Global Dimming: motivation for space habitats?

I thought TangoMan would find this article amusing. It describes a
situation that is bad for PV and is potentially argument for SSPS or
other large space developments (as well as maybe for burning more fossil
fuels). I'm sure anti-environmentalists out there will have some fun
with it. :-)

http://www.guardian.co.uk/life/feature/story/0,13026,1108853,00.html

Excerpt:

"Each year less light reaches the surface of the Earth. No one is sure
what's causing 'global dimming' - or what it means for the future. In
fact most scientists have never heard of it.

In 1985, a geography researcher called Atsumu Ohmura at the Swiss
Federal Institute of Technology got the shock of his life. As part of
his studies into climate and atmospheric radiation, Ohmura was checking
levels of sunlight recorded around Europe when he made an astonishing
discovery. It was too dark. Compared to similar measurements recorded by
his predecessors in the 1960s, Ohmura's results suggested that levels of
solar radiation striking the Earth's surface had declined by more than
10% in three decades. Sunshine, it seemed, was on the way out.

The finding went against all scientific thinking. By the mid-80s there
was undeniable evidence that our planet was getting hotter, so the idea
of reduced solar radiation - the Earth's only external source of heat -
just didn't fit. And a massive 10% shift in only 30 years? Ohmura
himself had a hard time accepting it. "I was shocked. The difference was
so big that I just could not believe it," he says. Neither could anyone
else. When Ohmura eventually published his discovery in 1989 the science
world was distinctly unimpressed. "It was ignored," he says.

It turns out that Ohmura was the first to document a dramatic effect
that scientists are now calling "global dimming". Records show that over
the past 50 years the average amount of sunlight reaching the ground has
gone down by almost 3% a decade. It's too small an effect to see with
the naked eye, but it has implications for everything from climate
change to solar power and even the future sustainability of plant
photosynthesis. In fact, global dimming seems to be so important that
you're probably wondering why you've never heard of it before. Well
don't worry, you're in good company. Many climate experts haven't heard
of it either, the media has not picked up on it, and it doesn't even
appear in the reports of the Intergovernmental Panel on Climate Change
(IPCC).

"It's an extraordinary thing that for some reason this hasn't penetrated
even into the thinking of the people looking at global climate change,"
says Graham Farquhar, a climate scientist at the Australian National
University in Canberra. "It's actually quite a big deal and I think
you'll see a lot more people referring to it.""

Discussed and first seen at:
http://science.slashdot.org/article.pl?sid/12/18/1350226&mode=thread&tid4&threshold=2

======

I read a Scientific American article a decade or so ago that argued the
Sun has been increasing in brightness over its life, and C02 in the
Earth's atmosphere strangely has been decreasing enough year to year to
offset this over the past few billion years (from an initially very high
level), but that in about 100 million years or so this effect would end
(when C02 reached zero) and the Earth would soon become uninhabitably
warm. [So maybe Gaia or the Bacterianet decided to risk making smart
tool using creatures to make daughter space habitats? :-)] Ice ages and
such were smaller cycles within this larger trend. Unfortunately, adding
CO2 to counter a local ice age won't help in the long term as this will
just heat up things more as the sun continues to brighten.

Anyway, I'll be interested to see how this solar dimming thing plays out...

I'm definitely all for considering solar shades or mirrors placed in
orbit around Earth long term if this is a big problem. If people want to
make a case for global presence in space managed by a big centralized
concern for addressing a specific short term global problem to drive the
development of space habitats for orbital construction, this might be it
(more than SSPS IMHO).

--Paul Fernhout