Dear David,
I believe you were considering a form of geoengineering that doesn't
come under "solar radiation management" (SRM), but rather "thermal
radiation management" (TRM), i.e. by removing cloud cover and increasing
thermal radiation into space from the surface of land and sea.
We need as much negative forcing (i.e. cooling) as we can quickly get
in/into the Arctic, because of the perilous state of some of the methane
in the Arctic, particularly in the area of the East Siberian Arctic
Shelf (ESAS), where the methane could get discharged in huge quantities
without warning to immediately boost global warming by many times [1].
Cloud brightening can cool the Arctic through cooling the surface water
of currents entering the Arctic from the Atlantic, but there is a limit
to how far one can go with that before it starts affecting climate in
Europe! And this method could take years to cool the ESAS waters by the
several degrees needed to slow methane discharge and stabilise the
situation. So we will almost certainly need stratospheric aerosols to
produce a general cooling effect over the whole Arctic during the spring
and summer months. However cloud removal could be a useful supplement,
especially because of uncertainties in the logistics and effectiveness
for rapid aerosol deployment [2].
One could remove the clouds either by evaporating them, as Mark Massmann
is suggesting (see email appended below), or by making them discharge
their H2O content as snow. The latter approach has the advantage of
increasing albedo of land and ice surfaces below, where they are not
already covered by fresh snow; so it has an SRM aspect - making it a
double-edged sword.
I look forward to your suggestions for the most effective combination of
geoengineering techniques, considering the desirability of readiness for
full-scale deployment next spring - if this were possible and shown to
be the best risk-minimisation strategy!
Best wishes,
John
[1] Shakhova and Semiletov estimate that up to 50 Gt methane could be
discharged "at any time" [3], boosting atmospheric content by around 11
times the present (~5 Gt). The resulting climate forcing would be at
least 20 times the present methane forcing (0.48 W/m-2) because of
indirect forcing effects [4]. Such a discharge could be produced by
earthquake, and part of the ESAS is prone to earthquakes. Thus the
probability of such a discharge happening cannot be known exactly, but
the risk is enormous because of the fatal consequences, assuming:
risk = probability x magnitude
[2] The tethered balloon method of stratospheric aerosol deployment
could take years to develop, so I assume we'd use stratotankers or
similar. It is also conceivable (though extremely unlikely in my view)
that some adverse side-effect would appear such as to force a
termination of deployment, in which case TRM could become the key
technology for general Arctic cooling. Anyhow we need a belts and
braces approach in this precarious situation.
[3] http://en.wikipedia.org/wiki/Arctic_methane_release
[4]
http://www.atmos.washington.edu/academics/classes/2011Q2/558/IsaksenGB2011.pdf
--
On 02/07/2011 11:15, Mark Massmann wrote (under subject "Modified Lair
concept")
John and Kevin-
I've been going through calculations for various Lair strategies, and
in the process have found some new strategies for Lair.
1. One is to reduce global cirrus clouds. By releasing Lair over
cirrus clouds (say 50,000 ft), it will expand over 7,000 times into
perfectly dry air and cause cirrus to sublimate (basically drying them
out). This effect could be done on a very large scale and should last
much longer than creating new clouds, because once a cirrus region is
dry and cirrus free, it would stay that way until new cirrus is formed.
2. The other is to add salt-CCN's to brighten marine clouds (i.e.
replace MCB). Here, Lair would primarily be used as a disbursent for
salt-CCN's, where the CCN's would be added to Lair so that they mix
and are suspended in it, so that when Lair is released the CCN's would
be evenly disbursed over a large region. This way you could
essentially replace the function of MCB- and do this ASAP to help cool
the arctic instead of waiting on a fleet of MCB vessels to be
manufactured (at least 5 years down the road).
Please let me know what you think of these, and I will make a new
posting outlining them to the group.
Also John- please let me know what cloud area is needed to help
protect the arctic (I'm assuming it's smaller than what's needed to
globally offset global warming, though it could be close if you
wanted much more cloud coverage per area).
Thanks!
Mark
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