I'll copy this from one of my earlier posts on this:
Given that we add pollution to the atmosphere, why doesn't this mean
that less sunlight gets through and why don't we consequently
experience global dimming, rather than global warming? One view of the
greenhouse effect is that what actually takes place is a combination
of global warming and global dimming. As the proportion of particles
(including water vapor) in the atmosphere gets higher, it becomes both
harder for sunlight from outside to penetrate the atmosphere (more
gets reflected), as well as for light and heat to escape the
atmosphere (more gets trapped, as in the traditional presentation of
the greenhouse effect). The idea of this combined effect, however, is
that overall temperatures are increasing, partly because of the huge
amounts of extra heat that has been added over the past few decades as
fossil fuel is burned and as nuclear power also adds heat. I've
discussed this before and I'd love to get more feedback on it.
Also see my page here with more details on this:
http://groups.google.com/group/geo-engineering/web/global-warming-and-the-impact-of-extra-heat
So, it may make sense to add more particles, as long as we reduce the
amount of extra heat we add into the atmosphere.
Anyway, there are some who believe that we should reduce the amount of
sunlight coming in.
Cloud seeding is proposed by John Latham and Stephen Salter, who
suggest to spray droplets of seawater high up into the air, so that
the tiny particles of salt from these droplets will make clouds
thicker and more reflective.
http://www.youtube.com/watch?v=fg7J8P-uXqM
Another proposal is to add sulpher to the atmosphere. Paul Crutzen,
who won the Nobel Prize for chemistry when he discovered the causes of
the hole in the ozone layer, plans to fire hundreds of rockets loaded
with tons of sulphur into the stratosphere creating a vast, but very
thin sunscreen of sulphur around the earth.
Both initiatives are discussed in the BBC documentary 'Five ways to
save the world'.
http://news.bbc.co.uk/1/hi/programmes/6298507.stm
Again, such proposals may make sense, as long as we reduce the amount
of extra heat we add into the atmosphere. If we use such proposals as
a justification to continue burning fossil fuels, then the end-result
will be increased global warming. We should proceed with care and what
makes most sense is to tax supply of fuel that adds heat and use the
money to subsidize energy supply that doesn't add extra heat. Geo-
engineering should be discussed widely and international treaties may
be wise, since such projects will affect anyone in the world.
Cheers!
Sam Carana