date: Mon, 01 Oct 2007 02:29:01 +0200
from: Bo Vinther <b.vintheratXYZxyz.ac.uk>
subject: Re: 20th century
Just looked a bit more into the SO2-emissions....
Based on fig. 1 in the attached paper on European/Russian SO2-emissions we might consider
to reverse the forcing as late as 1975.
Especially since modeling efforts suggest that Arctic sulphate comes mostly from Europe and
Russia (see fig. 3 in the second attached paper).
Greenland - being quite close to North America probably gets more of the North American
SO2-emissions than does most of the Arctic (North American emissions peaked in the period
1965-75 - as seen in Greenland).
Thomas Kleinen wrote:
Thanks for sending that Greenland data.
The volcanic aerosols are independent from the anthropogenic. Therefore it's
no problem at all to keep them.
I'll look into creating a suitable aerosol forcing timeseries during the next
couple of days.
On Thursday 27 September 2007, Bo Vinther wrote:
I really like the idea of mirroring the sulphate - based on the
Greenland data (see attached), I would go for reversing the forcing in
1970 (without reversing the sulphate from volcanoes - if we can avoid it?).
If feasible, I do think it would be interesting to run the model a bit
longer than 2007 - maybe to 2020 - to see what is ahead of us....
Thomas Kleinen wrote:
Well, control run is done with fixed orbital conditions (supposedly late
20th century), so I guess we can leave that.
I have volcanic & solar timeseries until 1999/2000, and my original idea
was to include those for as long as we have them to get the historical
forcings right, and then not worry about the few years afterwards
(doesn't matter in the volcanic case anyway). We can still update them
later if we decide we need solar variability after 2000 (the volcano code
assumes 0 aerosol optical depth after 2000). Since it will take a
fortnight to reach 1990 anyway, we need to decide on the forcings for the
earlier part now, though.
I have Sulphate emissions / albedo change patterns until 2100 for the SRES
A2 (the ozone file for some reason is for the B2, but that shouldn't make
a big difference in those first years).
So my idea was to run one experiment with the SRES forcings, and one with
the forcings changed in the N Atlantic / Arctic area, just as you
suggested. I'll have to look at the scenario data to decide on the best
time for the switchover to reductions, though, I haven't quite made up my
mind there yet. (As I indicated earlier, we still have time to decide on
On Thursday 27 September 2007, Tim Osborn wrote:
I think orbital doesn't matter either way, so whatever is easiest and
also consistent with the initial conditions (i.e. if control run is NOT
set up with 1860 orbital forcing, you would have an unwanted step in
forcing if you began from that and suddenly switched to 1860 orbital
forcing; on the other hand, if it has been run with 1860 orbital
conditions, then clearly the orbital option becomes possible and the
decision is yours!).
Solar also probably won't have a large influence, though volcanoes might.
But are you running up to 2000 or 2007 and do you have solar/volanic
forcing up to that point? Of course, with little activity since
Pinatubo, the volcanic forcing that you do have -- perhaps to 1999? --
might already have returned to low constant aerosol optical depth values
which could be continued on at a constant level to 2007? Solar, if
used, would need to be updated too, assuming you are running through to
GHGs you will hopefully get from Sarah.
Aerosols, did you think my suggestion of running with existing forcing
through to ~1965 and then running reverse forcing (for N. Atlantic/Arctic
region only?) 1965..1925 for 1966-2007 is workable? Would need some
careful consideration, but since we cannot redo the sulphur transport and
indirect effect modelling, we will do better with potential referees if
we do something deliberately idealised rather than a poor attempt at a
more realistic forcing.
Also, presumably we will want to do 2 runs, one with all these forcings
and the OLD too high aerosols, and then a second with all forcings
identical except for the NEW lower aerosols in N. Atl. and Arctic. So,
if running as far as 2007, we need OLD too high aerosols up to 2007 as
well. Not sure how to get/extrapolate these?
You might want to forward this to Bo & Keith in case they have different
On Thu, September 27, 2007 12:21 pm, Thomas Kleinen wrote:
I still need to do a more detailed check, but right now it looks like
the modern climate run might actually be working.
Therefore I am wondering how to set it up exactly - should I include
solar and volcanic forcing as well?
I guess it might be best to do as realistic a run as possible.
GHG I would start from control run levels - doing it from the Nat run
also involve adjusting the vegetation fields (and running from 1750,
right now I am planning on running from 1860), and I'd prefer not to do
What do you think?
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