date: Wed, 16 Sep 1998 14:08:02 -0700 from: "Pitcher, Hugh M" subject: RE: WGI emissions/scenarios conference to: 'Mike Hulme' 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. cheers, hugh -----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. and 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 much 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 able to run all 4 emissions scenarios through their GCM. From an impacts perspective I believe this would be very desirable and would enable a fair range of climate change scenarios to be used in impacts work using direct GCM output (without the need for scaling). And if all four Markers could 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) to explore, to get us away from single number 'answers'. amen 2. If a single emissions scenario *has* to be adopted by some GCM groups, 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 probably 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) should 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 with the SRES stories and emissions wherever possible. The internal consistency 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 scenarios. 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 values (and the fact that 1990s C emissions diverge from those observed) is more serious. By 2000 the four Markers range in C emissions from energy sources 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 hence (as Tom Wigley has pointed out). For example, by the time TAR is published 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 this will take up to 12 months to be agreed and published. Should not someone (WGI or WGIII TSUs) impose a temporary solution now for climate modellers? 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. CH4 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 least we need some assurance from SRES that there has been some investigation into these differences and that they will withstand scientific scrutiny in peer review. Again, maybe the open-process may lead to revisions, but what 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 cases]. 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. Mike **************************************************************************** Dr Mike Hulme Reader in Climatology tel: +44 1603 593162 Climatic Research Unit fax: +44 1603 507784 School of Environmental Science email: m.hulme@uea.ac.uk University of East Anglia web site: http://www.cru.uea.ac.uk/~mikeh/ 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 ****************************************************************************