Climategate 3.0: NASA scientist on hockey stick: ‘what Mike Mann continually fails to understand, and no amount of references will solve, is…’

“… that there is practically no reliable tropical data for most of the time period, and without knowing the tropical sensitivity, we have no way of knowing how cold (or warm) the globe actually got. (And similarly, without knowing the tropical sensitivity for the LGM, we don’t know what it’s global cooling was, and without knowing it for 2xCO2, we don’t know what the future sensitivity would be.) It cannot be reconstructed with any confidence from the extratropical response, even if we were to know that well, because the extratropical response is partly driven by in situ feedbacks, so can occur with a variety of tropical responses….”

The e-mail is below.

###

To: Jonathan Overpeck ,
Eystein Jansen
From: David Rind
Subject: Re: [Wg1-ar4-ch06] Review comments
Hi Jonathan and Eystein,
First a quick word about my situation (or lack thereof), and then some
comments about
the reviews. Apparently the typhoid vaccine will finally become available
in the near
future, perhaps as early as later this week. However, it’s a moot point –
NASA requires
a 2 month lead time for international travel, so the timing is fine for a
China meeting
in August (which Ron Miller here at GISS will now be able to go to), but
not for
anything before July. If there was any flexibility here (and Jim Hansen was
not allowed
to go to India with a 2 week lead-time) it would not apply to me, because I
don’t yet
have a ‘government’ passport. I could not get the government passport ahead
of time
because it is only issued in conjunction with approved international
travel, which
starts with the medical clearance. Nobody will say so directly, but I bet
the reason it
wasn’t available (and as I was told, many travelers were ‘inconvenienced’),
was that the
government was stockpiling it in case of a terrorist attack on the water
supply. [It
truly wasn’t available – not here in NY, nor in several other cities along
the east
coast where I had friends call up and ask – as the people at the Cornell
Medical Center
told me it wouldn’t be. The fact that they were so sure implied to me they
knew what was
going on.]
Anyway – I’ll do what I can in conjunction with whatever comes out of the
meeting – and
I’ve already sent you my opinions about the document as it stands, as well
as the
overlap with chapters 2 (primarily the solar forcing), and chapter 9. I
looked at
chapter 10 (the other chapter I’m the liaison for), and there are just a
few points of
overlap which could be discussed some other time.
As far as the reviews are concerned:
1)The suggestion about reorganizing the chapter should be considered
seriously – there
are many points over overlap, and some inconsistently from one section to
another – but
I don’t know that one suggested format (to go by historical time period) is
proper
either. For one thing, it is boring, and it will also lead many readers to
just ignore
sections prior to the last 1000 years (as NOAA apparently is already
doing!). The
ability to understand and model more extreme climates is an important part
of why the
paleochapter is here – if climate warms by 4∞C in the next 100 years,
looking at the
climate, the consequences, and modeling capability for climate changes of
0.5∞C does not
help very much. I’ve already laid out what I think the inconsistencies are,
and we could
work to merge sections that really have repetition, but I think it is
important to
evaluate models over the suite of time-scales, forcings and magnitudes of
response that
paleoclimate situations offer. Having it together I think gives readers a
sense of what
models can and cannot do, and the uncertainties. If these are all relegated
to their
individual time-slices, I think you lose that perspective. I also like
having the
Synthesis and Implications for Climate change combine ideas from the
different time
periods – it gives paleoclimate studies more of an unified feel, as if it
were a real
discipline rather than a bunch of people doing their own time-period thing.
That’s
necessary for IPCC, and necessary for the outside community to see as well.
So I would
vote for keeping the general order, but eliminating the overlap and
inconsistencies in
ways that seem most reasonable.
2) Concerning the hockey stick (which took up probably 3/4 of the review
pages!): what
Mike Mann continually fails to understand, and no amount of references will
solve, is
that there is practically no reliable tropical data for most of the time
period, and
without knowing the tropical sensitivity, we have no way of knowing how
cold (or warm)
the globe actually got. (And similarly, without knowing the tropical
sensitivity for the
LGM, we don’t know what it’s global cooling was, and without knowing it for
2xCO2, we
don’t know what the future sensitivity would be.) It cannot be
reconstructed with any
confidence from the extratropical response, even if we were to know that
well, because
the extratropical response is partly driven by in situ feedbacks, so can
occur with a
variety of tropical responses. [We have a paper in press (two papers,
actually),
discussing this aspect – I’ve actually sent them to IPCC and several of the
chapter
leads with respect to their discussions of AO/NAO variations with climate.]
Therefore
the detailed comments Mike provides concerning the extratropical issues –
how much does
snow cover alter the ground temperature versus the surface air temperature
– are to some
extent beside the point. I’ve made the comment to Mike several times, but
it doesn’t
seem to get across – during the 20th century, according to Jim Hansen’s
temperature
reconstruction, the tropical warming has been 60% of that in the
extratropics (and that
includes the amplifying AO/NAO extratropical change). I believe that in
Mike’s
reconstruction, it averages about 30%. How well we know the numbers for the
first part
of this century is also somewhat uncertain, so I can’t say Mike is wrong –
but the point
is, I don’t know that he’s right, nor do I think anybody else knows either.
So what should we do about it? Basically I think we should indicate that
there are
conflicting views concerning the actual global climate change during this
time period –
quote the references (including the one’s Mike provides), note that there
are
uncertainties concerning the magnitude of the extratropical response, and
that there is
a paucity of tropical data – and leave it at that. Unsatisfying, perhaps,
since people
will want to know whether 1200 AD was warmer than today, but if the data
doesn’t exist,
the question can’t yet be answered. A good topic for needed future work.
3) Concerning Mike’s comment about the importance of volcanism for the 17th
century
cooling – again, what is the evidence for the aerosol optical depth?
Everything is
indirect, so much so that different authors come up with very different
values, as I’ve
quoted in the chapter. The safest and most honest approach for this and
other similar
subjects, is that when something is uncertain we should say it. I know
uncertainty lies
in the eyes of the beholder, but I think it will also be found in the eyes
of the
reviewers, and here I would suggest a democratic approach – let’s not use
one person’s
dogmatic view, but by quoting what the community thinks (as in the case of
solar
forcing), let the uncertainty be made apparent. And if there is uncertainty
in the ice
sheet reconstruction (e.g., how different are the U of Maine results), we
should say
that as well. I’m not suggesting we don’t use our understanding to evaluate
what has
been published – if it is clear to the community as a whole that a segment
of the
differing results are clearly inferior, we should say that – and offer the
proof the
community has provided.
4) And the question of dogmatism versus uncertainty extends to modeling
results,
particularly (though not only) in the case of EMIC results, and results
using coupled
ice sheet models, or vegetation models (e.g., Colin Prentice’s comments).
Both
mechanistically and theoretically, there are major uncertainties in the
results from
such models – matching of time scales and resolution for ice sheets,
understanding the
way plants actually operate, and all the simplifications inherent in EMICs
– these
should be emphasized to be conceptual results primarily. I discussed this
at some length
with Peter Stone, who himself runs an EMIC, and is very familiar with all
of them, and
he agreed entirely. What this means in practice is that results that are
obtained
through the use of such models not be given the dogmatic air of
‘explaining’ the
problem, but rather of suggesting an explanation. It leaves the question
open for
further understanding, which I think is the most accurate approach. For
GCMs, as in the
prediction chapter, the use of a variety of models giving different answers
already
makes it clear that there is uncertainty in their results.
That covers the majority of the comments. Note that “Batch B” is not about
our chapter,
as far as I could tell.
David
—
Jonathan T. Overpeck
Director, Institute for the Study of Planet Earth
Professor, Department of Geosciences
Professor, Department of Atmospheric Sciences
Mail and Fedex Address:
Institute for the Study of Planet Earth
715 N. Park Ave. 2nd Floor
University of Arizona
Tucson, AZ 85721
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http://www.geo.arizona.edu/
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