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Evidence, not consensus, is what counts

My latest (and last) Mind and Matter column in the Wall Street Journal:

Last week a friend chided me for not agreeing with the
scientific consensus that climate change is likely to be dangerous.
I responded that, according to polls, the “consensus” about climate
change only extends to the propositions that it has been happening
and is partly man-made, both of which I readily agree with.
Forecasts show huge uncertainty.

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.

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

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.

I have decided that this is my last Mind & Matter
column, having written about 130 since September 2010. I am
delighted to hand the torch to Alison Gopnik and others. Thanks,
kind readers.


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

“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

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. Here’s a

“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

I am sorry, but Mr Plait really should do his journalistic
research better. He has missed important developments on both

Matt Ridley

By Matt Ridley | Tagged:  rational-optimist  wall-street-journal