A Blast From The Past: James Hansen on 'The Global Warming Debate' from 13 years ago

Guest post by Floyd Doughty

Some years ago when I was investigating the climate change issue in my spare time, I ran across a short article by James Hansen on the GISS website under “Education Resource Materials”, dated January, 1999. James Hansen is arguably the father of modern Anthropogenic Global Warming dogma. So I saved the web page for future reference because of some of the predictions contained within it, as well as the incredibly balanced and well-reasoned attitude expressed regarding the philosophy of scientific investigation. We could all benefit from Dr. Hansen’s wisdom. For example,

“Skepticism thus plays an essential role in scientific research, and, far from trying to silence skeptics, science invites their contributions. So too, the global warming debate benefits from traditional scientific skepticism”.

And another gem:

“Although scientists have a right to express personal opinions related to policy issues, it seems to me that we can be of more use by focusing on the science and carrying that out with rigorous objectivity. That approach seems to be essential for the success, as well as the “fun”, of scientific research”.

Given what has transpired in the intervening 13 years, it is not surprising that I can no longer find the article on the GISS site (but I may not have dug deeply enough). Therefore, I am making my copy of the article available to you for your reading pleasure. There is such a wealth of fascinating statements contained in this short document, it is impossible to decide where to begin. I suspect others will find numerous points to comment on. By the way, the embedded link to Dr. Hansen’s book review is still working, and I found that to be an interesting read as well.

I found Dr. Hansen’s chart of projected global temperature anomalies intriguing, particularly in light of the observational record of the last decade:

This chart, as displayed in the January, 1999 document, is a replica of the global temperature projections, considering three scenarios that Dr. Hansen presented during his celebrated 1988 United States Senate testimony, but updated with the actual observed GISS temperature record as of 1998.

Scenario A represented projected global temperatures assuming “a fast growth rate for greenhouse gases”. Scenarios B and C “have a moderate growth rate for greenhouse gases until year 2000, after which greenhouse gases stop increasing in Scenario C”. I thought it might be enlightening, or at least entertaining, to compare the current GISS global temperature record with what was presented in January, 1999. The “… traditional analysis … global annual-mean surface air temperature change …” data series was downloaded from

http://data.giss.nasa.gov/gistemp/graphs_v3/ (http://data.giss.nasa.gov/gistemp/graphs_v3/Fig.A.txt)

This time series was plotted in Microsoft Excel. Unfortunately, time series data values that were used to produce the original chart did not seem to be available. Therefore, the Excel chart of the current GISS global temperature record was rather crudely scaled and overlain onto an image of the original chart, with the following result:

The data shown in red are from the original image published in 1999. The blue points are what are currently available for download at the GISS website. The slight apparent time shift in the vertical grid lines was necessary because, for some reason, Dr. Hansen originally plotted yearly averages between tick marks rather than centered on tick marks. The vertical scales have not been altered, and are as exact as I can make them with the manual overlay. The blue observational data points seem to roughly lie between Dr. Hansen’s Scenario B (moderate, continued growth rate in greenhouse gases) and Scenario C (moderate growth rate in greenhouse gases until year 2000, after which greenhouse gases stop increasing). Interestingly, the data currently available for download (blue) seem to be indicating a slightly warmer trend than what was presented in 1999 (red). After manually applying a slight downward bulk shift (or “bias”) to the overlay of the current record (blue), the two time series seem to be in slightly better agreement:

It seems the historical GISS temperature record has been somewhat altered, or “adjusted” since January of 1999, such that historical global temperature anomaly values are now slightly more positive than what was published at that time. Perhaps a base line change was applied to the data since the 1999 article. But data after 1988 appear to be “adjusted” to a greater extent than data prior to 1988. Well, it is what it is, and the best we can do is to calibrate the current GISS temperature time series to the years prior to 1988, under the charitable assumption that perhaps the points that were added to the original 1988 chart in the 1999 article were accidentally mis-posted.

Now that the current version of historical temperature measurements are approximately calibrated to the historic record as presented by Dr. Hansen to the United States Senate in 1988, it seems that the GISS record in the years following 1988 have roughly approximated Dr. Hansen’s Scenario C. But wait – that scenario was a projection of temperature variations assuming greenhouse gases stop increasing after the year 2000. Did I miss something? Was the IPCC wildly successful after all?

It is also illustrative to compare Dr. Hansen’s 1988 prediction with the satellite record. UAH NCDC temperature data from analyses by Roy Spencer and John Christy was downloaded from Dr. Spencer’s website:

http://www.drroyspencer.com/latest-global-temperatures (http://vortex.nsstc.uah.edu/data/msu/t2lt/uahncdc.lt)

Since these data are monthly averages of global temperature derived from satellite measurements, the global temperature data series was further averaged over each calendar year to enable direct comparison with the raw, currently available GISS data. The UAH NCDC chart was then manually scaled and bulk shifted in order to calibrate with the original 1999 GISS data (since the base periods for the two data sets are different). The result of this crude scaling exercise is shown with the UAH NCDC data in green, compared with the current, unbiased GISS data in blue:

After applying the manual bulk shift to compensate for the different base line periods, it appears that the satellite data agree reasonably well with the current, unbiased GISS surface station data – except for the trend, as others have pointed out. GISS estimates since 1998 seem to be consistently higher than the UAH NCDC satellite estimates. More accurately stated (since the calibration was visual only), the GISS trend appears more positive than the UAH NCDC satellite data trend. Interesting. Now it looks like Dr. Hansen’s Scenario C global temperature forecast that he presented to the United States Senate in 1988 was amazingly accurate, according to the satellite-derived global temperature record. That is truly a remarkable achievement. So now let’s employ a bit of faulty logic that is similar to that which is routinely applied by AGW proponents: “The observational data fit the model, so the model must be accurate”. Anthropogenic greenhouse gas emissions must have ceased in the year 2000. And I missed it. Rats.

In the interest of full disclosure, I must unambiguously state that I am a state board-certified Professional Geophysicist nearing retirement after more than 38 years spent in the search for new oil and gas reserves. As such, AGW proponents may simply dismiss my comments as the ravings of an “oil company shill”. There is no statement that I can swear to that would convince them otherwise. So be it. The truth is that the observations, opinions, and views I have expressed are the result of independent critical thought, are strictly my own, and do not in any way represent those of my employer, the oil industry in general, or any other entities.

Floyd Doughty

May 10, 2012

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Source – the Wayback machine: http://web.archive.org/web/20010223232940/http://www.giss.nasa.gov/edu/gwdebate/

The Global Warming Debate

By James Hansen — January 1999

The only way to have real success in science … is to describe the evidence very carefully without regard to the way you feel it should be. If you have a theory, you must try to explain what’s good about it and what’s bad about it equally. In science you learn a kind of standard integrity and honesty. — Richard Feynman

In my view, we are not doing as well as we could in the global warming debate. For one thing, we have failed to use the opportunity to help teach the public about how science research works. On the contrary, we often appear to the public to be advocates of fixed adversarial positions. Of course, we can try to blame this on the media and politicians, with their proclivities to focus on antagonistic extremes. But that doesn’t really help.

The fun in science is to explore a topic from all angles and figure out how something works. To do this well, a scientist learns to be open-minded, ignoring prejudices that might be imposed by religious, political or other tendencies (Galileo being a model of excellence). Indeed, science thrives on repeated challenge of any interpretation, and there is even special pleasure in trying to find something wrong with well-accepted theory. Such challenges eventually strengthen our understanding of the subject, but it is a never-ending process as answers raise more questions to be pursued in order to further refine our knowledge.

Skepticism thus plays an essential role in scientific research, and, far from trying to silence skeptics, science invites their contributions. So too, the global warming debate benefits from traditional scientific skepticism.

I have argued in a recent book review that some “greenhouse skeptics” subvert the scientific process, ceasing to act as objective scientists, rather presenting only one side, as if they were lawyers hired to defend a particular viewpoint. But some of the topics focused on by the skeptics are recognized as legitimate research questions, and also it is fair to say that the injection of environmental, political and religious perspectives in midstream of the science research has occurred from both sides in the global warming debate.

So, what to do? Most scientists are willing to spend part of their time communicating with the public about how science works. And they should be: after all, the financial support for most research is provided ultimately by the public. But one quickly learns that such communication is not easy, at least not for many of us.

In late 1998, I was asked to debate the well-known greenhouse skeptic Dr. Patrick Michaels of the University of Virginia. I summarize here some key points in the debate, “A Public Debate on the Science of Global Warming”, held at the New York Hilton, Nov. 20, 1998, and organized by the American Association for the Rhetoric of Science and Technology. A copy of my entire contribution may be downloaded as a PDF document (Note: This document is 597 kB and requires a special viewer such as the free Adobe Reader.).

I agreed to participate in this debate with Dr. Michaels after learning that he had used (or misused) a figure of mine in testimony to the United States Congress. The figure showed the first predictions made with a 3-D climate model and time-dependent climate forcings — it was a figure from a paper that we had published in the Journal of Geophysical Research in 1988 and it had been a principal basis for testimony that I gave to the United States Senate in 1988.

The figure that we published is reproduced here as Fig. 1.

Fig. 1: Climate model calculations reported in Hansen et al. (1988).

It shows the simulated global mean temperature for three climate forcing scenarios. Scenario A has a fast growth rate for greenhouse gases. Scenarios B and C have a moderate growth rate for greenhouse gases until year 2000, after which greenhouse gases stop increasing in Scenario C. Scenarios B and C also included occasional large volcanic eruptions, while scenario A did not. The objective was to illustrate the broad range of possibilities in the ignorance of how forcings would actually develop. The extreme scenarios (A with fast growth and no volcanos, and C with terminated growth of greenhouse gases) were meant to bracket plausible rates of change. All of the maps of simulated climate change that I showed in my 1988 testimony were for the intermediate scenario B, because it seemed the most likely of the three scenarios.

But when Pat Michaels testified to congress in 1998 and showed our 1988 predictions (Fig. 1) he erased the curves for scenarios B and C, and showed the result only for scenario A. He then argued that, since the real world temperature had not increased as fast as this model calculation, the climate model was faulty and there was no basis for concern about climate change, specifically concluding that the Kyoto Protocol was “a useless appendage to an irrelevant treaty”.

Although scientists have a right to express personal opinions related to policy issues, it seems to me that we can be of more use by focusing on the science and carrying that out with rigorous objectivity. That approach seems to be essential for the success, as well as the “fun”, of scientific research.

Fig. 1 is a good case in point. We now know (Hansen et al. 1998a, 1998b) that the growth rate of greenhouse gases in the period 1988-1998 has been flat, very similar to scenarios B and C (which are nearly the same until year 2000). Thus we can compare real world temperature changes in the past decade (filled circles in Fig. 1) with model calculations for the B-C scenarios. Taking account of the fact that the real world volcano occurred in 1991, rather than 1995 as assumed in the model, it is apparent that the model did a good job of predicting global temperature change. But the period of comparison is too short and the climate change too small compared to natural variability for the comparison to provide a meaningful check on the model’s sensitivity to climate forcings. With data from another decade we will be able to make a much clearer evaluation of the model.

As the opinions in the global warming debate do not seem to be converging, it seems to me that one useful thing that can be done is to clearly delineate the fundamental differences. Then, as our scientific understanding advances over the next several years, we can achieve more convincing evaluations of the global warming issue. (Stated less generously, this is a way to pin down those who keep changing their arguments.)

Table 1 summarizes chief differences that I delineated for the sake of a discussion with Richard Lindzen, who has provided the intellectual underpinnings for the greenhouse skeptics, in October 1998. I also used this list (Table 1) as the principal fodder for my “affirmative closing argument” in the debate with Pat Michaels.

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Table 1. Key Differences with Skeptics

1. Observed global warming: real or measurement problem?

Hansen: global warming is 0.5-0.75°C in past century, at least ~0.3°C in past 25 years.

Lindzen: since about 1850 “…more likely … 0.1±0.3°C” (MIT Tech Talk, 34, #7, 1989).

2. Climate sensitivity (equilibrium response to 2xCO₂)

Lindzen: ~< 1°C

Hansen: 3±1°C

Comments: paleoclimate data, improved climate models, and process studies may narrow uncertainties; observed climate change on decadal time scales will provide constraint if climate forcings are measured; implicit information on climate sensitivity can be extracted from observed changes in ocean heat storage.

3. Water vapor feedback

Lindzen: negative, upper tropospheric water vapor decreases with global warming.

Hansen: positive, upper and lower tropospheric water vapor increase with global warming.

References: (these include references by Lindzen stating that, in response to global warming, water vapor will decrease at altitudes above 2-3 km).

Comment: accurate observations of interannual changes (several years) and long-term changes (1-2 decades) of upper tropospheric water vapor could provide defining data.

4. CO₂ contribution to the ~33°C natural greenhouse effect

Lindzen: “Even if all other greenhouse gases (such as carbon dioxide and methane) were to disappear, we would still be left with over 98 percent of the current greenhouse effect.” Cato Review, Spring issue, 87-98, 1992; “If all CO₂ were removed from the atmosphere, water vapor and clouds would still provide almost all of the present greenhouse effect.” Res. Explor. 9, 191-200, 1993.

Lacis and Hansen: removing CO₂, with water vapor kept fixed, would cool the Earth 5-10°C; removing CO₂ and trace gases with water vapor allowed to respond would remove most of the natural greenhouse effect.

5. When will global warming and climate change be obvious?

Lindzen: I personally feel that the likelihood over the next century of greenhouse warming reaching magnitudes comparable to natural variability remains small.

Hansen: “With the climatological probability of a hot summer represented by two faces (say painted red) of a six-faced die, judging from our model by the 1990s three or four of the six die faces will be red. It seems to us that this is a sufficient ‘loading’ of the dice that it will be noticeable to the man in the street.” J. Geophys. Res. 93, 9341-9364, 1988.

6. Planetary disequilibrium

Hansen: Earth is out of radiative equilibrium with space by at least approximately 0.5 W/m² (absorbing more energy than it emits).

Comments: This is the most fundamental measure of the state of the greenhouse effect. Because the disequilibrium is a product of the long response time of the climate system, which in turn is a strong function of climate sensitivity, confirmation of the disequilibrium provides information on climate sensitivity and an indication of how much additional global warming is “in the pipeline” due to gases already added to the atmosphere.

This disequilibrium could be measured as the sum of the rate of heat storage in the ocean plus the net energy going into the melting of ice. Existing technology, including very precise measurements of ocean and ice sheet topography, could provide this information.

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Differences 1 (reality of global warming) and 2 (climate sensitivity) are very fundamental. From my perspective, strong evidence is already accumulating that weighs heavily against the skeptics contentions that there is no significant global warming and that climate sensitivity is low. These issues will become even clearer over the next several years.

Difference 3 (water vapor feedback) is related to climate sensitivity, but is so fundamental that it deserves specific attention. The topic has resisted definitive empirical evaluation, because of the poor state of water vapor measurements and the fact that tropospheric temperature change has been small in the past 20 years. Ozone depletion, which affects upper tropospheric temperatures, has also complicated this problem. This situation will change if, as I would anticipate, ozone depletion flattens and global temperature continues to rise.

Difference 4 has an academic flavor, and is perhaps not worth special efforts. But it illustrates a lack of understanding of the basic greenhouse mechanism by Lindzen.

Difference 5 is fundamental because substantial efforts to curb global warming may require that climate change first be apparent to people. If our assessments are right, we are in fact on the verge of warming being noticeable to the perceptive person-in-the-street. (See related material Global Temperature Trends and the Common Sense Climate Index.)

Difference 6, concerning the planetary “disequilibrium” (imbalance between incoming and outgoing radiation) is the most fundamental measure of the state of the anthropogenic greenhouse effect. The disequilibrium should exist if climate sensitivity is as high (and thus the ocean thermal response time so long) as we estimate, and if increasing greenhouse gases are the dominant climate forcing mechanism. We have presented evidence (Hansen et al. 1997) of a disequilibrium of at least 0.5 W/m². This imbalance is the basis by which we could predict that record global temperatures would occur within a few years, that the 1990s would be warmer than the 1980s, and that the first decade of next century will be warmer than the 1990s, despite the existence of natural climate variability. I do not know of a reference where Lindzen specifically addresses planetary radiation imbalance, but his positions regarding climate sensitivity and the ocean response time clearly imply a smaller, negligible imbalance.

The important point is that the planetary radiation imbalance is measurable, via the ocean temperature, because the only place this excess energy can go is into the ocean and, probably to a less extent, into the melting of ice. If our estimates are approximately right, this heat storage should not escape detection during the next several years.

In summary, all of these issues are ones that the scientific community potentially can make progress on in the near future, if they receive appropriate attention. The real global warming debate, in the sense of traditional science, can be resolved to a large extent in a reasonable time.

References:

• Hansen, J. 1998. Book review of Sir John Houghton’s Global Warming: The Complete Briefing. J. Atmos. Chem. 30, 409-412.
• Hansen, J., I. Fung, A. Lacis, D. Rind, S. Lebedeff, R. Ruedy, G. Russell, and P. Stone 1988. Global climate changes as forecast by Goddard Institute for Space Studies three-dimensional model. J. Geophys. Res. 93, 9341-9364.
• Hansen, et al. 1997. Forcings and chaos in interannual to decadal climate change. J. Geophys. Res. 102, 25679-25720.
• Hansen, J., M. Sato, J. Glascoe and R. Ruedy 1998a. Common sense climate index: Is climate changing noticeably? Proc. Natl. Acad. Sci. 95, 4113-4120.
• Hansen, J., M. Sato, A. Lacis, R. Ruedy, I. Tegen, and E. Matthews 1998b. Perspective: Climate forcings in the industrial era. Proc. Natl. Acad. Sci. 22, 12753-12758.