Andrew
Several computer models show that tropospheric cloud brightening can
offset at least 4 or maybe 6 watts per square metre . The log term
means that it gets progressively harder but not impossible to increase
the offset. We get the choice about where to spray so we have control
of initial conditions and so may be able to exert some control about
getting more or less precipitation or at least avoid the very bad
places. We should know more about this quite soon. If the climate
situation changes, perhaps by another Pinatubo we can stop very quickly
(a few days) or increase quite quickly if there are enough vessels.
I understand that stratospheric aerosols can do a similar amount
offset. I had thought that the effect was linear but there has been a
suggestion that the more you spray the greater the chance of particles
coalescing and falling out more quickly. The effects last about two
years depending on height so you cannot do a sudden turn off. The
obvious solution is to use both with the cloud albedo tweeter doing fine
adjustments to the stratospheric sulphur woofer.
The costs given in the Royal Society report for a cooling of one watt
per square meter were made on the sumption that the entire spray fleet
was scrapped each year. If you follow the reference to the Robock paper
for costs of the aircraft launch system you will see that they assumed
that the capital cost of planes was zero and all they were paying for
was fuel, spares and and crew time. However the costs of both
techniques are so much smaller than Stern predicts for doing nothing
that you can ignore them.
If you are worried about ocean over turning you could look at the file
/Hurricanes carbon and fish in the /Hurricanes folder at the site below
my signature.
Stephen
Emeritus Professor of Engineering Design
Institute for Energy Systems
School of Engineering
Mayfield Road
University of Edinburgh EH9 3JL
Scotland
Tel +44 131 650 5704
Mobile 07795 203 195
www.see.ed.ac.uk/~shs
On 10/04/2011 14:54, Andrew Lockley wrote:
Hi
I wonder if anyone can shed light on the potential of geoengineering
in a high GHG atmosphere ?
If we have massive methane excursions from the arctic, will we be able
to create a safe climate? The paleoclimatic record shows dramatic
cooling through volcanism, but that wasn't in a high GHG world .
If there's a whole load of methane around, there will be a massive
polar amplification. This reduces the ocean over turning circulation
, and potentially lead to an anoxic event, and possibly further
methanogenesis.
I am not sure that, even with a maximal SRM effort, we can avoid the
climate transitioning into a state in which society is
unsustainable due to an anoxic event.
If this is the case, we potentially have a very brief window in which
to geoengineer, perhaps only five or ten years
I'd value comments on this.
Thanks
A
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