Comments on: Hansen Scenarios A and B – Original

By: George M

George M — Fri, 18 Jan 2008 22:01:43 +0000

Steve:

These formatting limitations suck. Why not use the form “3%/yr” instead of “3%yr-1″, which to me is subject to lots of different misinterpretations? Or is that format what happens when you cut and paste?

By: Phil.

Phil. — Fri, 18 Jan 2008 20:04:22 +0000

Business as usual appears to have assumed that the Montreal protocol wouldn’t be implemented which would be ‘business a usual’.
I’m not sure what your units for CFCs are, as I recall CFC 11 peaked at about 270ppt and CFC 12 at about 540ppt so I assume the units are ppt? I don’t know how well those levels were known in 1987, Hansen’s data appeared to be based on production.
Regarding Methane the rate of increase started in to drop off in 92 reaching zero on 2000, NOAA’s data appears to start in 1983 at ~ 1620ppb. Notably higher values were observed in the N hemisphere (upto ~1900ppb)
A NASA report in 1989 (http://www.nap.edu/catalog.php?record_id=1193) gives a contemporary value of 1690ppb which is reasonably consistent with Hansen’s value.

It would be a mistake to assume that the values now attributed to the atmosphere in 1987 were known at that time.

By: Steve McIntyre

Steve McIntyre — Fri, 18 Jan 2008 20:02:15 +0000

#3. No, it’s more than a typo. The first part of the text (which I quoted) says:

In Scenario A, … CCl3F (F-11) and CCl2F2 (F-12) emissions are from reported rates (Chemical Manufacturers Association (CMA) 1982] and assume 3% yr-1 increased emission in the future with atmospheric lifetimes for the gases of 75 and 150 years respectively. ,, In Scenario B… the annual growth of CFC11 and CFC12 is reduced from 3% yr-1 today to 2% yr-1 in 1990, 1% yr-1 in 2000 and 0 in 2010….

This constructs Scenario A and Scenario B in the same way up to 1990 when Scenario B growth is reduced. This form of expression for other GHGs yields identical results. The Scenario A values seem way off.

By: Steve Geiger

Steve Geiger — Fri, 18 Jan 2008 19:44:37 +0000

NGS – are you confusing emissions with the forcing (or conc.)?

By: nanny_govt_sucks

nanny_govt_sucks — Fri, 18 Jan 2008 19:31:13 +0000

In Scenario B… the annual growth of CFC11 and CFC12 is reduced from 3% yr-1 today to 2% yr-1 in 1990, 1% yr-1 in 2000 and 0 in 2010…. In Scenario C, CFC11 and CFC12 abundances are the same as scenarios A and B until 1990; thereafter CFC11 and CFC12 emissions decrease linearly to zero in 2000.

I don’t see CFC11 or CFC12 decreasing to 0 at all in your graphics above, unless I’m missing something…

By: PI

PI — Fri, 18 Jan 2008 19:30:14 +0000

I don't know if it's exactly the same code as what Hansen used (probably has bug fixes and other updates), but NASA does have the code for GISS Model II, which is the core of their educational EdGCM project. The original Model II is what Hansen used. It may be possible to run the available code using Hansen's 1988 forcings, and if it reproduces his 1988 projections, then run it with updated modern forcings to make the more relevant comparison. I expect that even with updated forcings, the 1988 model will still produce a somewhat higher temperature hindcast than what has been observed post-1988, since Model II's climate sensitivity (4.2 C) is on the high end of current estimates. (Actually, IIRC EdGCM does have some changes that puts its sensitivity even higher, ~5 C, so maybe it wouldn't be as useful a comparison.)

By: Gary

Gary — Fri, 18 Jan 2008 19:18:02 +0000

In Scenario C, CFC11 and CFC12 abundances are the same as scenarios A and B until 1990; thereafter CFC11 and CFC12 emissions decrease linearly to zero in 2000.

From the graphs labeled Hansen 1988: CFC11 (and the CFC12 one) is looks like “the same as scenarios A and B until 1990;” is a typo and should have only said “scenario B” instead of “A and B.” Now whether the text or the graph correctly represents the model, I can’t say.

As for “business-as-usual” it hard not to hear this being used pejoratively as a condemnation of CFC use with the intent of moving an agenda.

By: Mike B

Mike B — Fri, 18 Jan 2008 19:11:59 +0000

But it looks to me like forcings are coming in below even Scenario B projections. Thus, if Hansen’s projections over-state what we’re experiencing in 2005-2010, then this does not per se invalidate Hansen’s model, as some people are too quick to conclude.

Also make sure to examine the volcanic forcings. It looks to me like the cooling effect of the simulated volcano was greatly over-estimated.

By: Roger Pielke. Jr.

Roger Pielke. Jr. — Fri, 18 Jan 2008 18:46:20 +0000

Steve- Excellent.

I have posted up a comparison of Hansen, IPCC, and observed trends 1990-2007 here:

http://sciencepolicy.colorado.edu/prometheus/archives/climate_change/001330temperature_trends_1.html

If you’d like to create a separate thread for that here to focus discussion, that is fine. Otherwise, people can take their chances with our comments (be warned to save anything before submitting!) or just send me an email.