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 fast as their “scenario A” prediction.

Even so, climate alarmists frequently claim that their 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.

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 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.