Hansen 1988 Revisited

Hansen’s 1988 temperature projections have recently received quite a bit of attention, e.g., RealClimate, WUWT and SkS. The pro-AGW sites state than Hansen has done very well, whereas the anti-AGW say that he hasn’t. Therefore, I thought that it would be a good time to revisit Hansen’s work to determine how well he did?

Temperature Sensitivity & What Can We Learn?

Dana1981 @ SkS states that:

“The observed temperature change has been closest to Scenario C, but actual emissions have been closer to Scenario B. This tells us that Hansen’s model was “wrong” in that it was too sensitive to greenhouse gas changes. However, it was not wrong by 150%, as Solheim claims. Compared to the actual radiative forcing change, Hansen’s model over-projected the 1984-2011 surface warming by about 40%, meaning its sensitivity (4.2°C for doubled CO2) was about 40% too high.

What this tells us is that real-world climate sensitivity is right around 3°C, which is also what all the other scientific evidence tells us. Of course, this is not a conclusion that climate denialists are willing to accept, or even allow for discussion.”

Perhaps. Climate sensitivity may be ≈ 3°C but we can also learn several other things as discussed below.

How Well Did Hansen Do?

Hansen Compared With the Real World

Figure 1 shows Hansen’s scenarios compared with the GISS Land-Ocean Index (LOTI). I have also added Dana1981’s data as Scenario D. This is the Scenario B data but with the temperature sensitivity reduced from 4.2°C to 2.7 °C. Dana did this by multiplying the Scenario B data by a factor of (0.9*3/4.2), which equates to temperature sensitivity of 2.7 °C (see SkS for the data). The SkS estimate for Scenario D appears to be based on Schmidt (2009).

Figure 1: Hansen’s 1988 Scenarios compared with Real-world Temperatures

It is evident from Figure 1 that the best fit for real world temperatures is Scenario C. However, the pro-AGW in SkS state that Scenario C is irrelevant because it uses the “wrong” sensitivity of 4.2°C and incorrect emissions. Therefore, perhaps I should modify my conclusion to real-world temperatures are following Scenario D, which has the “right” temperature sensitivity of 2.7°C and emissions that are close to actual emissions. It makes no difference; Scenarios C and D are similar, although Scenario D has tended to under-predict temperatures for the last 30 years or so.

2012 Projections

Hansen’s temperature projections for 2012 are compared with the LOTI data in Table 1. It should be noted that the 2012 LOTI temperature estimate is based on the 12-month running average from Jun-2011 to May 2012.

Scenario

2012 Anomaly (°C)

Comparison

With LOTI

(%)

Source

A

1.18

226%

Hansen (1988a)

B

1.77

205%

Hansen (1988a)

C

0.60

116%

Hansen (1988a)

D

0.67

128%

Dana (2011)

LOTI

0.52

100%

GISS LOTI

Note: The comparison with LOTI is based on Scenario/LOTI.

Table 1: Comparison of Hansen’s 1988 Temperature Projections for 2012

Comparing Hansen’s temperature projections with LOTI, it is evident that Hansen’ didn’t do very well.

Scenarios A and B overestimated real-world temperatures by a whopping 126% and 105% respectively. Scenario D over-predicts by 28% and even the no-increase-in-emissions Scenario C over-predicts real-world temperatures by 16%.

What do we learn? We could argue that climate sensitivity should be reduced to ≈ 2.1°C to correspond to the 28% over-prediction in Scenario D. However, I would suggest that we wait a few more years to determine the trend more accurately.

2019 Projections

The timeline for Hansen’s temperature projections for 2019 is presented in Table2. A summary of the comments made by different commentators are included to show how the favoured scenario/projection evolved with time.

Scenario

2019 Anomaly (°C)

Comparison

With

Scenario D (%)

Source

Comments
B

1.10

160%

Hansen (1988a)

In May 1988, Hansen states in AGU paper that, “Scenario A, assumes that growth rates of trace gas emissions typical of the 1970s and 1980s will continue indefinitely…[but]…since it is exponential, must eventually be on the high side of reality in view of finite resource constraints…Scenario B is perhaps the most plausible of the three cases.”
A

1.57

227%

Hansen (1988b)

In June 1988, Hansen states to US Congressional Committee that Scenario A was “business as usual.”
B

1.10

160%

Hansen (2005)

Hansen states that, “In my testimony in 1988, and in an attached scientific paper… Scenario A was described as “on the high side of reality”…The intermediate Scenario B was described as “the most plausible”… is so far turning out to be almost dead on the money.”
B

1.10

160%

Hansen (2006)

Hansen assesses the predictions and states that the close agreement, “for the most realistic climate forcing (scenario B) is accidental.” He states current estimate for sensitivity is 3 ± 1°C.
B-

1.00

144%

Schmidt (2007)

RealClimate blog, Schmidt states that forcings in Scenario B are “around 10% overestimate.”
B-

1.00

144%

Schmidt (2009)

RealClimate blog, Schmidt states that Scenario B, “is running a little high compared with the actual forcings growth (by about 10%)”
B

1.00

144%

Schmidt (2011)

RealClimate blog by Schmidt, “As stated last year, the Scenario B in that paper is running a little high compared with the actual forcings growth (by about 10%)”
D

0.69

100%

Dana (2011)

Skeptical Science blog, climate sensitivity reduced from 4.2 to 2.7°C for Scenario B. Use this as the benchmark for comparison.
?

?

?

Schmidt (2012)

RealClimate blog, Schmidt states that Scenario B, “is running warm compared to the real world (exactly how much warmer is unclear)”
C

0.61

88%

Hansen (1988a))

Hansen’s original Scenario C. This is the commitment scenario with emissions held at year 2000 levels. Include this as a measure of how well the other scenarios perform.

Note: The comparison with Scenario D is based on Scenario/Scenario D

Table 2: Evolution of Hansen’s 1988 Temperature Projections for 2019

It is evident from the timeline and narrative in Table 2 that the evolution in temperature is generally downwards; apart from the brief upwards spurt for US Congressional Committee presentation in June 1988 (more on this in unethical conduct later in this blog).

The following points are also evident:

  • There is a large reduction in the estimate for the 2019 temperature anomaly from Hansen’s estimate of 1.57°C in 1988 (as presented to the US Congress) to Dana’s estimate of 0.69°C in 2011.
  • Until recently (Schmidt, 2012) the overestimate in Scenario B was portrayed as ≈ 10% but Dana at SkS (2011) showed that the overestimate was ≈ 44%.

What do we learn? All of the pro-AGW blogs states that the Hansen Scenario B was pretty good estimate. I suggest that an error of ≈ 44% is pretty bad.

Unethical Behaviour

Hansen’s paper Hansen (1988a) was published in August 1988 but it is important to note that it was accepted for publication on 6 May 1988. This date is particularly relevant because Hansen stated on 6 May 1988 that:

Yet, one month later Hansen (1988b)
in his congressional testimony here he described Scenario A as “business as usual” (see below):


Notice that Scenario A is stressed to be “business as usual”. No mention to Congress that Scenario B was “most plausible” and that Scenario A was “on the high side of reality”.

Later (2006), Hansen re-worded his 1988 congressional testimony to be Scenario A, “was described as on the high side of reality”.


From the foregoing, it is evident that Hansen did not describe to Congress in 1988 that Scenario A was on the “high side of reality”. At best, he has been economical with the truth by re-writing history and (at worst) he has been unethical and totally unprofessional.

Conclusions

I offer the following conclusions regarding Hansen 1988:

  • Temperature forecasts (sorry, should I use the politically correct term projections?) for 2019 have plummeted from 1.57°C in 1988 to 0.69°C in 2011.
  • Estimates of temperature are in error by ≈ 60 for Scenario B and 127% for Scenario A.
  • Climate sensitivity has also fallen from ≈ 4.2°C to ≈ 2.1-2.7°C, i.e., it has fallen to 50-64% of Hansen’s 1988 estimates.

These sorts of errors do not represent pretty good estimates.

Hansen’s 1988 Climate Models: Response to Julien in Deltoid 2 August 2008

In Deltoid #203 on 29 July 2008 Julien Emile-Geay wrote:

It is simply astounding how climate skeptics have gotten cornered into such a tiny fraction of disinformation space that they must exhume 20-year old models to vainly poke holes into the current scientific literature.

Hence, McIntyre and his clique can’t get over Mann Bradley and Hughes (1998, 10 years old), and a lot of those who have no clue about GCMs think it’s fair game to throw dirt at Hansen’s GISS model predictions (1988). Meanwhile climate scientists have moved on : some results have survived, some have not, but the basic result remains – AGW is real, no amount of disingenuous PR will make it go away.

Given the simplicity and low resolution of Hansen’s 1998 model (which didn’t have anything remotely close to an ENSO, for instance), it is indeed remarkable that it was able to predict the temperature of the next 20 years to such accuracy. What the Skeptics keep missing (Mr McFarlane in particular) is that numerical modeling and computer power have done quite a bit of progress in the past 20 years, and no climate scientist is retarded enough to be hanging their hat over 1988 results.

Sure, there still are legitimate questions concerning the relative importance of natural vs anthropogenic climate variability, some of which have implications for policy initiatives, and that would deserve healthy debate. Yet the Skeptics are so blinded by their political prejudices that they keep fighting old windmills.

I can’t speak for every climate scientist, but the only reason why I’d ever show the Hansen 1988 figures at this day and age would be to demonstrate that the physics of greenhouse warming are rather basic (indeed, Arrhenius)
had figured it out over a century ago), and that a good radiative transfer code (which is what the GISS model is known for) is enough to produce credible global temperature trends given a realistic forcing.

Current GCMs are now focused on getting the regional scales right – that’s where the money is, and intelligent skeptics (I heard there were some) would be well inspired to get out of their rut and on board that train. If they keep whining at the 1988 stop we soon won’t be able to hear them.

So, now that we’ve got that one cleared, can we please talk about something more interesting ? Abrupt climate change, operational climate prediction, regional climate variability, link with tropical cyclones, to name a few…

Or is it that there just isn’t any stone left for the AGW skeptics to hide ?

My response on 2 August 2008 was:


Wow Julien! So many comments in such a brief response, but, unfortunately, liberally sprinkled with remarks such as disinformation, disingenuous, retarded, prejudices, etc. Nevertheless, I shall try to respond in a more rational manner.

Exhumation of 20-Year Old Models

It is simply astounding how climate skeptics have gotten cornered into such a tiny fraction of disinformation space that they must exhume 20-year old models to vainly poke holes into the current scientific literature.

If you read my posts above it is clear that I didn’t exhume Hansen’s 1988 model. Jim Hansen did. Furthermore, he published his models here in 2006 and stated here in 2006 that Scenario B “was dead on the money”. In addition, Tim Lambert said in #47 in this blog that:

Scenarios B and C don’t diverge until after 2006. Results so far are close to both B and C. In a few more years we’ll see if temperatures now stabilise (scenario C) or continue to increase (scenario B).

I agree with Tim, but my chart below shows that what looked to be a reasonable fit with Scenario B in 2006 does not look very good in 2008.

I reiterate my statement in #195, that:

It is early days yet, but it would appear that our planet is following the zero-emissions Scenario C.

From the foregoing, I contend that it is reasonable for me to comment on Hansen’s 2006 papers and posts in this blog without being accused of exhuming 20-year old models. Julien, perhaps you should target your responses at Jim Hansen. He was responsible for the initial exhumation of his 20-year old models.

Mann, Bradley & Hughes 1998 [MBH98]

I thought that McIntyre & McKitrick (M&M) did a well-balanced due-diligence on MBH98. Furthermore, despite more recent papers from the “Hockey Team” over the last 10 years, it would appear that M&M’s core conclusions still stand, namely: “no bristlecones, no hockey stick”.

Incidentally, the MBH98/M&M discourse was one of the reasons why I began to doubt the AGW hypothesis.

AGW is Real

AGW is real, no amount of disingenuous PR will make it go away.

Perhaps, but AGW is still currently a hypothesis. It has not yet been raised to a law of physics.

ENSO

Thank you for the Wikipedia link, but I didn’t need it. Nevertheless, I was half expecting a response stating that one of the reasons for the temperature drop in 2008 was that 2007-2008 was a La Nina.

Computer Power

A large part of my day job involves running complicated computer models and, therefore, I am well aware of the increased computational power available and the evolution of current GCMs. However, the GCMs that I am aware of “…don’t do clouds very well”, which may lead to incorrect temperature predictions.

Retarded Climate Scientists

… no climate scientist is retarded enough to be hanging their hat over 1988 results

I wouldn’t call Jim Hansen retarded for exhuming his 1998 model, but, if you so wish; it is your choice.

Arrhenius

I can’t speak for every climate scientist, but the only reason why I’d ever show the Hansen 1988 figures at this day and age would be to demonstrate that the physics of greenhouse warming are rather basic (indeed, Arrhenius)

I am well aware of Arrhenius’s work, but it would appear that this one should also be sent to Jim Hansen, because it refers to his exhumation of his 1988 models.

Other Topics

…can we please talk about something more interesting ? Abrupt climate change, operational climate prediction, regional climate variability, link with tropical cyclones, to name a few…

I agree. In 2007, my company employed Weather Intelligence, UK, to carry out research for us on regional climate variability and operational climate prediction.

Importance of Hansen’s Models

Chris O’Neill said on Deltiod

Gee, and I thought that twenty year old model was the be-all and end-all of climate forecasting.

My respnose was:

Chris, Hansen’s 20-yer old models presented in #109 are very important. They  are the  cornerstone of IPCC/your government policy. If they are wrong then your government is going the wrong way on CO2.

Yet in 2006 Hansen said here that Scenario B “was dead on the money”. It would now appear that he was wrong. Planet Earth appears to be tracking below the zero-emmissions Scenario C and Scenario B is not “dead on the money”; it is way too high.

GISS Temperature Data January-June 2008

Eli Rabbett re #192 on Deltioid wrote that

“This is the one with January standing for all of 2008”.

My response to Eli was that I stated that the temperature figures were for the first six months of the year. You can check the GISS surface station figures here or the land ocean data here.

I summarise the GISS Jan-Jun 2008 figures below for ease of reference:

GISS Temperature Data 

2008      Land       Land-
         Stations      Ocean

Jan               35             14
Feb               32             25
Mar               72             60
Apr               52             42
May              45             39
Jun               26             26
Average = 44           34

Note: 

  1. Surface Station Data Jan-Jun 2008 average = 0.44 °C.
  2. Land-Ocean Data Jan-Jun 2008 average = 0.34 °C.

The latest figures are well below my original Jan-May graph posted in Deltoid #190. It is evident from my graph, and the latest GISS figures, that the 2008 temperatures will be significantly below recent temperatures. They will probably be as low as 1995 or even, God forbid, 1990! It would appear that our planet is currently tracking below Hansen’s Zero-Emissions Scenario C. Good old planet Earth!

I reiterate, is it possible that a stabilisation of temperatures and/or global cooling, as predicted by the solar-cycle/cosmic-ray fraternity, is beginning to happen?

Eli, I look forward to your response.