurement or if it was, what is shown is a scaled up version of values measured. Undocumented tricks like this are not helpful." Well, you started with a false premise and arrived to the wrong conclusion, no surprise. And to cast unsupported doubts is not helpful. Didn't you notice any difference between the data shown here and the one you linked to? The transmittance is zero above 14 μm and below 8 μm. Is this an undocumented trick as well? -
Albatross at 06:41 AM on 21 May 2010Unprecedented Warming in Lake Tanganyika and its impact on humanity
I'd like to second Doug's comments at #32. Thank you Dr. Tierney. -
Doug Bostrom at 05:53 AM on 21 May 2010Unprecedented Warming in Lake Tanganyika and its impact on humanity
A sincere Thank You to Dr. Tierney for putting in a appearance here. To be treated to such detailed attention from the first author of this paper is remarkable gift. I hope everybody here appreciates our good fortune whatever quibbles some of us may have with the paper in question. -
jtierney at 05:47 AM on 21 May 2010Unprecedented Warming in Lake Tanganyika and its impact on humanity
Hi, #27 and #28, thanks for writing good questions. First #27, how do we know that the local temp. rise in East Africa is due to global warming? Well, in part that was why we chose in our study to reconstruct the "history" of temperature in this region by using a proxy. Instrumental data from the Lake already have shown that the lake is warming (cf. O'Reilly et al., 2003 Nature and Verburg et al., 2003 Science) but what we didn't know before now was whether such warm temperatures could happen by chance or in response to natural climate forcing vis a vis AGW. That's because the instrumental data are sparse, and only go back to 1913. What we we've shown now with our new proxy data is that we don't see 26 degrees occurring naturally in the lake in the recent past, and in fact on my website I show that it is likely that we haven't seen that the lake is as hot as it is now since 6000 years before present! So that suggests that something is happening right now that is distinctly different. We know that the planet is warming, and that humans are causing it, so it is very likely that that is the culprit. In terms of the match between NH temps and our record, you are right that they are different in places. I think the post above re: the temp. distribution during the MWP illustrates that there is a lot of spatial differences in temp. change in the past. In other words, you might not expect a perfect match between our local record and the global average. But BOTH records do show the same trend during the past 150 years - a big warming. #28: Great question, and in an ideal world we would have sediment cores from a lot of locations in the lake. However, as you can imagine is it pretty difficult to get these cores...we are operating in 100s of meters of water out of modified shipping or fishing boats, in a very remote place of the world! Again, as I mentioned in response to #27, previously published work shows that instrumental data from the lake show a warming. These data are plotted in the inset which you can see on my website. They are from farther down the water column, so the warming is not as big as at the surface, but the trends are clear. To the extent that our proxy data agree very well with these water temperature trends as well as air temperature trends, we trust that our cores are doing their job. btw, the reason why we "spliced" the core records was because only MC1 had sediment coming up to present; the top of KH1 was not recovered by our corer. So we had to combine two cores and overlap to get a full record. Hope that helps -Jessica -
embb at 05:26 AM on 21 May 2010Unprecedented Warming in Lake Tanganyika and its impact on humanity
If I understand the argumentation correctly the people living around the lake are not responsible for the environmental degradation as "these unprecedented temperatures and a corresponding decrease in productivity can be attributed to anthropogenic global warming, with potentially important implications for the Lake Tanganyika fishery." No overfishing, deforestation or any other local environmental effects play a decisive role - the damage comes from AGW. It also follows that aside from fighting the CO2 emissions globally there is no point in starting local environmental actions, as they are clearly pointless against AGW. As truths go this must be really convenient. I wonder if it is also true ? -
Albatross at 05:21 AM on 21 May 2010Unprecedented Warming in Lake Tanganyika and its impact on humanity
This is an interesting study and the results are, IMO, concerning. Some here seem to be making some rather odd critique of the paper and analysis. For example, it is odd to make unsubstantiated statements that the analysis is compromised because alleged logging in the area (and other land use changes) may have affected the lake temperatures or sediment deposition. Scientists who work with these sediment data are, of course, very well aware of the processes which both generate and affect the sediments. The sampling site at Lake Tanganyika is located near 6 degrees south, so it is debatable whether either the N or S hemisphere temperature reconstructions are appropriate. They used the N. Hemi., and that is probably acceptable given the close proximity of the site to the equator and the fact that the N. Hemi reconstructions are more reliable. Anyhow, that critique in no way refute this work or calls it into question and is really just a red herring being used by Eschenbach (and Eschenbach is definitely not an expert on lake sediments). If there were a proxy dataset close by, then that could perhaps have been used. Someone asked when their reconstruction ended; their last sampling point corresponds to 1996. What some people seem to be ignoring is the significance of cumulative impacts. The lake is a critical food source and is subject to numerous stresses, including over fishing, degradation of water quality from anthro activities etc. Now a new stress has been added to the system, rapid warming of water temperatures. Indications are that this warming is associated with the energy imbalance arising from higher levels of GHGs from human activities. Claiming that deforestation in the region is somehow warming LSTs of the second largest lake (by volume) on the planet by 2 C since 1900 is a huge reach and, as with many contrarian arguments, unsupported. The authors did compare the TSI and LST records and found that while in the past they were in fairly good agreement, they note that "...TSI variability clearly does not explain the dramatic twentieth-century increase in LST..". The fish have adapted to conditions in the lake, and cannot simply move on to more favourable habitat. The authors note that "our data demonstrated that the LST and primary productivity are are closely related in both the pre-anthropogenic and anthropogenic eras, confirming that warm surface temperatures increase the degree of stratification within Lake Taganyika and reduce primary productivity. Apart from fishing intensity, the present decline in primary productivity is likely to impact the clupeid fishery, with potential dire implications for the communities". So yes, other factors may be affecting productivity and lake temperatures, but they alone do not explain the dramatic increase in temperatures observed since 1900. Eschenbach and other critics are clearly grasping at straws and trying to detract from yet more evidence of the detrimental impacts of the enhanced greenhouse effect. Colour me unsurprised. -
embb at 04:38 AM on 21 May 2010Are we too stupid?
Jacob, you do not answer my question sohere it is again: How is this going to look like in real life: WTO-consistent border adjustment mechanism so that there won't be any "carbon leakage" of companies manufacturing things overseas in countries that don't manage their emissions. Imports from those countries will have to pay a fee at the border. Starting next year, say, the US will raise customs tax equivalent to the carbon tax on every product coming from a country that does not have an equivalent tax? Yes/no? Any thoughts you have on the impact of such a tax on the world economy? -
johnd at 04:14 AM on 21 May 2010Unprecedented Warming in Lake Tanganyika and its impact on humanity
jtierney at 00:39 AM, I visited your website and I notice from the calibration data in the supplemental information that it appears only two core samples were mentioned, MC1 and KH1, and then only part of each were combined to provide the one set of data. Were these core samples the only ones taken, and if so, how confident are you that they are truly representative of the lake as a whole, especially given that a portion of each had to be combined, and the anomalies at the bottom of KH1? If more than these two core samples were taken, why were the others discarded, and why was only a portion used of each of the two that were analysed? It is one thing to look for consistency within one sample, but it is more important to ensure that the sample used is truly representative of the subject being analysed and that confidence level can only be attained through multiple sampling. -
Marcel Bökstedt at 03:40 AM on 21 May 2010Unprecedented Warming in Lake Tanganyika and its impact on humanity
J Tierney> Hey you! It's really great that you take the time to visit us and comment on our attempts to discuss your article. e> Yes, I had missed that sentence in the introduction, they actually do state that the rise in local temperature is due to anthropogenic global warming. In the text of the article the formulation is a little weaker. They write that "the dramatic twentieth-century increase in lake surface water temperature, as global temperatures, is probably a response to greenhouse-gas forcing." The main argument for this is a diagram comparing the reconstructed local temperatures to North Hemisphere anomalies, but I don't see that diagram as a very close fit. Maybe I don't understand how the color coding works in the diagram. Anyhow, there is no statistical analysis. It is true that global temperature rises through the last century (almost certainly to a large extent due to AGW, but that is not the subject of this post), and it is also true that local temperatures rises in the same period. The part where I feel that the argument is not completely convincing is in the link between global and local temperature, that is, do we know that the local unprecedented rise in temperature is caused by AGW? -
mspelto at 02:03 AM on 21 May 2010Unprecedented Warming in Lake Tanganyika and its impact on humanity
The warmth of Lake Tanganyika parallels the demise of the glaciers in the nearby Rwenzori Mountains , Mountians of the Moon. Which have lost more than 75% of their area in the last century. -
Berényi Péter at 01:52 AM on 21 May 2010Has the greenhouse effect been falsified?
#44 sylas at 21:20 PM on 20 May, 2010 You currently my new best friend You are welcome :) As for the 80% transmittance, I think we may need to be a bit careful I think the atmospheric transmittance spectrum is for clear sky conditions. It can't be a global average, since about half the skies are covered by clouds at any moment and they are opaque to IR (zero transmittance). However, it is far from being opaque in the mid IR window (optical depth ~0.22). Still, Fig. 1 (a) has a problem. Using Planck's formula for blackbody radiation
with ν = 100cκ (c is the speed of light, κ is wavenumber in cm-1) at 260 K peak of spectral radiance is found at 510 cm-1 to be 100 mW m-2 sr-1 cm indeed as shown by the second dashed line from above in Fig. 1 (a).
On the other hand, since IR transmittance in window is ~80%, spectral radiance coming from the ice sheet surface and measured at an altitude of 20 km can not be proper blackbody radiation, it must be an attenuated version of it. In other words the surface is seen as a grey body from there with emittance around 0.8 even if the surface itself is a close approximation of a black body in this frequency range. This must be so as in the stopband atmospheric absorptivity is orders of magnitude higher than in the window, therefore according to Kirchoff's law, almost all of the absorbed radiation after having got thermalized, is re-emitted outside the window.
It means the radiance curve in Fig. 1 can not be produced by actual measurement or if it was, what is shown is a scaled up version of values measured. Undocumented tricks like this are not helpful.
BTW, there are some actual IR transmission data for two observation sites (Cerro Pachon, 2700 m and Mauna Kea, 4200 m). It looks like at high altitudes with low atmospheric moisture IR windows get quite transparent. However, Barrow, Alaska is at sea level (elevation 3 m).
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Philippe Chantreau at 01:49 AM on 21 May 2010Has Arctic sea ice returned to normal?
And Robhon, to answer your question @52, the folks at WUWT are probably not being totally disingenuous, at least not all of them. Some genuinely do not realize that there is no sunshine up there during winter time. Nofreewind's complete lack of comprehension of your question and his ensuing post, talking about other things, should give you a clue. -
Phila at 01:39 AM on 21 May 2010Unprecedented Warming in Lake Tanganyika and its impact on humanity
#22 Marcel Bökstedt "This could be due to global warming, but in principle it could also be due to other factors. Bérenyi Péter bring up deforestation, that is certainly an alternative to consider." AGW and "other factors" are not mutually exclusive, of course. -
Philippe Chantreau at 01:38 AM on 21 May 2010Has Arctic sea ice returned to normal?
Checking again NSIDC today, it seems the recent slope has persisted and extent is now below the 2007 extent, over 2 standard deviations below average. That makes it a rather fast spring melt and it interestingly correlates with M. Pelto comment on this spring's fast snow melt. Anyone claiming that Arctic sea ice has returned to normal needs to have his/her head examined (and not by a blog scientist). -
Unprecedented Warming in Lake Tanganyika and its impact on humanity
Marcel writes "The article in question seems to establish that a rise in the local temperature of lake Tanganyika leads to a drop in biological productivity. It does not really discuss whether the local warming is related to global warming." Actually that's exactly what it does. From the abstract: "We conclude that these unprecedented temperatures and a corresponding decrease in productivity can be attributed to anthropogenic global warming, with potentially important implications for the Lake Tanganyika fishery." They conclude this based on close correlations between lake surface temperatures and global temperatures over the last 1500 years. -
Marcel Bökstedt at 00:55 AM on 21 May 2010Unprecedented Warming in Lake Tanganyika and its impact on humanity
The article in question seems to establish that a rise in the local temperature of lake Tanganyika leads to a drop in biological productivity. It does not really discuss whether the local warming is related to global warming. Even in the majority view, the relation is not so simple : There is supposed to have been local warming during the "Medieval warm period" but no global warming. Also, the local warming at Tanganyika is estimated by Tierney etc. to about 2 degrees from 1860-1990, much more than the usual estimates of global warming during the same period. In addition to this, the paper argues that the local warming during the last century has been unprecedented. This could be due to global warming, but in principle it could also be due to other factors. Bérenyi Péter bring up deforestation, that is certainly an alternative to consider. -
jtierney at 00:39 AM on 21 May 2010Unprecedented Warming in Lake Tanganyika and its impact on humanity
Hi Skeptical Science, thank you for your excellent post on our research! Brief comment about Willis' critique (Willis as many readers know is a climate change denialist). We did indeed calibrate our proxy, and the calibration equation and data are available in the supplemental information which Willis himself provides a link to. For more info. on some of the common misunderstandings of our work, please visit the page on my website: Lake Tanganyika Warming -
thpritch at 00:32 AM on 21 May 2010Unprecedented Warming in Lake Tanganyika and its impact on humanity
I find it interesting that the two trend lines showing a decrease in surface air temperatures both stop at 1975 when all the actual recorded temperatures start to show a significant positive overall slope. I will concede however that the Tieney proxy lineis not accurately reflecting the temperature trends for the 1950-1975 time period probably due to some other factor affecting that proxy data. But after 1975, the proxy data seems to generally follow the rise in surface temperatures actually being recorded. Again, it is not an exact match but that is likely due to the contribution of whatever factor(s) was throwing of the 1950-1975 data. -
Riccardo at 00:02 AM on 21 May 2010Has the greenhouse effect been falsified?
sylas, we definitely need to be carefull before claiming something based on a graph which we do not know what's showing, as Berényi Péter did. Indeed, although the overall behaviour is similar in all the spectra one can find over the internet, typically they are just to illustrate the general behaviour, not intended for quantitative analysis. Here's an exaple of two spectra from the same site, one shows 90% trasmittance, the other 100%. But there's one more fundamental error that Berényi Péter did. He apparently thinks that there's a direct relation between transmittance level and temperature. Even without other light extintion mechanisms (e.g. scattering), there's no such relation except in the saturated part of the spectrum. Indeed in the intermediate cases scientists talk about brightness temperature, not temperature alone. Then, i find your claims in the context of the general description perfectly valid. -
tobyjoyce at 23:54 PM on 20 May 2010Unprecedented Warming in Lake Tanganyika and its impact on humanity
Willis Eschenbach has posted a critique of the paper at WUWT, of which the above is the centrepiece.
Bujumbura and Mbala are two weather stations on the lake, and the chart sows the air temperature. he therefore attacks the statement "The surface temp. tracks with the air temperature over the last half-century". However, WE conveniently takes the "last half-century" back to 1950.
His other criticisms may have more merit: showing a comparison with the Northern Hemisphere, rather than the Southern, since the lake is in the souther hemisphere.
He also claims the numbers disagree with a paper of the same authors published in 2008.
Another criticism which I do not understand is "not calibrating their proxy."
"It turns out that they used a proxy called TEX86, which has been used in other studies. But how did they calibrate the proxy to the lake surface temperature (which they call “LST”)?
Well … they didn’t calibrate it. In their theory, no calibration is needed. However, that seems like a very problematic assumption, as there are always confounding factors for proxies that mean that they need to be calibrated to the instrumental record. Some of these factors are listed in their Supplementary Information."
On balance, I don;t think any of these stands up, except maybe for the last one. He did not mention the decline in productivity of the lake.
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dhogaza at 23:53 PM on 20 May 2010Unprecedented Warming in Lake Tanganyika and its impact on humanity
Oh, that should be "described" species - there are undoubtably more. The lake is big, as was pointed out above by someone. -
dhogaza at 23:52 PM on 20 May 2010Unprecedented Warming in Lake Tanganyika and its impact on humanity
This lake also has the most diverse cichlid population in the world, biological diversity which is at risk. Here's a chart showing a single genera: http://www.uni-graz.at/~sefck/Lake.jpg and there are something like 40 genera and 150 cichlid species endemic to the lake. -
Turboblocke at 23:31 PM on 20 May 2010Unprecedented Warming in Lake Tanganyika and its impact on humanity
Surely land change uses etc are irrelevent for the surface temperature of a lake that's nearly 700km long and 50 wide? Looking at it on Google Earth, it doesn't seem to be densely surrounded by habitation. -
Ari Jokimäki at 23:10 PM on 20 May 2010Unprecedented Warming in Lake Tanganyika and its impact on humanity
#5 paulm: This might be good place to look for lake reconstructions: NOAA Paleoclimatology, and here's their lake reconstruction index. -
michael sweet at 23:10 PM on 20 May 2010Unprecedented Warming in Lake Tanganyika and its impact on humanity
CBDunkerson x2. This blog describes the effects of global warming. That does not mean that the authors of this paper think deforestation is not important. The effects of deforestation are additional anthropogenic caused changes. Most changes in large biological systems will have multiple causes. Determining how much is due to different causes is the interesting science. This paper claims warming is a major cause of the decline of fisheries in this lake and provides data to support their claim. -
CBDunkerson at 22:40 PM on 20 May 2010Unprecedented Warming in Lake Tanganyika and its impact on humanity
Lake sediment analysis seems to be becoming an increasingly common proxy for temperature reconstructions. Hopefully this means that future studies will have more extensive southern hemisphere data to draw upon. As to whether temperature or land use change has impacted the fish... well, the Tierney 2010 paper seems to show that temperature has consistently done so in the past. Therefor, it seems likely to be doing so now as well... but that doesn't preclude the land use issues from ALSO being part of the current problem. -
sylas at 21:20 PM on 20 May 2010Has the greenhouse effect been falsified?
Berényi, you are right again. You currently my new best friend, and I really appreciate the editing work you are doing for me. D'oh. I was looking at the lines as being 20K separated, but of course it is 10K, and so the numbers in the post need to be fixed. I put this together in a bit of a rush before going on an overseas trip... and in fact I am posting this now from an airport hotel. As for the 80% transmittance, I think we may need to be a bit careful. There's a difference between the general mean over the whole planet and a specific spectrum observed at a certain time and place, which I am told was under clear sky conditions. But for the time being the worst error is with the numbers and I'll get that fixed first. What I am trying for here is something that is as straightforward as I can make it, suitable for a wide range of readers. I do appreciate there are all kinds of subtleties involved in obtaining surface temperatures with microwave brightness, but I did think these particular two spectra, which were taken simultaneously, gave one of the clearest direct observations of the greenhouse effect I have seen. I know that Tobin's team did take measurements over Barrow, but I am not 100% sure that this is from there. The diagram itself is not from a published paper, but from data that David Tobin provided to Grant Petty, and which he plotted for his text book. If you have concrete suggestions for better wording in any part of the essay, please go ahead and made the suggestions. You've been a great help! Sorry if I am a bit rushed over the next week or two, but I'll try and pop in here periodically while I am on the road. -
Arkadiusz Semczyszak at 21:06 PM on 20 May 2010Unprecedented Warming in Lake Tanganyika and its impact on humanity
1. "The deforestation that has occurred in Mt Kenya, Mau, Aberdare, Mt Elgon and Kaptagat forests has negatively affected watersheds." "Due to the loss of forest cover, the ability of water catchment areas to regulate run-off has been reduced, with subsequent flooding. The area under forest cover has rapidly diminished from 165,000 hectares in 1988 to 80,000 hectares in 2003." "The deforestation of the Mau Forest has continued unabated, Nuttal said, noting that charcoal burning and farming activities were the main causes of the destruction. An estimated 11,000 sq km of the forest have been affected by the destruction. Contrary to conventional wisdom, an estimated 62 percent of precipitation occurs over land as a result of evapotranspiration from lakes and wetlands and dense vegetation, particularly forests, which pump ground water into the sky ." Kenya's annual deforestation rate in 1990 - 2005: 12,000 ha / year (...) Does this anthropogenic pressure does not affect on the fish? 2. Palynological evidence of climate change and land degradation in the Lake Baringo area, Kenya, East Africa, since AD 1650, Lawrence M. Kiage and Kam-biu Liu, 2009, "The dry environment is punctuated by a succession of centennial- to decadal-scale wet and dry episodes, disjointed by SHARP TRANSITIONS, including two intense dry episodes that led to drying of the lake at ca. AD 1650 and AD 1720 which coincide with the Little Ice Age (LIA) period in Europe." It is worth noting, that Mann's team and other "hockey teams" - in their reconstructions - multi-proxy; not indicate significantly MWA and the LIA, or the difference between the current temperature (contra MWP) there is significantly greater, than in Tierney 2010 ... -
Berényi Péter at 20:48 PM on 20 May 2010Unprecedented Warming in Lake Tanganyika and its impact on humanity
Before concluding it is just another consequence of global climate processes induced by increasing atmospheric carbon dioxide levels, some reality check is advisable. Effects of Landscape Disturbance on Animal Communities in Lake Tanganyika, East Africa Simone R. Alin at al. Conservation Biology, pp. 1017-1033 Volume 13, No. 5, October 1999 Sediment inundation resulting from large scale watershed deforestation, soil erosion, municipal and industrial discharges, road building, high and ever increasing population density, refugee influx from war zones, etc. may have something to do with decreasing fish production. These local disturbances can even influence lake surface temperatures. -
Riccardo at 19:53 PM on 20 May 2010There's no empirical evidence
PaulK, if the system reached the saturation level of the OLR any change in slope of the forcing, not a reduction, will produce a temporary rising/lowering of the OLR. More, any deviation from perfect linearity of the forcing will produce a trend in OLR as well. The only LW output from climate models i can remember right away is in Forster and Taylor 2006. -
Berényi Péter at 19:32 PM on 20 May 2010Has the greenhouse effect been falsified?
Chris Ho-Stuart at Wednesday, 19 May, 2010 wrote: When you look down from aircraft at 20km altitude (Fig 1a), what is "seen" is the thermal radiation from Earth that gets out to that height. Some of that radiation comes from the surface. This is the parts of the spectrum that follow a line corresponding in the diagram to about 275K. No. The part of the spectrum in the atmospheric IR window (between 8 and 13 μm, i.e. wavenumber 770 and 1250 cm-1) has an approximate temperature of 268 K (-5°C), not 275 K (+2°C), provided the dashed lines do stand for blackbody radiation of temperatures indicated by labels in the figure. A 7 centigrade difference is not negligible. However, not even all of this radiation is coming from the surface. As you can see, clear sky atmospheric transmittance in window is below 80% at all frequencies, variable.
Therefore some of the IR window radiation is absorbed on its way up, thermalized on a different local temperature and re-emitted, quite possibly on frequencies outside the window.
This is why determining actual surface temperature of the ice sheet below (near Barrow, Alaska) from IR window radiation can get quite tricky, even if emissivity spectra of ice and snow makes them almost perfect blackbodies in this frequency range.
Anyway, an ice sheet surface temperature of 275 K as claimed is not possible.
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HumanityRules at 18:57 PM on 20 May 2010Unprecedented Warming in Lake Tanganyika and its impact on humanity
Thanks for the reply. it's just in previous discussions of paleoclimate reconstructions there has been a suggestion that they don't capture the most recent past including the dramatic past 30 years and generally miss the end of the blade of the hockey stick. My memory is that the blade on the Mann reconstruction only becomes greater than the natural variation of the past when you splice on the instrument record. Anyway, I discovered some further reading on the subject. There was a similar paper in Nature in 2003 Nature 2003 A comment by Willis W. Eschenbach Eschenbach comment And a reply to that by the original authors Reply to Eschenbach -
HumanityRules at 18:30 PM on 20 May 2010Unprecedented Warming in Lake Tanganyika and its impact on humanity
Sorry John I know you said no MWP here but everybody else is, and I have to follow the crowd. It's worth noting if Johns global MWP global image is from Mann 2009 then there is only one single data set for the whole of Africa on that reconstruction. My understanding of that Mann global is from the scarse data in the MWP they have assumed a La Nina type weather pattern and have filled in the large expanses of the globe that have no data. #4 Barry If there are 40-odd data sets covering teh MWP then very few (~6) cover the whole of the SH. John do you have any idea what date the sediment record would be measuring to? (i.e. does this technique capture the temperature of the past few decades?)Response: "I know you said no MWP here but everybody else is, and I have to follow the crowd"
I lose control of the class all too easily :-(
"do you have any idea what date the sediment record would be measuring to?"
A close-up of their temperature reconstruction (in the paper, the Figure 1a inset) seems to indicate the data ends in the late 1980s (best guestimate from eyeballing the graph is 1988) but I can't find anything stating that date explicitly. Maybe it's in the supplementary material which I don't have my hands on right now. -
thefrogstar at 18:21 PM on 20 May 2010Has the greenhouse effect been falsified?
.....but if it was so cold that the water vapor froze out of the atmosphere, then life might not have evolved, so the earth might still have a reducing atmosphere with lots of ammonia and methane which might warm the earth up so that life could evolve which....... !!!!! Is LOL the word? -
tobyjoyce at 18:11 PM on 20 May 2010Unprecedented Warming in Lake Tanganyika and its impact on humanity
@barry & sceptical student, Sorry to bang on about the Medieval Waming Period,but its seems to me to begin later in the Lake Tanganyika chart (more like 1100 than 950, which is usually considered the start of the European MWP), so it is offset from the European phenomenon - which is what John stated. -
Paul D at 18:02 PM on 20 May 2010Has the greenhouse effect been falsified?
35 Monkhausen, re water vapour. There is a significant difference between water and CO2 though in the range of temperatures that exist on earth. That is water can rapidly change between gas, liquid and solid. CO2 doesn't. Hence it is more likely that CO2 will influence water, eg. more or less water vapour, depending on how much CO2 is in the atmosphere. Making water a feedback mechanism. Although water vapour may be a greenhouse gas, I think water in general and its relation to CO2 at earth temperatures gives a bigger and better 'picture'. -
Paul D at 17:50 PM on 20 May 2010Has the greenhouse effect been falsified?
Thanks Chris @ 28. A nice and clear explanation. -
Arkadiusz Semczyszak at 17:47 PM on 20 May 2010Unprecedented Warming in Lake Tanganyika and its impact on humanity
"... and that the recent anomalous warming is a response to anthropogenic greenhouse-gas forcing." East Africa is the least appropriate place is to prove similar assertions. 1st Over the past half century there has been unimaginable to the land-use change - deforestation. 2nd At this time there appeared a huge natural increase - the largest in the world and human history. "In addition to land use change, aerosol forcing in the NBL may play a role. In East Africa the common practice of burning biomass for warmth, cooking, and light, especially in the early evening, tends to fill the shallow NBL of these communities, where most weather stations are sited, with a visible layer of smoke. Additionally, the large smoke aerosols, smaller hygroscopic aerosols, and larger coated organic aerosols may readily swell when the humidity reaches 80% (common in East African evenings). In combination, these produce a nighttime pall that is characteristic of the underdeveloped world. Although the magnitude of aerosol forcing in East Africa is not known, model studies in Los Angeles, California, where the concentration of large thermally active aerosols is likely much smaller than East Africa, showed that the presence of aerosols accounted for an enhancement of nocturnal downwelling radiation of 13 W m~2 (Jacobson 1997). A recent study in India, where aerosol forcing may be similar to East Africa, attempted to account for their role and estimated a daily mean of downwelling radiation enhancement from aerosols of 6.5 to 8.2 W m^sup -2^ (Panicker et al. 2008.)" - Surface Temperature Variations in East Africa and Possible Causes, Journal of Climate 2009, Christy et. al. 3rd Although the final proposal, however, the work is valuable - makes clear MCA (which everyone noticed). -
MarkR at 17:42 PM on 20 May 2010Unprecedented Warming in Lake Tanganyika and its impact on humanity
Skepticstudent; it may be another case of how many graphs you're shown are cut off in 1950. If you cut the Tanganyika graph off in 1950 it looks like the MWP was comparably warm there, which is a reasonably common outcome. Like barry, I'm interested in how you've concluded that a) it was warmer on a global average and b) it was probably therefore warmer everywhere than today, when most composites say different. -
thefrogstar at 17:20 PM on 20 May 2010The significance of the CO2 lag
fydijkstra (#29) Your first paragraph: Good point, I think. I think it helps illustrate some of the problems with feedback-effects in what I would loosely call "self-referencing systems" By way of a verbal analogy (and with no political point), this reminds me of "strong market" Economists who can be very fond of heavy-duty mathematics without emphasizing some of the pitfalls. Strong- (or "efficient")-market theories hold that the movements of markets are forward-looking, efficiently and rapidly incorporating all important information as it becomes available. So (in the absence of earthquakes etc) stock-market prices today already efficiently anticipate the future, which is why individuals can't "beat the market". And there are some good reasons to believe this, not least because central bankers effectively tell banks what the next interest-rate movement will be, (even though they won't tell the rest of us.) But as soon as you ask the question "So do efficient-markets anticipate the actions of the market itself ?" then it rapidly appears that you may have stumbled on a paradox, and that "The Emperor has no Clothes". -
Paul Magnus at 17:14 PM on 20 May 2010Unprecedented Warming in Lake Tanganyika and its impact on humanity
Thought the MWP was only in Europe? Do we have any other lake reconstructions? That would be interesting? -
barry1487 at 17:12 PM on 20 May 2010Unprecedented Warming in Lake Tanganyika and its impact on humanity
skepticstudent, Can you not see a warming bump around the MWP period in that time series? It looks to be in roughly the right place - 1100 to 1400 AD. From where do you get the notion that medieval temps were warmer than today's? The mainstream conclusion is that this is unlikely (though not absolutely certain) - for the Northern Hemisphere. How does a 'skeptic' arrive at a certain opinion on the MWP? You may be familiar with this map from skeptical webssites, entitled "The Medieval Warm Period - A Global Phenomenon". However, an examination of the time series therein shows that MWP for different regions are offset by as much as 500 years. From the 40-odd data sets, we see that MWP was a regional event, with the timing quite different in different parts of the world. Crunching the numbers we get an MWP from ~950 to ~1250 with a lower amplitude than that suggested by certain data sets. Paleoreconstructions of the period rest on anywhere between ~20 to hundreds of data sets. What study/s gives you absolute confidence that "the temps then were much higher", and how do you manage to hold that opinion when the weight of evidence (the great majority of scientific studies) posit alternatively? http://agwobserver.wordpress.com/2009/09/08/papers-on-the-mwp-as-global-event/ Note: the IPCC considers MWP for the Northern Hemisphere, assessing that there is not enough data for a global analysis with much statistical significance. Lake Tanganyika is just below the equator. -
skepticstudent at 16:38 PM on 20 May 2010Unprecedented Warming in Lake Tanganyika and its impact on humanity
I am kind of curious that even though their graph looks like it has no corellation to the medevil warming period like a certain other chart mentioned in comments 1 and 2. How do they correlate no high temperatures in the lake at a time when the temperatures were considerably warmer than they are now? Shouldn't the left of that chart be much higher than it is since the temps then were much higher than the right side of the chart? I know I'm not a scientist but something just seems wierd. I suppose one could stretch the hypothesis by saying that it was cooler regionally in this particular spot than the rest of the known world.Response: It's an interesting question and in fact, the paper does compare the Lake Surface Temperature (LST) to the Northern Hemisphere temperature reconstruction. I left that part of the paper out of my blog post for reasons of brevity (okay, I was lazy, are you happy?!). Here's the graph with the black area showing the LST and the coloured range showing the Northern Hemisphere 'hockey stick':
Note that while certain regions during the Medieval Warm Period were hotter than current condition, the global average was cooler than today. Here's a temperature map of the Medieval Warm Period. Temperatures are relative to the 1961 to 1990 period. So if a region is yellow, orange or red, it's warmer than the 1961 to 1990 period. There are various regions that were warmer than the late 20th Century. But there were other regions that were cooler also, denoted by the blue regions.
I suggest discussions of the Medieval Warm Period are best conducted at the Medieval Warm Period page. -
Bern at 16:23 PM on 20 May 2010Unprecedented Warming in Lake Tanganyika and its impact on humanity
doug_bostrom: yes, it does look somewhat familiar... would that be an MCA in the middle and a (shock!) 'hockey stick blade' at the right? :-D It's interesting, though, to see more papers like this coming out, where scientists are tying reconstructions of temperature to other data types, and working out the potential effects of temperature change. -
HumanityRules at 16:22 PM on 20 May 2010Has the greenhouse effect been falsified?
33.chris Thanks Chris very clear, I think it was the word "required" that's throwing me. I'm going to say I get it now. -
Doug Bostrom at 15:20 PM on 20 May 2010Unprecedented Warming in Lake Tanganyika and its impact on humanity
"Salmon then feed off the algae." I'm thinking you meant sardines there, John! That graph has an eerily familiar shape to it.Moderator Response: Oops, thanks for spotting that. Fixed. -
scaddenp at 14:58 PM on 20 May 2010Has the greenhouse effect been falsified?
Actually this has been both discussed and calculated. See the detail with links to calculation and code at: Calculating the greenhouse effect Short answer - it would be very cold without water. Around 20 deg colder. -
shawnhet at 13:46 PM on 20 May 2010The significance of the CO2 lag
A couple of points to keep in mind here: CO2's feedback effect is very small, compared, say to the hypothetical water vapor feedback. A degree C increase leads to a release of ~10ppmv of CO2, which by the logarithmic relationship of CO2 and temperature increases the temperature by ~.1 times the sensitivity. Ultimately, this means that we can't use the CO2 time lag to diagnose sensitivity in *either* direction(as either positive or negative). Secondly, it is pretty hard to take the 20ppmv/deg C number seriously, when just by eyeballing the graph of CO2 and temps, we see that there the actual relationship is more like 10ppmv/deg. C. If, in fact, the 20ppmv number were the correct one, we would be forced to conclude that the correct pre-industrial value should be approximately 340ppmv CO2(ie the depths of the ice age had temps 8C lower at a CO2 concentration of ~180ppmv if each degree of warming released 20 parts of CO2, the 1600s should've had an atmospheric CO2 level of ~340ppmv. Cheers, :)
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