Global Dimming: motivation for space habitats?

that may explain what causes Ice ages, except of course we should still have
to find out what causes the dimming in the first place... :)

Cheers,

Claudio

>
> 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=t
hread&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