Gareth wrote:
> A couple of points occur to me: with so much summer daylight and a
> marked reduction in ice extent and therefore albedo, the polar ocean
> will warm in addition to the effect of warm water arriving from the
> Pacific or Atlantic. As we approach little or no summer ice, so we
> accelerate towards the point where there's so much ocean heat that the
> area of winter refreezing becomes rapidly smaller.
It's true that sea-ice has a high albedo when covered with fresh snow,
perhaps as great as 90%, which is the conventional wisdom at lower
latitudes. However, during the summer melt season, the surface snow
melts rapidly and then ponds form on the top of the ice, which reduces
the albedo to less than 50%. The ocean's albedo at low latitudes is
very small at local noon, when the sun's zenith angle is small, as low
as 0.5%. Again, the Arctic is different, as the solar zenith angle is
large, even at the summer solstice. As a consequence, the Arctic
Ocean's albedo may be quite large for direct incident radiation, as
great as 30% (or more). Thus, in summer, when it counts, there's not
much difference. Also, the sea-ice minimum extent usually occurs in
September or early October, when the sun at the North Pole is just
slipping below the horizon for the winter. Even if there was a large
difference in albedo at that time of the year, the cosine effect means
that there isn't much solar energy available at the surface.
Obviously, any albedo difference means nothing during the winter months.
--~--~---------~--~----~------------~-------~--~----~
You received this message because you are subscribed to the Google Groups
Global Change ("globalchange") newsgroup. Global Change is a public, moderated
venue for discussion of science, technology, economics and policy dimensions of
global environmental change.
Posts will be admitted to the list if and only if any moderator finds the
submission to be constructive and/or interesting, on topic, and not
gratuitously rude.
To post to this group, send email to [email protected]
To unsubscribe from this group, send email to [EMAIL PROTECTED]
For more options, visit this group at
http://groups.google.com/group/globalchange
-~----------~----~----~----~------~----~------~--~---
