Tuesday, March 27, 2012


date: Wed, 16 Sep 1998 14:08:02 -0700
from: "Pitcher, Hugh M" <hugh.pitcheratXYZxyz.gov>
subject: RE: WGI emissions/scenarios conference
to: 'Mike Hulme' <m.hulmeatXYZxyz.ac.uk>

Hi Mike,

As an internal constructor, I have concerns about GNP growth rates being much
too high, leading to per capita incomes in 2100 that are a factor of two to
three too high--implying impacts wiol be less of a problem. From a carbon point
of view, these high GNP levels are offset by high reductions in final energy
demand, and high rates of decarbonization, leading to carbon scenarios that are
not too bad. I am working on a spreadsheet model that will allow a quick and
dirty way to redress these issues. But the modeling groups have already put in
a lot of work, and are not likely to be willling to go back to square one and
redo things. This is particularly an issue for compute intensive tools such as
message, image, and Maria.

see below for my reactions to the points you make.

could you send this on to scenario discussion group. Outlook is not treating me
well on trying to get the message to everybody.


-----Original Message-----
From: Mike Hulme [SMTP:m.hulme@uea.ac.uk]
Sent: Tuesday, September 15, 1998 4:23 PM
To: scenarios
Subject: WGI emissions/scenarios conference

Dear All,

Here are three comments on the questions raised by WGI TSU on 7 Sept.
by some of the other contributions to the discussion about scenarios for
IPCC TAR. I am commenting from the perspective of a climate scenario
constructor servicing the impacts research community:

1. The SRES Working Group have identified 4 Marker Scenarios (out of a
larger range, although these 4 largely capture the range). I think the
choice is good. I do not see why some modelling centres should not be
to run all 4 emissions scenarios through their GCM. From an impacts
perspective I believe this would be very desirable and would enable a
range of climate change scenarios to be used in impacts work using
GCM output (without the need for scaling). And if all four Markers
be run through more than one GCM (i.e., with different climate
sensitivities) then impacts work would have an even better sample of the
possible climate change space to analyse. These aspects of uncertainty
seem to me to be critical for impacts people (and integrated assessors)
explore, to get us away from single number 'answers'.


2. If a single emissions scenario *has* to be adopted by some GCM
B2 seems to have the recommendation from Naki (and maybe SRES too - the
storyline refers to it as 'dynamics as usual'). I think there are
good reasons why SO2 emissions fall so much in this storyline - regional
rather than global solutions and the encouragement of environmental
protection. The fact that the reduced C emissions relative to IS92a are
offset by the big fall in SO2 emissions (the net global warming in B2 is
actually slightly higher than IS92a if aerosol effects are included)
simply be seen as a reflection of a more carefully worked out storyline
than was the case with IS92a. I do not think it a good idea (indeed, I
think it would be a very *bad* idea) for GCM centres to mix-and-match
elements of IS92 and SRES98 scenarios - the TAR should try and stick
the SRES stories and emissions wherever possible. The internal
in these storylines (and hopefully emissions) is important to maintain
(especially later on for impacts work), and the thinking behind the SRES
scenarios is considerably better than was achieved in the IS92

I agree about not mixing. the real issue is finding a good way to fill
in emissions that are not estimated by a given group. We may need an explicit
table that each group fills in that gives which sources they do estimate. see
response to question 4.
3. The problem of different Markers having different 1990 emissions
(and the fact that 1990s C emissions diverge from those observed) is
serious. By 2000 the four Markers range in C emissions from energy
from 6.6GtC (B1) to 8.0 GtC (A1). Given where we are right now (about
6.7GtC in 1997) it seems daft to have such a range for only 2 years
(as Tom Wigley has pointed out). For example, by the time TAR is
we will know that A1 C emissions for 2000 are too high by, say, 15%.
Surely we need to impose a 'fix' on all 4 Markers to account for this.
Such amendment may occur as a result of the SRES 'open-process', but
will take up to 12 months to be agreed and published. Should not
(WGI or WGIII TSUs) impose a temporary solution now for climate

The problem is that different models use different baseline data sets,
and this is very expensive to redo. One approach is to adapt a common 1990 data
set and then apply model based rates of change to get to predicted levels. This
does not solve the year 2000 problem, or the year 2005 or 2010 problem. The
larger issue here is that most of the long term scenarios that are available
have economic growth rates that are implausibly high, and this was true before
the current financial crisis began. Good sceanrios for the short term require
very different kinds of tools than we are using for the long term scenarios. I
would be willing to vote for a uniform set of emissions values for the year 2000
and then let the models diverge from there, based on their growth rates. We
would still have to come to an agreement about what the economic activity and
emissions levels would be for the year 2000.

Similarly, something needs to be done for CH4 and N20 1990 emissions.
1990 emissions range from 281 to 481Tg in the 4 Markers (compared with
506Tg in IS92). Surely this range is not defendable. I think at the
we need some assurance from SRES that there has been some investigation
into these differences and that they will withstand scientific scrutiny
peer review. Again, maybe the open-process may lead to revisions, but
do climate modellers do in the meantime? [By the way, the difference in
global warming by 2100 that the SRES CH4 and N2O scenarios generates
relative to those in IS92a is between 0.05 and 0.3degC - lower in all

the issue here is that all the models do not do ag and land use
emissions, leading to lower values because these emissions are omitted. Another
issue that has recently arisen here is that animal manure is a significant
source of n20--latest ipcc protocol on emissions--and is apt to grow rapidly.
this changes our understanding of the potential role of agriculture when it
comes to trying to stabilize climate.

Dr Mike Hulme
Reader in Climatology tel: +44 1603 593162
Climatic Research Unit fax: +44 1603 507784
School of Environmental Science email: m.hulmeatXYZxyz.ac.uk
University of East Anglia web site:
Norwich NR4 7TJ

Mean temp. in Central England during 1998 is running
at about 1.2 deg C above the 1961-90 average
The global-mean surface air temperature anomaly estimate for the
first half of 1998 was about +0.60 deg C above the 1961-90 average,
the warmest such period yet recorded


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