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Reactions to tighter hurricane intensity/SST link

Filed under: — gavin @ 20 March 2006

There was another twist to the hurricanes/global warming issue in Science Express on Friday where a new paper from the Webster/Curry team just appeared. This study, lead by Carlos Hoyos, crosses a few t’s and dots a couple of i’s on the connection of increasing numbers of intense hurricanes (Cat. 4 and 5) to sea surface temperatures (SST). Basically, they looked at a number of other key variables for hurricane intensity (like wind shear and humidity) and examined whether there was any pattern to those variables across the different ocean basins that they study. Bottom line? None of the other variables have as much explanatory power for the long term trends as SST which is the only consistently trending constituent in the mix. So far, so un-surprising. However, one interesting aspect of this story is that almost all the key players in the ongoing debate were interviewed by different journalists in various media and those comments are probably more useful for gauging the state of play than the details of the new paper itself.

First off, Chris Landsea, a serious researcher in the ‘dissenting’ camp, in the WSJ story (reprinted here) and in a Newsday article is quoted as saying that the data (particularly from the early 70s and the Northern Indian Ocean) aren’t good enough to come to these conclusions. However, Curry riposts that for the doubling of Cat 4 + Cat 5 storms to be an artefact, half the Cat 1 + Cat 2 storms in the early records would have had to have been mis-classified Cat 4 storms instead and she thinks that unlikely. More oddly, Landsea also makes the point that the sensitivity of the hurricane intensity disagrees with model predictions and theory. This is odd, not because it’s not true (and is the principle reason why the attribution of more intense hurricanes to GW is not yet set in stone), but because Landsea has previously been much more of a champion of favoring observations over modelling.

In the same National Geographic piece, Roger Pielke Jr. is broadly supportive and makes his standard comment that the increasing damages from hurricanes is mostly related to increased development rather than changes in intensity, but that obviously, future potential increases in intensity will be an additional factor.

Fox News interviewed Kerry Emanuel (author of a related study last year, which was slightly modified following comments by Landsea in Nature), who is also unsurprised that the longer term trends are related to SSTs and not to any of the other factors. Kevin Trenberth (also in the Fox News piece) made a good point though. The authors of the study used the NCEP reanalysis as the source of their data. A reanalysis is a re-running of the current state-of-the-art weather forecasting model for all the sources of data that were available in the past (i.e. a hindcast of what all the 6 hour weather forecasts would have been if they had used today’s model). These projects (and there are two main ones – NCEP and ERA-40) have a problem in that the amount of useful data increases as you go along – most significantly around 1979 when satellite data starts to be significant. So estimates of key quantities are likely to be worse prior to 1979. Not mentioned, but conceivably important is that the NCEP reanalysis is tied in some respects to the radiosonde data, which, as we discussed last year, may have some spurious trends. This doesn’t obviously affect the results significantly, but it does suggest that doing the analyses again using the ERA-40 data might be a useful check.

So where does that all leave us? Basically, although everyone acknowledges that there are data problems early in the record, it seems clear that there has been a global rise of the most intense hurricanes over the last 30 years and the most obvious explanation is that this is related to the contemporaneous increases in tropical SST in each basin. However, the magnitude of the correlation cannot yet be explained in terms of our basic theoretical understanding, and is significantly stronger than some modelling work has suggested it should be. Possibly the theory needs work (hurricanes are a complicated business!) or there are other factors at play that haven’t yet been considered. Since the SST changes are global, and almost certainly tied to greenhouse gas driven global warming, there are the beginnings of a corroborated link between increases in hurricane intensity and GW – however, so far there are only a couple of ducks in a row.


136 Responses to “Reactions to tighter hurricane intensity/SST link”

  1. 101

    Re #100 (comment)

    Thanks Stefan for your comment. Although I have spent halve of my professional life as process engineer, amongst (many) other things involved with heat flow (be it for chemical processes), I learn everyday a bit more…

    As far as I have read in several of the messages and publications, the THC is the most important item in heat flow from the Atlantic equator to the North Atlantic.
    In a simple heat exchanger, if the heat flow is reduced for any reason (like scaling) the side of the heat source will become hotter (even to rupture in extreme cases) while the heat inflow remains constant, and the other side gets colder. Of course, the oceans are not such simple constructions. But a continuous positive heat inflow at the equator with a reduced heat flow to the poles must lead to an increased heat content (and temperature) of the equatorial oceans, if the laws of thermodynamics still hold. This may be dissipated to the SH (as the graphs you pointed to indicate), but there is little southward surface flow in the Atlantic and I suppose that at least some of the heat should remain in the tropics (as one need a driver for general increased southward flows)…

    Of course, there are other means to dissipate heat to space and other parts of the earth. Like storms and cyclones, changes in cloud cover and air currents. But the latter seems to reduce in a hotter environment too (see Fedorof ea.).

    But, that was not the most important point in my comment. The increase in heat content / temperature of the North Atlantic subtropics may be the result of recent changes in cloud cover, which is – according to Chen and Wielicki – probably all natural. And interesting enough to start a more detailed investigation.

    Btw, the Nature article about the possible solar origin of the 1470 yr climate cycle during ice ages, triggered by shorter cycles, is very interesting.

    [Response: If you’re an engineer it is very easy to understand: the northward branch of the THC flows from South Africa through the Atlantic right up to the Nordic Seas, and it flows through the region we’re talking about (i.e., the hurricane region, ranging roughly from 10N to 30N). It enters this region from the south (coming across the equator) at a warmer temperature than it leaves this region with the Gulf Stream at, say, 30 N. Therefore, the THC acts to heat this region – more so when the THC is stronger, and less when it is weaker. Hope this is clear? You were just looking at one end, and forgot to take into account the connected inflow at the southern end. -stefan]

  2. 102
    Steve Bloom says:

    Re #92: Thanks, Stefan, for that very neat summary. As I’m sure you know, it has long been rumored that that we will be seeing a paper by the NHC’s Bell and Chelliah outlining their case for natural cycle causation. It sounds as if you haven’t seen it or that you’re obligated to stay quiet about its contents as a condition of having seen it pre-pub. Bell will be giving a talk on this subject at a conference in NYC that Chris Mooney will be attending next week, so I imagine we’ll be seeing something on his blog shortly after that.

    What do you think of the Japanese study Chris quotes in #41?

    [Response: Bell and Chelliah (2006) is now available here: http://ams.allenpress.com/amsonline/?request=get-abstract&doi=10.1175%2FJCLI3659.1 – gavin]

  3. 103
    Hank Roberts says:

    > tropics warm up if the THC speeds up
    Perhaps — just guessing — there’s a minimum amount of time any given parcel of water has to reside in the tropics, to pick up all possible heat? If so, a slower THC lets the water hang around to pick up more heat, while a faster THC moves each parcel of water on through while it hasn’t picked up all it could, leaving more behind

    That’s of course ignoring much else. Just saying it can’t be that simple a thermodynamic heat exchanger — much else going on. How much mixing happens while a parcel of water is there, does the THC water always move on the surface or can it slip past below the warm surface, etc.

    Isn’t the AURA satellite study due to be providing some info soon on the whole question of what’s happening with convection in the tropics (from flights in January and February of this year by NASA)?

  4. 104
    Steve Bloom says:

    Re #s 100 and 101: Ferdinand, in #100 you use the phrase “natural influences can’t be ruled out,” which is fair enough, but then like Dr. Strangelove’s arm out pops “probably all natural” in #101. It seems that you are compelled to presume natural causes in everything. Just out of curiosity, why? But anyway, here are the relevant quotes from the relevant papers:

    Wielicki et al: “Whether the changes seen in the radiative balance in the last two decades are the result of natural variability or are a response to global change remains to be determined.”

    Chen et al: “The possibility that lapse rates were decreasing instead before 1980 (23) suggests that the observed intensification of the Hadley-Walker cell may be due to natural variability on decadal or longer time scales rather than to a forced climate change; however, the length of the satellite data record is too short to distinguish between these two driving mechanisms.”

    That seems clear enough.

    Also, with regard to your comment that this would be a fruitful area for more research, note that those two papers are about four years old. Haven’t those authors or anyone else done further work by now? If not, given the timing of the AR4, wouldn’t it be fair to say that this line of research has been abandoned? But please do check and let us know if you find anything that’s more up to date.

  5. 105
    Steve Bloom says:

    Re #s 100 and 101: Well, Ferdinand, it appears it might be a dead end after all, although I didn’t have time for a thorough search so don’t just take my word for that. Have a look at the comment by Trenberth in the same issue of Science as the two papers, the response to the comment and then the remarks on page 6 of the more recent review http://www.cgd.ucar.edu/cas/trenberth.papers/CLConfPaperds.pdf . It’s not clear how much is left of the issue at this point, but perhaps not a lot other than the perennial satellite calibration problem. If you don’t have a Science sub, let me know and I’ll email you the comment and response.

  6. 106

    Re #104 and #105,

    Steve, the issue of instrument accuracy and decay is indeed one of the most important problems as good as on earth (an engineers joke: one instrument in a line is always exact, until you fit a second in the same line…) as even more problematic on satellites. This has given much discussion and reason for corrections in the past (and probably in the near future), until new generations of multi-material/physical different and self correcting instruments are in use. Thus I can understand (and hope with) Trenberth that a lot of money will be spend on better methods to measure and understand what really happens with our climate.

    But despite the (relative small) problems with the radiation budget satellite instruments, even recent (Science May 2005) publications with corrected data show an increase of 0.16 W/m2/yr of global insolation in the period 1983-2001. In the full article, the trend in the tropics is described and even more pronounced: 0.18 W/m2/yr, or over 3 W/m2 for the full period (but in fact increasing only after 1990) of measurement. In the tropics, the difference is mainly (if not completely) from changes in cloud cover.

    This brings us to natural or not. The change in CO2 levels 1983-2001 is app. 30 ppmv. This results in a radiation change of app. 0.3 W/m2 over the full period. This is one order of magnitude less than what is observed. This all points to natural variability.

    Chen and Wielicki use stronger statements in “A Delicate Balance” pages of NASA:

    “We are likely seeing a decadal fluctuation here. Right now we are looking at what might lead to such a fluctuation,” says Chen. He believes that this is a natural climate anomaly much like El Nino, La Nina, or the North Atlantic Oscillation. It is a natural part of the rhythms of the Earth’s climate system. But unlike these other anomalies, the Hadley-Walker cell fluctuates over the course of decades instead of years. Chen feels that this phenomenon has no direct relation to global warming or any other hypothesis related to climate change, including the Iris Hypothesis.

    and

    Wielicki agrees with Chen’s assessment. He adds, “What we are seeing is that the climate system has multiple ways it can arrange itself and still accomplish a heat balance. In this case as the clouds change, the Earth absorbs more heat at the surface while it radiates more heat from the atmosphere.” Wielicki explains that even from the start, this phenomenon appeared to be a climate fluctuation unrelated to global warming or greenhouse gases.

    And have a look at the last pages, which compare the results of climate models and observations. I don’t know if AR4 models are better in equatorial (and Arctic) cloud cover/radiation balance calculations, but if not, then they still are not very good in projecting any future climate…

  7. 107

    Re #101 (comment)

    Thanks Stefan for your comment. I was wondering where the inflow was for the THC, which – in the rough schematics – comes all the way from near Antarctica. Still there are some problems with the overall picture: If one looks at the different Atlantic currents of interest at the Miami University graphs (the Carribean current, the loop current, the Gulf stream and the subtropical countercurrent) for seasonal temperatures, then it happens that the highest temperatures in the summer months, leading to tropical storms are in the 10N-20N band (including the Gulf of Mexico), thus an increase of inflow from the South (due to increased outflow via the Gulf Stream) should have a cooling effect… But an increase in the other seasons can create already warmer waters for the next hurricane season…

    All together quite complicated and rather counterintuitive…

  8. 108
    Peter Webster says:

    I have followed the THC discussion with some interest as the speeding up of such has been used as a shrill argument to explain the increase in intensity of hurricanes in the North Atlantic. Alas, it is a pity that the explanation fails even in the NATL (Bryden et al.). Even if it were successful (i.e., sans Bryden’s research) it would have difficultly explaining like increases that occur over the globe. So without the THC argument, there is a need to find a “global mechanism” to explain the universal change in hurricane characteristics. And Chelliah and Bell (2004, 2006) appear to have such an explanation with the finding of a 100-year cycle called the Tropical Mulitdecadal Mode which, more or less, has a common sign over the tropics.
    Alas, there are problems. C&B use the NCEP/NCAR reanalysis constructed for the period 1950-2000 or so to define a 100-year cycle. The problem is how do C&B differentiate between a 50-year trend and a 100 year oscillation using a 50-year data set? Statistics are tricky things and EOF or Principal Component packages are very adept at producing oscillations longer than the data set if the data set is not detrended.
    Why bother with papers that may have such very basic statistical flaws? Well, these are the papers quoted by NOAA administration in their statement that global warming has nothing to do with the changes in hurricane characteristics during the last decade.
    Please expect vigorous comments (peer-reviewed) on the latest Chelliah-Bell paper.
    PW

    [Response: For that matter, with a 50 year record, how do you distinguish one “mode” which affects SST more or less globally from the global warming trend, which does rather similar things? It sounds a little like the fancy statistics of Bell and Chelliah have just succeeded in renaming the AGW signal the “Tropical Multidecadal Mode.” –raypierre ]

    [Response: Good point. If the tropics had warmed more (or with a differnt time evolution) than the global mean, I’d be looking for a special tropical phenomenon to explain it. But they haven’t. So if you want to explain tropical warming by a special tropical mechanism, you’d also need to explain (a) why this mechanism works exactly in step with global warming, and (b) why anthropogenic global warming has spared the tropics, so that there is room for another explanation. See my comment #92. -stefan]

  9. 109
    Steve Bloom says:

    Re #106: Ferdinand, thanks for citing to a more recent paper, but please note that it doesn’t lend support to your contention that “this all points to natural variability.” The NASA page you quote is just a re-hash of the 2002 papers and is equally out of date. Also, you should have a look at the three related papers and articles in that same May 2005 issue of Science.

    Finally, I’m a little mystified as to the implications of your calculation of CO2 forcing. See http://www.realclimate.org/index.php?p=220 .

  10. 110

    Re #109:

    Steve, the comment of Chen and Wielicki doesn’t need an update, as their original calculation came with a 2 W/m2 increase of insolation in 1.5 decades, while the newer work calculates this as over 3 W/m2 in a similar period.
    The calculation of CO2 forcing for different concentrations can be done at the Archers site. You need to fill in the amount of CO2 for 1983 (~340 ppmv) and 2001 (~370 ppmv), both without changing the rest, except for tropical atmosphere, measurement at 0 km and looking upward. The difference between the two results is what gives you the extra amount of heat coming back to the surface, due to the increase of CO2.

    Of course, this is without water feedback (but that seems to be negative in the period of interest: -upper- tropical humidity reduces with higher Hadley/Walker cell speed) or other feedbacks, but these are probably of lesser importance than CO2 and water (except for clouds). The other important greenhouse gas, methane, has (in the Modtran program) no measurable addition to the result.

    Thus the calculated increase in forcing by CO2 is ~0.3 W/m2, while the observed increase by solar forcing (mainly from cloud cover changes) is ~3 W/m2 in the same period of time. Only if there was a direct short-term strong (tenfold!) influence of CO2 changes on insolation via cloud cover, then this could be mainly/all anthropogenic. But the period 1983-1990 shows a decrease in insolation, with increasing CO2 levels. Thus the change in insolation (and consequently most of the recent warming in the tropical oceans – and beyond?) is largely of natural origin.

    The other related papers in part reinforce the foregoing reasoning.
    The first paper by Charlson ea. points to differences in results between methods to detect changes in radiation budget, calculated as equivalent changes in albedo.
    But several methods detect large changes in radiation budget (in both directions) within 1-2 decades, at the same order of magnitude as the change in GHGs since the start of the industrial revolution…
    The Wielicki e.a. paper is not relevant here, it only discusses the satellite vs. earthshine differences, where satellite measurements are more consistent with observations.
    The paper of Wild ea. confirms that the change in insolation is much too large (decline 6-9 W/m2 1950-1990, increase ~5 W/m2 1992-2001) and variable in sign to be of anthropogenic origin. Neither GHGs or aerosols can explain these near worldwide changes (even in the low aerosol SH). Water vapor/cloud changes seems to be better candidates…

    [Response: Ferdinand, if you’re trying to understand the greenhouse effect by looking at the effect of CO2 on the downward IR into the surface, you are misguided. See my post on “A Busy Week for Water Vapor”. As for the rest, I’ve tried by I really don’t see what point you’re trying to make. You are just quoting a lot of random observations without any real understanding of what they mean. –raypierre]

  11. 111

    Re #110 (comment)

    Raypierre, as usual (bad habit of mine) I was going too fast…
    The discussion was triggered by the comment of Stefan in #92. There he concludes that the increase in SST (and thus tropical cyclones) in the relevant area can not be explained by natural causes. The influence of GHGs may be true (in part) over the long term (1945-2005), but there is a large natural fluctuation, of the same order as the total GHG forcing since the start of the industrial revolution, with a frequency of 2-4 decades (or longer) over the same area. That the change in direct insolation in the tropics (coupled to cloud cover changes) is natural was challenged by Steve Bloom, but it is hardly possible to blame that on GHGs, if the sign of the insolation changes follows its own rhythm, unrelated in area and time frame to aerosols and GHGs.
    Of course, the change in CO2 induced forcing is only a part of the greenhouse effect story, but some of the feedback effects in this specific case, especially water vapor, seems not to follow the normal rules (less upper tropospheric humidity, hence less cloud cover in the down welling branches and overall tropics). But that may be different at lower levels (due to higher SSTs). Anyway, CO2 changes in the past 1-2 decades can’t explain the large change in heat content/SST in the tropics for the most recent period, while one order of magnitude larger changes in forcing by clouds/insolation can do that job.

    Therefore it may be of interest to look at the specific area of interest (and southward to the inflow areas) for areal changes in cloud cover and insolation…

  12. 112
    alisa brooks says:

    In reference to #73: I really do appreciate your answering me without blasting me, but I’m going to stick my neck out one more time on the same issue. Please don’t hit me too badly for being dense.

    I understand that the mesosphere CURRENTLY has very little effect on GW. But reading the following articles keeps me coming back to the question: If GHG is contributing to a colder, denser mesosphere (by way of ice formation triggered by some sort of pollutant), wouldn’t this eventually have a significant effect in overall GW.

    http://geo.arc.nasa.gov/sgp/aero/aerocloud3.html

    http://www.gsfc.nasa.gov/gsfc/earth/atmos/ozone.htm

    http://aim.hamptonu.edu/

    I promise I’ll not bring this up again if I’m reading the wrong papers, have totally missed the mark on what the papers are trying to convey, or am totally off base.

    Thanks!

    [Response: It’s absolutely clear that gaseous radiative effects in the mesosphere have essentially no effect on the Earth’s radiation budget. With clouds, it’s not completely obvious from a back of the envelope calculation, since a quite tiny mass of cloud particles can have quite a large effect, particularly if the particles are very small. Titan’s haze clouds, which have the dominant effect on that body’s radiation budget, are all in the very outer reaches of the atmosphere, which has a tiny share of the atmospheric mass. Shaidlov’s preprint (discussed in the “Meteors, Nuclear Weapons, etc.” posting, is still nonsense,because (among many other things) he argues in terms of the gaseous effect of mesospheric water vapor, not a presumed cloud effect. I have never heard that mesospheric clouds have any significant effect on the radiation budget of Earth. Indeed, they are much optically thinner than polar stratospheric clouds, and the latter already do hardly anything. Without knowing more about the mesosphere, though, I couldn’t easily rule out that mesospheric clouds could never do much. Are there any mesosphere experts out there that could chime in on this matter? –raypierre]

  13. 113
    Hank Roberts says:

    Alisa, what led you to asking about the mesospheric clouds, if I may ask? Sometimes it helps to know where you found the info that inspires the question. I asked something similar recently — I was confusing polar stratospheric and noctilucent clouds); something I’d read five years ago didn’t distinguish between them.

    Llewelly’s answer to your 73 was about gases, but your question is about clouds (I think there are clouds other than water ice — but again I may be confusing stratospheric with mesospheric clouds).

    Reading your links (disclaimer –I’m an amateur here, just a reader)
    — the first is fascinating for astrobiology, if it’s discussed anywhere else please point me there.
    — The second is to Drew Shindell’s info on the 2000 ozone hole, and stratospheric clouds, the ones where the ozone chemistry is happening. The newer info from that area isn’t encouraging, it’s discussed elsewhere at RC.
    — The third link is the home page for NASA’s AIM satellite — currently being built. Once in orbit that program can start collecting data toward the very question you ask, and it appears to have been designed specifically to look at mesospheric clouds, changes in them recently, and climate effects they may have in the future.

    It’s not clear whether they are increasing, from what I read, or whether they mean the photos from the Alpha, er, the International Space Station, are showing more of them developing, or just that they can see them.

    So — if your question is “would changes in mesospheric clouds change climate” then the answer may be on the AIM satellite’s Mission page:

    “These data can be obtained only by a complement of instruments on an orbiting spacecraft because of the need for global coverage and because extinction and foreground emissions compromise optical sensing from the ground.”

    Maybe our hosts can invite someone from that project to start a topic on the satellite, though before it flies, I suspect they’re just as curious as we are! But they could talk about why they got the project going, there must be some interesting chemistry behind the proposal being funded.

  14. 114
    alisa brooks says:

    Thank you Hank!

    My question was based on conversations regarding:
    Meteors, Nuclear Tests and Global Warming

    Shaidurov’s paper prompted me to find relevant information related to noctilucent clouds. From there I started looking at where they were formed (at what altitude), then how the mesosphere functions and interacts with our current climate. I then became curious to find out the effects continued pollution may have on it (if any). This all lead me to my question.

    Thanks Hank!

  15. 115
    Steve Bloom says:

    Ferdinand, what I challenged was your citation of those dated papers in support of your assertion that the referenced change is “probably all natural” (from comment #101). I probably sounded a little exasperated because you’ve referred to the same papers in support of the same idea on at least a couple of other occasions on RC.

    The citation part is just a matter of blog etiquette — I know it’s a pain to do the research, but it’s very misleading to people reading this site to not check your own work prior to making comments of this sort. The authors are volunteers, and expecting them to step in and make corrections every single time on such things is unfair. In any case, you’re obviously very keen on the science and should want to know what the current thinking is.

    Of course the interaction between the AGW signal and natural variation is complex and not perfectly understood, especially when it come to clouds, but the science simply doesn’t support an assertion of “probably all natural.” If you can quote a paper or climate scientist saying so, great; if it’s just your opinion, please make clear that it’s you and not the paper or scientist.

  16. 116

    Re #115

    Steve, my fault, I am reading pretty much about climate these days and pick up the interesting parts of different publications and what I write is mostly a syntheses of my view of what I have read.
    In the case of the Chen ea. and Wielicki ea. papers, the basic information (that there are huge changes in radiation budget in the tropics as result of cloud cover changes) didn’t change since 2002. The opinion of both is that this is a natural phenomenon (as expressed on the NASA web site).

    If you have a look at the heat budget of the oceans by Levitus ea., in figure 1, one can see a cooling trend in the period 1980-1990 and a warming trend 1990-2000+. This coincidenses with the periods of “global dimming”, where there is a decrease in insolation in the previous period and an increase after 1990 for most of the observations. This also coincidences with a decrease and increase of cloud cover and more/less reflection of (short wave) sunlight in the tropics (and beyond).
    And it differs from the emissions of aerosols: sulfate emissions are rather steady-state since 1975 (sorry lost the reference, thought it was on the IPCC site), but with a large regional difference: huge reductions in Europe (and N.A.), compensated by a huge increase in SE Asia. But in both cases (except India) there is an increase in insolation after 1990 (see Wild ea. Fig. 1). GHGs may contribute to the overall increase 1945-2005, but can’t be responsible for the huge cooling 1980-1990.

    Thus the recent increase in tropical heat content/temperature and Atlantic cyclone activity is largely a result of (a) natural cycle(s) (as the work of Bell and Chelliah also alludes to), and in part of GHGs forcing over the long term. But what drives what in the natural cycles is quite difficult to know…

    [Response: As noted previously, Bell and Chelliah can be discounted, since there is no way then can discriminate long term “natural” variability in the data they are using. Also, among many other things, you are making far too much of the Wielecki study. The authors themselves were very cautious about their results, both as to whether they are real and whether the changes were triggered in part by GHG. Splicing together multiple satellites into a long time series is perilous, and their caution is justified. As noted in the Trenberth article cited in Comment 105, yet another error was discovered in 2004, which needs to be taken into account. I wouldn’t be surprised if there were more to come. It took a long time to shake out all the problems with the MSU data analysis, and in some ways even that work isn’t done yet. There is no question that at least part of the tropical warming is attributable to GHG increases, at least since the 1970’s. If you are saying that some part of the warming may also be due to natural variability, that’s certainly in the cards but it doesn’t in any way follow from the arguments you are making, even if Wielecki’s data were right. Finally with regard to global dimming, you have to distinguish between changes in the surface insolation and changes in the top of atmosphere radiation budget, which are quite different things and have quite different effects on climate –raypierre]

    [Response:There are a few other points to keep in mind about the widely misinterpreted Wielecki et al study. First, there is no manifest evidence even in that paper for a large net driving of climate by the fluctuations they see (even if they are real). Look at the bottom panel of Fig. 2, which gives the net top of atmosphere tropical flux. The big event you see there is Pinatubo, but there is no long term trend in the TOA net. Now, to make life even more complicated for you, if the SST has time to come into equilibrium you wouldn’t expect to see any change in the net TOA budget even if CO2 (amplified by feedbacks) were causing a large surface warming during this time, or even if you were completely right and cloud effects were causing a warming. That’s because, once things reach equilibrium, what goes in must equal what comes out. All you can see in the TOA budget, without making use of a model in the interpretation, is the disequilbrium. This makes the data completely unsuitable for trying to draw the kinds of conclusions you are after. Now, the real significance of the paper is in Figure 3, which suggests (remaining to be confirmed) that models have some problem with the seasonal cycle of tropical clouds. This is not completely news, since we know many ways models have problems with clouds, but the observations certainly will help modellers fix things. I’m less concerned by the problems in the simulated trends in Fig. 4, since that may go away with further satellite data processing, and the simulations used were not the optimal ones for comparing with data of this type. Finally, I have taken the time to provide you with some detailed feedback on your misinterpretation of radiation budgets this time, but you’ve introduced the same faulty reasoning many times over, so please don’t expect me to comment any more on this topic. Readers will please not jump to the conclusion that I agree with Ferdinand just because I refrain from responding to future arguments of this type. –raypierre]

  17. 117
    Hank Roberts says:

    On repeating corrections — a plea.

    Many discussions online bog down and die when dogged repetition overwhelms attempts at citation, explication and comprehension. At which point the thread gets taken over by disinformants advertising PR talking points. Choke.

    I’m sure that’s not your intent, but beware the outcome: plopping one idea no one supports into many threads hides your other contributions. Readers get exhausted — it’s like using the same lunchmeat in everything on your menu, eh? No matter how tasty, repetition overwhelms the taste.

    Can you pick one place and you can work it out mathematically, post your cites, let us read and discuss and watch people with some expertise check the math and perhaps find someone who has experimental results on it?

    And to Raypierre — please don’t stop correcting (maybe an index of Frequent Unsupported Hypotheses is needed, there are plenty — if the comment software here supports posting a link instead of repeating a correction — would serve everyone well.

    And to all — please, use blank lines and paragraphs? Aging eyes need some formatting.

    Blush. Sorry for the run-on metacomment.

  18. 118
    Muthuvel Chelliah says:

    This is with respect to comment #108 and the discussion that ensued.

    My very brief and only response here will be strictly limited to those addressed on my 2 papers (Chelliah and Bell, 2004 and Bell and Chelliah, 2006) with Gerry. Anybody can use anything to support any position. That’s not my call. I can only defend for myself and the science in my papers and what is claimed there.

    Can anyone please tell me where the words “100 year cycle” or the “100 year oscillation” is used anywhere in our papers (Chelliah and Bell, 2004; Bell and Chelliah, 2006) and where we are suggesting such cycles and their implications. Can you please read the papers thoroughly before commenting on them in the public domain, particularly if those comments are very negative and are quite critical?

    Besides addressing other issues, the BC2006 paper has everything to do with an attempt to explain the observed overall increase in N.Atlantic hurricane activity since 1995 and how it could be linked to local and tropics-wide SST (see also CB2004), ENSO and other global climate conditions. These two papers together constitute the basis of NOAA’s long lead North Atlantic Hurricane outlooks issued since 1998 and the East Pacific’s Hurricane outlooks since 2002. The main thrust of the paper is to explain how the recent increase in North Atlantic Hurricane activity is quite possibly associated with the recent increase in SST in the Atlantic basin and in that sense how it is much different than similar higher levels of Hurricane activity observed in the 1950’s and 60’s.

    These papers have nothing to do with global warming or an explanation of the possible relationship between increase in the number of major hurricanes and increased SST values quite possibly associated with global warming.

    I am looking forward to answer fully all those questions on my paper from those who have taken the time to read it completely and thoroughly, but not here. The papers have been well peer reviewed; all major concerns of the anonymous reviewers satisfactorily addressed by us, and thus heavily scrutinized by competent scientists just as any of your papers are. Let’s have some respect for the American Meteorological Society and its ‘Journal of Climate’s peer review system. Please!

    Thanks for the opportunity.

  19. 119
    Hank Roberts says:

    Dr. Chelliah, as a nonscientist reader here, I appreciate _very_much_ your saying that much here. It’s appropriate! One repeated big lesson for us watching the experts here is — read the primary source, verify firsthand what’s claimed about anyone’s work to the extent we can understand it, and ask help.

    I hope wherever the further discussion happens, we nonexperts can read that eventually. It’s the best possible continued education about how this all works. Will your full papers available to the general public somewhere you can point us to?

    Gavin, the link you gave in #102 (and Ferdinand also in #115) the later abstract seems to be broken.

    [Response:It works for me… -gavin]

  20. 120

    Re #116 (comment),

    Raypierre, I am a little surprised by your response.
    The discussion was about the warming of the tropical oceans, especially the part of the North Atlantic, where the Atlantic tropical cyclones are born, not about climate in general.

    The Chen/Wielicki papers point to the fact that there is a satellite derived increase in solar radiation at the surface (~2 W/m2) in the tropics since begin 1990’s.

    This is confirmed by later work from Pinker ea., which compares satellite data (~3 W/m2 increase in the tropics after 1990) with ground data (described in the full article) and is published on 6 May 2005, probably taken into account any previous detected errors in the satellite data.

    This parallels the “global dimming” trends from ground stations of Wild ea. with only one low-latitude station in the Atlantic: Bermuda, which shows a 5 W/m2 increase in all sky conditions, but none in cloud-free conditions, which points to a change in cloud cover.

    This parallels the changes in heat content of the oceans of Levitus ea., fig. 1. While there are no specific data given for individual areas, the 10N-30N ocean band of interest (fig. 2) shows the largest increase in heat content since 1955.

    These three independent data series are quite consistent with each other, but inconsistent with aerosol data, either for area as in time frame. And are inconsistent with GHG trends in magnitude and sign for (multi)decadal time frames (how do you explain the decrease 1980-1990 of ocean heat content with increasing GHGs and steady state SO2 emissions?).

    Thus of Chen/Wielicki, only the increase in insolation at ground level (SW in fig. 2 of Wielicki) is relevant here, the TOA budget, (which points to tropical atmospheric cooling?) is relevant for climate in general, but not (directly) for tropical ocean warming.

    And the problems of models with clouds go beyond the seasonal cycles, see the work of Allan and Slingo. Although mainly about outgoing LW radiation, this is related to cloud radiation properties/cover, see Fig.1.
    Further, climate models significantly don’t capture any natural cycles between 10-100 years, see Fig. S1 in the supporting on line material of Barnett ea.

    Thus in IMHO, that the recent ocean warming (specifically in the tropical Atlantic) is mainly of natural origin still stands. But if I am wrong (based on better data), I have no problems to accept that (and will not reuse these arguments).

  21. 121
    Steve Bloom says:

    Re #118: The picture begins to clarify a little. Of course researchers should be left alone to do their work, but unfortunately it appears that NOAA has intentionally mischaracterized and continues to mischaracterize the Bell and Chelliah work as supportive of the position stated by the NOAA PR flack in the newspaper article (pasted below) from last Sunday’s Providence (RI) Journal. B+C aren’t named, but I’m not aware of any other work that could be the basis for the position. As stated in the now-infamous NOAA statement on hurricanes from last fall:

    “Research by NOAA scientists Gerry Bell and Muthuvel Chelliah, currently in press with the Journal of Climate, describes the tropical multi-decadal signal and shows that it accounts for the entire inter-related set of conditions that controls hurricane activity for decades at a time. Their study also shows that the tropical multi-decadal signal is causing the observed multi-decadal fluctuations in Atlantic hurricane activity since 1950.”

    So apparently some liberties were taken by whoever approved the contents of that page (presumably Max Mayfield or someone higher up). As well, it appears that the NOAA gag order continues in place, albeit less officially than before.

    —————————————-

    NOAA hiding truth about hurricanes, scientists say

    The national agency is accused of fudging data and censoring top scientists who link hurricane intensity with global warming.

    01:00 AM EST on Sunday, March 26, 2006
    BY PETER B. LORD
    Journal Environment Writer

    Hurricanes are getting worse because of global warming.

    Kerry Emanuel, a veteran climate researcher at the Massachusetts Institute of Technology, made that assertion to a roomful of University of Rhode Island scientists a few months ago. He also charged the federal government’s top science agency with ignoring the growing research making that link.

    Instead of telling the public the truth, he said, National Oceanic & Atmospheric Administration officials are insisting that hurricanes are worse because of a natural cycle.

    Emanuel’s comments made little impact at the time. But during the last three months, his comments and those of other scientists have become like hurricanes — more frequent and more severe. Finally, they are reaching the public.

    James E. Hansen, the top climate scientist at the National Aeronautics and Space Administration, was quoted in The New York Times in January as saying he had been threatened with “dire consequences” by some NASA political appointees if he continued to call for limits on emissions of gases linked to global warming.

    Many climate scientists at the NOAA may no longer take calls from reporters, the story went on to say, unless the interview is approved by administration officials in Washington, D.C., and is conducted with a public-affairs officer present. But where scientists’ views on climate change align with those of the administration, The Times said, there are few restrictions on speaking or writing.

    In February, New Republic magazine published a story about the NOAA’s insistence both in news conferences and on its Web site that global warming has no effect on hurricanes.

    Many respected climate scientists, including some working at the NOAA, believe that is wrong, according to the article. It quoted Don Kennedy, editor in chief of Science magazine, as saying, “There are a lot of scientists there who know it is nonsense . . . but they are being discouraged from talking to the press about it.”

    Last month, retired Navy Vice Adm. Conrad C. Lautenbacher Jr., the NOAA’s administrator, issued a statement saying that the media reports about muzzling NOAA scientists are incorrect. He urged the NOAA’s scientists to speak freely and openly.

    He was almost immediately contradicted by Jerry Mahlman, a former director of one of the NOAA’s top laboratories in New Jersey, who said climate scientists at the NOAA have, “indeed, recently been systematically prevented from speaking freely to anyone outside NOAA” about “our inexorably warming planet.”

    Finally, NASA’s Jim Hansen appeared on 60 Minutes last Sunday night and repeated his story of government censorship. The story also introduced Rick Piltz, who resigned from the U.S. Climate Change Science Program last year because, he said, the White House kept softening his annual reports on climate change.

    When Emanuel raised his criticisms of the NOAA in December, the worst hurricane season in modern history had just ended, and it had broken records set by the 2004 season.

    Worsening storms are no coincidence, Emanuel said. They are feeding off ever-warming ocean waters.

    Emanuel said in passing that the NOAA, the nation’s leading science agency — home of the National Weather Service and the National Hurricane Center — was telling the wrong story.

    “NOAA talks about natural cycles, but there is no evidence this is cyclic,” Emanuel said.

    Despite growing scientific evidence that global warming is making hurricanes more frequent and more severe, Emanuel said the NOAA has adopted the stance that there is no global-warming effect on hurricanes.

    This was not the first time for such accusations. Two years ago, 60 of the country’s leading scientists had signed a statement calling for an end to the “distortion of scientific knowledge for partisan political ends” by the Bush administration.

    The scientists charged that, to support President Bush’s decision not to regulate emissions that cause climate change, the administration has “consistently misrepresented” findings by government scientists. They also found the administration had been working to undermine government science used to deal with childhood lead poisoning, endangered species, air pollution and environmental-health issues. Since then, more than 8,000 other scientists have signed on.

    Emanuel said new stories of scientific censorship emerged at a meeting with NOAA scientists last fall.

    “Scientists at NOAA have been told there is a gag order on [discussing the impact of] global warming,” Emanuel said. “A U.S. government organization should not have a gag order on science. Even in Cuba, scientists can’t talk about politics, but they can say anything they want about science.”

    SOON AFTER Emanuel’s appearance at URI to discuss his research and his new book, Divine Wind: The History of Science and Hurricanes, The Providence Journal sought to test his conclusions.

    The first call was to Isaac Held, a senior research scientist at the NOAA’s prestigious Geophysical Fluids Laboratory, in Princeton, N.J. It was there, last fall, that Emanuel said he first heard about NOAA censorship. Held said he hadn’t been affected, but he advised calling Thomas Knutson, a NOAA scientist whose research showed a link between climate change and hurricane intensity.

    “Stick to hurricanes. Talk to Tom,” Held advised.

    Knutson wouldn’t talk.

    “When we’re contacted by reporters, we have to have clearance before we can speak about issues. This is NOAA’s media policy,” Knutson said. He suggested calling Jana Goldman, in NOAA’s public-affairs office.

    Is this a new policy? he was asked.

    “Check with her,” Knutson said. “I’m not sure when the policy was implemented.”

    Calls to NOAA’s public-affairs office led to Kent Laborde, who was described as the public-affairs person who focuses on climate-change issues.

    Laborde made it clear that the NOAA has discounted the research tying global warming to worsening hurricanes.

    “What we’ve found is, if you look at a couple segments of science, observational or modeling, there is no illustrated link between climate change and hurricane intensity,” Laborde said. “We actually have periods of intensity followed by periods of lower intensity. We have evidence of periods going back to the 1930s. It follows a clear pattern.”

    Laborde was asked if he would approve an interview with Knutson.

    What is the topic? he asked.

    Emanuel’s theories linking climate change to worsening hurricanes.

    “Chris Landsea would be better. He’s an observational scientist,” Laborde said.

    Landsea is a top meteorologist at the NOAA, often called upon for expert testimony to Congress or to speak at news conferences. He also very publicly quit an international climate-change panel last year, because one of its leaders had publicly linked global warming to hurricane severity.

    At Laborde’s request, Landsea cheerfully discounted Emanuel’s theories in an interview with The Journal.

    Landsea says he believes what we are really experiencing is a return to an active period of hurricanes, similar to what happened in the late 1940s to the 1960s.

    He argued that Knutson’s research reflects only a small link between global warming and hurricane intensity.

    As for Emanuel’s work, Landsea said, “My opinion is his study is very unconvincing.”

    Landsea insisted that, although he represents the NOAA, there is no official NOAA stance on the impact of global warming on hurricanes.

    “There are different scientists with different points of view,” He said. “Talk to people at Princeton. Tom Knutson has different opinions than I. But he’s allowed to speak.

    EMANUEL SAID he has no problem with engaging in a scientific debate. What concerns him, he said, is that the NOAA seems to be ignoring the debate, and has come down on just one side.

    At the annual convention of the American Geophysical Union last December in San Francisco, a conference that draws 11,000 scientists, Emanuel said he chided the NOAA’s restrictions during a scientific presentation — and was greeted with a standing ovation.

    “The intensity and frequency of storms are increasing,” Emanuel said. “And that is almost certainly because of global warming. There is no evidence of ‘natural cycles.’ ”

    More work needs to be done, he said. But the NOAA should at least acknowledge the theory.

    “There are lots of pieces of evidence, like in a trial,” Emanuel said. “All point in a certain direction. I think the evidence is really decisive. And most of my colleagues agree.”

    The Government Accountability Project, a nonprofit organization that supports federal whistleblowers, last week announced that it is sponsoring the watchdog organization Piltz had created after leaving his government post last summer.

    The new organization, Climate Science Watch (at http://www.climatesciencewatch.org), reports on political meddling on government climate-change research.

    Piltz said he resigned because his annual climate-change reports were repeatedly watered down by an administration staff lawyer who previously had worked as an energy-industry lobbyist. Piltz said he is well aware that NOAA policies “require political preapproval on all science contacts with the media.”

    “If this administration had a different reputation — respect for science — we wouldn’t be so upset,” he said.

    “I’m all for honest exchanges, but we’ve got science and politics co-mingled here,” Piltz said. “What happens when the world of science collides with the world of politics? I know that world.”

    The NOAA’s actions are often subtle, he said, “but they reflect a pervasive pattern of deflecting the public’s attention and manipulating the way science is presented to the public.”

    “Federal scientists should be able to communicate with the public,” Piltz said. “Especially if it is about an important issue. We are paying for this stuff.”

    Last week, Emanuel said he had noticed one change at the NOAA since he made his complaints public, but it’s a small one, and it appears only in a footnote in tiny print at the end of the page. It is, he said, “a little disingenuous.”

    NOAA Magazine, an online publication, had carried a story at the end of November that wrapped up the terrible 2005 hurricane season. Its headline; “NOAA Attributes Recent Increase in Hurricane Activity to Naturally Occurring Multi-Decadal Climate Variability.”

    Last month, in small print at the end of the 12-page report, this editor’s note had been added: “The consensus in this on-line magazine story represents the views of some NOAA hurricane researchers and forecasters, but does not necessarily represent the views of all NOAA scientists. It was not the intention of this article to discount the presence of a human-induced global warming element or to attempt to claim that such an element is not present. There is a robust, on-going discussion on hurricanes and climate change with NOAA and the scientific community.”

    The note says the headline should have read: “Agreement Among Some NOAA Hurricane Researchers and Forecasters.”

    plord@projo.com / (401) 277-8036

  22. 122
    Hank Roberts says:

    Gavin, is the abstract only for subscribers? Maybe my character encoding is garbling it. I’ll fiddle with it.

  23. 123
    Steve Bloom says:

    Re #122: Hank, I can see it too, but anyway it seems appropriate to just post the text:

    Interannual and multidecadal extremes in Atlantic hurricane activity are shown to result from a coherent and interrelated set of atmospheric and oceanic conditions associated with three leading modes of climate variability in the Tropics. All three modes are related to fluctuations in tropical convection, with two representing the leading multidecadal modes of convective rainfall variability, and one representing the leading interannual mode (ENSO).

    The tropical multidecadal modes are shown to link known fluctuations in Atlantic hurricane activity, West African monsoon rainfall, and Atlantic sea surface temperatures, to the Tropics-wide climate variability. These modes also capture an eastâ??west seesaw in anomalous convection between the West African monsoon region and the Amazon basin, which helps to account for the interhemispheric symmetry of the 200-hPa streamfunction anomalies across the Atlantic Ocean and Africa, the 200-hPa divergent wind anomalies, and both the structure and spatial scale of the low-level tropical wind anomalies, associated with multidecadal extremes in Atlantic hurricane activity.

    While there are many similarities between the 1950â??69 and 1995â??2004 periods of above-normal Atlantic hurricane activity, important differences in the tropical climate are also identified, which indicates that the above-normal activity since 1995 does not reflect an exact return to conditions seen during the 1950sâ??60s. In particular, the period 1950â??69 shows a strong link to the leading tropical multidecadal mode (TMM), whereas the 1995â??2002 period is associated with a sharp increase in amplitude of the second leading tropical multidecadal mode (TMM2). These differences include a very strong West African monsoon circulation and near-average sea surface temperatures across the central tropical Atlantic during 1950â??69, compared with a modestly enhanced West African monsoon and exceptionally warm Atlantic sea surface temperatures during 1995â??2004.

    It is shown that the ENSO teleconnections and impacts on Atlantic hurricane activity can be substantially masked or accentuated by the leading multidecadal modes. This leads to the important result that these modes provide a substantially more complete view of the climate control over Atlantic hurricane activity during individual seasons than is afforded by ENSO alone. This result applies to understanding differences in the â??apparentâ?? ENSO teleconnections not only between the above- and below-normal hurricane decades, but also between the two sets of above-normal hurricane decades.

  24. 124
    Steve Bloom says:

    Now this is interesting. It turns out that the disclaimer added to the bottom of the NOAA magazine article reads as follows:

    *EDITOR’S NOTE: This consensus in this on-line magazine story represents the views of some NOAA hurricane researchers and forecasters, but does not necessarily represent the views of all NOAA scientists. It was not the intention of this article to discount the presence of a human-induced global warming element or to attempt to claim that such an element is not present. There is a robust, on-going discussion on hurricanes and climate change within NOAA and the scientific community.

    ‘The headline and paragraph could have more clearly stated:

    ‘”Agreement Among Some NOAA Hurricane Researchers and Forecasters”

    ‘There is agreement among a number of NOAA hurricane researchers and forecasters that recent increases in hurricane activity are primarily the result of natural fluctuations in the tropical climate system known as the tropical multi-decadal signal.â??

    ‘Reference: Goldenberg, Stanley B., Christopher W. Landsea, Alberto M. Mestas-Nunez, William M. Gray. July 20, 2001. The Recent Increase in Atlantic Hurricane Activity: Causes and Implications. Science, Vol. 293. no. 5529, pp. 474 – 479.’

    The detail I had missed is that the reference for this statement very pointedly was not any of the Bell and Chelliah work, but rather an old (as these things go) Science paper. The abstract reads:

    “The years 1995 to 2000 experienced the highest level of North Atlantic hurricane activity in the reliable record. Compared with the generally low activity of the previous 24 years (1971 to 1994), the past 6 years have seen a doubling of overall activity for the whole basin, a 2.5-fold increase in major hurricanes (50 meters per second), and a fivefold increase in hurricanes affecting the Caribbean. The greater activity results from simultaneous increases in North Atlantic sea-surface temperatures and decreases in vertical wind shear. Because these changes exhibit a multidecadal time scale, the present high level of hurricane activity is likely to persist for an additional ~10 to 40 years. The shift in climate calls for a reevaluation of preparedness and mitigation strategies.”

    The paragraph relating to global warming reads:

    “One may ask whether the increase in activity since 1995 is due to anthropogenic global warming. The historical multidecadal-scale variability in Atlantic hurricane activity is much greater than what would be “expected” from a gradual temperature increase attributed to global warming (5). There have been various studies investigating the potential effect of long-term global warming on the number and strength of Atlantic-basin hurricanes. The results are inconclusive (48). Some studies document an increase in activity while others suggest a decrease (49). Tropical North Atlantic SST has exhibited a warming trend of ~0.3°C over the last 100 years (38); whereas Atlantic hurricane activity has not exhibited trendlike variability, but rather distinct multidecadal cycles as documented here and elsewhere (12, 13, 17). The extreme activity in 1995 has been attributed in part to the record-warm temperatures in the North Atlantic (25). The possibility exists that the unprecedented activity since 1995 is the result of a combination of the multidecadal-scale changes in Atlantic SSTs (and vertical shear) along with the additional increase in SSTs resulting from the long-term warming trend. It is, however, equally possible that the current active period (1995-2000) only appears more active than the previous active period (1926-1970) due to the better observational network now in place. During the previous active period, only 1966-1970 had continual satellite coverage (33, 50). Further study is essential to separate any actual increase from an apparent one due to more complete observations.”

    So even this referenced paper doesn’t strictly support the disclaimer’s assertion that “recent increases in hurricane activity are primarily the result of natural fluctuations.” What research does?

  25. 125
    Hank Roberts says:

    OK, I can see the abstract now too.

    Per Dr. Chelliah’s request in #118, as one who can’t read and understand the full papers, I’ll wait and hope more appears here after those discussions elsewhere, and thank Dr. C. again for saying that much.

    I did find Dr. C’s words in #118 helpful stating clearly both what “The main thrust of the paper is” and what “These papers have nothing to do with.” I commend those clear statements to others, while we wait. They limit the claims others could make about what’s proved by them, narrowly and precisely.

  26. 126
    Urs Neu says:

    Re 108 and comments

    The problem of rather speculative oscillations reminds me on something I have mentionned before but got no reaction. I see also some trouble with the AMO, which is claimed to be responsible for the SST increase in the Atlantic and the corresponding increase in hurricanes. I’ve put now some graphs on the web for illustration:
    http://www.proclim.ch/products/misc/amopictures.html

    1. The AMO, which corresponds to the detrended North Atlantic SSTs, looks very similar to the detrended global surface temperature (DGT, see graphs). It has a very similar amplitude and a very similar period length and very similar patterns. The AMO looks very much like the regional expression of the global temperature evolution. And the very nice “pseudo oscillation” of the DGT is most probably not the result of a physical oscillation but the accidental result of the superposition of different non-regular forcings (solar, volcanoes, aerosols, GHG’s).
    It is very unlikely that the AMO determines the multidecadal variability of the global temperature so strongly, because the amplitude of the AMO, which represents only a small part of the globe, would be clearly dampened in the global signal. Since the amplitudes are similiar, it is much more likely that the AMO represents a result of the global signal.

    2. Looking at a reconstruction of the AMO back to 1600 by Gray et al. 2004 (see graphs), it is very hard to find any apparent regularity which would assist the idea of an oscillation. You can find many possible oscillation frequencies (200 years, 100 years, or less…), but none of them is really apparent. The only one which seems to emerge somewhat is at about 100 years, and not 70 as in the 20th century…

    3. The only physical explanation for an AMO presented until now is the fact, that some models produce oscillations in the order of 100 year periods due to THC variations. However, given the variability of the period lengths in relation to the limited number of periods to compare (only a few, only 2 measured), this “correlation” seems rather speculative. I haven’t seen a simulation yet which fits nearly as well as the global temperature…

    If the AMO would really only be the result of global temperature evolution (with some additional regional signals, of course), this would mean that the recent increase in Atlantic hurricane activity is strongly linked to global warming…

    To be discussed…
    Urs

    [Response: Thanks. Your points are very well taken. – gavin]

  27. 127
    Steve Bloom says:

    Re #s 118 and 121 (first two paragraphs): Just to clarify in case anyone is still reading this, after going back and double-checking the source material it became clear that Bell has been out (primarily last fall) making statements in support of the official NOAA “all natural cycle” hurricane hypothesis while Chelliah has not. Of course co-authors are entitled to interpret their joint work in defferent ways, but it remains interesting that only those at NOAA who agree with the official agency position have spoken to the press.

    Speaking of NOAA, this coral bleaching story from two days ago features yet another NOAA representative denying the impact of GW while other scientists speak out.

    Then there’s this story about the increasing effects of acidification in the Pacific, although in this case the NOAA scientist is simply silent on the GW connection while others discuss it.

  28. 128
    Pat Neuman says:

    re 85.

    Another flip of the coin turns up heads on the Red River. Is this more bad luck or just another global warming fingerprint? Are more frequent and larger winter-spring rainfall driven Red River floods part of polar/upper latitude amplification of the hydrologic cycle?

    GF/EGF: Red tops its banks
    Apr. 01, 2006
    http://www.grandforks.com/mld/grandforks/14238344.htm

    Excerpts:

    The river could hit “major” flood stage 46 feet or higher by next
    week, according to the National Weather Service forecast office in
    Grand Forks. That would be the highest the river has been since the
    Flood of 1997. …

    The highest crest since 1997 was 45 feet in the spring of 2001.

    See also: Historical Peak Streamflow
    USGS 05082500 RED RIVER OF THE NORTH AT GRAND FORKS, ND
    http://nwis.waterdata.usgs.gov/mn/nwis/peak/?site_no=05082500&agency_cd=USGS

  29. 129

    With reference to Dr. Cheliah’s response (# 109), he is quite correct. Cheliah and Bell do not in either of their papers (and I have read both in great detail) refer to a “cycle” or “an oscillation” of a 100-year period. But they do refer to a “mode” of 50 years with one minimum and one maximum. They note that the “mode” changes sign (between the minimum in the 1950s to the maximum late 1990s) at the time of the global changes in general circulation character commented on by many in the past and therefore. But how can one differentiate between the C&B mode and a trend? Why was tghe dat not detrended prior to the analysis? Why was the possibility that the “mode” may be a trend and one associated with GW not be mentioned? These are the questions I ask.

    Dr. Cheliah makes the point that the two papers were not intended to discuss global warming and hurricanes. But others in high places in NOAA have used these articles as evidence that the changes that we have seen over the last few decades and espacially in the Atlantic in the last 11 years are just natural variations of the climate system with the inference that we understand what these cycles are, how they come about and what they will do in the future. I recognize that one cannot be responsible for what use someone else makes of a paper one writes but ir would seem to me that with a little thought where one says “mode” that “mode or trend” could have projected a neutral stance for the paper.

    I am sorry that Dr. Cheliah has taken umbrage at my comments. They were not menat to be personal nor were they meant in disrespect to the American Meteorology Society’s J. Clim. review process. (God forbid, I publish there a lot too so how could I argue that the review process is nothing less than exemplary (a joke!)) I applaude C&B for publishing their work and avoiding what many in the hurricane-global warming discussion have done: criticize through commentary and not thorugh the peer-reviewed process. In fact, one could raise an eyebrow becasue that is probably what I have done here. Apologies! But because something is published does not mean it is correct. Not even the AMS is that clairvoyant. The scientific method stipulates that all work should be examined carefully and commented on critically. C&B and other scientists will build upon what is said in the two papers or modify conclusions accordingly. That is the way we move ahead. I just happen to query the suitability of the C&B statistics and what one can infer or cannot infer from the methods they have used. We will continue our examination and publish a response in due course. PW

  30. 130

    Re #126:

    Urs and Gavin,

    While there may be some similarity between global temperatures and the AMO, the effects of the AMO can be seen on longer time scales than the recent upswing in temperatures.
    – there is a 70-80 year oscillation in European-wide summer temperatures visible, based on the longest instrumental records, combined with tree rings. See Shabalova and Weber
    – the AMO not only is connected to temperature (and precipitation) variations in Europe, but also precipitation in the USA and Middle-East/Africa, thus may be seen in overall NH and global climate. See Sutton and Hodson.

    But IF the detrended AMO correlates well with the detrended global temperature change, and IF tree rings are good indicators of past climate, the AMO can be used as a proxy for pre-instrumental temperature variations, which indicate a (totally natural) variation of up to 0.6 degr.C 1570-1850 (see Betancourt ea., page 27, but the other pages are interesting too), larger than the variation in the 20th century, which still is 0.4 degr.C (page 23). That besides the influence of the increased solar strength in the first halve of the past century on the SST trend… Thus it is rather speculative to blame today’s higher Atlantic SST’s mainly on GHGs…

    Btw, I only have an empty page when opening the link to the ProClim AMO graphs.

  31. 131
    Urs Neu says:

    Re 130

    Ferdinand, since the AMO is correlated to global temperature variations, any regional climate signal which is in some way correlated to global temperature (and there is quite a number of them), will also be correlated to the AMO. Thus it is no surprise that you will find an ‘influence’ in the whole Northern Hemisphere and in global climate. A global response of the AMO in fact supports the suggestion that the AMO more or less represents the global temperature and maybe nothing else. Where is the evidence that the signals you mention are influenced by the AMO and not just by the global signal?

    And where is the evidence that the AMO is a regular signal? Just the one complete period we have in the measured data?
    If you look at the Betancourt graph (meanwhile published in Gray et al. 2004, ref. see below), you find negative peaks roughly 120,100,100, and 70 years apart, and positive peaks roughly 110, 100, 90, and 60 years apart. And there might be a 250 year cycle superposed, and there is a huge signal before 1600 out of order anyway, etc. I can’t see any regular signal at all. The 60-80 year ‘oscillation’ you only can find since 1870 where the measurements start.

    Btw, I don’t see a reason to use a tree-ring derived AMO reconstruction for the NH temperature, if we have NH temperature reconstructions which include more tree-rings and additional data. You do not gain anything, do you?

    Gray, S. T., J. L. Graumlich, J. L. Betancourt, and G. T. Pederson, 2004: A tree-ring based reconstruction of the Atlantic Multidecadal Oscillation since 1567 A.D. Geophys. Res. Lett., 31, L12205, doi:10.1029/2004GL019932

    I don’t know why you can’t see the graphs on our page, I’m sorry. It shows the AMO from Knight et al. 2005 and the reconstructed AMO from Gray et al. 2004 (similar to Betancourt). The detrended global temperature from CRU-data you easily can calculate yourself.

  32. 132

    Re #131

    Urs, sorry for the late reply, we are just in the (hopefully!) last phase of in-house renewal…

    The AMO is the result of detrended Atlantic SST’s, thus it is quite normal to use tree rings along the Atlantic coast to reconstruct the AMO before the instrumental era. Although there may be better proxies (sediments?) than tree rings (which are influenced by many other items than temperature alone), there is more variability in the AMO tree ring reconstruction than in the MBH98/99 NH reconstruction, but less than for other NH reconstructions (like the Esper all tree ring reconstruction), thus the link between AMO and NH/global temperatures in amplitude is not so sure.

    And is it not the opposite, that Atlantic Ocean heat content/SSTs are influencing the whole NH climate?

    Further, the variations in Atlantic (and general tropical) ocean heat content are much too large to be caused by aerosol/GHG combinations. Even the timing is not consistent with the increase in aerosols (1945-1975) or GHGs (mainly after 1945 until current) for ocean heat content (decreasing 1980-1990!).

  33. 133

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