0887057295 - From Tom Wigley <[email protected]> To Mike Hulme Subject Re New MAGICC/SCENGEN Date Mon 9 Feb 1998

Info iconThis preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon
From: Tom Wigley <[email protected]> To: Mike Hulme <[email protected]> Subject: Re: New MAGICC/SCENGEN Date: Mon, 9 Feb 1998 15:48:15 -0700 (MST) Reply-to: Tom Wigley <[email protected]> Cc: [email protected], [email protected] Mike, Thanks for the quick response. Responses to responses follows. ... (1) I tried the composite GHG plus UIUC SUL on Norm's machine, in just the way you said. However, the results for the USA seem to be identical to those using *only* UIUC GHG input. I'll try again. (2) You are right in saying one shouldn't scale GHG patterns by GHG+SUL dTs. However, to be strictly consistent one should never allow GHG patterns to be used alone. So you are *not* being consistent if you allow this---which you do. The point then is to minimize the extent of the inconsistency. It is unarguably correct that the global-mean temperature to use is the one containing all forcings (i.e., column 6 in *DRIVE.OUT). The choice then is what pattern(s) to use. If we had no SUL information, we would have to use GHG patterns; as in the original SCENGEN. Scaling these with the MAGICC GHG output would give both incorrect patterns and incorrect global-mean warming. Scaling with column 6 at least gets the global-mean warming correct (within MAGICC uncertainties). You seem to have chosen to get *both* things wrong, instead of just the patterns. I can see some logic in your method; I just think (strongly) that it is wrong. At the very least, it will be confusing to the user. If the user selects only GHG model patterns, then won't they wonder why the global-mean temperature is inconsistent with MAGICC? To take an extreme case, suppose the full dT is 2degC and the GHG-alone dT is 3degC. Is it better to scale an approximate pattern (i.e., the GHG pattern) by 2degC or 3degC? In my view, GHG scaled by 2degC would be much closer to GHG+SUL scaled by 2degC than GHG scaled by 3degC. Surely the real issue (given that it is impossible to be entirely consistent in this case) is to get a result that is as close to the 'right' result as possible. I feel quite sure that scaling by column 6 is best on this basis---especially given that the patterns are much more uncertain than the global-means. I think this is absolutely beyond doubt. The bottom line here is that consistency is impossible if one uses only GHG patterns. Column 6 was included deliberately, and after some thought (along the lines noted above). Of course, it is possible to get column 6 results by adding columns 2, 3, 4 and 5 as they now stand (and as they are in the version that you have). However, one cannot do this with the correct *raw* column 3, 4, and 5 output because of the nonlinear direct forcing effect. It just happens that, in your version, I 'faked up' column 5 as the
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 2
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 12/16/2009 for the course CLMT 0032456 taught by Professor Ellison during the Spring '09 term at Abraham Baldwin Agricultural College.

Page1 / 5

0887057295 - From Tom Wigley <[email protected]> To Mike Hulme Subject Re New MAGICC/SCENGEN Date Mon 9 Feb 1998

This preview shows document pages 1 - 2. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online