About “scientific consensus on climate change”
About “scientific consensus on climate change”
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IAntropogenic Global
Warm’m writing this personal
opinion about a “hot” topic: the
ing (AGW) consensus.
In EPN 44/6, John Cook
presents the conclusions of a paper by
himself et al., published in
Environmental Research Letters 8 (2013)
doi:10.1088/1748-9326/8/2/024024,
where almost 12000 abstracts of
papers dealing with global warming,
published since 1991,are classified
depending on their position about AGW.
It is immediately clear from the
abstract that two thirds of the
analyzed papers do not express a position
on AGW: this should be indicative of
the scientific uncertainty on the issue.
However, this figure is not taken into
account and the authors focus on the
remaining 33% of the papers.
Among these 33% papers, 97%
support the AGW: papers stating that
“humans are contributing to global
warming without quantifying the
contribution” are considered to support
AGW.It is practically impossible to find
a climate scientist against such a
statement (it would be like saying that CO2
is not a greenhouse gas), but this is well
different from being in agreement with
AGW,which – as Cook et al. remind us
– means that“humans are contributing
more than 50% of global
warming,consistent with the 2007 IPCC statement
that most of the global warming since
the mid-20th century is very likely due to
the observed increase in anthropogenic
greenhouse gas concentrations”.
Indeed, an analysis of the papers
classified in the support category (which
can be done by following the link“online
supplementary data”) shows that papers
by famous climate scientists known to
be againstAGW (e.g.,Lindzen and
Shaviv) fall among those in favour.
Trying to reduce the percentage of
papers that do not express a position,
Cook et al. contact the authors via
e-mail: only 14% respond to such a
query.At this point it would not make
sense to proceed because the sample is
drastically reduced and, more
important, such a sample can no longer be
considered “unbiased” (the analysis is
based only on those who have decided
to respond and it is reasonable to
assume that this is a polarised sample).
J. Cook et al. proceed anyway and
35% of the authors,among the 14% who
answered to such a query, confirm that
they do not have definite position with
respect to AGW: a rather high
percentage to claim an almost complete
consensus, as Cook et al. would like to do.
Finally, the reasons given by Cook
et al. to find a justification to the high
number of papers that do not take
a position, show an internal logical
contradiction: AGW would be such a
scientific certainty that it is no longer
needed to specify the authors’position
in the abstract. Besides the fact that
this assertion is contradicted by the
35% that confirms “no position”, even
if it were true, why is the research by
Cook et al. based on such abstracts?
Given that the verification of the
scientific hypothesis is not based on
the level of consensus they get but on
a tighter comparison with reality, all
of the above has nothing to do with
the consistency of AGW.
If any meaning may be given to
the work about the AGW consensus, I
would say it does not point to a
unanimous consensus,rather to a scientifically
still quite open issue,taking also into
account that the percentage of papers that
do not take a position grows with time.n
John Cook responds
Gianluca Alimonti comments that
because 67% of abstracts fail to state
a position on anthropogenic global
warming (AGW), this indicates
scientific uncertainty.As discussed in Cook
et al. (2013), this is explicitly not the
case.To quantify the degree of scientific
uncertainty, we re-examined 1000 of
the“no position”papers and found only
5 expressed uncertainty on the issue.
The relevance of “no position” papers
was discussed by Naomi Oreskes in
2007. She predicted that as a
consensus strengthened, less papers should
see the need to restate the consensus
position. For example, few
astronomy papers state the consensus
position that the Earth orbits the sun.
Our data confirms Oreskes’
prediction, with the proportion of “no
position” abstracts increasing at the
same time that the consensus among
relevant climate abstracts
increases. The significance of “no position”
papers is discussed in our paper.
Alimonti is correct about one point:
verification of a scientific hypothesis
is based on empirical confirmation,
not consensus. However, the general
public use expert opinion as a
heuristic to guide their views on
complicated scientific matters. As there is a
large gap between perceived
scientific agreement and the 97% reality, this
necessitates communication of the
overwhelming consensus. n (...truncated)