Thursday, May 24, 2012


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):
>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!
>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IPCC ("do not quote, do not cite" projections for GLOBAL temperature for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!
>>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
>>> - 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
>>>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
>>>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 Oldfield
>>>Executive Director
>>>Barenplatz 2
>>>CH-3011 Bern, Switzerland
>>>Phone: +41 31 312 3133; Fax: +41 31 312 3168
>>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:
>>Paleoclimatology Book Web Site (1999):
> Professor Michael E. Mann
> Department of Environmental Sciences, Clark Hall
> University of Virginia
> Charlottesville, VA 22903
>e-mail: Phone: (804) 924-7770 FAX: (804) 982-2137
Professor Michael E. Mann
Department of Environmental Sciences, Clark Hall
University of Virginia
Charlottesville, VA 22903
e-mail: Phone: (804) 924-7770 FAX: (804) 982-2137

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