Hansen’s 1988 projections
At Jim Hansen’s now famous congressional testimony given in the hot summer of 1988, he showed GISS model projections of continued global warming assuming further increases in human produced greenhouse gases. This was one of the earliest transient climate model experiments and so rightly gets a fair bit of attention when the reliability of model projections are discussed. There have however been an awful lot of mis-statements over the years – some based on pure dishonesty, some based on simple confusion. Hansen himself (and, for full disclosure, my boss), revisited those simulations in a paper last year, where he showed a rather impressive match between the recently observed data and the model projections. But how impressive is this really? and what can be concluded from the subsequent years of observations?
The bottom line? Scenario B is pretty close and certainly well within the error estimates of the real world changes. And if you factor in the 5 to 10% overestimate of the forcings in a simple way, Scenario B would be right in the middle of the observed trends. It is certainly close enough to provide confidence that the model is capable of matching the global mean temperature rise!
Updated figure now at http://www.columbia.edu/~mhs119/Temperature/T_moreFigs/ or http://www.columbia.edu/~mhs119/Temperature/T_moreFigs/PNAS_GTCh_Fig2.pdf .
Steve,
you ARE factoring in that Hansen has said repeatedly that his forcing of 4.2° is wrong?
But then, he did NOT have that attributed to him in a Salon article, so I guess it is not credible.
Below scenario C.
100 year projections get changed every few years, but they are good for 100 years.
5-10% overestimate? Hmm, being generous. 1C – (1.0*0.1)= 0.9C for their scenario B that says that Hansen was “pretty close” on. So, no, not even when their fudge factor is introduced.
You ARE factoring that you’re defending a man who has said repeatedly that his original findings were wrong by 40% and quite possibly more than 100% (his revised estimate of 3°C±1°C could be 2°, or he could be saying it’s still 4°. Funny how that works when your estimate can vary over 33% ).
And to top it all off said in a 2006 paper that “Nevertheless, it is apparent that the first transient climate simulations proved to be quite accurate“
Also, if I remember correctly, you once told me that a 10% drop in Arctic ice levels was possibly significant, Yet you don’t seem alarmed that Hansen’s original climate sensitivity estimates we’re off anywhere between 40%-120%.
Care to explain?
One additional comment:
Have you ever pondered the question: What happens if, in another 20+ years, the estimates are revised down again? I’m sure you believed Hansen when he stated a 4° sensitivity in ’88(I know I did)
Hansen will color in the pinks and reds as needed for his forecast to verify. Also keeps coming up with revolutionary methods for angel counting on pins.
This man is one tough customer, especially with the media lapping up whatever he throws out there. But it’s all the the name of saving our planet, from dumb asses like us.
Looks perfectly straight-forward to me :
GHG emissions are proceeding as per Scenario “A”.
Global Temperatures are proceeding as per Scenario “C”.
Add them together, and divide by two, and you get Scenario “B”.
Top-quality science bought into your living-rooms by the people at Real Climate!
If scenario A is not realized then the entire model is Bullshit and the lies being used to to defend this piece of garbage science provide evidence that no science is being practiced.
Hansen should live by his original projections or admit the failings. The defendres live in a fantasy world!
Does that sink in Tony!