Estimation of natural and anthropogenic contributions to twentieth century temperature change
w...@bas.ac.uk
Note that this, in contrast to some postings I've seen here,
suggests that the early 20th C warming was a mix of GHG and
natural factors. The idea that the early 20C warming was
entirely natural seems to have taken hold in some quarters.
They confess to the troposphere problem...
-W.
Estimation of natural and anthropogenic contributions to twentieth century temperature change
Tett SFB, Jones GS, Stott PA, Hill DC, Mitchell JFB, Allen MR, Ingram WJ, Johns TC,
Johnson CE, Jones A, Roberts DL, Sexton DMH, Woodage MJ
JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES 107 (D16) 4306 AUG 27 2002
Abstract:
[1] Using a coupled atmosphere/ocean general circulation model, we have simulated
the climatic response to natural and anthropogenic forcings from 1860 to
1997. The model, HadCM3, requires no flux adjustment and has an interactive
sulphur cycle, a simple parameterization of the effect of aerosols on cloud
albedo (first indirect effect), and a radiation scheme that allows explicit
representation of well-mixed greenhouse gases. Simulations were carried out in
which the model was forced with changes in natural forcings (solar irradiance
and stratospheric aerosol due to explosive volcanic eruptions), well-mixed
greenhouse gases alone, tropospheric anthropogenic forcings (tropospheric ozone,
well-mixed greenhouse gases, and the direct and first indirect effects of
sulphate aerosol), and anthropogenic forcings (tropospheric anthropogenic forcings
and stratospheric ozone decline). Using an "optimal detection''
methodology to examine temperature changes near the surface and throughout the
free atmosphere, we find that we can detect the effects of changes in
well-mixed greenhouse gases, other anthropogenic forcings (mainly the effects
of sulphate aerosols on cloud albedo), and natural forcings. Thus these have
all had a significant impact on temperature. We estimate the linear trend in
global mean near-surface temperature from well-mixed greenhouse gases to be
0.9 +/- 0.24 K/century, offset by cooling from other anthropogenic forcings of
0.4 +/- 0.26 K/century, giving a total anthropogenic warming trend of 0.5 +/-
0.15 K/century. Over the entire century, natural forcings give a linear trend
close to zero. We found no evidence that simulated changes in near-surface
temperature due to anthropogenic forcings were in error. However, the simulated
tropospheric response, since the 1960s, is similar to50% too large. Our
analysis suggests that the early twentieth century warming can best be explained
by a combination of warming due to increases in greenhouse gases and
natural forcing, some cooling due to other anthropogenic forcings, and a
substantial, but not implausible, contribution from internal variability.
In the second half of the century we find that the warming is largely caused by
changes in greenhouse gases, with changes in sulphates and, perhaps, volcanic
aerosol offsetting approximately one third of the warming. Warming in the
troposphere, since the 1960s, is probably mainly due to anthropogenic forcings,
with a negligible contribution from natural forcings.
--
William M Connolley | w...@bas.ac.uk | http://www.nerc-bas.ac.uk/icd/wmc/
Climate Modeller, British Antarctic Survey | Disclaimer: I speak for myself
I'm a .signature virus! copy me into your .signature file & help me spread!
news.cis.dfn.de
<w...@bas.ac.uk> wrote in message news:3ed3...@news.nwl.ac.uk...
> An interesting abstract from the Hadley Centre.
>
> Note that this, in contrast to some postings I've seen here,
> suggests that the early 20th C warming was a mix of GHG and
> natural factors. The idea that the early 20C warming was
> entirely natural seems to have taken hold in some quarters.
> They confess to the troposphere problem...
>
> -W.
>
> Estimation of natural and anthropogenic contributions to twentieth century
temperature change
> Tett SFB, Jones GS, Stott PA, Hill DC, Mitchell JFB, Allen MR, Ingram WJ,
Johns TC,
> Johnson CE, Jones A, Roberts DL, Sexton DMH, Woodage MJ
> JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES 107 (D16) 4306 AUG 27 2002
>
> Abstract:
> [1] Using a coupled atmosphere/ocean general circulation model
BINGO!!
Any resemblence between this article and reality exists only in the minds of
the seriously deluded.
w...@bas.ac.uk
><w...@bas.ac.uk> wrote in message news:3ed3...@news.nwl.ac.uk...
>> Note that this, in contrast to some postings I've seen here,
>> suggests that the early 20th C warming was a mix of GHG and
>> natural factors....
>>
>> Estimation of natural and anthropogenic contributions to twentieth century
>temperature change
>> Tett SFB, Jones GS, Stott PA, Hill DC, Mitchell JFB, Allen MR, Ingram WJ,
>Johns TC,
>> Johnson CE, Jones A, Roberts DL, Sexton DMH, Woodage MJ
>> JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES 107 (D16) 4306 AUG 27 2002
>>
>> Abstract:
>> [1] Using a coupled atmosphere/ocean general circulation model
>Any resemblence between this article and reality exists only in the minds of
>the seriously deluded.
Ideally you'd read it to find out, but your prejudices are able to think
for you.
By some magic you think you know what caused temperature changes at
various times. But you need to study the data to find that out, and the
only method that can truly disentangle the various forcings is a
good AOGCM.
-W.
Roger Coppock
AN optimal detection methodology:
Which optimal detection methodology?
Could you list several other optimal detection methodologies?
How can there be more than one optimum?
--
"One who joyfully guards his mind
And fears his own confusion
Can not fall.
He has found his way to peace."
-- Buddha, in the "Pali Dhammapada,"
~5th century BCE
-.-. --.- Roger Coppock (rcop...@adnc.com)
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w...@bas.ac.uk
>w...@bas.ac.uk wrote:
>> Using an "optimal detection''
>AN optimal detection methodology:
>Which optimal detection methodology?
>How can there be more than one optimum?
Its just the name for a particular technique, which is optimum in
a particular sense. In brief, rather than look at some arbitrary
function of geographical sfc t (ie, rather than just avg(sfc t))
you select the function to have a better noise-avoiding and
signal-maximising behaviour.
>> methodology to examine temperature changes near the surface...
-W.
--
William M Connolley | w...@bas.ac.uk | http://www.antarctica.ac.uk/met/wmc/