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. 3½ months after it was pub­lished, the United Nations cre­ated the Inter­gov­ern­mental Panel on Cli­mate Change, to com­bat the per­ceived 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:
https://www.youtube.com/watch?v=SOKBOFLhgqM#t=7m25s

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
https://www.wunderground.com/hurricane/accumulated_cyclone_energy.asp?basin=gl&MR=1)

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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