Thursday, December 1, 2011

0300.txt

date: Mon, 16 Mar 2009 14:08:31 +0100
from: Bo Christiansen <bocatXYZxyz.dk>
subject: Paper on climate reconstructions
to: gerd.buergeratXYZxyz.fu-berlin.de, wahleatXYZxyzred.edu, Francis.ZwiersatXYZxyzgc.ca, ammannatXYZxyzr.edu, ycen@bgc-jena.mpg.de, geqs@igsnrr.ac.cn, guiotatXYZxyzege.fr, boli@ucar.edu, mschofield@maths.otago.ac.nz, jsmerdonatXYZxyzo.columbia.edu, zhengjy@igsnrr.ac.cn, storchatXYZxyzs.de, k.briffaatXYZxyz.ac.uk, mannatXYZxyz.edu, stephen.mcintyreatXYZxyzronto.ca, srutherfordatXYZxyz.uri.edu, p.jonesatXYZxyz.ac.uk, eduardo.zoritaatXYZxyzs.de, anders.mobergatXYZxyzgeo.su.se, Juerg Luterbacher <juergatXYZxyzb.unibe.ch>, Andrew Weaver <weaveratXYZxyzc.ca>, Alexey Kaplan <alexeykatXYZxyzo.columbia.edu>, john.christyatXYZxyztc.uah.edu, g-northatXYZxyzu.edu, fbiondi@unr.nevada.edu, bloomfieldatXYZxyzt.ncsu.edu, kcuffey@berkeley.edu, robted@eas.gatech.edu, edruffel@uci.edu, nychkaatXYZxyzr.edu, ottobliatXYZxyzr.edu, C.N.RobertsatXYZxyzmouth.ac.uk, karl.turekian@yale.edu, wallaceatXYZxyzos.washington.edu, Peter Thejll <pth@dmi.dk>, Torben Schmith <tsatXYZxyz.dk>, riedwyl@giub.unibe.ch, bocatXYZxyz.dk

Dear All,

Our paper "A surrogate ensemble study of climate reconstruction methods:
Stochasticity and robustness" has now been published in J. Clim.

It is here:
<http://ams.allenpress.com/perlserv/?request=get-abstract&doi=10.1175%2F2008JCLI2301.1>

or here
<http://web.dmi.dk/fsweb/solar-terrestrial/staff/boc/reconstr_reprint.pdf>

A VERY brief summary:

Methods:
1) Seven different reconstruction methods are tested
on the same data. These methods include both direct reconstructions
of the NH mean temperature and field reconstruction methods.
The field methods include both the original method of Mann et al. 1998,
the RegEM Ridge and RegEM TTLS methods used in more recent work.

2) We use a field surrogate method to estimate the stochasticity that
is always present in regression methods.

Results:
1) All methods strongly underestimates the amplitude of
low-frequency variability and trends. This means that
it is almost impossible to conclude from reconstruction studies that
the present period is warmer than any period in the
reconstructed period.

2) There is a large element of chance in the reconstructions.
This might also explain some of the opposing results obtained
in previous studies.


In a new paper we have submitted to J. Clim. (under review) we
use the the same methodology to test sea level reconstruction methods.
The paper is here:
<http://web.dmi.dk/fsweb/solar-terrestrial/staff/boc/sealevel.pdf>

These methods are closely related to the temperature reconstruction methods.
Now tide-gauge measurements take the place of temperature proxies,
and satellite altimetry the place of temperature observations.
For the sea level reconstructions the situation is simpler than for
temperature reconstructions because the tide gauges are direct measurements
of sea level and do not include noise. We can therefore easier
identify the sources of the errors in the reconstructions
and stratify the errors into contributions from limited spatial coverage
of gauges and non-stationarity of the sea level field.


Best wishes -Bo

--
Bo Christiansen E-mail: bocatXYZxyz.dk
Danish Climate Centre Phone : (+45) 39 15 74 29
Danish Meteorological Institute Fax: (+45) 39 15 74 60
Lyngbyvej 100, DK-2100 Copenhagen O, Denmark
http://www.dmi.dk/solar-terrestrial/staff/boc/homepage.shtml

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