Thank you for the article. What impact, if any, does soot and black carbon from fires have on the glaciers of Kilimanjaro?
[Response: I was wondering about soot myself, given that the high reflectivity of pristine snow plays such a role in the energy budget of all glaciers. On Kilimanjaro (the Kibo peak, more properly), the albedo measurements have only been in for a little while, and have not yet been published. The modeling in Moelg and Hardy is done using an albedo model for clean snow and ice, which yields similar values to those measured in the Antarctic. It will be interesting to see if the measured albedo in situ calls for some revision in this. It occurs to me that it would be possible to check for dust and snow effects directly by just melting snow/ice and filtering, but I'm not aware that this has been done with an eye to determining soot content. Perhaps if one of the glacier-observing crowd out there is reading this they can chime in. Given the altitude, if I had to guess, I'd guess that soot and dust was not playing a big role at this site. -- rtp ]
Reading this, I am struck by how such small warming changes in the tropics have set off big changes in low-latitude high-altitude glaciers, just as small changes in the Milankovitch variables create large-scale climate changes making the Ice Ages and interglacials over thousands of years. In this case, however, the changes are very rapid — these glaciers have been robust over the same time scale (many millennia). The misleading use of Kilamanjaro (deforestation?) by skeptics is reprehensible given the general meltdown. Glad to see Lonnie Thompson’s work here on RC.
“…Analysis of satellite data by [Fu et al, 2004] reveals a tropical mid-tropospheric temperature trend that continues into the post-1979 period, at a rate of about .16 degrees C per decade…”
Wasn’t the referenced Fu et al, 2004, the Nature article that John Christy and Roy Spencer claimed was due to improper methodology they had previously throw into the trash? Wasn’t it the article whose methodology was criticized in another Nature publication later in the year (Tett and Thorne) – particularly when it came to the tropics? Didn’t Fu susequently change his methodology for a publication later that year in the Journal of Climate?
[Response:This comment has largely been addressed by subsequent responses. Fu did not "change his methodology," but rather re-computed the results using somewhat different methods as a cross-check, and indeed found that the results were robust. Teasing reliable trends out of satellite data will never be easy, and I'm not claiming that Fu will necessarily be the last word on this subject. Still, it's a very defensible methodology. What is clear is that Spencer and Christy's analysis was contaminated by stratospheric cooling effects; Fu provides one way to compensate, and no doubt other ways will emerge in the future. If we had a completely reliable instrumental record of tropical mid-tropospheric warming, we wouldn't be talking so much about using tropical glaciers as indicators of climate change, would we? What strikes me as strange in the satellite business is that, in a subject where everybody agrees that the data analysis is hard and difficult to do, Spencer and Christy just accepted their original analysis, no matter how inconsistent it appeared with other data, and trumpeted it widely. One cannot fault them for making mistakes in this area, but one can fault them for leaving it to other groups to find and correct their mistakes. --rtp]
Comment by Michael Jankowski — 24 May 2005 @ 8:51 AM
The Fu article must have still reached the requirements under the peer-review process if it made it into Nature. I guess the later criticism, even if it were valid, did nothing to throw the article’s findings into disrepute. Maybe the Tett and Thorne criticisms were taken into account and Fu improved on the previous study (which would make the J. of Climate article’s findings even more solid).
Many thanks for the interesting and detailed article.
Regarding the satellite data, there is a detailed (4 Mb pdf) article by Scott Church which I found informative- page 59 onwards discusses the Spencer and Tett and Thorne criticisms.
Along the same lines, have you considered a RealClimate article on the satellite record? Even though the exact warming trend seems to be hotly contested and not clear, it would at least be a useful counter to those claims (still repeated) that it doesn’t show warming or falsifies the surface record, as well as being interesting in its own right.
[Response:It would be an excellent idea to have a RealClimate piece on the satellite record. I volunteer to do that in the Fall, after Fu's new article comes out, provided somebody reminds me. If there are any takers who want to do it sooner, please be my guest.--rtp]
Re#4 – I’ve seen conflicting reports of what the Dec 2004 Journal of Climate trend was reported to be. Spencer says it’s as low as 0.09 deg C/decade for the whole troposphere, which is much closer to what Christy and Spencer report for the lower troposphere. But I’ve seen press releases claim Fu shows a full 0.2 deg C/decade, which is what the Nature article had claimed. Maybe those are just the high and low end estimates based on error?
The Tett and Thorne criticisms were published at basically the same time as Fu’s JofC article, so I’m not sure they were incorporated. Christy and Spencer still see methodological flaws they feel introduce errors.
Re#5 – One of Spencer and Christy’s complaints was that they didn’t get an opportunity to review and comment on Fu’s article despite being arguably the top experts in the area (and despite usually getting to review submissions on the topic). They found some of the errors embarassing and unacceptable for publication. Other people see otherwise, but it still seems peculiar they wouldn’t have been asked to review.
Re#6 – That’s a lot to digest! I did see a few things upon cursory review of the section on Fu that I have issues about. I’ll have to revisit it when I have a lot of free-time!
Comment by Michael Jankowski — 24 May 2005 @ 2:09 PM
This is a great post. It took a long time to read it all but it is very informative. Many thanks to Raymond Pierrehumbert and to Thomas Moleg for the comment on the previous post.
I like to think that I have learned a good amount of the basics of climate change science from reading Realclimate. I am going to but some of my new-found knowledge to the test:
re #1 my educated guess about the effects of soot on glaciers would be if the soot were to settle on the glaciers it would have the same effect of natural soil and rock. Snow reflects most of sunlight but soot, like soil and rock has a lower albedo (am I using the term correctly?) and instead of reflecting sunlight absorbs it. When the soot absorbs the sunlight it warms and could increase the melting of the glacier.
On the other hand, this is a big maybe, soot and other pollution when it is in the air I am guessing could reduce the strength of sunlight that reaches the glacier and this possibly could reduce the melting.
If I don’t know what the heck I’m talking about please feel free to tell me!
[Response: You are mainly correct. Soot levels in alpine glaciers for instance are much larger than in Greenland (because of the proximity to the sources) and the same is likely to be true for tropical glaciers near areas of biomass burning. However, although this can have an effect on the albedo (as can dust from the Sahara), most mountain glaciers are extremely 'dirty' already and are only really bright when there is fresh snow fall. Maybe someone knows a study that has specifically addressed that for tropical glaciers? - gavin]
[Response: The ablating "tongue" regions of midlatitude Alpine glaciers are very dirty. Oerlemann's albedo parameterization gives albedos as low as around .3 for ablating ice, which looks a lot like pure dirt. In their Kilimanjaro modelling, Moelg and Hardy adjusted the albedo model to give values more like those of clean Antarctic ice, and get reasonable-looking ablation with these values. That suggests that the high Tropical glaciers are pretty clean. More will be known once the albedo measurements are available. --rtp ]
Comment by Joseph O'Sullivan — 24 May 2005 @ 6:15 PM
A related story:
New research published in Science Express reports on results showing the East Antarctic ice sheet is thickening, thus partially offsetting sea level rise due to the melting in the WAIS, Greenland and the world’s glaciers. Here’s a Science Daily news release A race through thick and thin ice on the story. A related story about some results of the British Antarctic Survery has been published here by the Chicago Tribune.
These results confirm behaviour predicted by climate models showing that greater snow cover should occur in this ice sheet.
Read the article with great interest. Thanks for author’s effort.
Although I might not take it for granted that the horizontal homogeneity of temperature due to the dynamic adjustment in the tropics would guarantee the horizontally uniform temperature changes in the decadal scale, the data do show it! The attached figure shows the tropospheric temperature
trends versus the surface temperature trends in units of K per decade for 1979 – 2004: the tropospheric temperature trends are astonishingly uniform along the equator with a variation of about a factor of 5 smaller than that in the surface temperature trends. For 1979-2004 over the tropics (30S-30N) the tropospheric temperature trend is about 0.195 K/decade.
Hello, slightly offtopic here, but recently there were press reports about findings of very fast and extended glacier retreats in the Swiss Mountains several times during the last 7 or so millennia. To my impression, these findings don’t in any way contradict AGW findings, rather give more detailed insight in local glacier growth and retreat in history. Yet the “sceptics” jump on these findings similar as they did with tropical glacier retreat (hence my article here). Any comments?
Re#4 – It’s my understanding that the warming of the whole troposphere went from 0.2 deg C/decade (according to press releases) in the first pub to 0.09 deg C/decade in the 2nd (according to Roy spencer). Press releases still claim that the 2nd article backs-up the 1st claim of 0.2 deg C/decade. Maybe the varying reports are due to low and high range error bars?
Re #5 – Christy and Spencer have been quite critical that as arguably the top experts in the analysis of satellite date for temperature information, they have stopped receiving papers for review as part of the peer review process (in particular, they were upset at not receiving the Nature article for review due to the errors they felt were significant and obvious to them).
I don’t think Fu’s 2nd paper took into account T&T’s critique because they were both published at about the same time (same month, I believe).
Comment by Michael Jankowski — 26 May 2005 @ 12:26 PM
In regards to Michael Jankowski’s comment (#11), the Fu et al. (2004, Nature) article showed that the satellite record of tropospheric temperature trends, based on the Microwave Sounding Unit channel 2, is contaminated by stratospheric cooling on the order of -0.08 K/decade. When this contamination is removed from the Remote Sensing Systems channel 2 record, the resulting tropospheric trend is 0.18 K/decade during 1979-2001. When it is removed from Spencer and Christy’s channel 2 record, the trend is 0.09 K/decade. Fu and Johanson (2004, J. Climate) derived the same stratospheric contamination in the channel 2 record as Fu et al. (2004), but through alternate methodology. This article served as an independent check of the original results.
The issues raised by Tett and Thorne (2004, Nature) were effectively rebutted by Fu, Seidel, Johanson, and Warren in the same issue of Nature (Dec, 2004). See the response to Tett and Thorne here.
Comment by Celeste Johanson — 26 May 2005 @ 1:59 PM
I’d like to thank Quian Fu (#9) for commenting here. And since he as done so, perhaps comments like Michael Jankowski’s could be addressed to him instead of me (#4) or Stephen Berg (#5).
What I get from Fu’s paper is that the tropics are warming at 0.13C/decade at the surface (citing Jones and Moberg, Journal of Climate 16, 206-223, 2003) and that the troposphere is warming at 0.18C/decade generally (Fu et. al 2004) and, from his comment here, 0.195C/decade in the tropics. This certainly speaks to the rapid ablation of tropical glaciers. The tropics are not warming nearly as much as the high latitudes of the northern hemisphere. So the tropical (30N-30S) surface warming is less than the global surface trend of about 0.17C/decade – but again, apparently still enough to have substantial effects on tropical glaciers.
I hadn’t noticed that Dr. Fu had posted here until now. I didn’t see my first posting (#7) show-up for a day or two, so I thought it had gotten lost or discarded for some reason, hence my second and quite simlilar post #12. I apologize for the duplicity.
As for the addressing of the posts to you or Stephen Berg, my comment about peer-review in #7 and #12 is a direct response to the issue raised by Stephen Berg in #5.
As for addressing my comments in general to Dr. Fu himself (had I known he was posting/reading here): I simply pointed-out that Christy and Spencer (and others) have taken issue with Fu’s approaches and results. I know Dr. Fu is well aware of this, but I was not sure all of the readers were.
Thanks for the clarifications. I hope to be able to read all of the satellite-derived temperature articles at some point instead of just getting what I can from press releases and commentaries.
Comment by Michael Jankowski — 27 May 2005 @ 9:16 AM
What I get from Fu’s paper is that ……and that the troposphere is warming at 0.18C/decade generally (Fu et. al 2004)
It depends which record you use, i.e RSS or UAH (Spencer & Christy).
It’s 0.18 K/decade for RSS but only 0.09 K/decade for UAH. I think what Fu & Johanson are saying is that Channel 2 receives about 85% of it’s signal from the troposphere and the rest from the stratosphere. Since the stratosphere has been cooling this has damped the effect of the warming in the troposphere. The cooling effect is about -0.08 K decade.
As far as I know Spencer & Christy don’t actually use Channel 2 (T2) readings directly but use some method which removes the stratospheric signal. This gives a warming trend of about 0.06 K/decade.
I’ve briefly read the Fu et al link. They seem to have used a linear combination of T2 and T4 (stratosphere exclusively) to determine the ‘true’ tropospheric temperature. They obtained the coefficients for T2, T4 by equating the readings with radiosonde observations.
Can anyone confirm that I have got this right – thus far?
If so why not just use the radiosonde readings?
I’ve just noticed that the last post to this thread was almost a week ago so I may be wasting my time.
[Response:Some of us are still reading the comments! You have the basic picture essentially correct. The reason for not using the radiosondes directly is that they have rather spotty spatial coverage. The idea is to leverage the radiosonde data by using them to help calibrate a satellite retrieval method in regions where there is overlapping data, which can then be applied to a much bigger data set. --rtp ]