cc: Eystein Jansen <Eystein.JansenatXYZxyz.uib.no>, Jonathan Overpeck <jtoatXYZxyzrizona.edu>, Francis Zwiers <Francis.ZwiersatXYZxyzgc.ca>
date: Wed, 20 Sep 2006 12:37:42 -0400
from: Gabi Hegerl <hegerlatXYZxyze.edu>
subject: Re: 5 to 7 centuries
to: Keith Briffa <k.briffaatXYZxyz.ac.uk>
I asked Tom about it, he says (but I realize he is one sample of the
volcano enthusiasts) it could
have been El Chichon, the eruption seems to be huge, but there is
concerns that different physics
would apply to such a large eruption making it cause different climate
impacts (he cites a paper
for that that I promplty forgot).
I am always slightly nervous about the fact that this one doesnt show up
in the data, and wondering
if there is a sliver of circularity, but I think results like my
detection stuff and probably also EPOCH
stuff (I could try) are quite robust to missing an eruption, even a biggie.
Keith Briffa wrote:
> Hi everyone - just been at a meeting all day so just seen this . I
> agree with Eystein et al . so no problems . Interested to know what
> you mean Gabi about the 1256 eruption - we have been looking at the
> empirical evidence for a contemporaneous cooling with ambiguous results
> At 20:16 19/09/2006, Eystein Jansen wrote:
>> Hi Gabi,
>> this is fine with me and does not seem to contradict Ch6.
>> At 15:06 -0400 19-09-06, Gabi Hegerl wrote:
>>> SOunds good - since forcing and temperature reconstrucitons are
>>> I think it was defensible to make a statement about role of forced
>>> response 700 yrs back in Ch9.
>>> Is it ok to keep 700 yrs about significant externally forced
>>> component in SPM?
>>> Susan is finetuning that bullet right now so thats why i thought it
>>> would be good to know if you guys are
>>> We justified ch9's assessment based on your figure 6.13 showing
>>> model and recon agreement, and on few detection
>>> studies and some qualitatative agreement studies all saying the
>>> agreement is not spurious.
>>> One issue going beyond further is 1256 eruption, which is not that
>>> well understood,
>>> so it gets a bit dicey beyond I think!
>>> Jonathan Overpeck wrote:
>>>> Hi Gabi - we do loose quite a bit (e.g., boreholes and other
>>>> proxies) back beyond 500, so that's why we drew the "very likely"
>>>> line there. But, we did stay as strong as the TAR back 1300, so
>>>> that was our compromise on certainty. I believe the forcing series
>>>> also start to get more uncertain pretty fast back beyond even 400
>>>> years ago, but I'm pretty impressed with the match between
>>>> simulated and observed NH climate back ca. 700 years (e.g., our
>>>> Figs 6.13 and 6.14). Thus, I bet you are right that we know back to
>>>> 700 pretty well, but not well enough to go with "very likely" in
>>>> the all important chap 6 bullet.
>>>> Not sure this helps, but we do need to pay attention as we do the
>>>> SPM to get the right balance.
>>>> I'll cc to Keith in case he wants to chime in, which would be
>>>> thanks, peck
>>>>> p.s. hope you are all recovered etc!
>>>>> I have one chapter question: We were waffling back and forth if we
>>>>> SHOULD go with the chapter 6
>>>>> assessment on the last 500 being better reconstructed than say
>>>>> last 700, but in the end, we stuck with
>>>>> last 700 because some results rely on using a long timehorizon to
>>>>> separate like ghg and solar signals.
>>>>> To say that very likely a substantial fraction of the variance on
>>>>> those records is externally forced (nother
>>>>> words, detectable external signals in reconstructions).
>>>>> Does this seem ok to you? In the SPM session we had some waffling
>>>>> about 5 vs 7 centuries.
>>>>> Jonathan Overpeck wrote:
>>> Gabriele Hegerl Division of Earth and Ocean Sciences, Nicholas
>>> School for the Environment and Earth Sciences,
>>> Box 90227
>>> Duke University, Durham NC 27708
>>> Ph: 919 684 6167, fax 684 5833 email: firstname.lastname@example.org,
>> Eystein Jansen
>> Bjerknes Centre for Climate Research and
>> Dep. of Earth Science, Univ. of Bergen
>> All�gaten 55
>> N-5007 Bergen
>> e-mail: eystein.jansenatXYZxyz.uib.no
>> Phone: +47-55-583491 - Home: +47-55-910661
>> Fax: +47-55-584330
> Professor Keith Briffa,
> Climatic Research Unit
> University of East Anglia
> Norwich, NR4 7TJ, U.K.
> Phone: +44-1603-593909
> Fax: +44-1603-507784
Division of Earth and Ocean Sciences,
Nicholas School for the Environment and Earth Sciences,
Duke University, Durham NC 27708
Ph: 919 684 6167, fax 684 5833
email: email@example.com, http://www.env.duke.edu/faculty/bios/hegerl.html