no they don't. "point of no return" is open to many interpretations.
you might take it to mean "greenland will melt" for example.
> http://archive.greenpeace.org/climate/database/records/zgpz0638.html
>
> "Runaway global warming" (RGW) is the best term I have found for this
> (based on googling). Is there a better term?
>
> What is the status of RGW in the scientific community these days? It
> is frige alarmist or mainstream?
no-one believes it
-william
> Is there any research that might sort out RGW, determine if its a real
> probability, put a probability on it?
>
> What are the time frames for RGW? Perhaps it would play out over such
> long time frames that it would not scare the public into action even
> if the mainstream of scientists considered it probable.
> >
>
--
William M. Connolley | www.wmconnolley.org.uk | 07985 935400
Don't worry, the International Biochar Initiative will save us.
-dl
> but I'll opine that Venus-style runaway is not possible here on earth
> (following threads and commentary on Real Climate).
"not possible" is hard to defend IMO.
I have a handful of model simulations which give a reasonable climate
under present day conditions but show runaway global warming under 2xCO2
and even 1.4xCO2 in one or two cases (about where we are now!). These
models are in the same class as the CPDN ensemble, ie a fully-fledged
atmospheric GCM coupled to a slab ocean, so designed for looking at
equilibrium climates, based on our detailed understanding of the myriad
interacting physical processes.
I suppose I should submit it to Nature :-) But when a Japanese model
gives a crazy result, everyone says "that's a crap model". When HadCM3
gives a crazy result, everyone say "ooh that's scary, we're all going to
die".
James
I have seen formal calculations about this; apparently we are a bit
too far from the sun for this to happen here, but not by a huge
margin. If the sun warms up just a little bit it will happen. If the
earth were a cylinder and not a sphere, hence tropical everywhere, the
oceans would boil away post haste. Unfortunately I didn't track this
down on the first attempt.
(It's a Ray P question if there ever was one, though I don't think he
was the author of the definitive analysis of the question if I recall
right.)
That doesn't mean there aren't exacerbating feedbacks. The clathrates
may provide one on a millenial time scale. There are other candidates.
But "runaway" isn't the right word for that unless you think the world
will tip into complete uninhabitability as a result.
mt
> > > What is the status of RGW in the scientific community these days? It
> > > is frige alarmist or mainstream?
> >
> > no-one believes it
>
> Why not?
> ...
> BTW, "runaway greenhouse effect" is better term, I think. But, as mt
> pointed out, it's ambiguous. Could be either Venus or the major
> factor in most or all warm periods in Earth's history. Everyone
> believes in the latter.
Fair enough, we all know its been warmer in the past, but RGE doesn't
mean that. To me at least it means a discontinuity in
forcing-response: past a certain (GHG) forcing the response suddenly
jumps to a new state (a tipping point, ha ha, to use a meaningless
phrase) that is *much* warmer. I suppose the methane clathrates might
satisfy this, but they are on the ocean bed where its deep and cold.
-W.
I doubt there are formal calculations that really *prove* anything,
though there may well be sensible approximations and assumptions that
support this conclusion. After all, we do not *know* bounds on what
the climate sensitivity is with *certainty*, and a high enough
sensitivity would generate this behaviour. It was indeed Ray P who
IIRC expressed some interest and/or surprise at our model results,
when I mentioned them on RC once.
James
Not much, not much, no-one, and handful in about 100 :-)
I take it as a salutory reminder of the limitation of this class of
model (experiment). You may not realise, but in these experiments the
atmosphere is "tied" to a sea surface which is forced to have
realistic temperatures and which (crucially) acts as an infinite
source or sink of heat (and freshwater, although this may not matter
so much). So the actual radiative behaviour of the atmosphere may not
be at all realistic when we push parameters to extreme values.
Furthermore, we can only evaluate the model by looking at equilibrium
situations (eg pre-industrial climate) and not explore the transient
response in any quantitative sense, since the model lacks the thermal
inertia of a deep ocean.
The only time I saw someone try a hindcast of the last 100 years with
a model that had a sensitivity of ~10C, it was completely crazy. High
sensitivity means low stabilising radiative feedback so the
temperature oscillated rather wildly, especially in response to
historical volcanic eruptions. In principle one might be able to get
such a model to work passably by adjusting other uncertainties such as
deep ocean heat uptake, but the amount of evidence you have to
handwave away in order to defend this makes the whole process a bit
fantastical...which is why I say that sensitivity is very likely close
to 3C, although it is not possible to formally *prove" that much
higher values are impossible.
James