cc: alverson@pages.unibe.ch, jto@u.arizona.edu, k.briffa@uea.ac.uk, mhughes@ltrr.arizona.edu, pedersen@eos.ubc.ca, whitlock@oregon.uoregon.edu, mann@multiproxy.evsc.virginia.edu date: Mon, 10 Jul 2000 12:46:59 -0400 from: "Michael E. Mann" subject: Re: the ghost of futures past to: "Raymond S. Bradley" , Frank Oldfield oops. that's "technical summary", not "executive summary"... At 12:42 PM 7/10/00 -0400, Michael E. Mann wrote: >Dear all, > >For a related perspective on this, you may be interested in >a graphic prepared last year by Dr. Michael Oppenheimer of EDF (also >a member of the IPCC TAR executive summary team): > >http://www.edf.org/programs/grap/y3k/ > >A version of this ran in Time magazine last year , though I forget exectly >when. I don't believe that TAR will be so bold as to show such a graphic. >Nonetheless, it does provide a very useful perspective on matters! > >mike > >p.s. look out for this Friday's "Science for some good stuff! > >At 08:57 AM 7/10/00 -0400, Raymond S. Bradley wrote: >>Sorry this kept you awake...but I have also found it a rather alarming >>graph. First, a disclaimer/explanation. >>The graph patches together 3 things: Mann et al NH mean annual temps + 2 >>sigma standard error for AD1000-1980, + instrumental data for 1981-1998 + >>IPCC ("do not quote, do not cite" projections for GLOBAL temperature for >>the next 100 years, relative to 1998. The range of shading represents >>several models of projected emissions scenarios as input to GCMs, but the >>GCM mean global temperature output (as I understand it) was then reproduced >>by Sarah Raper's energy balance model, and it is those values that are >>plotted. Keith pointed this out to me; I need to go back & read the IPCC >>TAR to understand why they did that, but it makes no difference to the >>first order result....neither does it matter that the projection is global >>rather than NH....the important point is that the range of estimates far >>exceeds the range estimated by Mann et al in their reconstruction. Keith >>also said that the Hadley Center GCM runs are being archived at CRU, so it >>ought to be possible to get that data and simply compute the NH variability >>for the projected period & add that to the figure, but it will not add much >>real information. However, getting such data would allow us to extract >>(say) a summer regional series for the Arctic and to then plot it versus >>the Holocene melt record from Agassiz ice cap....or....well, you can see >>other possiblities. >> >>[......At this point Keith Alverson throws up his hands in despair at the >>ignorance of non-model amateurs...] >> >>But there are real questions to be asked of the paleo >>reconstruction. First, I should point out that we calibrated versus >>1902-1980, then "verified" the approach using an independent data set for >>1854-1901. The results were good, giving me confidence that if we had a >>comparable proxy data set for post-1980 (we don't!) our proxy-based >>reconstruction would capture that period well. Unfortunately, the proxy >>network we used has not been updated, and furthermore there are many/some/ >>tree ring sites where there has been a "decoupling" between the long-term >>relationship between climate and tree growth, so that things fall apart in >>recent decades....this makes it very difficult to demonstrate what I just >>claimed. We can only call on evidence from many other proxies for >>"unprecedented" states in recent years (e.g. glaciers, isotopes in tropical >>ice etc..). But there are (at least) two other problems -- Keith Briffa >>points out that the very strong trend in the 20th century calibration >>period accounts for much of the success of our calibration and makes it >>unlikely that we would be able be able to reconstruct such an extraordinary >>period as the 1990s with much success (I may be mis-quoting him somewhat, >>but that is the general thrust of his criticism). Indeed, in the >>verification period, the biggest "miss" was an apparently very warm year in >>the late 19th century that we did not get right at all. This makes >>criticisms of the "antis" difficult to respond to (they have not yet risen >>to this level of sophistication, but they are "on the >>scent"). Furthermore, it may be that Mann et al simply don't have the >>long-term trend right, due to underestimation of low frequency info. in the >>(very few) proxies that we used. We tried to demonstrate that this was not >>a problem of the tree ring data we used by re-running the reconstruction >>with & without tree rings, and indeed the two efforts were very similar -- >>but we could only do this back to about 1700. Whether we have the 1000 >>year trend right is far less certain (& one reason why I hedge my bets on >>whether there were any periods in Medieval times that might have been >>"warm", to the irritation of my co-authors!). So, possibly if you crank up >>the trend over 1000 years, you find that the envelope of uncertainty is >>comparable with at least some of the future scenarios, which of course begs >>the question as to what the likely forcing was 1000 years ago. (My money is >>firmly on an increase in solar irradiance, based on the 10-Be data..). >>Another issue is whether we have estimated the totality of uncertainty in >>the long-term data set used -- maybe the envelope is really much larger, >>due to inherent characteristics of the proxy data themselves....again this >>would cause the past and future envelopes to overlap. >> >>In Ch 7 we will try to discuss some of these issues, in the limited space >>available. Perhaps the best thing at this stage is to simply point out the >>inherent uncertainties and point the way towards how these uncertainties >>can be reduced. Malcolm & I are working with Mike Mann to do just that. >> >>I would welcome other thoughts and comments on any of this! >> >>Ray >> >> >> >>At 01:34 PM 7/10/00 +0200, you wrote: >>>Salut mes amis, >>> >>>I've lost sleep fussing about the figure coupling Mann et al. (or any >>>alternative climate-history time series) to the IPCC scenarios. It seems to >>>me to encapsulate the whole past-future philosophical dilemma that bugs me >>>on and off (Ray - don't stop reading just yet!), to provide potentially the >>>most powerful peg to hang much of PAGES future on, at least in the eyes of >>>funding agents, and, by the same token, to offer more hostages to fortune >>>for the politically motivated and malicious. It also links closely to the >>>concept of being inside or outside 'the envelope' - which begs all kinds of >>>notions of definition. Given what I see as its its prime importance, I >>>therefore feel the need to understand the whole thing better. I don't know >>>how to help move things forward and my ideas, if they have any effect at >>>all, will probably do the reverse. At least I might get more sleep having >>>unloaded them, so here goes...... >>> >>>The questions in my mind centre round the following issues. If I've got any >>>one of them wrong, what follows in each section can be disregarded or (more >>>kindly) set straight for my benefit. >>> >>>1. How can we justify bridging proxy-based reconstruction via the last bit >>>of instrumental time series to future model-based scenarios. >>> >>>2. How can the incompatibilities and logical inconsistencies inherent in >>>the past-future comparisons be reduced? >>> >>>3. More specifically, what forms of translation between what we know about >>>the past and the scenarios developed for the future deal adequately with >>>uncertainty and variability on either side of the 'contemporary hinge' in a >>>way that improves comparability across the hinge. >>> >>>4. Which, if any, scenarios place our future in or out of 'the envelope' >>>in terms of experienced climate as distinct from calculated forcing? This >>>idea of an envelope is an engaging concept, easy to state in a quick and >>>sexy way (therefore both attractive and dangerous); the future could leave >>>us hoisted by our own petard unless it is given a lot more thought. >>> >>>1. I am more or less assuming that this can already be addressed from data >>>available and calculations completed, by pointing to robust calibration >>>over the chosen time interval and perhaps looking separately at variability >>>pre 1970, if the last 3 decades really do seem to have distorted the >>>response signatures for whatever reasons. I imagine developing this line of >>>argument could feed into the 'detection' theme in significant ways. >>> >>>2 & 3. This is where life gets complicated. For the past we have biases, >>>error bars that combine sources of uncertainty, and temporal variability. >>>For the future we have no variability, simply a smooth, mean, monotonic >>>trend to a target 'equilibrium' date. Bandwidths of uncertainty reflect >>>model construction and behaviour. So we are comparing apples and oranges >>>when we make any statement about the significance of the past record for >>>the future on the basis of the graph. Are there ways of partially >>>overcoming this by developing different interactions between past data and >>>future models? >>> >>>My own thinking runs as follows: Take variability. Do we need to wait for >>>models to capture this before building it into future scenarios? This seems >>>unnecessary to me, especially since past variability will be the validation >>>target for the models. Is there really no way of building past variability >>>into the future projections? One approach would be to first smooth the >>>past record on the same time-span as the future scenarios. This would get >>>us to first base in terms of comparability, but a very dull and pretty >>>useless first base in and of itself. It would, however, allow all kinds of >>>calculations of inter-annual variability relative to a mean time line of >>>the 'right' length. This in turn could be used in several ways, for >>>example: >>> - build the total range of past variability into the uncertainty >>>bands of each future scenario. >>> - take the 30,50 or 100 year period (depending on the scenario for >>>comparison) during which >>> there was the greatest net variability, or the greatest net fall >>>in Temperature, or the >>> greatest net increase in T. and superimpose/add this data-based >>>variability on the mean >>> trends. >>> - take the n-greatest positive anomalies relative to the trend and >>>use them to define an upper >>> limit of natural variability to compare with the (to my mind) >>>more realistic future scenarios. >>> >>>These and cleverer variants I cannot begin to think up seem to me to hold >>>out the possibility of linking future projections of GHG forcing with what >>>we know about natrual variability in reasonably realistic ways and perhaps >>>even of redefining the 'past data-future scenario' relationship in ways >>>that benefit both the paleo-community and the quality of future >>>projections. >>> >>>4. I also think the above kinds of exercise might eventually lead us >>>towards a better definition of 'the envelope' and more confidence in >>>deciding what is outside and what is not. The same sort of approach can be >>>taken towards projections of P/E I imagine and, more particularly, at >>>regional rather than global or hemispheric level. >>> >>>Sorry if all this sounds stupid or obvious. I got afflicted with the 'need >>>to share' bug. >>> >>>Frank >>> >>> >>>____________________________________________ >>>Frank Oldfield >>> >>>Executive Director >>>PAGES IPO >>>Barenplatz 2 >>>CH-3011 Bern, Switzerland >>> >>>e-mail: frank.oldfield@pages.unibe.ch >>> >>>Phone: +41 31 312 3133; Fax: +41 31 312 3168 >>>http://www.pages.unibe.ch/pages.html >>> >> >>Raymond S. Bradley >>Professor and Head of Department >>Department of Geosciences >>University of Massachusetts >>Amherst, MA 01003-5820 >>Tel: 413-545-2120 >>Fax: 413-545-1200 >>Climate System Research Center: 413-545-0659 >>Climate System Research Center Web Site: >><http://www.geo.umass.edu/c li >>mate/climate.html >>Paleoclimatology Book Web Site (1999): >>http://www.geo.umass.edu/clim at >>e/paleo/html >> >> >> >_______________________________________________________________________ > Professor Michael E. Mann > Department of Environmental Sciences, Clark Hall > University of Virginia > Charlottesville, VA 22903 >_______________________________________________________________________ >e-mail: mann@virginia.edu Phone: (804) 924-7770 FAX: (804) 982-2137 > http://www.evsc.virginia.edu/faculty/people/mann.html > > > _______________________________________________________________________ Professor Michael E. Mann Department of Environmental Sciences, Clark Hall University of Virginia Charlottesville, VA 22903 _______________________________________________________________________ e-mail: mann@virginia.edu Phone: (804) 924-7770 FAX: (804) 982-2137 http://www.evsc.virginia.edu/faculty/people/mann.html