dennis@home wrote:


"Martin Brown" wrote in message
...

Low level clouds cut both ways. Daytime they relfect sunlight back
into space with a cooling effect but at night they severely limit the
escape of heat by radiation from the ground so that the net effect is
much smaller and finely balanced than you might suppose. High level
thin clouds can give powerful warming effects because they don't stop
much light inbound but they do stop radiative losses at night.

Are you sure?

He is substantially correct in this respect yes.


Thin high level cloud reflects more IR..than it blocks.

Low level cloud reflects more daytime sun than it blankets you at night.


IIRC you only need about half a percent less low level cloud to account
for all the global warming of the last 50 years.

Clouds are PROBABLY the most significant driver of global temperature,
but the question then arises as to what drives the clouds....

...one theory I like is Svensmarks. No idea if its 'true' but it is
disturbingly close to providing another part of the climate jigsaw.

http://www.clarewind.org.uk/events-1.php?event=32

If he is correct, the solution to global warming could be something as
simple as pointing particle accelerators at the sky and switching them on...

...and CERN is ideally placed to guarantee snowfall on the Alps, for
skiers..:-)

Low level cloud is water droplets and absorb and reradiate some of the
sunlight as IR.
High level cloud is ice and reflect light without converting the solar
flux to infrared that is prevented from escaping by the greenhouse gasses.
Light that is reflected at a high level has little warming effect on the
planet while stuff lower down has a bigger warming effect.

Its a shame that the records of high level cloud cover are so inadequate
that its difficult/impossible to actually prove any effect on past
climate and we only have the things like 911 to give any indication of
its real power. IIRC the temps went up after 911 by a degree or two
indicating that its a very powerful effect.

Er no, they went down at night.

Daytime was largely unaltered.

It could also explain a lot of the rise in temps we have seen as high
level cloud cover has dropped since we cleaned up the emissions from
industry that was putting cloud forming pollutants into the upper
atmosphere.

No. Low level cloud cover has dropped. Its rare for particulate
emissions - which are definitely involved in cloud formation at lower
levels - to go up that high.


There is further evidence for these effects if you are actually
interested.. you could look at the effects of some of the volcanoes that
cause high level cloud and consequential cooling. Laki would be a good
start as its eruption killed millions due to cooling.

Dust is an effective screener of sunlight. But its all part of a giant
complex system - one that is far more complex than the IPCC want you to
BELIEVE.

We do now have satellites measuring the overall Earth's albedo IIRC by
the way: the data is slowly coming in..