Letters to the Editor
To the Editor:
The Tutorial of David Hafemeister & Peter Schwartz’s on the Basic Physics of Climate Change in the July 2008 edition of Physics & Society appears compact and straightforward. However, three major flaws or omissions make one doubt the validity of the main conclusion.
(1) In the discussion of CO2 content only anthropogenic fluxes are considered; the authors fail to mention that the 7.1 Gton/year are < 10% percent of the total fluxes within the biosphere. It is not until they reach the result that about 50% of the anthropogenic contribution disappears that they mention “sinks.” This omission is serious. For example, the “photosynthetic sink” is net 51.5 Gton/yr (IPCC, 2007). Secondly the magnitude depends upon the CO2 concentration in the atmosphere. Other natural fluxes are treated as a constant background, but in reality they are coupled and vary with temperature.
(2) The authors obtain the temperature gradient of the atmosphere as a result of radiative exchange layer-by-layer. In fact, radiation is only a part of the total energy flux through the atmosphere. Evaporation and latent heat are mentioned but never enter their calculations. In reality, these dominate the heat transportin the tropical zone, or wherever the humidity is large. The adiabatic expression gives almost the correct temperature gradient (approx 9 oC/km) by using ideal gas properties and gravity using no radiation at all. But considering only radiative transport or adiabatic pressure drop are extreme cases; both are insufficient in addition to not including latent heat.
(3) The conclusion about the insufficiency of solar variations as a cause for the global temperature increase is incomplete. The authors only discuss variation of the solar intensity at the top of the atmosphere instead of the intensity at sea level, which is strongly modulated by low clouds. Only a small increase (a few percent) in cloud cover is sufficient to explain the global temperature change. Workers at the National Space Institute of Denmark have proposed and partly demonstrated a detailed mechanism for solar influence upon the formation of clouds [1, 2].
Furthermore, it is not historically correct that Svante Arrhenius “first suggested in 1896 that... .”In this work Arrheniusreferenced Fourier and Tyndall for their much earlier suggestion that the climate was controlled by the amount of CO2 in the atmosphere. In this 1896 article he made the first quantitativeestimate of the climate sensitivity . Considering that the spectral results were poorly resolved and otherwise defect, the result 3-4 oC for doubling the concentration of CO2 was amazingly close to the IPCC claims today. However, it is very rarely mentioned that Arrhenius 10 years later published a calculation resulting in a much lower effect of CO2 .
Finally, the sentence “It is our belief that ‘theory leads experiment’ on climate change because all well-accepted atmospheric models predict a temperature rise” is unfortunate. If the models are based on the same incorrect assumption, their validity is not ensured by the fact that they agree. Furthermore it is should at least give reference to some experiments. For instance, references ,5-8 are based on measurements, and they all agree that the current climate models use climate sensitivity values that are significantly too large and thus exaggerate the importance of CO2, anthropogenic or not, in the atmosphere.
Carl G. Ribbing
Professor, Division of Solid State Physics
The Ångström Laboratory
Uppsala University, Sweden
Hafemeister & Schwartz respond:
We thank Professor Ribbing for his interest in our work. Our responses to the points he raised follow:
1. The large natural fluxes of CO2 are approximately balanced. The increase in CO2 emissions from humans raises the CO2 atmospheric concentration, which raises radiative forcing and surface temperature.
2. Our three-page paper, “Tutorial on the Basic Physics of Climate Change,” closely follows Chapter 8 in Hafemeister’s text, Physics of Societal Issues (Springer, 2007). Because of the need to be brief, we did not quantify the more difficult convective (lapse rate) and latent heat (evaporation) transport, but these are estimated in the text at pages 210-211. Kevin Trenberth’s article in the April 2009 issue of P&S has a more lengthy discussion of this and he gives energy flow rates of 17 W/m2 for convection, 80 W/m2 for evapo-transpiration and a net infrared flow of 63 W/m2 . An excellent discussion of the convective contribution is given by Thomas Ackerman . His Figure 6 shows the radiative-equilibrium and the radiative-convective-equilibrium temperatures to be similar at 15 km altitude, but with substantial differences at lower altitudes. Ultimately the best answers are obtained from General Circulation Model cellular calculations since closed form equations with no cellular structure are not sufficient.
3. Solar variations. The 2007 Intergovernmental Panel on Climate Change concluded that the anthropogenic radiative forcing in 2005 from CO2 was 1.66 W/m2 (1.49 to 1.83), plus another 1.35 W/m2 from five other greenhouse gasses. At this time aerosols make a negative contribution of –1.2 W/m2, but this is not expected to grow substantially, whereas the density of greenhouse gases is increasing. These contributions are much larger than the increased irradiance from solar-cycle variations and fluctuations of 0.12 W/m2 (0.06 to 0.30). The IPCC stated that the level of understanding of CO2 forcing was “high,” as compared to a “low” level of understanding for variations in solar cycle forcing . For one thing, it’s hard to explain the increased solar warming over the past thirty years when there hasn’t been an upward trend in solar intensity over the same time period . That is not to say that researchers don’t look at the impact of the sun. For example, the recent paper by Gerald Meehl, et al uses global climate models to explore how relatively small fluctuations of the 11-year solar cycle can produce the magnitude of the observed climate signal in the tropical Pacific associated with such capability . They note, however, that “This response cannot be used to explain recent global warming because the 11-year solar cycle has not shown a measurable trend over the past 30 years.”
4. Svante Arrhenius was the first to develop an energy budget model to quantify the rise in ground temperature . He obtained a rise of 3 to 3.5 oC from a doubling of CO2. In general terms he stated that “if the quantity of carbonic acid increases in geometric progression, the augmentation of the temperature will increase nearly in arithmetic progression.” Today, the Arrhenius greenhouse law for direct warming from CO2 (only) is written as , where F is radiative forcing, a is 3.75 W/m2, C is atmospheric CO2 concentration, and C0 is the pre-industrial level of 280 ppm.
David Hafemeister and Pete Schwartz
Cal Poly University, San Luis Obispo, CA 93405
 K. Trenberth, “Changes in the Flow on Energy through the Earth’s Climate System,” Physics and Society 38, 11-16 (April 2009) and “An Imperative for Climate Change Planning: Tracking Earth’s Global Energy,” Current Opinion in Environmental Sustainability 1, 19-27 (2009).
 T. Ackerman, “A Tutorial on Global Atmospheric Energetics and the Greenhouse Effect,” Global Warming: Physics and Facts, AIP Conference Proceedings 247 (1991), ed. by B.G. Levi, D. Hafemeister and R. Scribner.
To the Editor:
The article on the medical isotope shortage [Physics & Society 38(4), 13-16, October 2009] covered the topic quite well, except for one very important production alternative that the author does not mention. It is feasible to produce very large quantities of Mo-99 in any CANDU power reactor because of its on-power refueling capability. The thermal neutron flux in a CANDU is about 50% greater than in a MAPLE reactor, and the standard 37-element fuel bundle could be modified to accommodate a number of MAPLE “target” elements. The refueling machines could be employed to load several “target” bundles into just one of the (several hundred) fuel channels and remove them after one week of irradiation.
This option has been known for a long time, but has not been pursued because it is inconvenient for the CANDU operator. However, the very important significance of the Mo-99 shortage is leading to a reassessment of this alternative.
An Expression of Interest (EOI) to produce Mo-99 by this method has been submitted to the Isotope Expert Review Panel, established by Natural Resources Canada this past summer. This panel is reviewing the 22 different EOIs that were received; it will make recommendations in November.
To the Editor:
Elizabeth Dowdeswell’s article in the October 2009 edition of Physics & Society describes the Canadian campaign to create social acceptance of nuclear waste and identify a community that will host a repository . Left unstated in her article is that part of the reason for the necessity of this extensive effort is the perception, shared by many in the scientific community, that any ionizing radiation exposure caused by human activity can cause cancer deaths . This perception is a barrier to on-going and increased use of nuclear energy.The linking of nuclear technologies to an increased risk of cancer mortality (and congenital malformations) is traceable to the linear no-threshold (LNT) assumption of radiation carcinogenesis. This assumption holds that cancer mortality increases linearly with exposure, with no minimum threshold for causing cancer deaths. A 2001 article in P&S questions the validity of the LNT concept .
The Health Physics Society and the American Nuclear Society have both issued position statements that there is no statistically significant evidence that a low radiation dose causes cancer [4, 5]. Indeed, there is evidence that low doses produce beneficial health effects in all living organisms, and a model of this phenomenon has been formulated . However, regulatory authorities ignore this information, and risk analysts continue to calculate the number of fatal cancers that will be caused by a very small “population exposure.” Lauriston Taylor, former president of the National Council on Radiation Protection and Measurement, denounced the calculation of the number of deaths per year resulting from x-ray diagnoses: “These are deeply immoral uses of our scientific heritage.” “No one has been identifiably injured by radiation while working within the first numerical standards set by the International Commission on Radiological Protection (ICRP) in 1934 (safe dose limit: 0.2 rad per day)” [7, 8].
Another issue is that society has accepted the notion that used nuclear fuel is “waste,” but this material really represents an enormous energy resource for future generations. Compared with fossil fuel combustion products, the amount of used nuclear fuel is very small and it is being stored in very heavy, robust containers made of steel and reinforced concrete. No one is being injured by used fuel and there is no reason to believe that anyone will be injured by it in the foreseeable future.
For nuclear energy to play a significant role in meeting future needs, it is essential that the regulators reexamine the scientific evidence and communicate the real health effects. Negative images and implications of health risks derived by unscientific extrapolations of harmful effects of high doses must be dispelled. Furthermore, scientists need to explain to society the nature of (slightly) used nuclear fuel, pointing out the enormous energy potential of the unfissioned uranium and transuranic materials and identifying the real waste, i.e., the fission products, which are not difficult to manage.
 Cameron, J. “Is Radiation an Essential Trace Energy?” Physics & Society 30(4), 14-16 (2001).
 Health Physics Society. “Radiation Risk in Perspective,” Position Statement (2004).
 American Nuclear Society. “Health Effects of Low-Level Radiation,” Position Statement (2001).
 Cuttler, JM and Pollycove, M. “Nuclear Energy and Health, And the Benefits of Low-Dose Radiation Hormesis,” Dose-Response 7, 52-89 (2009).
 Taylor, LS. Health Physics Society testimonial (2008). Available at: http://hps.org/aboutthesociety/people/inmemoriam/LauristonTaylor.html
 Taylor, LS. “Some Non-Scientific Influences on Radiation Protection Standards and Practice in Radiation Protection: A Systematic Approach to Safety,” Proc. 5th Congress of the International Radiation Society, Vol. I, Jerusalem (1980). Pergamon Press, pp 3-15. See also Health Phys 39, 851-874.
These contributions have not been peer-refereed. They represent solely the view(s) of the author(s) and not necessarily the views of APS.