As a non-native English speaker, I often encounter new words. One such word is “equivocation” (using the same word for different things or the use of such word in multiple senses throughout an argument, leading to a false conclusion). The first time I heard about it, I recognized it as something that is frequently used in global warming/climate change communication.

At the end of last week, when searching for something related to the consensus, I landed at the Skeptical Science page titled The 97% consensus on global warming (intermediate version). I am pretty sure that I must have read this before, but having “equivocation” at the back of my mind, gave it a new dimension.

As the title suggests, its subject is the 97% consensus. It starts from the statement of the Petition Project that “there is no convincing scientific evidence that human release of carbon dioxide will, in the foreseeable future, cause catastrophic heating of the Earth’s atmosphere”.

The Skeptical Science author calls this a myth and tackles it by explaining that a consensus of around 95% is found in papers like Cook et al 2013 & 2016, Oreskes 2004, Doran 2009 and Anderegg 2010. Also mentioned are the Vision Prize poll that basically found something similar and a list of scientific organizations that endorse the consensus.

I don’t know much about the Petition Project, but from the excerpt given in the Skeptical Science article, it is clear that the Petition Project statement is very specific. They claim that there is no consensus specifically on the catastrophic nature of global warming caused by human emissions.

The Skeptical Science author however is trying to counter this specific statement with evidence of a consensus on the much broader “Global Warming”. A consensus on Global Warming is the sum of those who agree that:

  1. the Earth is warming caused by natural causes
  2. the Earth is warming caused by human activity (AGW), from which Catastrophic Anthropogenic Global Warming (CAGW) is a subset.

Only a consensus based on that CAGW subset can counter the specific statement of the Petition Project.

Unless of course there is a consensus on the catastrophic nature of global warming, but judging on the papers that are presented as evidence, I don’t think this is the case. I wrote already several posts on most of these papers, so I will keep it really short here.

The Cook 2016 is a collection of several papers, including some that are mentioned further in the article. According to the article, the main conclusions are:

  1. Depending on exactly how you measure the expert consensus, it’s somewhere between 90% and 100% that agree humans are responsible for climate change, with most of our studies finding 97% consensus among publishing climate scientists.
  2. The greater the climate expertise among those surveyed, the higher the consensus on human-caused global warming.

Even as a skeptical mind, I don’t have a problem with those two conclusions. On the contrary, I am rather surprised that it is not 100%. The definitions of “Global Warming” are so broad that also skeptics could find themselves agreeing on it.

More importantly, the time that I read that paper (now almost two years ago), I didn’t find that these scientists agreed on the catastrophic nature of Global Warming. They agreed on something much broader.

The next paper, Cook et al 2013, is a survey of almost 12,000 abstracts of scientific papers matching the topics “global climate change” or “global warming” and took a position on AGW. It was found that 97% of those abstracts explicitly state or imply that humans cause global warming.

To get to that 97%, the authors lumped together those who:

  • explicitly state that humans are the primary cause of recent global warming (category 1)
  • explicitly state that humans are causing global warming or state anthropogenic global warming/climate change as a known fact (category 2)
  • imply that humans are causing global warming (category 3).

There is a lot to be said about this paper, but in this context it is clear that Cook et al 2013 didn’t investigate the consensus on “Catastrophic” Anthropogenic Global Warming.

By the way, the term “catastrophic” was mentioned only once in that paper and it was in an example phrase of how to recognize category 6 papers (explicit rejection without quantification). If the abstract of a paper contained something like “the global temperature record provides little support for the catastrophic view of the greenhouse effect” it was categorized in category 6, which also is an indication that the authors of Cook 2013 seem to equal GW and AGW with CAGW.

It is certainly possible that there were papers that agreed on the catastrophic nature of global warming, but Cook and his fellow investigators were not specifically looking for them.

Oreskes 2004 is a survey of all peer-reviewed abstracts on the subject “global climate change” published between 1993 and 2003 figuring out how many papers disagreed with the position of the US National Academy of Science and the IPCC:

Human activities … are modifying the concentration of atmospheric constituents … that absorb or scatter radiant energy. … [M]ost of the observed warming over the last 50 years is likely to have been due to the increase in greenhouse gas concentrations

She found none. Which is not exactly surprising. Humans are emitting greenhouse gases, therefor increasing the concentration of these gases in the atmosphere and since these have a warming effect, follows that, everything else being equal, humans are responsible for at least part of the warming.

I think many skeptics or “deniers” can agree with that.

In the context of the debunking in the Skeptical Science article, Oreskes 2004 did not investigate whether Global Warming is/will be catastrophic.

Doran 2009 asked two questions concerning global warming to the participants:

  1. When compared with pre-1800s levels, do you think that mean global temperatures have generally risen, fallen or remained relatively constant?
  2. Do you think human activity is a significant contributing factor in changing mean global temperatures?

If I had to answer these questions, then I would answer a “yes” to the first question. The second question is a bit more nuanced, it depends on what is meant by “significant” and “contributing factor”, so no clear “yes” or “no” could be given. If pressed for an answer, I would say rather “yes” than “no”.

It might be that scientists who agreed on the catastrophic nature of increasing greenhouse gas were counted in that 97%, but they were not quantified in this paper.

Anderegg 2010 assessed this statement:

Report that it is very likely that anthropogenic greenhouse gases have been responsible for most of the unequivocal warming of the Earth’s average global temperature in the second half of the 20th century.

This is a very vague and broad statement. Anderegg 2010 also does not quantify those who agree that these anthropogenic greenhouse gases have catastrophic effects.

I didn’t look into the Vision Prize poll yet, but according to the explanation in the Skeptical Science article this is the result:

Approximately 90% of participants responded that human activity has had a primary influence over global temperatures over the past 250 years, with the other 10% answering that it has been a secondary cause, and none answering either that humans have had no influence or that temperatures have not increased.

An “influence over global temperatures” is rather broad. It might include those who agree on the catastrophic nature of global warming, as well others who don’t.

Finally, the scientific organizations endorse the consensus position that:

Most of the global warming in recent decades can be attributed to human activities.

Which probably most skeptics could agree to as well.

The common theme is that they polled (climate) scientists whether they believed that temperatures were rising and in how far humans are responsible. However, none of those investigated whether global warming is or will be catastrophic. So how could this be used to disprove this specific statement made by the Petition Project?

As often when I read a page on the Skeptical Science website, I now wonder whether the author knows that none of those papers actually investigated the catastrophic nature of global warming and if yes, why he thinks it doesn’t matter.

Concluding, I can agree with this statement of the Petition Project as used in the Skeptical Science article. I even have no problem believing that there is a consensus on increasing temperatures and that humans have an influence on these. But, as far as I know, no consensus is found on the catastrophic nature of this temperature increase and the examples that the Skeptical Science article cites confirm this.

My guess is that the author of the Skeptical Science article equals “Global Warming” and “Anthropogenic Global Warming” to “Catastrophic Anthropogenic Global Warming”. This way the author can rely on a much broader consensus than actually exists for what he actually want to prove.


7 thoughts on “GW = AGW = CAGW?

  1. AngryWxGuy

    Excellent post. Was wondering the same thing myself. Are the alarmists who argue for catastrophe with the 97% consensus just logically illiterate or are they deliberately misusing language to convince the gullible public? Neither one would surprise me.

    With respect to catastrophe, I don’t think we even know what the SIGN of carbon externalities are, let alone whether they are catastrophic. Richard Tol is a great resource in that regard.


    1. trustyetverify Post author

      I don’t think they are logically illiterate. My guess is that they think that they are right anyhow and that it is just a matter of figuring out how to convince the public of this. But that is just my little theory.


  2. manicbeancounter

    Skeptical Science do not seem to have directly referenced the Petition Project, so that the reader can compare their claims to the original.
    I will help here.

    Compare Doran and Zimmerman 2009 (the earth has warmed, and humans are a significant contributing factor) with the petition project – there is no evidence for CAGW. Many could, without contradicting themselves, assent to both. At the age of 11 I was taught about Venn diagrams – the visual representation of set theory. Members of set of those who believe in human caused warming (AGW) can include those who do do not believe in CAGW. Indeed the set of CAGW is a proper subset of those who believe in AGW. It is the belief in CAGW that can justify policy, but the surveys only include the most banal form of AGW. The climate alarmists do not ask the question of whether there is convincing evidence for CAGW, as this would separate out the activists from those that stand up for scientific integrity. My belief is that such a survey would get a very low response rate.


    1. trustyetverify Post author

      There is a link to the Petition Project in the skepticalscience article, but I also glossed over it initially.

      I remember those Venn diagrams from a long time ago. However, when I read back my post, I noticed that my explanation of that subset was rather confused. I will try to rephrase that part.

      Maybe such a Venn diagram would make the story clear in a more visual way, instead of the textual way of the post. I will try to represent this story via such a diagram and append it to the post.

      Liked by 1 person

  3. manicbeancounter

    In a post three years ago I looked at this issue and produced my own little diagram.
    My point then was to illustrate how climatology could either be viewed over time as scientifically progressing or regressing.
    I included climate change (CC) as the outer ring, as Global Warming is one type of climate change. Therefore
    CAGW ⊂ AGW ⊂ GW ⊂ CC

    The important point is here is to remember that evidence for climate change is not necessarily evidence for CAGW.

    In my diagram, using very weak evidence from the surveys like Cook et al. 2013 is a sign of degeneration. They only supports the weakest form of AGW. Progressive science would have been making short-term predictions that turn out to be true, like acceleration in the melting rates of polar ice-caps, more extreme hurricanes after New Orleans in 2005, greater famines in Africa, more heatwaves in Europe after the 2003 event, collapsing polar bear populations, thawing out of the Siberian permafrost with increased methane emissions etc. etc.
    Another way of progressing is to develop standards in data collection and analysis. Yet another is moving away from opinion-based statements, to more empirically-based statements.

    I hope this helps, but if you think it does not capture your own thoughts, please use to help develop your ideas.

    Liked by 1 person

    1. trustyetverify Post author

      I was thinking about something rather similar (without the cc and progressing/regressing arrows). Just to illustrate the discrepancy between the statement of the Petition Project and the SkS argument, but also I will try to contrast it with what I think is the view of the SkS author(s).


      1. manicbeancounter

        My first diagram was without the arrows.

        The problem is fitting in observable events. Extreme weather events can be catastrophic without been human caused. Natural climate change can also be catastrophic as well. For instance. a few thousand years ago much of North Africa changed from savanna to the largest desert on earth.



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