Some people believe the famous 97% global warming consensus paper, published by the people at Skeptical Science, should be described as finding:

There’s a 97% consensus supporting the AGW theory, and 1.6% put the human contribution at >50%.

One member of the project, Tom Curtis, says “[t]hat position, however, is also incoherent.” Another member of the project, Rob Honeycutt, says (in an inline response) of that statement:

[RH] It is a misinterpretation of the results.

In fact, it seems the only person who believes that statement is reasonable may be Dana Nuccitelli, second author of the paper and creator of the scale used in the paper. When he created the scale, Nuccitelli explained:

The way I see the final paper is that we’ll conclude ‘There’s an x% consensus supporting the AGW theory, and y% explicitly put the human contribution at >50%’.

Which is word-for-word the statement the Skeptical Science team labels an “incoherent” “misinterpretation,” just with the numbers from their paper plugged in.



In fact, Nuccitelli seems to agree with the critics of this paper. When he first introduced the scale the paper would wind up using, Nuccitelli said:

As another option, we could have two different consensuses (consensi?). The first being ‘humans are causing most of the observed warming’, the second just being ‘humans are causing global warming’. The first is a stronger point, but relatively few papers will qualify as endorsements (but it should still be a clear consensus). The second is a weaker point, but you’ll have a much larger consensus.

I think every critic of the paper agrees with Nuccitelli. Almost all of them agree there are two different issues. Most of them say the issue, “Is global warming real?” is already resolved. Almost everyone agrees humans have some impact on the planet’s temperatures. They just disagree about how large an impact it is.

Nuccitelli said we should clearly distinguish between “humans are causing global warming” and “humans are causing most of the observed warming.” Skeptics around the world cheer at that idea. They like the idea of saying there is only a 1.6% consensus humans are the dominant cause of global warming.

Nuccitelli was prescient about this, explaining how to avoid letting the skeptics get away with that:

Maybe it turns out that very few papers explicitly endorse AGW > 50%. That’s fine, then don’t use that as the consensus definition. But if it turns out that a lot papers do explicitly endorse AGW>50%, that’s critical information. I’m just saying don’t limit yourself before you’ve even started the project. If you leave your options open and collect as much info as possible, who knows what you’ll find.

If lots of papers say humans are the dominant cause, Nuccitelli thinks they should use that as the “consensus” definition. If not many papers say humans are the dominant cause, Nuccitelli thinks they should use a different definition of “consensus.”

In fact, Nuccitelli explained how to measure the two different definitions of the “consensus” his scale could measure:

Explicitly endorses and quantifies AGW as 50+% cause of the observed warming (or consistent with the IPCC, or something similar) Explicitly endorses but does not quantify AGW Implicitly endorses AGW (by definition does not quantify) Neutral Implicitly minimizes AGW (i.e. says the sun is playing a big role) Explicitly minimizes AGW (less than 50%, less than IPCC, less than consensus, etc.) Explicitly says there’s no anthropogenic effect on climate/temperature For ‘humans are causing most of the warming’, #1 qualifies as an endorsement, while #5 through 7 are rejections. For ‘humans are causing warming’, #1 through 3 are endorsements, while only #7 is a rejection. With those categories, we can just go ahead and rate the papers and see how the percentages turn out for each possible consensus position. It gives us more flexibility than if we choose one or the other definition of AGW beforehand.

A naive person might think Nuccitelli’s ideas about defining the “consensus” are unremarkable. A naive person might see categories specifically labelled as “does not quantify” and think the categories should not be used to measure the idea “humans are causing most of the observed warming.”

But the Skeptical Science team thinks otherwise. Tom Curtis explained why we should believe a paper which merely says methane is a greenhouse gas endorses the idea “humans are causing most of the observed warming” by saying:

It is my opinion that interest in the reduction of greenhouse gases, the only criteria under which the treatment was tested, is only relevant if greenhouse gases are the major contributor to global warming, and only a recommendation of greenhouse gases are the major contributor to global warming. Hence implicitly the abstract assumes that greenhouse gases are the major contributor to global warming (which is also implicitly assumed to be a bad thing).

Or maybe the team doesn’t think that way. Nuccitelli did warn against the exact sort of argument Curtis makes:

In short, in case I’m not being clear, my problem is that if you define AGW as “>50% observed warming over the past ~century is anthropogenic”, then either: you’re forced to make major assumptions in claiming that a large percentage of papers are endorsing that definition (for which you’ll be criticized, and rightly so), or you can break out those which explicitly endorse that definition and those which simply endorse “AGW”, in which case you’re not making any such assumptions (which IMO also makes it less subjective, though perhaps you can replace much of my ‘subjectivity’ concerns with ‘assumption’ concerns). If you go back up to John’s update on the first post above, he asked: “…all these papers endorse the consensus because we say they do?” That’s my concern too. Replace “we say they do” with “we assume they do” – same thing.

So who is right in all this? Are Tom Curtis and Rob Honeycutt right to call Dana Nuccitelli’s envisioned description of the results an “incoherent” “misinterpretation”? Was Nuccitelli, the guy who created the scale used in the paper, a complete buffoon when he explained why he made the scale the way he did?

It’s hard to say. I agree with Nuccitelli. I know a lot of the paper’s critics agree with him too. We all think, like he said, it is right to describe the results by saying:

There’s a 97% consensus supporting the AGW theory, and 1.6% put the human contribution at >50%.

But we need to find out who is really right. If multiple people working on the same project can’t agree, the obvious solution is to ask the project leader. The project leader for this paper was John Cook. Fortunately, he’s already answered our question:

So what is annoying about Dana is when we have a long, convoluted discussion and at the end, I end up just agreeing with what Dana was saying at the very start of the conversation.

So since Dana Nuccitelli said we should describe the results as:

There’s a 97% consensus supporting the AGW theory, and 1.6% put the human contribution at >50%.

John Cook apparently agrees we should describe the results as:

There’s a 97% consensus supporting the AGW theory, and 1.6% put the human contribution at >50%.

Yet somehow the group keeps saying things like:

C13 classified abstracts of climate science papers based on the level of endorsement that most of the recent global warming is man-made (AGW, Categories 1–3)

Even though Nuccitelli clearly explained the 95.4% of the papers which endorse the “consensus” in Categories 2 and 3 are:

not endorsing “the consensus position” – we have to demonstrate what the consensus is. They’re endorsing the AGW theory in general without being specific about the human contribution to AGW. This is the assumption problem I was talking about earlier. We can’t assume that just because a paper says “anthropogenic global warming” that they agree the human contribution is >50%, but they have explcitly endorsed that humans are contributing. Thus they go in category #2.

How does this work? I agree with Dana Nuccitelli. Every critic of the paper I’ve talked to would agree with him too. What he said when designing the scale for this project is the same thing we’ve been saying all along. The critics of the paper agree with the person who designed the scale of the paper.

And John Cook agreed with him. That means the critics of the paper agree with the lead authors of the paper! It’s surreal. Apparently the people responsible for this paper agreed with the critics of the paper… until they saw their results. Then they changed their tune. Maybe finding a 1.6% consensus did that to them.