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Long story short: I'm here: http://www.eastangliaemails.com/emails.php?eid=455 and here's what I'm reading: At 15:44 20/12/2004, Kevin Trenberth wrote: Hi all I have received comments on this from Albert, David, Dave, and Jim. Some below. As I commented to Jim, the choice of a base period affects the zero line. In some of our plots, namely the ones that have series of bars from the zero line to the anomaly value, thereby infilling between the anomaly and the zero, the zero base value is greatly emphasized. This is in contrast to a simple time series with points joined, especially if the zero line is not also drawn. In the latter case, it is simple to move the axis up or down to fit with the new base period. But it makes a bigger difference to the bar plots. Now maybe that is a comment on the use and utility of bar plots, because the relative values do not change. The choice also affects any anomaly plots for any subperiod. But this is where the comparison with models is most likely to occur. In this case there is a spatial pattern to the offset, namely the difference between means for 1961-90 and 1981-2000. We could also derive that difference for certain fields and provide it to modelers to enable comparisons with our plots. For trends over certain subperiod, this makes no difference. It seems that whatever we do, we will need an extra appendix explaining some of this and perhaps even giving plots of these differences. In the meantime, let me suggest to those of you making computations, that you consider doing it both ways, rather than having to go back and do it over later. Regards Kevin I agree with Albert, this would make comparisons with the TAR figures difficult. Dave Klein Tank, Albert wrote: Hi Kevin, My immediate response is that the choice for another base period will probably not affect our assessment of results, but it will change all figures w.r.t the TAR. This will be difficult to communicate and will take much more space to explain. Albert. --- Original Message ---- Subject: Re: [Fwd: Re: "Model Mean Climate" for AR4] Date: Mon, 20 Dec 2004 13:06:44 +0000 From: Parker, David (Met Office) [1] To: Kevin Trenberth [2] References: [3]<41C34CDA.3060304@xxxxxxxxx.xxx> Kevin It is obviously possible to use 1980-2000 though it would require some data-processing work. The main objection is that anomalies (of temperature) would appear to be reduced relative to previous publications and readers/policymakers could become confused. A minor objection is that 1980-2000 is a bit short. Satellite data are of course in its favour. In due course, 1981-2010 will be ideal! Regards David " end quote Happy hunting, everyone!!! LOL! Sorry for the crappy formatting, not my intention.