date: Tue, 26 Jul 2005 14:27:29 -0400 (EDT)
from: Jason E Smerdon <jsmerdonatXYZxyzch.edu>
subject: Re: NH Borehole Timeseries
to: Tim Osborn <t.osbornatXYZxyz.ac.uk>
Attached are three borehole reconstruction time series for the Southern
Hemisphere, Africa and Australia. I have also included a pdf file
containing the plots for the three series and the corresponding SAT time
series that I used to reference the boreholes.
There are several things to keep in mind with regard to the SH
reconstructions. The SH dataset is much smaller than the NH dataset.
There are a total of 165 sites in the SH, as compared to the 695 sites in
the NH. The African and Australian subsets include 92 and 57 sites,
respectively. The SH hemisphere is therefore much more sparsely sampled.
As such, we have only computed point averages in each of the included
reconstructions and noise may be more of a factor in the SH than in the
Additionally, more than half of the holes in the SH were measured before
1980. While this is true of places in the NH as well, the hemisphere
includes many more measurements during the 80s and 90s. Many of the
measurements in the SH therefore have missed much of the extreme warming
in the latter two decades of the 20th century. We have taken this into
account by referencing the boreholes to shortened periods in the 20th
century SAT record, i.e., we used SAT trends from 1900 (1910 in the case
of Australia) to the median borehole logging dates. The fact that the
boreholes have not measured the late 20th-century warming is clearly
visible in each of the plots that I have included.
Each of the above points necessitate cautious interpretations of the SH
record. Given that the provided reconstructions have been assembled in a
bit of a hurry, Henry and I hope that we will have further chances to
refine the reconstructions themselves (if needed) and their subsequent
interpretation. It would also be very helpful to see the ensemble
comparison including all of the SH reconstructions once it is completed.
In the meantime, let me know if you need anything else.
I hope that all is well. Best of luck with the IPCC duties and I hope
that the included reconstructions are helpful.
____ ____ Jason E. Smerdon, Ph.D.
[ \ / ] Dept. of Geological Sciences
| \/ | University of Michigan
| | 1100 N. University Ave.
| |\/| | Ann Arbor, MI 48109-1005
| | | | Phone: (734) 657-9747
[____] [____] Fax: (734) 763-4690
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