Hi all
The change from an untreated cloud to a treated one is much smaller than
that from a cloud to clear sky let alone day to night. The contrast
change needed to offset double CO2 with 18% low cloud cover is well
below the detection threshold of a human eye.
Stephen
On 26/04/2017 17:40, Russell Seitz wrote:
Andrew wrote On Sunday, April 23, 2017 at 9:40:00 PM UTC-4:
I don't think hydrosols will behave like CNN, in terms of their
radiative properties. As I understand it, CCN act to brighten
existing cloud cover. They won't, therefore, work on cloudless
days. Likely, relative efficacy will depend on whether acute or
chronic thermal stress is most important. Furthermore, hydrosols
will cause a lasting increase in diffuse radiation. In terrestrial
models, this has impacted NPP.
I'm no expert on this niche - but that's my initial thoughts.
Hope it helps
It will take field experiments and further modeling to quantify the
Net Photosynthetic Product impact of surface water brightening , but
Andrew should bear three things in mind
1. Backscattering light does not have the same effect as casting
shade, because most plankton and algae can absorb light in all
directions,
2. Hydrosols scatter the infalling light in all directions, - they
change the geometry of the euphotic zone in a diffferent manner than
extensive cloud cover.
3. Doubling surface brightess at high sun angles , from ~ 7% to 14%
reduces the underwater light flux by about 7%, which while obviously
significant, is a small reduction relative to full cloud cover, which
often reduces surface light more than twice as much, as white
clouds in the air can have an albedo of up to .55.- m
It may l accordingly take as much NPP research to sort out the
ecological meaning of the physically uncontroversial cloudy day
analogy as that of CCN shading of overheated seas , both triopical
and circumpolar.
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