Are there arguments for using ACRIM over PMOD, or vice-versa?

Question

There is a very interesting discussion of these 2 TSI measurements here:

http://tamino.wordpress.com/2007/07/27/pmod-vs-acrim-part-2/

which points out:

"One of the greatest sources of difficulty in matching up the various satellite data sets is the “ACRIM gap.” The lauch of ACRIM II was delayed, due to the shuttle Challenger explosion, so there is a roughly 2-year gap between the end of the ACRIM I data set and the beginning of ACRIM II, from early/mid-1989 to late 1991. However, two different data sets are available which overlap both missions: HF (Nimbus 7) and ERBS. Unfortunately, these two show different trends during the ACRIM gap. Depending on which one accepts as more reliable, one gets decidedly different results when joining ACRIM I to ACRIM II."

Willson & Mordvinov (2003, Geophysical Research Letters, vol. 30, pg. 1199) conclude that ACRIM is the more accurate composite, but the author here argues that PMOD is better.

Anyone know of another argument for either?

Yeah the IRMB and Kitt Peak comparisons were discussed in my link. That seems like a good reason to favor the PMOD composite.

There have been a few discussions of that Scafetta & West paper

http://answers.yahoo.com/question/index;_ylt=AoeuTAY_gk.e9tXGWvoGKfwjzKIX;_ylv=3?qid=20071012155438AAM95Xn
http://answers.yahoo.com/question/index;_ylt=Ahj_9Ts6XCPlEPR8x0ZiSSPsy6IX;_ylv=3?qid=20071026173006AAbnszA

According to RealClimate, they made some unrealistic assumptions. More realistic assumptions would result in a 0 and 10% solar irradiance contribution to the forcing since 1980 using PMOD and ACRIM, respectively.

Even if they are correct in their assumptions, it's quite interesting that the most they can attribute to solar irradiance is one-third of the forcing.

And that one-third of the warming attribution also used the ACRIM data.

Answer 1

PMOD also agrees with the IRMB data and with the Kitt Peak magnetograms (see links below). ACRIM does not agree so well. Agreement with two independent estimates would suggest that PMOD is to be preferred. However, even if the ACRIM trend is correct, the increase only accounts for at most a third of the observed warming from 1980-2000. ACRIM might be correct, but it still can't account for the observed warming.

There is a reason the IPCC AR4 concludes strongly the observed warming over the last 25 years is due mainly to radiative forcing from CO2.

edit:

Dana: At the risk of forming a little mutual support group, I agree with your assessments, I was just trying to put the debate into the context of the peer-reviewed literature. You are also correct that the fact that using the most liberal assumptions and the ACRIM data only accounts for 35% of the observed warming implies solar forcing is not responsible for the recent increase in global temperature. It is observations like this that explain why the IPCC AR4 is so definitive in its conclusions. There are simply no credible mechanisms besides greenhouse gas forcing to explain the observed warming.

The situation with respect to climate change and the skeptics reminds me of Pete Duesberg and HIV, where Duesberg's objections to a causal link between HIV and AIDS were whittled away to nothing. Here is a review of a book by Duesberg from Nature:

http://www.nature.com/nature/journal/v380/n6572/pdf/380293a0.pdf

Like Duesberg, the skeptics arguments are being whittled away until all that is left is venom, and maybe fear.

Answer 2

I think I am going to have to stick with ACRIM, Dana, just so you don't tell me at some future debate that we have already been over this and the matter was settled, let it be known there are some technical issues with the PMOD correction. And any assesment of climate change which involves PMOD is utilizing data that is in dispute.

Secular total solar irradiance trend during solar cycles 21–23
Richard C. Willson
Center for Climate Systems Research, Columbia University, Coronado, California, USA
Alexander V. Mordvinov
Institute of Solar-Terrestrial Physics, Russian Academy of Sciences, Irkutsk, Russia

Conclusions:

[24] Construction of TSI composite databases will not be
without its controversies for the foreseeable future. However
we believe the ACRIM composite and trend represents
the best interpretation of the information presently available
for solar cycles 21–23.

Further..

The absence of a minima-to-minima trend in the
PMOD composite is an artifact of uncorrected ERBS
degradation. ERBS degradation during the gap equals the
trend difference and the PMOD offsets (within computational
uncertainty).