WC Archive

Further, it must be noted that dimming has many negative effects that may outweigh its attentuation of warming trends. First of note is the effect on rain patterns, which have already been severely altered by extensive logging (forests appear to help produce rain clouds [anyone have a good link to back this up?], and hold in water that does come down). As the BBC explains, "Scientists are now worried that dimming, by shielding the oceans from the full power of the Sun, may be disrupting the pattern of the world's rainfall." Columbia University's Earth Institute News has more thorough coverage of dimming in general and effects on rain in particular.

Other effects that come to mind: how does reduced sunlight impact crop yields? solar power generation? And of course the cause of the dimming is also the cause of acid rain — man-made particulates with high-levels of sulphur or nitrogen — which as we know causes all kinds of problems.

from http://www.mongabay.com/0902.htm

Additionally, the forest adds to local humidity through transpiration (the process by which plants release water through their leaves), and thus adds to local rainfall. For example, 50-80% of the moisture in the central and western Amazon remains in the ecosystem water cycle. In the water cycle, moisture is transpired and evaporated into the atmosphere forming rain clouds before being precipitated as rain back onto the forest. When the forests are cut down, less moisture is evapotranspired into the atmosphere resulting in the formation of fewer rain clouds. Subsequently there is a decline in rainfall, subjecting the area to drought. If rains stop falling, within a few years the area can become arid with the strong tropical sun baking down on the scrub-land.

Thanks for the link!

That more sunlight is reflected, due to (sulphate) aerosols is proven false.

As you may know, we have some satellites flowing around out of the atmosphere, which measure reflected sunlight (SW reflection) and heat (LW emission) from below.

For the (sub)tropics, in the period 1985-2001 the amount of sunlight reflected by clouds reduced with ~2 W/m2. (see: http://www.atmos.ucla.edu/csrl/publications/pub_exchange/Wielicki_et_al_2002.pdf , confirmed for the 30N-30S (sub)tropics in http://pubs.giss.nasa.gov/docs/2002/2002_ChenCarlsonD.pdf )

In the same period, there was a loss of cloud cover, both in the tropics and sub tropics (and even up to 60N-60S).

If there is global dimming at the surface, the only explanation possible is that more sunlight is retained in the atmosphere. Which is (only) possible with (dark brown and black) soot particulate.

If soot particulate is to blame, then a reduction of them would have a cooling effect, not a warming effect!

See also the amount of reflected sunlight from earth on the moon ("eartshine"), which parallels the "global dimming" trend, while it should have opposite trends, at: http://www.bbso.njit.edu/science_may28.html

Ferdinand

I think global dimming in consistant with global warming. The measure of global dimming is really simple. You simply measure how quickly radiant heat from the sun heats up a black disk. The extra Co2, water vapour and other greenhouse gasses captures some of that radiant energy high in the athmosphere so it never gets to the disk as radiant energy in the first place!. (However it does heat the earth eventually by convection, etc.So, the air might be a half degree warmer round that black disk but this parameter is not measured. I bet it is simply one of the byproducts of global warming.
Brian White

Whatever the precise mechanism that is in play here may be, the scale of the observed phenomena and the implications for climate change when compared to the risks to us as a species if we do nothing, would suggest that urgent action is prudent. But where to start? Yes we can ratchet up support for sustainable development in all its forms and reduce the net CO2 input from fossil fules to the atmosphere; we can capture methane emissions through eliminating landfill and using anaerobic digesters etc. to process biodegradeable wastes. But what about carbon fixing? what can we do about agriculture and forestry etc? There are enormous potential social and economic benefits in supporting more traditional land management techniques that have a high level of community involvement through social enterprises, co-operatives etc. but what can we grow enough of and fast enough that will start to lock enough Carbon away into a longer cycle? Structural use of timber products instead of plastics or fired ceramics/bricks/concrete would be more sustainable. Does anyone have any references to work in this area? I'd be keen to know.

Colin Keyse. Grant Manager Environment; Wales Council for Voluntary Action.

hi, i think this website is the best website in the world wide web. i think it is a very important issue, globabl dimming rules!!! This is better than msn, i know what I am doing tonight instead of watching Eastenders!!!
All the way!!!!!!!!!!!!

With respect to global warming and global dimming changing our natural environment, where would the safest place to live be in the future?

After reading about globale dimming via the BBC website, I watched the related program which was quite astounding.

The simplest experiment to prove whether or not global dimming is a reality, was given by an American scientist. He was studying the effects aircraft contrails have on the enviroment. But since the airspace he was monitoring always contained contrails, he experiment was limited. However after 911 when aircraft were grounded for a number of days, he recorded a 1 degree Celcius increase during the daytime, and a 0.5 degree Celcius decrease during the nighttime, during the period when the aircraft were grounded. When they resumed flying, the temperatures went back to the pre 911 values.

Scary stuff...