Posted on 04/07/2006 12:53:25 PM PDT by Izzy Dunne
Reduced air pollution and increased water evaporation appear to be adding to man-made global warming.
Research presented at a major European science meeting adds to other evidence that cleaner air is letting more solar energy through to the Earth's surface.
Other studies show that increased water vapour in the atmosphere is reinforcing the impact of man-made greenhouse gas emissions.
Scientists suggest both trends may push temperatures higher than believed.
But they say there is an urgent need for further research, particularly at sea.
Dimming no more
Between the 1950s and 1980s, the amount of solar energy penetrating through the atmosphere to the Earth's surface appeared to be declining, by about 2% per decade.
This trend received some publicity under the term "global dimming".
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But in the 1980s, it appears to have reversed, according to two papers published last year in the journal Science.
The decline in Soviet industry and clean air laws in western countries apparently reduced concentrations of aerosols, tiny particles, in the atmosphere.
These aerosols may block solar radiation directly, or help clouds to form which in turn constitute a barrier; or both effects may occur.
The lead researcher on one of those Science papers was Martin Wild from the Institute for Atmospheric and Climate Science (IACETH) in Zurich, and this week he has been discussing the implications of those findings at the European Geosciences Union (EGU) annual meeting in Vienna.
Correlations and causality
The reversal of "global dimming" has been proposed in some circles as an alternative explanation for climatic change, removing the need to invoke human emissions of greenhouse gases.
Dr Wild dismissed this picture. His analysis suggests that "global dimming" and the man-made greenhouse effect may have cancelled each other out until the early 1980s, but now "global brightening" is adding to the impact of human greenhouse emissions.
"There is always this argument that maybe the whole temperature rise wasn't due to greenhouse warming but due to solar variations," he told the BBC News website.
 "Solar brightening" may now be adding to greenhouse warming
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"During the solar dimming we had really no temperature rise. And only when the solar dimming disappeared could we really see what is going on in terms of the greenhouse effect, and that is only starting in the 1980s."
Analyses of global temperature indicate that a sharp upward trend commenced in the early 1980s.
But, said Dr Wild, there are strong regional variations in the "solar brightening" trend.
"In Eastern Europe, we see a very strong recovery [in solar radiation] - almost back to what it was before dimming began," he said.
"But India continues with the dimming - that's very much thought to be due to increasing air pollution.
"The general position is that air pollution is still increasing in the tropics, but decreasing outside the tropics; so probably that will amplify warming a little bit outside the tropics but not inside."
Data deficit
There are, Dr Wild admitted, holes in the picture of change.
"The term 'global dimming' is a bit dangerous," he said. "I usually call it 'solar dimming' not 'global dimming' because we really only know about this where we have measurements; and we don't have measurements at many places, for example over the oceans, or land in the tropics."
More research facilities are needed, he said, in tropical regions, particularly sub-Saharan Africa, and especially the oceans.
As well as extending measurements of solar energy reaching the Earth's surface, he urged more research on aerosol concentrations in the atmosphere and on trends in cloud cover.
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Rolf Philipona from the World Radiation Center in Davos, Switzerland, is attempting to improve aerosol measurements in northern Europe.
"We're trying to put a paper together which shows the aerosol depth and the amount of aerosol in the air column from about six to eight stations in Europe," he told the BBC News website.
"In Germany and Switzerland we would have stations very high up, extending all the way to the North Sea."
Last year Dr Philipona released research indicating that European warming is largely driven by increases in humidity.
The mechanism is that rising levels of what are conventionally called "greenhouse gases", such as carbon dioxide and methane, cause more evaporation of water, which in the atmosphere is itself a greenhouse gas.
He believes this is having more impact than changes to the transmission of solar energy through the atmosphere.
"From my results I believe it's the greenhouse warming and in particular the water vapour feedback," he said.
"Studies and papers are also coming now which are looking more closely at what water vapour is doing in other regions; and there are several pieces of work showing water vapour is increasing over land areas like the United States."
Satellites and ships
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A further implication of "global brightening" is that the temperature difference between night and day may reduce.
The "blanket" of greenhouse gases in the atmosphere has a net heating effect during day and night, whereas changes in solar energy reaching the surface are felt only in daytime.
Disproportionately higher night-time temperatures have already been noted in many parts of the world, and research in the Philippines has linked this trend to a reduction in rice yield.
The conclusions presented here present two major challenges to the research community.
One is to find ways of extending experimental investigations into the oceans and the developing world.
The second is to integrate them into computer models of climate, something which is only just beginning to happen.
Richard.Black-INTERNET@bbc.co.uk
The 'science' of globull warming is so settled, it changes everyday.
global warmingcooling
There; fixed that.
These people don't know what the heck they are talking about, and prove it every day.
When science becomes a way to advance a political agenda, it often becomes a mass of deception and confusion.
Well, if that's the truth it explains why the decided to go ahead with deliberately seeding the skies with various chemicals to form faux-cirrus clouds to radiate the sun's heat back into space -- and continue the clean air ecology at the same time. Sort of like having your cake and eating it too.
http://www.venusproject.com/ethics_in_action/Weather_Modification_Bill.html
Says it all.
I think "global dimming" is obvious when climate emergencies are discussed.
Give me that old time religion. I would think that water vapor at high altitudes would form ice crystals that could deflect the Sun's heat.
Is it true that San Francisco just disappeared after it was sucked up it's own fargin icehole.
Yeah, but those somananbachin bastidges had it coming!
Don't you love how they make theories sound like fact? Man made global warming....sure.
yes now if we clean the air it will give us all global warming and it remains Bush's fault
...yeah baby
I'm showing my age but in Chicago back the olden days of Steam Locomotives, Coal, Coke and Oil heat (the early 50's to the 60's), the sky was very seldom clear even on sunny days. There was always a haze - except after two weather occurrences;So undoubtedly, now with our almost always clean clear sky, more heat is going to reach the ground, and heat everything up.Now as to England, specifically London. Well you know their famous London Fog (not the neat trench coat), well it's all gone now. It wasn't Fog at all, but SMOG from coal & wood heat stoves and water vapor. As soon as the Brits went all gas heat in the 80's(?), the London Fog went away. True fact, read that in a science magazine.
- One kick @$$ rain, flood the viaducts, thunderstorm in summer, when afterwords the air actually smelled and was clean, from the ionization from the lightening.
- In winter after a block the door, get out the snow shoes, put on the tire chains, blizzard. The next day the temp usually dropped to -87 gazillion below zero, but the sky was actually sky blue and you could see for miles from inside the house.
Now, clear blue skies are the norm when it's supposed to be clear and sunny.
(gotta run, guitar practice time)
Doncha think it is time for Liberals to permit the UN to tax the heck out of international air passengers? UN taxation on international travel is on the agenda which is why we keep seeing all these global warming articles on it.
Blast the tops off a few volcanoes, then they'll be crying...
How was the air after Mrs. O'Leary's cow started the Great Chicago Fire?
Now that would be really showing your age. ;^D
(Denny Crane: "I Don't Want To Socialize With A Pinko Liberal Democrat Commie. Say What You Like About Republicans. We Stick To Our Convictions. Even When We Know We're Dead Wrong.")
...until you consider that you're paying for it either way.
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