Monthly Archives: September 2014

Is there a consensus whether global warming is dangerous?

One of the many things that I found remarkable in the Cook presentation was the slide with the well known tweet of the President of the United States (actually the organization that manages his tweet account):

twitter 20130516 ninety-seven-percent

This tweet was not a surprise as such. I have seen this tweet many times before and I know how it was used. The surprise is that it was presented here.

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It is all about perception

Looking back at my trip to Bristol, it was a wonderful experience. Bristol is a nice city and I made several enjoyable walks in Clifton and surroundings. I also had the opportunity to be in the presence of other skeptics. I was humbled by so many prominent bloggers. Being able to experience that was a honor to me. Many thanks to Richard and Caroline for making this possible.

The lectures on the other hand were a weird experience. There was a strange lacking of science. I was expecting a bit more scientific backbone in both talks. They didn’t deliver on that one and stayed very superficial. “The debate is over” and all that.

The biggest thing I realized from the lectures is: this has nothing to do with the science anymore. The science is used to gain trust of the public. That is where the consensus comes in. If the public has the perception that there is a consensus between scientists, it increases their acceptance and support of climate policies. It is political in nature. There is no doubt that this was the goal of the Cook et al paper. They written it in the introduction as well as in the conclusion.

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The Mann lecture: the science missing in action


Been to the Mann lecture “The Hockey Stick and the Climate wars – the battles continues” yesterday. It was a weird experience, to say the least.

The lecture itself was bland. There was absolutely no depth and it was extremely one-sided.

We saw Mann the green activist, the political activist, the noble man, the preacher, the sales man, stirrer of emotions, the poor victim. I missed one person on stage and that was Mann the scientist.

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The accuracy of the proof or the accuracy of the selection?

cook presentation 97% consensus

There wasn’t anything new in the Cook lecture, yet there was one thing that showed me a new way of looking at the consensus. I already knew there were different studies and I knew they show about the same results, but I had not yet seen the results shown in one image.

If I would look at it with the eyes of somebody who was ignorant on the matter, I would be really impressed by such results. They get the same result every time, even with different methodologies. Looking like that, I would surely think that this 97% value is a pretty plausible figure, a robust quantification of the consensus.

But by looking at those numbers next to each other, it dawned on me. My first thought was: “No way!”. I looked into the methodologies of those three studies earlier and I must admit that I have a hard time believing that with such crude methodologies and rather ambiguous statements, one could get about the same results with just a couple tenths of a percent difference!

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The Mother Of All Hockey Sticks

My visit to Bristol wasn’t reserved for the Cook and Mann lectures alone. Some months ago, I was already planning for visiting this area of the UK, some undefined time in the future. Both lectures were the perfect opportunity to make this trip a reality, sooner than I was thinking. So I am more or less functioning in holiday mode right during my stay.

Today I went for a long hike in Clifton, Cliftonwood and the Old City. I combined two hikes and improvised an additional part. Accumulating quite some miles with my faithful hiking shoes.

It was a diverse route with beautiful lanes, cozy parks, steep hills with a view, a stroll along the river Avon and many boats, old and young, displayed along it. Above all the weather was real nice. Although the locals seem to be dressed much lighter than me. I guess they are used to much cooler weather. I even forgot to bring sun protection, I thought that “Britain and sun milk were not really compatible”.

Wrong. Wrong. Couldn’t be more wrong. Probably has to do with, ahem, global warming, or so.

Anyway, I will have a nice tan tomorrow 🙂

I arrived at the hotel in the early evening, took a well deserved hot bath and went for a bite. Refreshed and replenished I checked my email and the WordPress Dashboard. Nothing could prepare me for what I saw next in the stats:

stats 20140921

Woooooow, what’s that?!?! That is not even a hockey stick, that is The-Mother-Of-All-Hockey-Sticks! When I last looked at it in the morning, I counted exactly five views. That is on average the normal amount for this tiny little blog, so I thought that would be it for the day. Now after the hike my blog suddenly had more views in one day than I would have in two months! The same was true for the comments. And the day wasn’t even over yet (in the meanwhile when I am posting this it seems total views were well above 300-mark and had to rescue some comments from the spam folder).. It caught me completely by surprise.

Is it already enough to be in the same city as The Mann to notice hockey sticks all over the place?

The answer to the mystery was a bit more down to earth. Most of the traffic came from wattsupwiththat. Anthony linked to my previous post. Thanks, Antony. Thanks also for the many visitors for passing by and for the commenters who took the effort to write their valued thoughts or corrected me were needed.

You all made my day.

One analogy too far

Several times in the Cook lecture I couldn’t resist smiling and thinking that he couldn’t believe that himself. Could he? The first time was when Cook said that for complicated issues we rely on the experts and then gave an analogy: bridges. The public is trusting those who build bridges. They trust that bridges are save to cross. The implication seems clear. Why shouldn’t we give the same trust to our climate scientists? Those are the “experts” when it comes to the climate.

I heard that one in several variations and it is rather funny if you think about it.

Sure, I trust that crossing a bridge is save. I realize that bad things can happen (like for example the Tacoma bridge), but this happens rather seldom. It is fair to say that bridge engineers know what they are doing and I have no problem trusting their expertise when walking across a bridge.

Analogies are great, but only go as far as the similarities go. Climate science is a different kind of breed compared to engineering. People build bridges for many thousand years. In engineering the basis is well established, the properties of the materials well known. Feed this into a model and it will work pretty reliable.

Compare that to climate science which is a fairly new science that is studying a very complex matter. Many things are not (well) known, observational data is only available from the end of the 1970s, uncertainties are huge, the science politicized,…

So the comparison is rather flawed. Let’s make the correct comparison.

Suppose you knew that the technology of building bridges was fairly new. Suppose you knew that the technology of bridge building was based on scarce and incomplete observational data. Suppose you knew that only few bridges were build and that most of them collapsed. Suppose you knew that the properties of the materials were hardly known, there were huge uncertainties on how all these things fit together and nobody knew exactly how they would act under a load.

Would you be able to cross that bridge in a relaxed way?


When lookingt at other commentaries they seem to focus more on the question “if 97% say the bridge will collapse and 3% who say the bridge will not collapse, who to believe?”. Maybe I missed something while making notes. For some reason I connected the “expert” statement with the analogy, probably because they followed each other. Have to check with the video how it was actually brought.

Whatever be the case, the analogy will always fail because of the incorrect comparison of bridge engineers (who study a well defined, well understood topic) with climate scientists (who study a complex system with huge uncertainties). Therefor it can easily be reversed. If that 97% agreement is based on incomplete data, processes not yet (well) understood,… then whatever the level of agreement is that the bridge will fail, it will be basically meaningless.

There are also many other possible analogies. See below in the comments for additional thought experiments.

The consensus explained: cats are difficult to herd, but apparently can agree with each other

Just a quick post on the Cook lecture yesterday. It was an interesting lecture and there seemed to be quite some skeptical voices present. For whatever reason, there were however a lot of seats still empty.

In general I didn’t hear anything new in the lecture. If one reads his paper and visited the skepticalscience blog it would all be very recognizable.

It started a bit odd however. Cook showed the statement that scientists rely on testable evidence and that they are like cats, difficult to herd. To be honest, I didn’t really expect such quotes. These are usually used by skeptics. It made me even more curious about what would come next. His research can not possibly follow from those … this promised this be an interesting lecture…

Then came a question to the public if someone could explain the process global warming. He said he asked it several times in other occasions, yet only one seemed to have answered it correctly until now. To him it was a two way process and most of the people who answered it, explained only one of them.

The two processes are: carbon dioxide is transparent for sunlight, but laying a blanket over the earth so less heat escapes to space. To him these were testable processes. Less heat escapes to space, more heat getting trapped, so a cooling of the upper atmosphere, hence shrinking, etcetera, etcetera. He says that the observations of these lines are consistent with carbon dioxide being the main culprit.

Then came the jump. The fact that scientists agree with each other (despite being cats which are difficult to herd) means there must be many lines of evidence. Otherwise it would been impossible to agree with each other…

Wow, I am not sure if I follow that one!

In school we learned about logical fallacies. The teacher explained us that a conclusion can only be reliable if all the premises are valid. In this case there are two premises. The first is: scientists are like cats, difficult to herd. One could of course debate everything, but this one I could accept.

The second premise is a bit more tricky. When history teaches us something, it is not necessarily true that scientists agree on something because of multiple lines of evidence. It can be true that some scientists agree with the theory of global warming because of multiple lines of evidence or the evidence they found their field. But this is not necessarily true for all the scientists who have an opinion on the issue. In the Cook survey most, if not all, papers were not on attribution, but the theory was their starting point. These authors believed in it, but it is not sure if they concluded that from the different lines of evidence or that they did it because they just had trust. In the Cook survey it was not analyzed WHY they endorsed it.

In short, there are several reasons possible why scientists agree with each other. Knowing the evidence could be one of them, but this is not certainly the only one.

Put a scientist in a place where his tenure or his income depends on adhering the consensus and that could change the game completely. Or consider a scientist in a very polarized debate where the respect of his peers comes into the line (see the peer pressure on Bengtsson). Then we have a different situation were contradicting the current theory is not that interesting anymore, yet adhering is. Also climate is a very complex system, involves different specialization, comes with huge uncertainties and very little reliable data before the 1980s. In such a system it would be a downright miracle if scientists agree with each other in such a high degree.

To me that is the Achilles heel of this survey. Sure they made a big effort in analyzing the title/abstracts of 12,000+ papers and I admire them for their persistence. Yet the basis of their conclusion is not holding much water.

The (political) nature of the consensus

Some quick thoughts before going to the Cook lecture this evening.

One question that kept popping up when looking at the consensus is why some people feel the need to prove that there is a “scientific consensus” on Global Warming. It has obviously nothing to do with science. The Cook paper was an eye-opener in that regard.

Just look at how it starts:

An accurate perception of the degree of scientific consensus is an essential element to public support for climate policy (Ding et al 2011). Communicating the scientific consensus also increases people’s acceptance that climate change (CC) is happening (Lewandowsky et al 2012). Despite numerous indicators of a consensus, there is wide public perception that climate scientists disagree over the fundamental cause of global warming (GW; Leiserowitz et al 2012, Pew 2012).

Also look how it ends:

The public perception of a scientific consensus on AGW is a necessary element in public support for climate policy (Ding et al 2011). However, there is a significant gap between public perception and reality, with 57% of the US public either disagreeing or unaware that scientists overwhelmingly agree that the earth is warming due to human activity (Pew 2012). Contributing to this ‘consensus gap’ are campaigns designed to confuse the public about the level of agreement among climate scientists. In 1991, Western Fuels Association conducted a $510 000 campaign whose primary goal was to ‘reposition global warming as theory (not fact)’. A key strategy involved constructing the impression of active scientific debate using dissenting scientists as spokesmen (Oreskes 2010). The situation is exacerbated by media treatment of the climate issue, where the normative practice of providing opposing sides with equal attention has allowed a vocal minority to have their views amplified (Boykoff and Boykoff 2004). While there are indications that the situation has improved in the UK and USA prestige press (Boykoff 2007), the UK tabloid press showed no indication of improvement from 2000 to 2006 (Boykoff and Mansfield 2008).

The narrative presented by some dissenters is that the scientific consensus is ‘…on the point of collapse’ (Oddie 2012) while ‘…the number of scientific “heretics” is growing with each passing year’ (All` gre et al 2012). A systematic, comprehensive review of the literature provides quantitative evidence countering this assertion. The number of papers rejecting AGW is a miniscule proportion of the published research, with the percentage slightly decreasing over time. Among papers expressing a position on AGW, an overwhelming percentage (97.2% based on self-ratings, 97.1% based on abstract ratings) endorses the scientific consensus on AGW.

They didn’t hide their motivation. It is about the perception of the consensus, not if it is true or not. The more the public perceives that there is a consensus among scientists, the more they will support climate policies. By “proving” a consensus Cook and his team want to influence policy making in one direction. It is political in nature, not scientific. It should be considered the work of political activists, not of scientists.

I wouldn’t exactly agree that the scientific consensus is on the point of collapse, but I do have the (subjective) perception that the skeptical side is growing.

I never understood the “providing opposing sides with equal attention”-statement. I don’t have that perception. At least in my country, the mainstream media is dominating with a very one-sided story, focusing primarily on the alarmist side and basically ignoring or even ridiculing the skeptical voices. Also, at least in my country, that “vocal minority” is hardly heard in the media. That is far from receiving equal time.

My own experience tells me that it is very difficult for a member of the public to get information about both sides of the issue. It is therefore even more surprising to see skepticism … grow. So obviously something else is at play here.

Despite the claim of the contrary, global warming is still a theory, not a fact. As far as I know there isn’t conclusive evidence yet and the grounds of the evidence very shaky. There is however overwhelming circumstantial evidence, but only if you look at it in a one-sided way.

But, you might say, isn’t it convincing that this is the “most comprehensive analysis” until now? Extending the analysis of Oreskes and both pointing in the same direction. Isn’t that part of this overwhelming evidence? Well, yes and no. As mentioned before, this is not a scientific analysis. At the very best it analyses how many papers endorse the theory, not whether the science is solid. I agree that the number of papers rejecting is indeed a minuscule proportion of the published research, but I am not really sure this has to do with scientists knowing the science is solid, but rather with the polarization of the debate, peer pressure,…

This paper doesn’t analyze WHY scientists endorse the theory. It could be that they know the evidence, but it could well be that they just have trust that anthropogenic global warming is real, without having a look at the evidence themselves. Since most, if not all, of the papers that were used in the survey were unrelated to the attribution question, I think that last option will be much closer to the truth.

The term “accurate perception” made me smile. “Accurate” is not a synonym for “correct”. Just as for example a thermometer can measure a wrong temperature very accurately (for example when it is badly sited), a survey with a bad methodology can measure a consensus where there is none. As seen in the previous post, the papers used in the analysis were not relevant to the question asked (whether the warming over the last 100+ years is caused by humans). With such a flawed methodology, no matter how many papers they might have examined in the process, be it 1,000 or 12,000 or even a million, that wouldn’t even make a difference.

The “relevant” papers that the consensus is based on

Something in the introduction for the Cook Lecture of next Friday stood out for me. This is how the Consensus Project is presented (my emphasis):

In 2013, John Cook lead the Consensus Project, a crowd-sourced effort to complete the most comprehensive analysis of climate research ever made. They found that among relevant climate papers, 97% endorsed the consensus that humans were causing global warming.

Relevant can of course mean many things, it all depends on what they want to prove with the survey. According to their paper (my emphasis):

We examined a large sample of the scientific literature on global CC, published over a 21 year period, in order to determine the level of scientific consensus that human activity is very likely causing most of the current GW (anthropogenic global warming, or AGW).

What they actually did was searching for papers in which the terms “global warming” or “global climate change” were mentioned in the title or the text of the abstract. But it is not because the term “global warming” or “global climate change” is in the title/abstract of a paper that it is relevant to the cause of global warming.

It should be no surprise that they got a bunch of papers that don’t deal at all with the physics of global warming or with the causes. Most of the papers are on Impacts and Mitigation. Those papers already assume global warming is real, that is their starting point. Mitigation also assumes the anthropogenic nature. None of the two say anything about whether humans are the cause, let alone how much.

There is even a category with non climate related papers. These papers obviously don’t deal with attribution.

The category Methods has the potential to come the closest to attribution, but as expected aren’t about cause. Of course they assume global warming and assume it is anthropogenic. It is also a bin for everything that can not be put in the other categories and it shows.

But, you could say, it is a starting point for many scientists in their research, doesn’t that indicate that they stand behind it? Well, yes, but it doesn’t say anything WHY they believe it. It could be that they understand the cause (not likely, otherwise they certainly would have published the proof), but could be any other reason. Looking at for example Lennart Bengtsson who had to resign from GWPF Advisory Board because of strong peer pressure. Would it be a surprise that in such a highly polarized debate skeptical scientists write neutral looking titles and abstracts and then be classified on the No position pile?

If we want an answer to the question how much the current global warming in the last, say, 100 years is caused by human activity, is a survey of papers the right instrument to do this? And which papers to select? The question about attribution is a very complex one that keeps scientists busy already some time and their opinions vary a lot. This raises the question: is a proof possible with our current understanding and with the limited data we gathered until now?

Even if we think a survey would be the best idea to clarify the physics of global warming, would the outcome matter? It is not because the majority thinks that something is true, that it therefor is true. And what is a consensus on anthropogenic global warming worth if the papers it was based on weren’t even related to studying attribution?

It’s the Ozone hole, Jim, but not as we know it

Ozone hole September 10, 2014

Ozone hole September 10, 2014. Source: NASA (

A couple days ago I found the triumphal message that the Ozone layer is recovering for the first time in 35 years. Attributed to the Montreal protocol. The brunt of the article was that, we people, can solve environmental problems and finally we could do the same thing with for example global warming. However in the article it is cautioned that it still is a “very brittle recovery”.

I had a hard time understanding this “recovery”. Not that long ago, at the end of last year, NASA revealed new results from inside the Ozone hole, in which was stated that the variation of the Ozone hole was mainly caused by natural processes like wind, temperature, solar radiation, and only for a small part by (anthropogenic) substances like CFC and HFC. It would take still decades before a recovery could be attributed to those diminishing substances.

Beginning this year there also was quite some commotion about new substances being found that attack the Ozone layer.

So where is this “recovery” coming from so suddenly? Telling to me was the “for the first time” and “brittle recovery” quotes. As far as I know the Ozone hole is very variable from year to year. In 2006 the Ozone hole grew larger than ever. The next year, in 2007, it was again an average sized. Surprisingly this “recovery” was also attributed to the Montreal convention. Was it a surprise that at that time it was 20 years ago that the Montreal treaty was signed…

Later in 2011 there was a new low, just above 2006 levels, but only a year later, in 2012, we had the second smallest hole in two decades. This recovery was attributed to “natural variation”. This could obviously not be attributed to the Montreal treaty without raising some hard questions…

But let me rephrase this part of history.

There was a change from the biggest Ozone hole to an average in just one year (2006-2007). Even more telling, several years after this the Ozone hole grew again to almost 2006 levels. It also took just one year (2011-2012) to change from the second biggest to the second smallest of two decades. This means that the natural variability of the Ozone hole is HHHUUUGGGEEE! Now we have the message that “for the first time in 35 years”, some “signs of recovery” were found and Hooray, Hooray, the Montreal treaty is a gigantic success story!



My guess is they use different metrics that lend more to a hooray story, more than the metrics that they have been using until now to describe the problem (area of the Ozone “hole”). This is misrepresenting the issue to the media/public/politicians who still think the authors of this story are talking about the recovery of the area of the Ozone hole, meaning the ozone hole is getting smaller. Yet, even when this would be the case, that would be quite meaningless because of the large natural variability the Ozone layer showed in the past observations.

This is not something new. There were triumphal stories about the “recovery” of the Ozone Hole several times in the past. All praising international action and saying we could tackle other environmental problems too. Humbled by reality afterwards.

This obviously is a political message and we should remember it as such.


For what it is worth, I found some more information at AP – Scientists say the ozone layer is recovering:

For the first time in 35 years, scientists were able to confirm a statistically significant and sustained increase in stratospheric ozone, which shields the planet from solar radiation that causes skin cancer, crop damage and other problems.

From 2000 to 2013, ozone levels climbed 4 percent in the key mid-northern latitudes at about 30 miles up, said NASA scientist Paul A. Newman. He co-chaired the every-four-years ozone assessment by 300 scientists, released at the United Nations.

That could explain a lot. These scientists seem to be talking about Ozone levels in the atmosphere at mid-northern latitude. Hey, what are those key mid-northern latitudes? When we think about the problem with the ozone layer, we think about the Ozone hole in the Southern hemisphere. As far as I know the problem with the Ozone layer is at the Southern pole, not at the mid-northern latitudes where the scientists seems to have found a 4% improvement in 14 years. So, we get the impression that it is getting solved while the real issue is still there.

I find it hard to track down the origin of this information. Maybe try again later.