Hansen et al 1988, retrospective

Reviewing the predictions of a seminal climate modeling paper, a quarter century later

In 1988 NASA's James Hansen and seven co-au­thors wrote a highly influ­en­tial, ground­break­ing cli­mate mod­el­ing paper entitled, Global Cli­mate Changes as Fore­cast by God­dard Insti­tute for Space Stud­ies Three-Di­men­sional Model (pdf). They used NASA GISS's GCM Model II (a pre­de­cessor of the cur­rent Model E2) to pre­dict future cli­mate change, under sev­eral scen­arios. They con­sidered the com­bined effects of five green­house gases: CO2, CFC11, CFC12, N2O, and CH4.

They pre­dicted a “warm­ing of 0.5°C per dec­ade” if emis­sions were not curbed. That was their “scen­ario A,” which they described as fol­lows: “Scen­ario A assumes that growth rates of trace gas emis­sions typ­ical of the 1970s and 1980s will con­tinue indef­in­itely; the assumed annual growth aver­ages about 1.5% of cur­rent emis­sions, so the net green­house for­cing increases expo­nen­tially.”

Now, I would agree that +0.5°C/dec­ade would be something to worry about! For­tu­nately, it was non­sense.

Un­der their “scen­ario A,” emis­sions would have increased by 1.5% per year, total­ing 47% in 26 years. In fact, CO2 emis­sions increased even faster than that. CO2 emis­sions increased by an aver­age of 1.97% per year, total­ing 66% in 26 years. Yet tem­per­at­ures increased only about one-fourth as much as their “scen­ario A” pre­dic­tion.

Even so, cli­mate alarm­ists fre­quently claim that the NASA GISS model was “re­mark­ably accur­ate.” Only in the massively politi­cized field of cli­ma­to­logy could a 300% error be described as remark­ably accur­ate. Even eco­nom­ists are embar­rassed by errors that large.

Addi­tion­ally, the Hansen et al claim that an annual 1.5% (i.e., expo­nen­tial) increase in GHGs causes an expo­nen­tial “net green­house for­cing” was a mind­bog­glingly obvi­ous blun­der. Even in 1988 it was com­mon know­ledge that CO2 (the most import­ant of the GHGs they dis­cussed) has a log­ar­ith­mic­ally dimin­ish­ing effect on tem­per­at­ure. So an expo­nen­tial increase in CO2 level causes a less-than-ex­po­nen­tial increase in for­cing (asymp­tot­ic­ally approach­ing lin­ear). Yet, appar­ently none of those eight illus­tri­ous authors recog­nized that that claim was wrong.

In fact, it wasn't just their tem­per­at­ure pro­jec­tions which were wrong. Des­pite soar­ing emis­sions, even CO2 levels nev­er­the­less rose more slowly than their “scen­ario A” pre­dic­tion, because of the strong neg­at­ive feed­backs which curbed CO2 level increases, a factor which Hansen et al obvi­ously did not anti­cip­ate.

In other words, Hansen et al 1988 was wildly wrong about almost everything.

IPCC founded

Most sci­ent­ists are cau­tious about mak­ing pre­dic­tions which are apt to embar­rass them in the future. But Hansen et al 1988 had a purpose. It was the basis for Dr. Hansen's famous June 23, 1988 Congressional testimony. 5½ months after that testimony, and 3½ months after the paper was pub­lished, the United Nations cre­ated the Inter­gov­ern­mental Panel on Cli­mate Change, to com­bat the per­ceived threat — a threat which turns out to have been much ado about very little.

So, even though the authors got just about everything wrong in their paper, it was nev­er­the­less a great suc­cess, because it accom­plished what it was inten­ded to accom­plish.

What did they learn from their mis­takes?

Of course 1988 was a long time ago. So do you think maybe they've got­ten smarter?

I'm kid­ding, of course. Con­sider Hansen's very loud, very pub­lic warm­ings about the threat of “ex­treme weather" due to anthro­po­genic cli­mate change. He even pub­lished a book in 2009 entitled, Storms of My Grand­chil­dren: The Truth About the Com­ing Cli­mate Cata­strophe and Our Last Chance to Save Human­ity.

(The next time some apo­lo­gists for cli­mate alarmism claim that the “C” in “CAGW” is a straw-man inven­tion of skep­tics, show 'em the title of Hansen's book!)

In his book Hansen claimed (p.250) that global warm­ing would warm higher lat­it­ude oceans less than lower lat­it­udes, which would cause stronger storms. Page 250 is not part of the free pre­view on Amazon, but You­Tube has a clip of Hansen on the Let­ter­man Show on tele­vi­sion, plug­ging his book and mak­ing the same claim, start­ing at 7 minutes 25 seconds:

Hansen said that the “in­creas­ing tem­per­at­ure gradi­ent [between high and low lat­it­udes] is going to drive stronger storms,” as lower lat­it­udes warm faster than higher lat­it­udes. But it is now known that that pre­dic­tion was exactly back­wards.

His book is com­pletely wrong. The real­ity is that in the north­ern hemi­sphere “po­lar amp­li­fic­a­tion” causes extreme lat­it­udes to warm much faster than most other places, and sta­bil­iz­ing neg­at­ive feed­backs reduce warm­ing in the trop­ics. So anthro­po­genic cli­mate change causes a reduced tem­per­at­ure gradi­ent, rather than increased.

Indeed, world­wide storm­i­ness actu­ally seems to have decreased slightly, rather than increased, as green­house gas levels have gone up. Hur­ricanes & trop­ical cyc­lones have no clear trend, and tor­nadoes are trend­ing slightly down:

(click individual graphs to enlarge)

(See also:  doi: 10.1002/2017GL076071,
http://policlimate.com/tropical/global_running_ace.png, and

I hes­it­ate to call the slight decline in trop­ical cyc­lones a trend, but severe tor­nadoes are cer­tainly down. Yet Hansen and other prom­in­ent cli­mate alarm­ists still won't admit that a ben­e­fit of anthro­po­genic cli­mate change might be a reduc­tion in extreme weather.

You've heard that “no news is good news?” Well, in cli­mate sci­ence it's the con­verse: “good news is no news!” Cli­mate alarm­ists and their allies in the press rarely report the good news, about reduced extreme weather, improved agri­cul­tural pro­ductiv­ity, and a green­ing planet, thanks to anthro­po­genic CO2.

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I'm certainly not the first person to have noticed the large divergence of reality from the predictions of Hansen et al 1988. The most complete examination was probably that of Steve McIntylre, in 2008:
There have also been many attempts to defend Hansen et al 1988; the strongest is probably this one, by Nick Stokes: