1. There is another consensus estimate in ERL. Carlton et al. interviewed 698 natural scientists at 10 universities in the USA about climate change. The paper is called "[t] climate change consenes extends beyond climate scientists". This undermines the earlier papers by Anderegg et al. and Verheggen et al., who reach a high consensus only by excluding non-experts.

    Carlton et al. highlight their consensus estimate of 92%. This is based on two questions:
    1. When compared with pre-1800's levels, do you think that mean global temperatures have generally risen, fallen, or remained relatively constant? (93% say risen)
    2. [if risen] Do you think human activity is a significant contributing factor in changing mean global temperatures? (97% agree)
    Note the ambiguity of the words "significant" -- it does not indicate anything about the size of the human contribution -- and "human activity" -- which includes greenhouse gas emissions, land use change, etc etc etc. 

    Carlton et al. do not cross-check the above result with three other questions.
    1. Variation in solar activity is responsible for the majority of the observed warming in the past century. (9% agree)
    2. Higher emissions of greenhouse gases will lead to greater atmospheric warming. (95% agree)
    3. Climate change is independent of atmospheric carbon dioxide levels. (5% agree)
    The second question is intriguing: In equilibrium, temperature is roughly proportional to the logarithm of the atmospheric concentration of carbon dioxide. That implies that an increase in emissions will lead to less additional warming. When read as a second derivative, 95% of respondents are wrong but when read in a colloquial way, 95% of respondents are correct. I double-checked with the lead author. Carlton tells me that this was not picked up in the pre-test.

    Carlton also tells me that 53 of the 55 people who claim that solar activity is responsible for the observed warming also believe higher greenhouse gas emission lead to greater warming -- and that 31 of the 55 also believe that human activity is a significant factor.


    It seems to me that a substantial share of the respondents did not take the survey very seriously, that the authors did not dig very deep, and the referees were not paying attention either.
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  2. I submitted the following to the Climate Spectator on Nov 13, after several attempts to get in contact with the editor.

    On October 3 and again on October 23, the Business Spectator published articles by Mr Robert E.T. Ward BSc criticizing my work. Mr Ward is a public relations professional in the employ of Lord Stern of Brentford. He is without formal qualifications in economics, the subject matter of his criticism. Although Mr Ward has been invited to publish his concerns in the academic literature, he has chosen the popular media instead.

    Mr Ward raises many trivia. I here focus on the two points of contention. First, Mr Ward disputes that climate change might have positive impacts. Such impacts are well documented and straightforward. Warmer winters imply lower heating costs and reduced cold-related illness. More carbon dioxide in the atmosphere means that crops grow better, particularly in dry areas. A number of studies have concluded that these positive impacts are larger than the negative impacts, at least for modest climate change. Mr Ward has not disputed these studies – instead he has targeted my work which merely summarizes earlier findings. In my latest synthesis, I reckon that incremental impacts will turn net negative in the near future. Indeed, that paper concludes that greenhouse gas emissions should be taxed.

    Second, Mr Ward disputes that the impacts of climate change on human welfare are not large. The Stern Review estimates that climate change would make the average person feel as if she had lost five to twenty percent of her income. Other studies find lower numbers. Twenty per cent may seem like a lot, but it is the impact of a century of climate change. Put in context, a century of climate change is about as bad as losing a decade of economic growth – or as bad as lowering the economic growth rate from 2.0% to 1.8% per year. That is by no means trivial – but it is not very large either compared to, say, the economic crisis in Greece. Similar estimates of the welfare impact of climate change have been reported in the last four reports of the Intergovernmental Panel on Climate Change and are shared by other economists, including Mr Ward’s colleagues Professors Fankhauser and Stern. This basic finding is supported by a large technical literature, but it is also in line with casual observations. If we compare hot and rich Singapore to the hot and poor Congo, cold and rich Sweden to cold and poor Mongolia, then we realize that climate is not a fundamental driver of economic well-being. Climate change is a problem, but we should not lose perspective.

    Mr Ward’s concerns are without merit.


    On Nov 24, Tristan Edis announced the discontinuation of this publication.
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