global dimming vs global warming

   Tonight, "Dimming Sun" was the latest Nova on PBS.

   Here is their summary:
   As global warming turns up the heat, researchers are stunned to discover
that our planet is actually growing dimmer. Increasing air pollution
allows less and less sunlight to reach earth's surface, a "global dimming"
that's linked to severe droughts. In an even more alarming twist, there is
concern that solving the dimming problem could greatly accelerate global
warming, melting ice caps and flooding coastal cities.

   Here is my outline of the show:
   Actually, the sun isn't dimming, but particulate pollution is "blocking"
some sunlight, and is also changing the characteristics of water droplets
in clouds (making them more numerous and smaller, which reflects sunlight
back upward more effectively), and the overall effect is less solar heating
at the earth's surface, hence "dimming."
   But greenhouse gases (CO2,...) are producing a warming effect.
   These two effects -- global dimming and global warming -- are in
conflict, with global warming stronger, on average. Nova estimated the
relative strengths at 2:1, with half the effects of global warming (2)
being overcome by dimming (1), on average.
   In the past few decades, global dimming has been "masking" the effects
of global warming, making us think the greenhouse effect is weaker than it
actually is. Each effect, dimming and warming, does unusual things to
climate patterns -- changing the winds, rain patterns,... -- which can
upset things locally. And if we clean up particulate pollution, global
warming won't be masked as much, and warming will accelerate. As explained
in the PBS summary, "there is concern that solving the dimming problem
could greatly accelerate global warming."

Interesting.

Craig
Received on Tue Apr 18 21:13:57 2006