Rebuttal of “Rebuttal of ‘On global forces of nature driving the Earth’s Climate

By | July 19, 2007


> In a recent paper, W. Aeschbach-Hertig (2006) of the Institute of Environmental Physics in the University of Heidelberg promotes his view that Khilyuk and Chilingar (2006) are wrong to suggest that the human influence on climate is negligible compared to natural forces driving the Earth’s climate. The two authors are members of the Faculty of Civil and Environmental Engineering at the University of Southern California. We shall consider his criticisms of Khilyuk and Chilingar’s paper seriatim, after first summarizing the paper itself.

Khilyuk and Chilingar say that a 1% increase in current solar radiation reaching the Earth's body translates directly into a rise of ~0.86°C in the Earth's global temperature. The earth's orbit about the sun changes over long periods of time, resulting in a modulation of up to 7.5°C in the earth's temperature. Outgassing alters the composition of the atmosphere over long periods, altering the temperature of the earth by more than 50°C. Microbial activities at the interface of the lithosphere and atmosphere also substantially alter the composition and temperature of the global atmosphere at geological time-frames. The scale of natural climate change is four or five orders of magnitude greater than the corresponding anthropogenic impacts on the Earth's climate (such as heating and emission of the greenhouse gases). Over the last 3,000 years the earth has cooled, and it has also cooled since the mediaeval warm period a millennium ago. The authors conclude:

“The human-induced climatic changes are negligible. … The global warming observed during the latest 150 years is just a short episode in the geologic history. The current global warming is most likely a combined effect of increased solar and tectonic activities and cannot be attributed to the increased anthropogenic impact on the atmosphere. … Humans may be responsible for less than 0.01°C of approximately 0.56°C (1°F) total average atmospheric heating during the last century”.

On the question of policies for mitigating climate change, the paper says:

“Any attempts to mitigate undesirable climatic changes using restrictive regulations are condemned to failure. … Thus, the Kyoto Protocol is a good example of how to achieve the minimum results with the maximum efforts (and sacrifices). Impact of available human controls will be negligible in comparison with the global forces of nature. Attempts to alter the occurring global climatic changes (and drastic measures prescribed by the Kyoto Protocol) have to be abandoned as meaningless and harmful.”

> Aeschbach-Hertig begins his rebuttal by questioning Khilyuk and Chilingar’s conclusion that “the entire energy generated by humans could heat the atmosphere by no more than 0.1C”. However, Oreskes (2004) defined the scientific “consensus” on climate change as an agreement that at least half the [0.4C] warming of the past half century was attributable to anthropogenic activity – i.e. that at least 0.2C of recent warming was anthropogenic. Therefore the conclusion of Khilyuk and Chilingar is not significantly out of line with the “consensus”.

> Furthermore, a current study of the abstracts of 539 papers on the ISI database published since the beginning of 2004 using Oreskes’ search term, “global climate change”, shows that several papers either explicitly or implicitly question the “consensus” as defined (and declared as unanimous) by Oreskes. It is possible, therefore, that Khilyuk and Chilingar are in the vanguard of a movement in the peer-reviewed literature away from even the limited definition of “consensus” in Oreskes (2004).

> Aeschbach-Hertig next criticizes Khilyuk and Chilingar for their conclusion that “changes in the global atmospheric temperature are closely correlated with the changes in solar activity”. Again, a growing body of peer-reviewed literature suggests a remarkable correlation between changes in atmospheric temperature and changes in solar activity. For instance, Willson (2003); Solanki et al. (2005); Buentgen et al. (2006); Svensmark et al. (2006) each reach this conclusion by different methods.

> Aeschbach-Hertig moves on to criticize Khilyuk and Chilingar’s statement that “the variations in the global average Earth insolation attributed to the planet’s orbital deviations can reach up to 10% of the long-term average radiation level,” preferring a figure of just 0.2%. However, he does not explain how it is that the Earth’s prehistoric temperature can have fluctuated by up to 7.5 degrees Celsius between glacial and interglacial periods if neither changes in solar activity nor the Milankovich cycles are responsible for any significant contribution to changes in mean global temperature.

> Aeschbach-Hertig then questions Khilyuk and Chilingar’s discussion of the possibility that tectonic activity may have contributed to the increase in methane in the atmosphere that has been observed over the past century. He makes this challenge partly on the questionable basis that the evidence cited by Khilyuk and Chilingar is a paper in Russian (Yasamanov, 2003) that is not accessible to the general reader. Yet one should not deny to scientists the right to make serious contributions to scientific debate on the ground that they write in languages other than English. The faculty of modern languages at Heidelberg (dean of faculty: Prof. Dr. Peter Paul Schnierer) would have been capable of translating Yasamanov’s paper.

> Though Aeschbach-Hertig says Khilyuk and Chilingar failed to take account of the corpus of literature on the sources and sinks of methane, he does not explain why none of the authors whom he cites predicted that seven years ago the increase in the concentration of methane in the atmosphere would startlingly cease, at a time when tectonic activity – as judged by proxies such as the incidence of volcanism – also seems to have stabilized.

> Khilyuk and Chilingar are next questioned for pointing out that the total mass of carbon dioxide degassed from the Earth’s mantle throughout geologic history is at least five orders of magnitude greater than all anthrogenic output since the commencement of the Industrial Revolution in 1750. Aeschbach-Hertig, in stating that the annual anthropogenic flux is about 50 times larger than the mantle-degassing flux, entirely miss the central point of Khilyuk and Chilingar’s paper, which is to set the comparatively insignificant anthropogenic influence on climate in a geological context. The rapidity of increases in anthropogenic greenhouse-gas emissions may be unprecedented in recent times: but Khilyuk & Chilingar’s comparison is nothing more than a perfectly proper restatement in geological terms of the fact that the anthropogenic enhancement is a very small fraction of the natural influences on climate. Indeed, the Intergovernmental Panel on Climate Change (2007) has reduced its estimate of the total anthropogenic effect on climate to 1.6 watts per square meter, whereas the natural greenhouse effect is 148 watts per square meter. The temperature effect of the natural greenhouse effect is ~20C, according to a communication received in 2006 from Sir John Houghton. Accordingly, the anthropogenic enhancement compared with the state of the climate in 1750 is little more than 0.2C – again, not significantly different from the ~0.1C suggested by Khilyuk and Chilingar.

> Aeschbach-Hertig then challenges Khilyuk and Chilingar’s assertion that “when the global temperature rises, the solubility of the carbon dioxide in the ocean water decreases, and part of the carbon dioxide content of the ocean water is transferred into the atmosphere, creating an illusion that the increased concentration of the carbon dioxide heating the atmosphere is a result of anthropogenic activity”. The basis of Aeschbach-Hertig’s challenge is that “the ocean actually acts as a sink for CO2 and warming of the ocean only decreases the oceanic CO2 uptake, rather than leading to CO2 release to the atmosphere”. The effect is the same either way: as the ocean warms, its CO2 content decreases, and (subject only to increases in sub-oceanic calcification with temperature which have been observed at temperate latitudes), the atmospheric CO2 concentration correspondingly increases. In fact, Khilyuk and Chilingar’s formulation adheres more closely to the classical understanding of Henry’s law than that of Aeschbach-Hertig. The point made by Khilyuk and Chilingar is correct: whether the warming of the ocean is induced (as they maintain) by increased solar activity or by decreased orbital eccentricity, or (as Aeschbach-Hertig implies) by anthropogenic enhancement of the atmospheric greenhouse effect, the diminution in the capacity of the ocean to hold CO2 in solution induces a climate feedback.

> Next, Aeschbach-Hertig criticizes Khilyuk and Chilingar for considering various geological theories about how the Earth’s atmosphere may evolve in the next half-million years. Again, much of the criticism is rooted in Aeschbach-Hertig’s objection to the fact that “much of the cited literature is in Russian, thus not easily accessible”. He disagrees with their conclusion that “the major causes of currently observed global warming are rising solar irradiation and increasing tectonic activity”, on the ground that these are “simply unsupported allegations”. However, as noted supra, a large and growing corpus of peer-reviewed literature attests to the effect of solar activity on climate variability: indeed, Solanki et al. (2005) conclude that the Sun has been more active, and for longer, in the past 50 years than at any similar period in the past 11,400 years. Nor does the citation by Khilyuk and Chilingar of papers in Russian imply that their conclusions are “simply unsupported”.

> Aeschbach-Hertig also questions Khilyuk and Chilingar’s use of a graph showing the mediaeval warm period as 2C warmer and the little ice age as 1C cooler than today. Aeschbach-Hertig says the graph came from a publication of the American Association of Petroleum Geology: however, that graph was in turn based on a graph in IPCC (1995) which clearly shows both the mediaeval warm period and the little ice age. He criticizes Khilyuk and Chilingar for not citing papers such as Moberg et al. (2005) or Briffa and Osborn (2002). However, a graph of Briffa’s findings in an earlier paper and of Moberg’s findings as presented in Wegman et al. (2005) clearly shows the mediaeval warm period as being almost 0.5C warmer than the present, and the little ice age as being up to 3.5C cooler, broadly supporting Khilyuk and Chilingar’s conclusion as to the magnitude of the changes in mean global surface air temperature that have arisen as a consequence of natural climate variability:


> Aeschbach-Hertig says: “One might expect that the authors would refer to the famous ‘hockey-stick’ curve of Mann et al. (1998, 1999, corrigendum 2004), which has been a major target of the criticism of climate change skeptics in recent years.” Khilyuk & Chilingar rightly ignored that graph, which a report by the US National Academy of Sciences (North et al., 2005) had described as having “a validation skill not significantly different from zero.” As to Aeschbach-Hertig’s implicit criticism of Khilyuk and Chilingar as “climate change skeptics”, T.H. Huxley said: “The improver of natural knowledge absolutely refuses to acknowledge authority, as such: for him, skepticism is the highest of duties; blind faith the one unpardonable sin.”

> Though Aeschbach-Hertig says Khilyuk and Chilingar, in saying that “the global average temperature dropped about 2C over the last millennium”, are “squarely at odds” with the literature, numerous studies demonstrate that the mediaeval warm period was real, global, and up to 3C warmer than the present. Each of the following illustrates the existence of the mediaeval warm period with a graph: Bjorck et al. (2006); Chu et al. (2002); Grinsted et al. (2006); Gupta et al. (2005); Hallett et al. (2003); Huang et al. (1997); Holzhauser et al. (2005); Khim et al. (2002); Kitagawa and Matsumoto (1995); Mangini et al. (2005); Noon et al. (2003); Pla et al. (2005); Qiang et al. (2005); Rein et al. (2004, 2005); Seppa and Birks (2002); Tyson et al. (2000); Williams et al. (2004); Wilson et al. (1979).

> Finally, Aeschbach-Hertig finds it “astonishing that the paper of Khilyuk and Chilingar could pass the review process of a seemingly serious journal such as Environmental Geology. With more justification, the same could be said of Aeschbach-Hertig’s rebuttal. Khilyuk and Chilingar have made a valuable and welcome contribution to climate-change research, by placing recent climatic trends within the sobering context of geologic time.

> References

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  Christopher Walter, Third Viscount Monckton of Brenchley, is a former policy advisor to Margaret Thatcher during her years as Prime Minister of the United Kingdom.  He may reached through SPPI, or directly at (+44 1882 632341)(

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