Opitmizing is what James does, and as a possibly incurable dabbler I
have done some of it too. I think he is more asking for precision of
language than arguing that large and rapid changes are likely to make
us better off.
We are "adapted" to the contemporary climate. The process of getting
ot that adaptation is akin to optimization but it's hard to say that
drier places getting a bit wetter and wetter places getting a bit
drier, for example, would not make us better off.
So it is not fair to say that a better climate is unimaginable, and
any argument based on that presumption is a fallacy. Many a
mathematical argument has such a flavor, so an insistence on precision
is defensible.
On the other hand the flavor of the argument remains convincing to me.
The likelihood that any substantial change in climate will be
beneficial in the net is quite small, because the adaptations we have
set up are local and costly. Some dry places are likely to get drier
and some wet places wetter, so the adaptations will be inadequate.
Some dry places will get much wetter and some wet places will get much
drier. Again the adaptations in place will be inadequate. The faster
and larger the changes, the more common and significant the
maladaptation. We are not likely to get the gentle zephyr breeze
version of climate change almost everywhere it matters, although such
a thing is conceivable.
Talking about optimization in a technical sense is a bit hair-splitty
to me especially in conversation with non-mathematicians. The
practical likelihood of a beneficial climate change is small, and
declines as the rate of change increases.
I would also point out, and this is something I haven't seen discussed
much, that nothing guarantees that local changes will be monotonic. My
intuition from linear systems is that the forced system will start to
ring in all its resonances on all time scales. The only indications in
model (or as far as I know data) of this happening on annual and
interannual time scales is the possibility of an enhanced El Nino,
which remains controversial though most models now seem inclined
against it.
My expectation that interannual oscillatory behavior in response to
strong forcing will increase is sufficiently strong and the evidence
of such behavior in GCMs sufficiently weak that it causes me to
suspect that GCMs have a sort of near-equilibrium bias. That is, I
suspect GCMs filter out forced transient variance on interannual to
decadal time scales. I have no sensible ideas as to how to investigate
this hunch, and it would likely be a more expensive proposition than I
can muster anyway, but I'd welcome speculation by others on the topic.
mt
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