Monday, July 8, 2013

Science Is About Evidence, Not Consensus

Besides, science does not respect consensus. There was once widespread agreement about phlogiston (a nonexistent element said to be a crucial part of combustion), eugenics, the impossibility of continental drift, the idea that genes were made of protein (not DNA) and stomach ulcers were caused by stress, and so forth—all of which proved false. Science, Richard Feyman once said, is "the belief in the ignorance of experts."
[image]Chris Silas Neal

My friend objected that I seemed to follow the herd on matters like the reality of evolution and the safety of genetically modified crops, so why not on climate change? Ah, said I, but I don't. I agree with the majority view on evolution, not because it is a majority view but because I have looked at evidence. It's the data that convince me, not the existence of a consensus.

My friend said that I could not possibly have had time to check all the evidence for and against evolution, so I must be taking others' words for it. No, I said, I take on trust others' word that their facts are correct, but I judge their interpretations myself, with no thought as to how popular they are. (Much as I admire Charles Darwin, I get fidgety when his fans start implying he is infallible. If I want infallibility, I will join the Catholic Church.)

And that is where the problem lies with climate change. A decade ago, I was persuaded by two pieces of data to drop my skepticism and accept that dangerous climate change was likely. The first, based on the Vostok ice core, was a graph showing carbon dioxide and temperature varying in lock step over the last half million years. The second, the famous "hockey stick" graph, showed recent temperatures shooting up faster and higher than at any time in the past millennium.

Within a few years, however, I discovered that the first of these graphs told the opposite story from what I had inferred. In the ice cores, it is now clear that temperature drives changes in the level of carbon dioxide, not vice versa.

As for the "hockey stick" graph, it was effectively critiqued by Steven McIntyre, a Canadian businessman with a mathematical interest in climatology. He showed that the graph depended heavily on unreliable data, especially samples of tree rings from bristlecone pine trees, the growth patterns of which were often not responding to temperature at all. It also depended on a type of statistical filter that overweighted any samples showing sharp rises in the 20th century.

I followed the story after that and was not persuaded by those defending the various hockey-stick graphs. They brought in a lake-sediment sample from Finland, which had to be turned upside down to show a temperature spike in the 20th century; they added a sample of larch trees from Siberia that turned out to be affected by one tree that had grown faster in recent decades, perhaps because its neighbor had died. Just last week, the Siberian larch data were finally corrected by the University of East Anglia to remove all signs of hockey-stick upticks, quietly conceding that Mr. McIntyre was right about that, too.

So, yes, it is the evidence that persuades me whether a theory is right or wrong, and no, I could not care less what the "consensus" says.


  1. Their logic and evidence must not be very strong if they have to quote a "consensus" to support their point. Science is not a democracy. For those who believe that consensus establishes science then they must believe without question that the earth is at the center of the universe and that the entire universe revolves around the earth. The earth centered universe was at one time the consensus and hence should still be because the science is settled and opinions otherwise should never have been tolerated by consensus believers. If there is a consensus, the science is settled, and no further research or differences of opinion should be tolerated. All those who believe in the settled science of AGW should stop researching and writing about it. The science is settled, it does not need to be defended, and there is nothing that can be added. If nature does not abide by computer simulations of climate then it must be mother nature that is wrong. Maybe the IPCC should be litigating mother nature in court.

    1. Yes, "consensus" has no place in science and is a last refuge to those who have no valid argument. In my field of science, and in every other field of science, nobody talks about "the consensus," it is unique to climate "science."

  2. Update: In response to an article at Slate criticising this article
    I tried to send the following comment but it did not appear:
    Sadly, Phil Plait's understanding of the literature in this area is very superficial and out of date. He also fails to rebut my arguments entirely. Indeed, he admits I am right in the first case:
    "First, it’s true that in the distant past (hundreds of thousands of years ago) a rise in carbon dioxide sometimes did follow a rise in temperature." Actually, this is invariably the pattern in the ice core record, not "sometimes".
    Moreover, as you can see on John Kehr's excellent graphs here
    the inconvenient truth is that at the end of the Eemian interglacial temperature fell steadily for thousands of years before CO2 levels fell at all. The argument that a small warming at the start of an interglacial causes a CO2 release which causes a large warming is one that has been tested and found entirely wanting. To quote from an excellent essay on the topic
    "Now, the standard response from AGW supporters is that the CO2, when it comes along, is some kind of positive feedback that makes the temperature rise more than it would be otherwise. Is this possible? I would say sure, it’s possible … but that we have no evidence that that is the case. In fact, the changes in CO2 at the end of the last ice age argue that there is no such feedback. You can see in Figure 1 that the temperatures rise and then stabilize, while the CO2 keeps on rising. The same is shown in more detail in the Greenland ice core data, where it is clear that the temperature fell slightly while the CO2 continued to rise.
    As I said, this does not negate the possibility that CO2 played a small part. Further inquiry into that angle is not encouraging, however. If we assume that the CO2 is giving 3° per doubling of warming per the IPCC hypothesis, then the problem is that raises the rate of thermal outgassing up to 17 ppmv per degree of warming instead of 15 ppmv. This is in the wrong direction, given that the cited value in the literature is lower at 12.5 ppmv."
    None of this contradicts the idea that CO2 is a greenhouse gas and will in the absence of other factors cause net warming, something I have always accepted. But as I have repeatedly made clear in my writings, that's not at issue -- at least in my mind. What is at issue is the question of whether current CO2 rises can cause dangerous warming, which I no longer think is likely, though it remains possible. Why do people like Mr Plait try to pretend that I am some kind of closet denier, rather than take on this argument, for luke-warming, and address it seriously? They are simply wasting their fire on a straw man.
    As for the hockey stick, Mr Plait repeats long discredited defences of the graph including the suggestion that other selections of data have confirmed it. Surely he knows (if only because it is in my article) that these confirmations rely on including Tiljander's lake sediments or bristlecone pines but that if you leave these now-debunked data sets out, then the effect vanishes. Please read Climate Audit to verify this.

  3. Here's a quote:
    "As CA readers are aware, the “big news” of Mann et al 2008 was its claim to have got a Hockey Stick without Graybill’s bristlecone chronologies (camouflaged as a “no-dendro” reconstruction). CA readers are aware that this claim depended on their use of contaminated modern portion of the Tiljander sediments and that the original claims for a “validated” no-dendro reconstruction prior to 1500 fell apart, even though no retraction or corrigendum to the original Mann et al (PNAS 2008) has been issued.As we learned (from an inline comment by Gavin Schmidt in July 2010), Mann et al have conceded that these claims fell apart, but did so using a “trick” (TM- climate science.) Instead of acknowledging the false assertions at the journal in which the assertions were made (PNAS), they acknowledged the failure of the no-Tiljander no-bristlecone reconstructions deep in the Supplementary Information of a different paper (Mann et al, Science 2009) – a trick for which the term “Mike’s PNAS trick” is surely appropriate (though the term “Mike’s Science trick” also merits consideration.)"
    And I am gobsmacked to find Mr Plaitt showing the Marcott et al graph, when this was comprehensively demolished within weeks of publication as evidence for unprecedented temperatures: see a good summary of the scandal here -
    Note that the authors themselves said:
    “[The] 20th-century portion of our paleotemperature stack is not statistically robust, cannot be considered representative of global temperature changes, and therefore is not the basis of any of our conclusions.”
    I am sorry, but Mr Plait really should do his journalistic research better. He has missed important developments on both questions.
    Matt Ridley