Re: GW: the 'hockey stick' unbent

Aaron Bergman wrote:
In article <1151611744.739989.257290@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>,
charles_the_average@xxxxxxxxx wrote:

Aaron Bergman wrote:

Where did you find a definition of 'plausible'? My reading of the report
(in the paragraph right before the use of the word 'probable') says that
the findings of Mann et al have been substantially confirmed.

From the first comment in the realclimate.org discussion. The commenter
is even more unforgiving, stating that "In IPCC-probability terms it
must rank well below 'likely' (66-90% probable) and I guess even below
'medium likelihood' (33-66% probable)." Not that "plausible" is given a
numerical meaning in the IPCC report; it is not one of the quantifiers
defined there. But then, Merriam-Webster (on-line at
http://www.m-w.com/) defines "plausible" as:
1 : superficially fair, reasonable, or valuable but often specious <a
plausible pretext>
2 : superficially pleasing or persuasive <a swindler..., then a quack,
then a smooth, plausible gentleman -- R. W. Emerson>
3 : appearing worthy of belief <the argument was both powerful and
plausible>
Pick your choice.

#3 seems to be the relevant one to me.

Yup, I too thought so.


And while at that, try substituting each of these
definitions in the NSA report statement saying "...the committee finds
it plausible that the Northern Hemisphere was warmer during the last
few decades of the 20th century than during any comparable period over
the preceding millennium." Only the third definition gives this
statement a meaning similar to what you appear to mean, but even in
this case I would not equate "appearing worthy of belief" to
"substantially confirmed".

p. 109:

The basic conclusion of Mann et al. (1998, 1999) was that the late 20th
century warmth in the Northern Hemisphere was unprecedented during at
least the last 1,000 years. This conclusion has subsequently been
supported by an array of evidence that includes the additional
large-scale surface temperature reconstructions and documentation of the
spatial coherence of recent warming described above (refs omitted) and
also the pronounced changes in a variety of local proxy indicators
described in previous chapters (e.e., Thompson et al. in press).

The next paragraph says that, in light of the above, they find Mann et
al's claim plausible. Given the juxtaposition of the two paragraph,
definition 3 seems the most, er, plausible to me.

(see also p. 106 for the statements about PCA.)


The next paragraph (on p. 109) also says that
"The substantial uncertainties currently present in the quantitative
assessment of large-scale surface temperature changes prior to about
A.D. 1600 lower our confidence in this conclusion compared to the high
level of confidence we placed in the Little Ice Age cooling and 20th
century warming. Even less confidence can be placed in the original
conclusions by Mann et al. (1999) that "the 1990s are likely the
warmest decade, and 1998 the warmest year, in at least a millenium." "

The same as in the overview, and not so reassuring as the phrase
immediately preceding it. I, for one, get the impression that the
writers of the NSA report cannot finish making their minds up. Which is
understandable, if they were paying any attention to their own graphs
at p.18 while writing this conclusions.

[...]

It's certainly true that confidence decreases as one goes farther back.
That's all I get out of the quoted paragraph.

Aaron

Huh? What about the part that says "Even less confidence can be placed
in the original conclusions by Mann et al. (1999) that "the 1990s are
likely the warmest decade, and 1998 the warmest year, in at least a
millenium." "?

That's certainly true. There is less confidence in that claim than the
others. This use of the phrase "less confidence" is in contrast to the
phrase "very little confidence" used on p. 112 to describe constructions
prior to AD 900.

Aaron

Unfortunately, they do not say how much confidence they have in the
original conclusion by Mann et al (1999) that temperatures at AD1000
were 0.8C cooler than now, and remained so for 900 years. This one
comes from the very same temperature reconstruction than the "late 20th
century warmth unprecedented in 1000 years" which they seem to endorse.
And is clearly contradicted by more recent reconstructions.

.