Hansen’s 1988 Predictions Redux

Reblogged from Watts Up With That:

Guest Post by Willis Eschenbach

Over in the Tweeterverse, someone sent me the link to the revered climate scientist James Hansen’s 1988 Senate testimony and told me “Here’s what we were told 30 years ago by NASA scientist James Hansen. It has proven accurate.”

I thought … huh? Can that be right?

Here is a photo of His Most Righteousness, Dr. James “Death Train” Hansen, getting arrested for civil disobedience in support of climate alarmism …

I have to confess, I find myself guilty of schadenfreude in noting that he’s being arrested by … Officer Green …

In any case, let me take as my text for this sermon the aforementioned 1988 Epistle of St. James To The Senators, available here. I show the relevant part below, his temperature forecast.

ORIGINAL CAPTION: Fig. 3. Annual mean global surface air temperature computed for trace gas scenarios A, B, and C described in reference 1. [Scenario A assumes continued growth rates of trace gas emissions typical of the past 20 years, i.e., about 1.5% yr^-1 emission growth; scenario B has emission rates approximately fixed at current rates; scenario C drastically reduces trace gas emissions between 1990 and 2000.] The shaded range is an estimate of global temperature during the peak of the current and previous interglacial periods, about 6,000 and 120,000 years before present, respectively. The zero point for observations is the 1951-1980 mean (reference 6); the zero point for the model is the control run mean.

I was interested in “Scenario A”, which Hansen defined as what would happen assuming “continued growth rates of trace gas emissions typical of the past 20 years, i.e., about 1.5% yr-1“.

To see how well Scenario A fits the period after 1987, which is when Hansen’s observational data ends, I took a look at the rate of growth of CO2 emissions since 1987. Figure 2 shows that graph.

Figure 2. Annual increase in CO2 emissions, percent.

This shows that Hansen’s estimate of future CO2 emissions was quite close, although the reality was ~ 25% MORE annual increase in CO2 than Hansen estimated. As a result, his computer estimate for Scenario A should have shown a bit more warming than we see in Figure 1 above.

Next, I digitized Hansen’s graph to compare it to reality. To start with, here is what is listed as “Observations” in Hansen’s graph. I’ve compared Hansen’s observations to the Goddard Institute for Space Studies Land-Ocean Temperature Index (GISS LOTI) and the HadCRUT global surface temperature datasets.

Figure 3. The line marked “Observations” in Hansen’s graph shown as Figure 1 above, along with modern temperature estimates. All data is expressed as anomalies about the 1951-1980 mean temperature.

OK, so now we have established that:

• Hansen’s “Scenario A” estimate of future growth in CO2 emissions was close, albeit a bit low, and

• Hansen’s historical temperature observations agree reasonably well with modern estimates.

Given that he was pretty accurate in all of that, albeit a bit low on CO2 emissions growth … how did his Scenario A prediction work out?

Well … not so well …

Figure 4. The line marked “Observations” in Hansen’s graph shown as Figure 1 above, along with his Scenario A, and modern temperature estimates. All observational data is expressed as anomalies about the 1951-1980 mean temperature.

So I mentioned this rather substantial miss, predicted warming twice the actual warming, to the man on the Twitter-Totter, the one who’d said that Hansen’s prediction had been “proven accurate”.