Toby Carlson Op-Ed “The Everlasting Argument Over Climate Change”

I invited a colleague of Barry Lynn who was listed on our e-mail interaction which culminated in the guest post

Guest Post By Barry Lynn Of The the Hebrew University of Jerusalem

to also write a guest post. I have known Toby Carlson for decades, and while we disagree on key issues that he discusses below, I respect Toby and want to give him this forum to present his views. His short biographical summary is below.

Dr. T. N. Carlson, Ph.D., Imperial College, University of London, is an emeritus Professor of Meteorology at the PennStateUniversity. Professor Carlson’s scientific contributions, over 90 papers published in refereed journals, reflect a wide range of interests: synoptic and dynamic meteorology, radiative transfer, severe local storms, plant-atmosphere interactions, aerosol transport and chemistry, remote sensing of land surface properties and surface energy processes, and, most recently, applications of remote sensing to the study of urban sprawl and small watershed runoff. In 1991 Professor Carlson published a widely used book on meteorology (Mid Latitude Weather Systems). He created two new web products related to his current interest in land surface processes: an online land surface process model (“Simsphere”) and a data base of impervious surface area and fractional vegetation cover determined from Landsat 5 digital imagery at 25 m resolution for all of Pennsylvania, 1985 and 2000. In addition he has helped create a web-based tool which allows one to assess the health (nutrient load) and surface runoff potential of a user-defined stream basin in Pennsylvania or in the Chesapeake Bay Basin.

Below is Toby’s Op-Ed, followed up a set of e-mail interchanges between Toby and I which are designed to expand on the Op-Ed [the e-mails were edited to focus on the  Op-Ed issues].

The everlasting argument over climate change

Until about a decade or so ago, I was a global warming skeptic. Back in the 1990s all sorts of claims were being made about climate change based on climate model simulations. At that time, the evidence was not clear and some of the research was underwhelming. I was resolved to not to remain skeptical unless and until it could be demonstrated that these models were capable of simulating the indisputable increase in global temperature that seems to have occurred during the previous century, by initializing the models with atmospheric conditions one hundred years earlier. Only when these models showed that they are capable of predicting changes over a century up to the present would I begin to take them seriously.

These set of conditions have finally been satisfied. Climate model simulations made by scientists have finally produced some convincing evidence of the effects of human activity on global climate change. Unlike previous types of computer simulations, the latest ones adopt the novel approach of predicting the present global temperature starting in the past, for example with the year 1890. I will now describe just one of several such climate simulations, albeit one of the first of its kind made over a decade ago.

Two series of four computer simulations were made under the auspices of the NationalCenter for Atmospheric Research (NCAR) and the Department of Energy using several different climate models, called General Circulation Models (GCMs). One series of computer runs included only the effect of volcanic eruptions and solar variations on the earth’s radiation budget. Aerosol particles such as sulfates and the notorious greenhouse gas, carbon dioxide, were kept constant at their 1890 levels. Another series of simulations allowed the sulfates and greenhouse gases to vary according to their observed values. For convenience, I refer to the temperature trend simulated by the first set of runs as the ‘natural’ variation and the second set as the ‘total’ variation, as the latter contains both natural and anthropogenic effects. The difference between the two sets of simulations constitute a measure of the human-induced effects on global climate. Unlike the unverifiable and more contentious predictions of future climate, these simulations are verifiable in that they can be compared with measured mean global temperature changes over the same period. In that sense the simulations can validate or invalidate themselves.

Results of the computer runs were summarized in a letter from Richard Anthes, president of the University Corporation for Atmospheric Research, to Senator John McCain of Arizona. In that letter, Dr. Anthes emphasized the role of human activity in global warming and urged the senator to treat global warming as a serious issue.

I redrew the graph included by Anthes in the letter to Senator McCain, smoothing out the wiggles to show only the essential details of the two series of simulations. Zero on the temperature scale is an arbitrary reference corresponding to the average temperature between 1890 and 1919. I don’t show the observations because they fall almost exactly on the smoothed temperature line for the total simulations, which therefore assume a high degree of credibility.

An interesting aspect of this graph is that the warming trend from the 19th century until some time after 1960 can be accounted for by natural variability. Yet, I am impressed that one can reasonably ascribe about 1°F in the temperature rise during the past thirty years or so to human activity; (the last point on each graph is extrapolated). According to Jerry Meehl, a scientist involved in these simulations at NCAR, carbon dioxide emissions have accelerated since 1960, raising global carbon dioxide concentrations by the year 2000 from about 315 parts per million to 360 parts per million during that time interval. (This is to be compared with about 275 parts per million in 1850.) As of the year 2012, the carbon dioxide concentrations have exceeded 390 parts per million.

For me (a once avowed skeptic of the global climate brouhaha) the graph is the first convincing evidence I have seen that global warming due to fossil fuel burning is significantly raising global temperature. Since then the evidence for a human cause of global warming has become even more convincing with yet more such simulations, accumulation of much more observational evidence, including temperatures showing an even steeper slope to the warming curve after the year 2000 than that shown in the figure, the 2007 IPCC report, including sea level rises, Artic ice disappearance, etc. And yet, even more such simulations reproducing the results originally made at NCAR with their climate simulations have subsequently been made. In my opinion, further denials of the global warming evidence are likely to be based more on political than on scientific, motives.

My Comment

Hi Toby

I will be asking questions on your views also, and you might like to add to your post based on this, which we can add. The first question is

“How do your reconcile your confidence in the model skill when the hindcast multi-decadal regional climate predictions are so poor, as i reported in my post

The second question is

“Which of the three hypotheses in

Pielke Sr., R., K. Beven, G. Brasseur, J. Calvert, M. Chahine, R. Dickerson, D. Entekhabi, E. Foufoula-Georgiou, H. Gupta, V. Gupta, W. Krajewski, E. Philip Krider, W. K.M. Lau, J. McDonnell,  W. Rossow,  J. Schaake, J. Smith, S. Sorooshian,  and E. Wood, 2009: Climate change: The need to consider human forcings besides greenhouse gases. Eos, Vol. 90, No. 45, 10 November 2009, 413. Copyright (2009) American Geophysical Union

do you see as not being refuted?”

Best Regards


Toby’s Reply

Roger, I have not involved myself so deeply in the controversy as to address your questions. I am simply something more than a layperson but not a specialist. The graph I showed was an amalgam of four simulations combined for each of two conditions, with co2 and without co2. The simulations were made by a reputable group at NCAR and the simulations reproduced the observations exactly with co2 and not without co2. That was enough to convince me. I don’t know what you mean by poor predictions. The one’s have seen more recently seemed a good fit, though I have not studied the papers in detail.

My Comment

Hi Toby

Those questions are central to the issue of attributing all, most, some or  none of the added to CO2 to the observed warming. That added CO2 has a  warming effect is not in disagreement by anyone. The ability of regional  models to explain behavior and provide attribution for changes in drought  frequency, heat waves, etc. is, in my view, the central issue. The global  average surface temperature is almost irrelevant in this.

If you prefer just to focus on the correspondence between CO2 increase and  the global average temperature increase without any further discussion, we  can still post your comments, but it may result in your being asked by readers to respond to the type of questions I asked. Do you still want to  post given this might occur?

I would also like to post your reply below to my questions, which you (as I  would understand) might not feel comfortable with. But let me know.


Toby’s Reply

Roger….. I neglected to add a few more reasons why I changed my mind about human impact on global warming a decade ago, but these are well known and more conventional reasons: the IPCC 2007 report, the loss of sea ice in the Arctic, the rise in sea level, etc.

My Comment

Thanks Toby!

I will work with what we have. It will post sometime next week with our mails and your statement.

We differ significantly in our viewpoints, but your perspective should be presented. I will add a short bio on you, but please send me a paragraph so I can introduce you on the post.

Best Regards


Toby’s Comment

Roger, I am really just a bystander in the global warming debate. I don’t want to get drawn into a kind of biblical debate here, the kind that theologists tend to have amongst themselves.

I am certainly familiar with the issue and the physics and, to some extent, the models. But I have no ax to grind. I am simply posting my educated opinion and the  reasons for my change of mind. I would not be able to handle detailed questions. For those, one should contact my PSU colleague, Michael Mann.

My arguments, besides that of the NCAR models and the hockey stick graph are as follows:

*  CO2 concentrations have increased almost 20% since 1960. This is unprecedented even in geological time. They are higher now than at any time in the past million years. If you want to argue that issue, see my other colleague, Richard Alley.

* Someone had made a calculation that the total amount of fossil fuel burned over some period of time corresponds roughly to the increase in the CO2 during that period. This would be a relatively easy calculation to make if one had the time to do it. Therefore, the CO2 increase is almost all human made

* To say that an increase of 20% in CO2 would not make a difference means that the laws of radiative transfer must be discarded. It is no good to resort to Richard Lindzen’s arguments that feedbacks mitigate the effect (I understand that he has considered only negative feedbacks) or that the warming (which even he admits is occurring) will be no more than 0.5 C; (even he would admit to a factor of two uncertainty in this sort of highly theoretical estimate.

Second, this is specious because his argument as to the unimportance of the increase is judgmental: that this is not an important increase. He made the same mistake that was made in a Wall Street Journal article saying that the increase in global temperature has only been 0.8 C over the past century; it’s really a bit more than that, but anyway…. But, he didn’t realize that the increase in global temperature since the little ice age is ‘only’ about that amount, he is saying that the rise in temperature is no more important than the difference in climate between the little ice age and the present. I don’t think he meant to emphasize the importance of such a small increase. Such is the WSJ mindset.

Anyway, I doubt if my article will really provoke many to reply. It is simply an opinion article and the facts are not really in question in any case. I was simply indicating the issues that changed my mind on the subject.

Thanks for taking this so seriously and for including the essay on your web site.


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