By Andy May
February 15, 2016 was the beginning of an in-depth debate on man-made climate change between two well-known experts in the field, Dr. William Happer and Dr. David Karoly, hosted by TheBestSchools.org. Both have been heavily involved in atmospheric research since the 1980s, but they have landed on opposite sides of the debate.
Dr. Happer is a physicist who has specialized in the interactions of radiation with matter, a key issue in greenhouse warming and optics. Happer, Princeton physics professor emeritus, invented the sodium laser guide star used by astronomers and the military to reduce atmospheric distortion of light and was a co-author of an early book on global warming, The Long-Term Impacts of Increasing Atmospheric Carbon Dioxide Levels (MacDonald 1981). Dr. Karoly, University of Melbourne (Australia) professor, is a climate scientist who has been heavily involved in several IPCC reports and first described the famous “atmospheric fingerprint” (cooling in the stratosphere and warming in the troposphere) that shows rising greenhouse gas concentrations have an impact on recent surface warming. Although the fingerprint does not allow the magnitude of human climate impacts to be computed, it does allow us to infer that human CO2 emissions have some finite impact on climate.
We are very fortunate to have this detailed record of a debate between two such prominent atmospheric physicists. Brief biographies of each and the man-made climate change positions they argue can be read in full here:
Unfortunately, Dr. Karoly backed out in the middle of the debate, so the responses to Dr. Happer’s statement and interview were written by Glenn Tamblyn, a blogger for the website skepticalscience.com.
The debate is fascinating, but the material provided by TheBestSchools is very long, often repetitive, and poorly organized. Here we summarize the debate by asking six key questions. The questions are:
- Is recent global warming unusual?
- How do we know the excess CO2, and other greenhouse gases, are from human activities?
- How do we know that the increase in CO2 and other greenhouse gases in the atmosphere have caused most of the recent global warming?
- Climate models have been used to compute the amount of warming caused by human activities, how accurate are they?
- How do we know global warming and more CO2 will have substantial adverse impacts on humans and the planet?
- Should anything be done to combat global warming?
There will be four posts in the series, in Part A we present the discussion of questions 1 and 2. The views of both scientists are given for all the questions. Many readers will find little new in this post but may enjoy reading the arguments from two such prominent scientists. Both are very familiar with the data but draw quite different conclusions from it, we try and show why. Debates on climate change between prominent scientists are rare, as discussed by Anthony Watts here. So, enjoy this one. Following are the overarching theses argued:
Dr. Karoly: “Science has established that it is virtually certain that increases of atmospheric CO2 due to burning of fossil fuels will cause climate change that will have substantial adverse impacts on humanity and on natural systems. Therefore, immediate, stringent measures to suppress the burning of fossil fuels are both justified and necessary.”
Dr. Happer: “There is no scientific basis for the claim that increases of atmospheric CO2 due to burning of fossil fuels will cause climate change that will have substantial adverse impacts on humanity and on natural systems. If fossil fuels are burnt responsibly to limit real pollutants like fly ash, oxides of nitrogen or sulfur, heavy metals, etc., the CO2 released will be a benefit to the world. Any resulting climate change will be moderate, and there will be very major benefits to agriculture and other plant life.”
Karoly and Happer agree that climate changes, that the world has become warmer over the past 120 years, and that adding CO2 to the atmosphere will cause some warming. They also fully agree that the CO2 concentration in our atmosphere is increasing about 2 ppm/year, which is about half of human emissions. The other half is absorbed by the ocean and biosphere. These facts are not in dispute. They differ on the projected impacts of the warming and additional CO2. Happer thinks the impacts will be net beneficial and Karoly thinks they will be detrimental to humans and nature. We will unpack this disagreement into the six key questions listed above, then provide the arguments from each scientist. The first three parts have no “discussion and comments” section, my views on the debate will be in a final post, Part D. This is all about Happer and Karoly, with a little supporting material added from IPCC AR5 (IPCC 2013), other references needed for clarity, and Glenn Tamblyn’s replies to Happer.
1. Is recent global warming unusual?
Karoly compares the relatively accurate, high-resolution modern global average temperature rise of 0.9°C over the past 100 years, to the sparse, very low resolution and poorly-dated temperature proxy records of the past 1,000 years and asserts that no 100-year temperature rise in the past millennium is as large as we have recently seen. To quote him:
“There are a number of estimates of the hemispheric average temperature using different methods and different proxy data, not just the one shown [below, Figure 1] by Michael Mann and his collaborators. They all show that the period around 1000 AD was relatively warm and that the period around 1600 to 1800 was relatively cool, just as the Hockey Stick does. However, they all show that the increase in Northern Hemisphere average temperature over the twentieth century was larger than in any other century over the last millennium and that the last 30 years was likely warmer than any other 30-year period over the last 1000 years averaged over the whole Northern Hemisphere.” From the Karoly Interview.
The “Hockey Stick” graph he refers to is from (Mann, Bradley and Hughes 1998). This paper is often abbreviated as MBH98. The hockey stick shown in Figure 1 is the same data, but from the third IPCC report, called “TAR.”
Happer says the following about the Hockey Stick:
“The hockey-stick temperature record was conspicuously absent from the latest IPCC report, which speaks volumes. My guess is that the hockey stick started out as an honest but mistaken paper, but one welcomed by the global-warming establishment. They had been embarrassed for years by the Medieval Warm Period, when Vikings farmed Greenland, and when emissions from fossil fuels were negligible. A.W. Montford’s book, The Hockey Stick Illusion (Anglosphere Books, 2015), is a pretty good summary of what happened.”
Another rebuttal to the Hockey Stick can be found in (McIntyre and McKitrick 2005) and as discussed by (McKitrick 2018) the National Academy of Sciences validated their criticisms. The events unfolded as follows, according to McKitrick:
“After publishing their 2003 E&E article and reviewing Mann’s unpublished responses to it, McIntyre and McKitrick [M&M] submitted an extended critique of the errors and misrepresentations in MBH98 to Nature magazine, which had published the first of the hockey stick papers. Nature solicited a response from Mann et al., and after examining it they ordered Mann et al. to publish a detailed correction and restatement of their methodology, which appeared in June 2006. M&M also extended their critique of Mann’s statistical methodology and submitted it to GRL, which had published the 2nd hockey stick paper, and after peer review GRL published their study. Mann et al. never submitted a response. A panel led by Professor Wegman later conducted an independent review of the mathematical and statistical issues and upheld the M&M critique. A panel of the National Academy of Sciences also conducted an examination of the whole issue of paleoclimate reconstructions and upheld all the technical criticisms M&M made of Mann’s work, going so far as to publish their own replication (North et al., 2006, pp. 90-91) of the spurious hockey stick effect M&M identified.” (McKitrick 2018)
A precise global temperature record, that can accurately show a one-degree change in 100 years, of the past millennium will probably never be created, the temperature proxies available are simply not that accurate. While the MBH98 “Hockey Stick” is not used by the IPCC anymore, there are a variety of other reconstructions they do use to show the range of possible temperatures over the past millennium, some are shown in Figure 2, from the most recent IPCC report, called “AR5” (IPCC 2013).
Rather than just showing the MBH98 graph (Figure 1), Figure 2 shows 15 temperature reconstructions of the Northern Hemisphere to illustrate the variability. Several of the reconstructions show one degree or larger changes in less than 100 years, further the range of temperature estimates in many 100-year periods is larger than one degree. One extreme example is from 1400 to 1500 AD. The graph also shows three modern high-resolution instrumental global temperature anomalies from the 19th century to 2000. The display portrays the uncertainty in the proxy reconstructions and clearly demonstrates that one cannot definitively say the recent 0.9 degree rise in global average temperature is unusual. It may be unusual, but the data are not accurate enough to establish the fact. The various reconstructions clearly show the Medieval Warm Period (roughly 900 to 1150 AD), which is a matter of historical record. As discussed in the IPCC caption, the red lines are land-only reconstructions, orange are land only extra-tropical, the light blue are land and sea extra-tropical reconstructions, dark blue are land and sea all latitudes.
Karoly disagrees with researchers that think the Medieval Warm Period (MWP) (~900-1200 AD) was warmer than today. However, the spread of values and the amplitude of the proxy temperature swings in Figure 2 shows we don’t know this. While historical records suggest Europe, Greenland and many other areas were warmer then, we do not have enough data to show the whole world was warmer. Estimates of temperature anomalies in the MWP, in Figure 2, range from -0.2° to +0.8°C. The records are ambiguous, Karoly could be correct, but the global average temperature during the MWP is unknown. Tamblyn also suggests that the speed of recent warming is unprecedented, but since the variability of the temperature changes in Figure 2 is larger than the recent warming and it is invalid to compare proxy temperatures to instrumental temperatures in any case, the assertion remains unproven. Further, the rate of warming from 1910-1945, before man-made CO2 was a factor, is nearly the same as the rate of warming from 1975 to 2005, which is a problem for Tamblyn.
2. How do we know the excess CO2, and other greenhouse gases, are from human activities?
Karoly explains that the recent increase in atmospheric CO2 is associated with a decline in the ratio of the carbon isotopes 13C to 12C, which is expected if some of the CO2 is from burning fossil fuels since plants prefer 12C. Fossil fuels have less of the long-lived 13C isotope of carbon, since they are mostly made from decaying plant material. In addition, there is a slight decrease of atmospheric oxygen as one would expect from burning fossil fuels.
“The increase in atmospheric carbon dioxide over the past 40 years agrees very well with the increase expected from emissions associated with burning fossil fuels, land clearing, and industrial activity, less the additional uptake of carbon dioxide into the oceans and the land ecosystems due to the higher concentrations.”
Karoly also points out that during the last 800,000 years of the Pleistocene Ice Age, Antarctic ice cores suggest that CO2 levels have never been above 300 ppm. Thus, the current level of 400 ppm is very unlikely to have a natural cause, such as volcanic eruptions or CO2 out-gassing from the warmer oceans.
Happer agrees that the observed increase in CO2 concentration in the atmosphere is due to human activity: burning fossil fuels and other industrial activity.
What is coming next?
Part B of this series will discuss the scientist’s views on questions three and four. These are:
- How do we know that the increase in CO2 and other greenhouse gases in the atmosphere have caused most of the recent global warming?
Climate models have been used to compute the amount of warming caused by human activities, how accurate are they?
In many ways these are at the heart of the debate. Stay tuned.
IPCC. 2013. In Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change, by T. Stocker, D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley. Cambridge: Cambridge University Press. https://www.ipcc.ch/pdf/assessment-report/ar5/wg1/WG1AR5_SPM_FINAL.pdf.
MacDonald, Gordon. 1981. Long-term Impacts of increasing Atmospheric Carbon Dioxide Levels. Ballinger. https://www.amazon.com/dp/088410902X/?tag=tbs242-20.
Mann, Michael E., Raymond S. Bradley, and Malcolm K. Hughes. 1998. “Global-scale temperature patterns and climate forcing over the past six centuries.” Nature 392: 779-787. https://www.nature.com/articles/33859.
McIntyre, Stephen, and Ross McKitrick. 2005. “Hockey sticks, principal components, and spurious significance.” GEOPHYSICAL RESEARCH LETTERS 32. http://www.climateaudit.info/pdf/mcintyre.mckitrick.2005.grl.pdf.
McKitrick, Ross. 2018. “Statement of Ross McKitrick.” https://www.rossmckitrick.com/uploads/4/8/0/8/4808045/nyc_lawsuit0.pdf.