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CATEGORIES:Isaac Newton Institute Seminar Series
SUMMARY:Bayesian estimation of the climate sensitivity bas
ed on a simple climate model fitted to global temp
erature observations - Aldrin\, M (Norwegian Compu
ting Centre)
DTSTART;TZID=Europe/London:20101208T113000
DTEND;TZID=Europe/London:20101208T120000
UID:TALK28316AThttp://talks.cam.ac.uk
URL:http://talks.cam.ac.uk/talk/index/28316
DESCRIPTION:Bayesian estimation of the climate sensitivity bas
ed on a simple climate model fitted to global temp
erature observations\n\nMagne Aldrin\, Norwegian C
omputing Center and University of Oslo Marit Holde
n\, Norwegian Computing Center Peter Guttorp\, Nor
wegian Computing Center and University of Seattle\
n\nThe climate sensitivity is a central parameter
in understanding climate change. It is defined as
the increase in global temperature due to a doubli
ng of CO2 compared to pre-industrial time. Our aim
is to estimate the climate sensitivity by modelli
ng the relationship between (estimates of) radiati
ve forcing and observations of global temperature
and ocean heat content in post-industrial time. Co
mplex general circulation models are computational
ly expensive for this purpose\, and we use instead
a simple climate model of reduced complexity. Thi
s climate model is deterministic\, and we combine
it with a stochastic model to do proper inference.
\n\nOur combined model is\n\nyt = mt(xt-\, S\, the
ta) + nt\n\nHere\, yt is the observed vector of gl
obal temperature and ocean heat content in year t
and mt the corresponding output from the simple cl
imate model. Furthermore\, the model input xt- is
the unknown radiative forcing in year t and previo
us years. S is the climate sensitivity which is th
e parameter of interest andī theta is a vector with
other model parameters. Finally\, nt is an autore
gressive error term accounting for model errors an
d measurement errors. We use a flat prior for the
climate sensitivity and informative priors for mos
t other parameters.\n\nThe model was fitted to obs
ervations of global temperatures from 1850 to 2007
and of ocean heat content from 1955 to 2007. The
work is still in progress\, so the estimate of the
climate sensitivity is preliminary. However\, thi
s preliminary estimate is a few degrees Celsius ab
ove zero\, which is comparable with other estimate
s.\n\nWe believe that this approach is a valuable
addition to other methods for estimating the clima
te sensitivity\, where physical knowledge and obse
rved data are linked together by statistical model
ling and estimation methods.\n\nFrom a statistical
point of view\, it is an example of calibration o
f computer models\, but with more emphasis on mode
lling the discrepancy between the observations and
the computer model\, than on using an emulator or
surrogate model for the computer model\, that has
been central in much of the recent work in this a
rea.
LOCATION:Seminar Room 1\, Newton Institute
CONTACT:Mustapha Amrani
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