Hansen's Sea Shell Game

Guest Post by Willis Eschenbach

There’s an old con game that has been played on the suckers for hundreds and hundreds of years. It is done in various forms, with various objects, under various names—three card monty, the shell game, Thimblerig, bottle caps, cups and ball, the game is the same in every one. The essence is, the con man puts a pea under a shell, then switches the shells around and asks which shell is hiding the pea.

Figure 1. The Conjuror, by Hieronymus Bosch, painted 1475-1480. The type of tricks the conjuror is doing are thought to be among the origins of the shell game.

I bring this up because our favorite conjuror, James Hansen, is up to his old tricks again. He has a new paper out, Paleoclimate Implications for Human-Made Climate Change, And as always, you have to figure out which shell is hiding the pea.

Here is his money graph, the one that is getting lots of play around the blogosphere. The main observation I’ve seen people making is that having been bitten by previous failed prognostications, Hansen is taking the well-tested Nostradamus route now, and is predicting sea level rise for when he’ll be 137 years old or so …

Figure 2. Hansen’s Figure 7: ORIGINAL CAPTION: “Five-meter sea level change in 21st century under assumption of linear change and exponential change (Hansen, 2007), the latter with a 10-year doubling time.”

Folks are saying that the bad news is, it looks like we won’t be able to tell until 2040 or so if Hansen’s claim is true. But that’s not the case at all. Those folks are not keeping close enough watch on the pea.

In the paper Hansen says:

Sea level change estimates for 21st century. 

IPCC (2007) projected sea level rise by the end of this century of about 29 cm (midrange 20-43 cm, full range 18-59 cm). These projections did not include contributions from ice sheet dynamics, on the grounds that ice sheet physics is not understood well enough.

Rahmstorf (2007) made an important contribution to the sea level discussion by pointing out that even a linear relation between global temperature and the rate of sea level rise, calibrated with 20th century data, implies a 21st [century] sea level rise of about a meter, given expected global warming for BAU greenhouse gas emissions. …

… Hansen (2005, 2007) argues that amplifying feedbacks make ice sheet disintegration necessarily highly non-linear, and that IPCC’s BAU forcing is so huge that it is difficult to see how ice shelves would survive. As warming increases, the number of ice streams contributing to mass loss will increase, contributing to a nonlinear response that should be approximated better by an exponential than by a linear fit. Hansen (2007) suggested that a 10-year doubling time was plausible, and pointed out that such a doubling time, from a 1 mm per year ice sheet contribution to sea level in the decade 2005-2015, would lead to a cumulative 5 m sea level rise by 2095.

The short version of that is:

• The IPCC predicts sea level rise of about a foot (30 cm), but they don’t take ice into account.

• Rahmstorf says a linear projection gives about a metre (3.3 feet) of sea level rise.

• Hansen 2007 says there’s a missing exponential term in Rahmstorf’s work, because the ice will be melting faster and faster every year.

OK, so Hansen 2011 rests on the claims made in Hansen (2007), which turns out to be Scientific reticence and sea level rise. At the end of Section 4 Hansen says that Rahmstorf estimates a 1-metre sea level rise, but that a non-linear ice melting term should be added to the Rahmstorf rise.

Under BAU [“Business As Usual”] forcing in the 21st century, the sea level rise surely will be dominated by a third term: (3) ice sheet disintegration. This third term was small until the past few years, but it is has at least doubled in the past decade and is now close to 1 mm/year, based on the gravity satellite measurements discussed above. …  As a quantitative example, let us say that the ice sheet contribution is 1 cm for the decade 2005–15 and that it doubles each decade until the West Antarctic ice sheet is largely depleted. That time constant yields a sea level rise of the order of 5 m this century.

So to get the final Hansen projection, we need to see what is happening in Rahmstorf, A Semi-Empirical Approach to Projecting Future Sea-Level Rise, paywalled, where we find the following graph of projected sea level rise.

Figure 3. The Rahmstorf estimate of sea level rise, to which Hansen says an exponentially growing ice term should be added.

ORIGINAL CAPTION: Past sea level and sea-level projections from 1990 to 2100 based on global mean temperature projections of the IPCC TAR. The gray uncertainty range spans the range of temperature rise of 1.4° to 5.8° C, having been combined with the best statistical fit shown in Fig. 2. The dashed gray lines show the added uncertainty due to the statistical error of the fit of Fig. 2. Colored dashed lines are the individual scenarios as shown in (1) [Ref. 1 is the IPCC TAR Bible, no page given]; the light blue line is the A1FI scenario, and the yellow line is the B1 scenario.

(In passing, let me again protest the use of the entire IPCC Third Annual Report, thousands of pages, as a reference without giving us chapter and verse in the way of page numbers. My high school science teacher would have slapped my hand for that, it’s a joke.)

The upper blue line is the one that gives us about a meter of sea level rise. So I took that as Rahmstorf’s 1 metre rise. To that I added, as Hansen claims we should, an amount that starts at 0.5 cm in 2000 and doubles every ten years. This is following Hansen’s claim that the non-linear ice disintegration is a separate term that starts small but will “come to dominate” the sea level rise over the century. The result is shown in Figure 4.

Figure 4. Rahmstorfs predicted rise (blue), Hansen’s projected additional rise from “non-linear ice disintegration” (dark red), and total sea level rise (green) predicted in H2011. I have included the last century’s rise of 16 cm, as calculated by Rahmstorf, in the lower right corner for comparison purposes. IMAGE SOURCE

OK, so what Hansen is actually predicting is the green line. However, his real forecast is actually much worse than that. Hansen again, emphasis mine:

The eventual sea level rise due to expected global warming under BAU GHG [greenhouse gas] scenarios is several tens of meters, as discussed at the beginning of this section.

I’m going with “several tens” to mean more than two, so he’s predicting a 30 metre sea level rise!!! … I guess he figured nobody paid any attention when Al Gore threatened us with a 20 metre sea level rise, so he’d better pull out all the stops and give us a real scare, something to make us shake in our panties.

There is a bit of good news, however. Both the Rahmstorf and the Hansen projections are already way above the reality. Since 1993, when the satellites started measuring sea level, we’ve gone up about 4.6 cm (1993-2011). Rahmstorf’s projection is 6.4 cm for that time period, about 40% too high already. Hansen’s larger projection is 7.2 centimetres rise over that time, or 55% too high.

The annual rise is also entertaining. According to the satellites, the trend 1993-2011 was 3.2 mm/yr, and has been declining recently. The change 2009-2010 was under a mm, at 0.9 mm/yr. And 2010-2011 was just about flat.

In 2010-2011, Rahmstorf’s projected rise is already 4.5 mm/yr, about fifty percent larger than the actual rate of the last 18 years. And Hansen’s annual rise is even worse, at 5.3 mm per year.

So both in terms of 1993-2011 rise, as well as current annual rise, both Rahmstorf and Hansen are already way above observations. But wait, there’s more.

Hansen’s rate of sea level rise is supposed to be accelerating, as is Rahmstorf’s rate. By 2020 Hansen says it should be rising at 6.3 mm per year, and everlastingly upwards after that. But in fact we’re already way under their supposed rates of annual increase, and the observed rate of rise is declining …

How does Hansen get these nonsensical numbers? Well, he noticed something in the observations.

This third term [melting ice] was small until the past few years, but it is has at least doubled in the past decade …

My high school science teacher, Mrs. Henniger, bless her, thought extending a linear trend into the future was a crime against nature, and I would hesitate to express her opinion on Hansen blithely extending a ~ 7% annual increase for a hundred years. That kind of compound interest turns a centimeter (3/8″) into 5 metres (16 feet). If Dr. Hansen had submitted this nonsense to her, you would not have been able to read it when it came back for the red pencil scribbles.

You can’t do that, folks. You can’t just observe that something has doubled in the last decade, and then extend that exponential growth out for a century. That’s beyond wishful thinking. That’s magical thinking.

Two final points. First, the pea under the walnut shells. Note carefully what Hansen has done. He has claimed that the sea level rise will be “several tens of metres”. This is at least thirty metres, or a hundred feet, of sea level rise.

He seems to be at least somewhat supporting this claim with his Figure 7 (my figure 2). But if you look at the caption, this is not a forecast, a projection, or a scenario of any kind. Instead, this is merely an “approximation” of what a linear sea level rise might look like and what an exponential rise might look like. You know, in case you didn’t understand “linear” and “exponential”. His actual forecast is under another walnut shell somewhere. We know his “Approximation” can’t be a real projection because it shows almost no rise occurring currently, or for some years.

Second, even this doesn’t begin to unravel the errors, deceptions, alarmism, and con games in Hansen’s work. Do you see the guy in the dark vest and the white pants and shirt at the left of Hieronymus’s painting at the top? See what he has in his hand while he’s looking all innocent at the sky? See who it’s chained to? Hansen’s not really the shell game conjurer, that guy’s a piker, he’s not making much money on the game.

Hansen’s the guy in the dark vest with his hand on your pocketbook …

w.