Hansen's 1988 scenarios and outcome

While arguing at WUWT, eg here, about Hansen's projections, I've been encountering arguments about which scenario should be applied. I did discuss that in last month's post on the projections. But I have since looked up more information on what they were, and how they panned out. In this post, I'll review the files, numbers, compare with current, and post what data we have. I'll also review a discussion by Stephen McIntyre at Climate Audit in 2008, and show some of his graphs. The conclusion is that based on input and outcome, the temperatures should lie between scenarios B and C.

People tend to want to argue in terms of what Hansen said about the scenarios. As I maintained earlier, that isn't the right test. Scientists work with scenarios because there are some inputs to the model that they just don't know (like how much carbon we'll burn). And there is no use parsing their language to learn more. What counts is what happened. But just to review, the usual claim is that H referred to Scen A as "Business as usual" in a Senate hearing. But that doesn't mean he thought that was what would happen. He actually said in the paper that Scen B was most "perhaps the most plausible". Hansen did muddy the waters by constantly referring to the scenarios in terms of emissions. In fact, his program used as input the actual gas concentrations, which he often describes as forcings. He does blur the two; a key discussion is on right, where he does describe the scenarios in terms of forcing.

While looking up scenario numbers, I found some detailed discussion in threads from 2008 on ClimateAudit (here, here, here, and here). They were calmer times, and the discussion is often reasonable. I'll quote from Steve McIntyre's conclusion of the second post

As to how Hansen’s model is faring, I need to do some more analysis. 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. To the extent that the differences lie in lower than projected forcings, I’m not prepared to place fault on the model for those defects. Whether the forcings account for the defects is a different matter and it would be interesting to run the 1988 model with actual GHG concentration changes – an experiment that’s long overdue and which would end much speculation about the merit or lack of merit of Hansen’s 1988 projections.

I think rerunning code from 20 years ago (then, now near 30) is less feasible than he thought.

There are two sources for the actual gas inputs to the GCM. One I linked to (RealClimate) in the last post. It was the original data for a paper in the following year (1989), so the numbers could have been updated slightly, but should be the same. The others were files made available through Gavin at RC. Their provenance is discussed length at CA; it seems to have involved a degree of digitisation. However, the general view sems to be that despite some noted oddities, they were basically accurate. The CA link is here. I have downloaded them, and made equivalent CSV files, which I have put into a zipfile here, including the 1989 file. In the CSV files, I have reduced the absurd precision (to 5 sig).

Here are the actual numbers for 2015, from that 1989 file, with CFC nums from here:

	CO2	N2O	CH4	CFC-11	CFC-12
	ppm	ppm	ppm	ppb	ppb
Scen A	403.0	0.34	2.78	1.398	2.4
Scen B	398.6	0.33	2.28	0.61	1.06
Scen C	367.8	0.31	1.916	0.26	0.51
Actual	399	0.328	1.83	0.23	0.52

Here are the corresponding numbers from the files sourced at CA:

Scen A  410.1  0.3426  2.336  0.814  1.333
Scen B  406.1  0.3364  2.284  0.719  1.182
Scen C  369.5  0.3364  1.929  0.366  0.618
Actual  399   0.328   1.83 0.23 0.52

I think the first (1989) set is more reliable. Hansen said in his 1988 paper, Appendix B, that CO2 in Scenario C settled to 368 ppm, and CH4 at 1.916 which matches. So on that basis, I think it is clear that CO2 is close to Scenario B, N2O also, while CH4 and the CFC's are below Scenario C. Actually there is a wrinkle here; Hansen doubled the CFC numbers to allow for other CFC species, so on that basis they are actually well below C. That is actually a tribute to the Montreal protocol, which came after Hansen's 1988 paper.

I was going to make graphs, but I think the CA ones (from here) will do, although they are based on the econd set of figures:


Finally, I'll include Hansen's Fig 2b, which shows the forcing effect combined with postulated volcanic eruptions in Scenarios B and C. The 1995 explosion was well matched by Pinatubo in 1991, but we're still waiting for the 2015 bang, though there have been several smaller ones.


Scenario data zipfile (txt and csv) here