Global Dimming vs Global Brightening

[BigBunny]

I am starting this thread in response only to a kind invitation. It is my own view that the debate about "Global Dimming vs Global Brightening" is nonsensical because it is simply two sides of the same coin. The posts following have been posted on Megasprayer before this time although not in a concentrated form. In all honesty finding the truth requires lateral thinking to get to the answers because the scientific community seems to be unwilling to be as direct as one would hope in their communications. So here goes:

Clearing smog has led to 'global brightening'

* 19:00 05 May 2005
* NewScientist.com news service
* Fred Pearce

The efforts of industrialised nations to cut smog pollution has had a bizarre side-effect - accelerating global warming.

New data show that after years of getting smoggier, our skies have become clearer since about 1990. And one effect has been to allow more solar radiation to reach the surface of the Earth.

The phenomenon known as “global dimming” has gone into reverse, according to research by Martin Wild at the Institute for Atmospheric and Climate Science in Zurich, Switzerland, and been replaced by “global brightening” (Science. vol 308, p 847). “There is no longer a dimming to counteract the greenhouse effect,” he told New Scientist.

Climate scientists say there have been two critical influences on global air temperatures in the past half-century. First, rising atmospheric concentrations of heat-trapping gases like carbon dioxide have warmed the Earth, by preventing more of the heat that reaches the Earth’s surface from escaping back into space.

But a parallel increase in smog particles has shaded the planet, partly offsetting the warming. Past studies have shown an increase in average aerosol particle levels in the atmosphere between 1960 and 1990 that were sufficient to reduce solar radiation reaching the Earth’s surface by about 5%.

The net effect of these two conflicting influences has been a warming of almost 0.5°C since 1960. But the rising levels of aerosols have led to concern that they might be masking greater underlying warming. And now the mask appears to be coming off.
Satellite corroboration

Wild’s new data - assembled from measurements of surface radiation made round the globe - show a widespread reduction in aerosols in the atmosphere since around 1990. His findings are corroborated by satellite data reported by Rachel Pinker, a meteorologist at the University of Maryland at College Park, US, in the same issue of Science (v 308, p 850).

The main cause of the global brightening, says Wild, is the clean-up of air pollution, especially in Europe and the former Soviet Union, where industrial decline has also played a role.

But the same trend emerges in data from North America, Australasia, Japan and, most recently, in China, where smogs have been reduced despite swift industrialisation. The exceptions, where dimming continues to worsen, are mainly in South Asia and Africa.

So should the world hurriedly reinstate smogs to stop global warming from accelerating? Probably not, as Wild points out that carbon dioxide lasts in the atmosphere for a century or more, whereas aerosols typically hang around for only a few days. So as carbon dioxide accumulates in future decades, we would need ever-thicker smogs to counteract it.

And another Science paper reports that current smog levels kill half a million people worldwide each year from heart and lung diseases.

www.newscientist.com/article.ns?id=dn7346

[BigBunny]

Doom may loom amid the gloom
By Kenneth Chang
May 14, 2004

In the second half of the 20th century the world became, quite literally, a darker place.

Defying expectation and easy explanation, hundreds of instruments around the world recorded a drop in sunshine reaching the surface of Earth - as much as 10 per cent from the late 1950s to the early 1990s, or 2 to 3 per cent a decade.

In some Asia, the US and Europe the drop was even steeper. In Hong Kong the amount of sunlight dropped 37 per cent.

No one is predicting it may soon be night all day, and some scientists believe the skies have brightened in the past decade as the suspected cause of global dimming, air pollution, clears up in many parts of the world.

Still, the dimming trend - noticed by a handful of scientists two decades ago, but dismissed at the time as unbelievable - is now attracting wide attention. Research on global dimming and its implications for weather, water supplies and agriculture will be presented in Montreal at a meeting of US and Canadian geological societies next week.

"There could be a big gorilla sitting on the dining table and we didn't know about it," said Veerabhadran Ramanathan, a professor of climate and atmospheric sciences at the University of California at San Diego. "There are many, many issues that it raises."

James Hansen, director of NASA's Goddard Institute for Space Studies in New York, said scientists had long known that pollution particles reflected some sunlight, but added that only now were they realising the magnitude of the effect.

"It has occurred over a long time period, so it's not something that perhaps jumps out at you as a person in the street," he said. "But it's a [significant] effect."

The dynamics of global dimming are not completely understood. Antarctica, which would be expected to have clean air, has also dimmed. "We don't really understand this thing that's going on," said Shabtai Cohen, an Israeli scientist.

The New York Times

[BigBunny]

May 13, 2004
Globe Grows Darker as Sunshine Diminishes 10% to 37%
By KENNETH CHANG

n the second half of the 20th century, the world became, quite literally, a darker place.

Defying expectation and easy explanation, hundreds of instruments around the world recorded a drop in sunshine reaching the surface of Earth, as much as 10 percent from the late 1950's to the early 90's, or 2 percent to 3 percent a decade. In some regions like Asia, the United States and Europe, the drop was even steeper. In Hong Kong, sunlight decreased 37 percent.

No one is predicting that it may soon be night all day, and some scientists theorize that the skies have brightened in the last decade as the suspected cause of global dimming, air pollution, clears up in many parts of the world.

Yet the dimming trend — noticed by a handful of scientists 20 years ago but dismissed then as unbelievable — is attracting wide attention. Research on dimming and its implications for weather, water supplies and agriculture will be presented next week in Montreal at a joint meeting of American and Canadian geological groups.

"There could be a big gorilla sitting on the dining table, and we didn't know about it," said Dr. Veerabhadran Ramanathan, a professor of climate and atmospheric sciences at the University of California, San Diego. "There are many, many issues that it raises."

Dr. James E. Hansen, director of the NASA Goddard Institute for Space Studies in Manhattan, said that scientists had long known that pollution particles reflected some sunlight, but that they were now realizing the magnitude of the effect.

"It's occurred over a long time period," Dr. Hansen said. "So it's not something that, perhaps, jumps out at you as a person in the street. But it's a large effect."

Satellite measurements show that the sun remains as bright as ever, but that less and less sunlight has been making it through the atmosphere to the ground.

Pollution dims sunlight in two ways, scientists theorize. Some light bounces off soot particles in the air and goes back into outer space. The pollution also causes more water droplets to condense out of air, leading to thicker, darker clouds, which also block more light. For that reason, the dimming appears to be more pronounced on cloudy days than sunny ones. Some less polluted regions have had little or no dimming.

The dynamics of global dimming are not completely understood. Antarctica, which would be expected to have clean air, has also dimmed.

"In general, we don't really understand this thing that's going on," said Dr. Shabtai Cohen, a scientist in the Israeli Agriculture Ministry who has studied dimming for a decade. "And we don't have the whole story."

The measuring instrument, a radiometer, is simple, a black plate under a glass dome. Like asphalt in summer, the black plate turns hot as it absorbs the sun's energy. Its temperature tells the amount of sunlight that has shone on it.

Since the 50's, hundreds of radiometers have been installed from the Arctic to Antarctica, dutifully recording sunshine. In the mid-80's, Dr. Atsumu Ohmura of the Swiss Federal Institute of Technology in Zurich sifted through the data to compare levels in different regions. "Suddenly," Dr. Ohmura said, "I realized it's not easy to do that, because the radiation was changing over time."

He recalled his reaction, saying, "I thought it is rather unbelievable."

After an analysis, he was convinced that the figures were reliable and presented his findings at a scientific conference.

Asked about his colleagues' reaction, Dr. Ohmura said: "There's no reaction. Very disappointing."

At that time, Dr. Gerald Stanhill of the Israeli Agriculture Ministry noticed similar darkening in Israel.

"I really didn't believe it," Dr. Stanhill said. "I thought there was some error in the apparatus."

Dr. Stanhill, now retired and living in New York, also looked around and found dimming elsewhere. In the 90's, he wrote papers describing the phenomenon, also largely ignored. In 2001, Drs. Stanhill and Cohen estimated that the worldwide dimming averaged 2.7 percent a decade.

Not every scientist is convinced that the dimming has been that pronounced. Although radiometers are simple, they do require periodic calibration and care. Dirt on the dome blocks light, leading to erroneous indications. Also, all radiometers have been on land, leaving three-fourths of the earth to supposition.

"I see some datasets that are consistent and some that aren't," Dr. Ellsworth G. Dutton, who heads surface-radiation monitoring at the National Oceanic and Atmospheric Administration, said. "Certainly, the magnitude of the phenomenon is in considerable question."

Dr. Beate G. Liepert, a research scientist at the Lamont-Doherty Earth Observatory of Columbia University, has analyzed similar information and arrives at a smaller estimate of the dimming than Drs. Stanhill and Cohen. Dr. Liepert puts it at 4 percent from 1961 to 1990, or 1.3 percent a decade. "It's a little bit the way you do the statistics," she said.

A major set of measurements from the Indian Ocean in 1999 showed that air pollution did block significant sunlight. Following plumes of soot and other pollution, scientists measured sunlight under the plumes that was 10 percent less bright than in clear air.

"I thought I was too old to be surprised by anything," said Dr. Ramanathan, who was co-chief scientist of the projects.

Dr. Ohmura said he hoped to finish his analysis of the numbers since 1990 by late next month or early July.

"I have a very strong feeling that probably solar radiation is increasing during the last 14 years," he said. He based his hunch, he said, on a reduction in cloud cover and faster melting rates in glaciers.

But clearer, sunnier days could mean bad news for global warming. Instead of cloudiness slowing rising temperatures, sunshine would be expected to accelerate the warming.

[BigBunny]

21 May 2004
Global Warming Could Mean Less Sunshine

For forty years scientists have observed a 1.3% per decade decline in the amount of sun reaching the Earth's surface. This phenomenon - "solar dimming" - is due to changes in clouds and air pollution that are impeding the suns ability to penetrate. Researchers believe that the combination of growing quantities of man-made aerosol particles in the atmosphere and increased moisture are causing the cloud cover to thicken.

Despite this decline in solar radiation, the Earth's surface continues to warm. Now, researchers led by Dr. Beate Liepert of Columbia University suggest an explanation for this paradox, as well as new findings that a warmer world may mean a dryer and dimmer world.

Published in Geophysical Research Letters, Liepert and fellow researchers' findings suggest that solar radiation is being both reflected and trapped in the clouds and aerosol layer, thereby decreasing the amount of radiation that would ordinarily hit the Earth's surface. It is widely agreed that greenhouse gas trapping is causing the Earth's surface temperatures to rise. What has not been understood until now is that temperatures would be rising faster or higher if the aerosol layer and cloud cover were not reflecting some of the radiation away. Further, the researchers conclude that the imbalance of less solar radiation with warming surface temperatures will lead to weaker turbulent heat fluxes resulting in a reduction in evaporation and precipitation, which will lead to a dryer world.

Although rising temperatures should moisten the atmosphere, the research shows that man-made airborne aerosols will condense the water to form smaller cloud droplets. This process is contributing to the observed thickening of the Earth's cloud cover. Smaller droplets are not heavy enough to sink through the air as rain. As a result, the cloud cover lasts longer and there is less rain.

"Water has a characteristic residence time in the atmosphere before it gets rained out. In a warmer world, this residence time is longer because a warmer atmosphere can hold more water. Aerosols affect clouds by suppressing rain and increasing its residence time. The overall effect is that rainwater is about half a day older," said Liepert.

Examples of data supporting this new hypothesis include studies indicating a steady decline of water evaporation in the Northern Hemisphere over the past 50 years. Over the last 60 years, large regions of Eurasia have seen soil moisture increase by more than one centimeter per decade, yet no significant changes in precipitation are being seen.

Solar dimming has also resulted in an observable difference in the lightness of daytime. The atmosphere is more polluted and therefore darker, even in remote areas. The fog we see today is about 3% thicker than it was 40 years ago.

Liepert conducted model simulations for this research that included pre-industrial aerosol and greenhouse gas conditions and present day conditions. Their models incorporated aerosol absorption of sunlight, heating of the aerosol layer, aerosol particles acting as cloud condensation nuclei and increasing reflective power, and cloud lifetime by the suppression of drizzle over oceans.

"Aerosols are highly variable in space and time, which is why aerosol forcing of climate has generally not been taken into account in climate studies. Furthermore, aerosols are found near the Earth's surface and affect mainly the fluxes of energy and water at the surface. Because good surface observations are sparse, validating models is a very difficult task. Carbon dioxide concentrations are much more homogeneous and easier to measure than aerosol concentrations," said Liepert. "These new ideas on the affects of aerosols might open up many avenues and solve more discrepancies in the climate change debate."


www.scienceagogo.com/news/20040420233456data_trunc_sys.shtml

[BigBunny]

Earth Brightens After Years of Dimming
Scientists Studying Light Reflected by Earth Say Planet Is Brightening After Years of Dimming

The Associated Press


WASHINGTON May 27, 2004 — Scientists studying earthshine the amount of light reflected by the Earth say the planet appeared to dim from 1984 to 2001 and then reversed its trend and brightened from 2001 to 2003.

The shift appears to have resulted from changes in the amount of clouds covering the planet. More clouds reflect more light back into space, potentially cooling the planet, while a dimmer planet with fewer clouds would be warmed by the arriving sunlight.

That means the changes in brightness could signal climate change, though it's too early to tell.

Steven Koonin, a California Institute of Technology physicist and co-author of the paper, said that "at the moment, the cause of these variations is not known, but they imply large shifts in the Earth's radiative budget. Continuing observations ... will be necessary to learn their implications for climate."

"This work is probably going to be used in arguments for and against global warming. Our paper neither proves or disproves the carbon dioxide effect," said Enric Palle, lead author of the report appearing in Thursday's issue of the journal Science.

"Our results are only part of the story, since the Earth's surface temperature is determined by a balance between sunlight that warms the planet and heat radiated back into space, which cools the planet," said Palle, of the Big Bear Solar Observatory in California, operated by the New Jersey Institute of Technology.

Climate change "depends upon many factors in addition to (reflected light), such as the amount of greenhouse gases present in the atmosphere. But these new data emphasize that clouds must be properly accounted for and illustrate that we still lack the detailed understanding of our climate system necessary to model future changes with confidence."

The researchers used two sets of records to establish the amount of light reflected from the Earth.

The records, which partly overlap, include measurements of cloud cover taken by satellites and an analysis of earthshine, which was determined by studying how much it illuminates the dark portion of the moon.

But the use of two separate types of measurements gave pause to James A. Coakley Jr. of Oregon State University, who studies climate change and satellite cloud data.

Observations of "sunlight reflected by the Earth are far from being well understood. At this stage, it's too early to tell how useful such observations might be as a measure of climate variability and climate change," said Coakley, who was not part of the research team.

Philip R. Goode of the New Jersey institute, a co-author of the paper, contended that the moon analysis is in fact quite accurate.

"Our method has the advantage of being very precise because the bright lunar crescent serves as a standard against which to monitor earthshine, and light reflected by large portions of Earth can be observed simultaneously," said Goode.

Earthshine brightening the face of the moon, he noted, was first described by Leonardo da Vinci.

Regular earthshine observations began in 1997, and the researchers suggested that the changes they observed may be part of a natural variation. Continuing the observations through an entire 11-year cycle of solar variability will be important to better understand the changes, they said.

The research was funded by the National Aeronautics and Space Administration.

abcnews.go.com/wire/Politics/ap20040527_1892.html

[BigBunny]

Why the Sun seems to be 'dimming'
By David Sington

We are all seeing rather less of the Sun, according to scientists who have been looking at five decades of sunlight measurements.

They have reached the disturbing conclusion that the amount of solar energy reaching the Earth's surface has been gradually falling.

Paradoxically, the decline in sunlight may mean that global warming is a far greater threat to society than previously thought.

The effect was first spotted by Gerry Stanhill, an English scientist working in Israel.

Cloud changes

Comparing Israeli sunlight records from the 1950s with current ones, Dr Stanhill was astonished to find a large fall in solar radiation.

"There was a staggering 22% drop in the sunlight, and that really amazed me." Intrigued, he searched records from all around the world, and found the same story almost everywhere he looked.

Sunlight was falling by 10% over the USA, nearly 30% in parts of the former Soviet Union, and even by 16% in parts of the British Isles.

Although the effect varied greatly from place to place, overall the decline amounted to one to two per cent globally every decade between the 1950s and the 1990s.

Dr Stanhill called it "global dimming", but his research, published in 2001, met a sceptical response from other scientists.

It was only recently, when his conclusions were confirmed by Australian scientists using a completely different method to estimate solar radiation, that climate scientists at last woke up to the reality of global dimming.

My main concern is global dimming is also having a detrimental impact on the Asian monsoon ... We are talking about billions of people
Professor Veerhabhadran Ramanathan
Dimming appears to be caused by air pollution.

Burning coal, oil and wood, whether in cars, power stations or cooking fires, produces not only invisible carbon dioxide - the principal greenhouse gas responsible for global warming - but also tiny airborne particles of soot, ash, sulphur compounds and other pollutants.

This visible air pollution reflects sunlight back into space, preventing it reaching the surface. But the pollution also changes the optical properties of clouds.

Because the particles seed the formation of water droplets, polluted clouds contain a larger number of droplets than unpolluted clouds.

Recent research shows that this makes them more reflective than they would otherwise be, again reflecting the Sun's rays back into space.

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.

There are suggestions that dimming was behind the droughts in sub-Saharan Africa which claimed hundreds of thousands of lives in the 1970s and 80s.

There are disturbing hints the same thing may be happening today in Asia, home to half the world's population.

"My main concern is global dimming is also having a detrimental impact on the Asian monsoon," says Professor Veerhabhadran Ramanathan, professor of climate and atmospheric sciences at the University of California, San Diego. "We are talking about billions of people."

Alarming energy

But perhaps the most alarming aspect of global dimming is that it may have led scientists to underestimate the true power of the greenhouse effect.

They know how much extra energy is being trapped in the Earth's atmosphere by the extra carbon dioxide we have placed there.

What has been surprising is that this extra energy has so far resulted in a temperature rise of just 0.6 degree Celsius.

This has led many scientists to conclude that the present-day climate is less sensitive to the effects of carbon dioxide than it was, say, during the ice age, when a similar rise in CO2 led to a temperature rise of six degrees Celsius.

But it now appears the warming from greenhouse gases has been offset by a strong cooling effect from dimming - in effect two of our pollutants have been cancelling each other out.

This means that the climate may in fact be more sensitive to the greenhouse effect than previously thought.

If so, then this is bad news, according to Dr Peter Cox, one of the world's leading climate modellers.

As things stand, CO2 levels are projected to rise strongly over coming decades, whereas there are encouraging signs that particle pollution is at last being brought under control.

"We're going to be in a situation unless we act where the cooling pollutant is dropping off while the warming pollutant is going up.

"That means we'll get reducing cooling and increased heating at the same time and that's a problem for us," says Dr Cox.

Even the most pessimistic forecasts of global warming may now have to be drastically revised upwards.

That means a temperature rise of 10 degrees Celsius by 2100 could be on the cards, giving the UK a climate like that of North Africa, and rendering many parts of the world uninhabitable.

That is unless we act urgently to curb our emissions of greenhouse gases.

You can see more on this report on Thursday's Horizon, BBC Two, at 9.00pm GMT.
Story from BBC NEWS:
news.bbc.co.uk/go/pr/fr/-/2/hi/science/nature/4171591.stm

Published: 2005/01/13 14:10:30 GMT

[BigBunny]

Global Dimming - Hidden Chemtrail Connection?

By Ted Twietmeyer
[e-mail]|
2-14-6


For many years scientists have noticed that the intensity of sunlight around the globe has been decreasing. Studies have quietly proved this is happening to our beautiful blue marble. To date, not one study has been publicized which connects the dimming problem with high altitude chemtrail spraying. Such a study is not likely, since no researcher will bite the hand that feeds them. Yet, many researchers must already be aware of the connection if they performed good science, and looked at causes for the problem. But we'll take another look at this issue and include other factors.

THE SATELLITE THAT WAS NEVER LAUNCHED

Scientists wanted a stationary satellite to monitor the dimming problem in order to obtain accurate data. Collected data from space will be free from numerous errors and problems inherent in ground-based observations. Such a satellite was planned for launch in 2001, but along came that terrible day in September which caused a postponement. The new bird would be called the Deep Space Climate Observatory, and it was first proposed back in the 1990s by Al Gore. It was planned to be a geostationary satellite which would monitor the entire side of the earth illuminated by the sun. [1]

When Columbia was destroyed, it further delayed the program.

The observatory project was finally finished off with a stroke of a pen when NASA cancelled the satellite project in early 2006 "for priorities and budget reasons". The pen is mightier than the sword, and it apparently carries more power than common sense.
The dimming of sunlight will create food chain problems, crop failures and water supply and weather problems as less water is evaporated from the oceans. But apparently to NASA this issue isn't important.

NOAA and NASA SILENT

One would also think that NOAA would sit up and take notice. NOAA stands for National Oceanic and Atmospheric Administration. If any branch of the government should be speaking out, it should be them. Yet all we hear from them is silence.

As of this writing, on noaa.gov we see "NOAA REPORTS RECORD WARM JANUARY ACROSS THE U.S. WARMER TEMPERATURES RESULT IN LOWER RESIDENTIAL ENERGY DEMAND" as their big headline. One doesn't need to be a scientist to make that discovery. In the north-central and north-east United States, people are now burdened by whopping utility bills that have increased their price per cubic ft. of natural gas about 40% - even though many of these utilities take gas straight out of the ground and were never affected by Katrina.

Someone must ask the question - "How do utilities get away with this?" What are the complex implications of global dimming?
According to one Chinese study, 3.7 watts of energy were lost per square yard in China in the past 50 years. Five hundred ground based instruments across that country were used to collect data for the long term study. This is probably happening globally as well.

FROM THE A-BOMB CO-FATHER: YET ANOTHER BRIGHT IDEA?

The infamous Teller paper in 1997 titled "Global Warming and the Ice Ages: Prospects for Physics-Based Modulation of Global Change" was also published in the Wall Street Journal as the article "The Planet Needs a Sunscreen." [2] It theorized that scattering high altitude metallic particles such as aluminum oxide or barium oxide would help reflect sunlight back into space to slow global warming. (More details about heavy metals can be found at [3].)

Is it merely a coincidence that heavy metals are found in chemtrails today? Internet photos and data about chemtrails date back more than 10 years. Clifford Carnicom has gathered more data on this subject, than perhaps any other researcher.

Would the Chinese be thrilled to find out that American-made chemtrails are accelerating their dimming problem? And if the Chinese are having this problem, it follows that the remainder of the world to a greater or lesser degree. Could it be possible that the satellite program was cancelled because it would expose the impact of chemtrail spraying on the entire planet?

Can it all just be a coincidence - or are there forces at work to keep a lid on chemtrail creation for weather control purposes? If military-owned weather control technology is supposedly for the global good - then why are government agencies so tight-lipped about this illegitimate program?

_____

A frequent contributor, Ted Twietmeyer is an inventor, patent holder and engineer who has worked in defense and NASA projects for more than 20 years. He also has written a startling new book about Mars which can be found at www.data4science.net/book

REFERENCES:
[1] abcnews.go.com/Technology/story?id=1566139
[2] www.holmestead.ca/chemtrails/waynehall.html
[3] en.wikipedia.org/wiki/Heavy_metals

[Swamp Gas]

Thank you very much Bunny!!!!

[BigBunny]

A world map showing current sunlight and cloud cover:

www.die.net/earth/

[BigBunny]

21 May 2004
Global Warming Could Mean Less Sunshine
For forty years scientists have observed a 1.3% per decade decline in the amount of sun reaching the Earth's surface. This phenomenon - "solar dimming" - is due to changes in clouds and air pollution that are impeding the suns ability to penetrate. Researchers believe that the combination of growing quantities of man-made aerosol particles in the atmosphere and increased moisture are causing the cloud cover to thicken.

Despite this decline in solar radiation, the Earth's surface continues to warm. Now, researchers led by Dr. Beate Liepert of Columbia University suggest an explanation for this paradox, as well as new findings that a warmer world may mean a dryer and dimmer world.

Published in Geophysical Research Letters, Liepert and fellow researchers' findings suggest that solar radiation is being both reflected and trapped in the clouds and aerosol layer, thereby decreasing the amount of radiation that would ordinarily hit the Earth's surface. It is widely agreed that greenhouse gas trapping is causing the Earth's surface temperatures to rise. What has not been understood until now is that temperatures would be rising faster or higher if the aerosol layer and cloud cover were not reflecting some of the radiation away. Further, the researchers conclude that the imbalance of less solar radiation with warming surface temperatures will lead to weaker turbulent heat fluxes resulting in a reduction in evaporation and precipitation, which will lead to a dryer world.

Although rising temperatures should moisten the atmosphere, the research shows that man-made airborne aerosols will condense the water to form smaller cloud droplets. This process is contributing to the observed thickening of the Earth's cloud cover. Smaller droplets are not heavy enough to sink through the air as rain. As a result, the cloud cover lasts longer and there is less rain.

"Water has a characteristic residence time in the atmosphere before it gets rained out. In a warmer world, this residence time is longer because a warmer atmosphere can hold more water. Aerosols affect clouds by suppressing rain and increasing its residence time. The overall effect is that rainwater is about half a day older," said Liepert.

Examples of data supporting this new hypothesis include studies indicating a steady decline of water evaporation in the Northern Hemisphere over the past 50 years. Over the last 60 years, large regions of Eurasia have seen soil moisture increase by more than one centimeter per decade, yet no significant changes in precipitation are being seen.

Solar dimming has also resulted in an observable difference in the lightness of daytime. The atmosphere is more polluted and therefore darker, even in remote areas. The fog we see today is about 3% thicker than it was 40 years ago.

Liepert conducted model simulations for this research that included pre-industrial aerosol and greenhouse gas conditions and present day conditions. Their models incorporated aerosol absorption of sunlight, heating of the aerosol layer, aerosol particles acting as cloud condensation nuclei and increasing reflective power, and cloud lifetime by the suppression of drizzle over oceans.

"Aerosols are highly variable in space and time, which is why aerosol forcing of climate has generally not been taken into account in climate studies. Furthermore, aerosols are found near the Earth's surface and affect mainly the fluxes of energy and water at the surface. Because good surface observations are sparse, validating models is a very difficult task. Carbon dioxide concentrations are much more homogeneous and easier to measure than aerosol concentrations," said Liepert. "These new ideas on the affects of aerosols might open up many avenues and solve more discrepancies in the climate change debate."

www.scienceagogo.com/news/20040420233456data_trunc_sys.shtml

[BigBunny]

Source: Ohio State University
Date: 2003-12-10
URL: www.sciencedaily.com/releases/2003/12/031210074720.htm
Atmospheric Compound Is Double-edged Sword In Climate Change

SAN FRANCISCO – Recent studies suggest that an atmospheric compound derived primarily from coal combustion may have contradictory effects on the earth's climate.

Under many conditions, sulfuric acid may cool the earth's atmosphere. Sulfuric acid particles seem to scatter ultraviolet light back into space before it has a change to enter the troposphere – the bottom layer of earth's atmosphere. But if conditions are right, this same chemical can warm the earth by combining with other compounds in the atmosphere to form clouds.

Researchers at Ohio State University looked at the interaction of sulfuric acid and methanol and what the compounds' combined effect might mean to global climate change. Both compounds are usually found in aerosol form in the upper atmosphere.

Scientists believe that methanol comes primarily from natural sources, such as oceans, forests and the decay of organic matter. While there are a few natural sources for sulfuric acid, such as volcanoes and marine sea spray, its precursor – sulfur dioxide – comes mainly from the burning of coal. In the atmosphere, sulfur dioxide is oxidized primarily by atmospheric moisture, resulting in sulfuric acid.

Sulfuric acid molecules in atmospheric aerosols can act as sort of a force field by reflecting light and heat back into space, said Heather Allen, a study co-author and an assistant professor of chemistry at Ohio State. This reflection contributes to a cooling effect on the earth. Methanol by itself doesn't really have an effect on climate change.

But when the two molecules get together – about 5 to 10 percent of the methanol in the atmospheric aerosols reacts with sulfuric acid – they form methyl sulfate. Methyl sulfate is less volatile than methanol, meaning there's less chance that methyl sulfate will evaporate or be vaporized.

And while it seems like a relatively small amount of methanol gets converted to methyl sulfate, it's still enough to have an impact on global climate change, Allen said.

She and colleague Lisa Van Loon, a doctoral student in chemistry at Ohio State, found that methyl sulfate's stability provides a springboard for cloud formation – water droplets collect on the stable molecules and eventually form clouds. Instead of causing light and heat to bounce back into space, most clouds create a warming effect by trapping light and heat in the atmosphere.

Van Loon presented the findings December 12 at the fall meeting of the American Geophysical Union in San Francisco.

The researchers used a laboratory technique called Raman spectroscopy to analyze the behavior of methanol, sulfuric acid and methyl sulfate. They focused a beam of laser light onto a sample of each substance in order to analyze differences in the bonds that hold the molecules together. The frequencies of the resulting wavelengths told the researchers how the compounds behaved, and also how methanol and sulfuric acid interacted. From this information, they could determine what each compound might do in the atmosphere.

The researchers found that sulfuric acid combines with a small amount of methanol– essentially starting points for cloud formation.

But the conditions must be right in order to create methyl sulfate, Allen said.

"The atmospheric chemistry community is trying to understand what conditions let these atmospheric particles combine, or cause them to stay aerosol-sized," Allen said, adding that cloud particles are about three times the size of aerosol particles.

The interaction between sulfuric acid and methanol affects global climate change and the aerosol picture, Allen said.

"Right now these aerosols are probably helping to slow down the human-induced warming effect on the earth, but it's a complicated balance that we're struggling to fully understand," she said. "We certainly know that the earth is warming at a rate that isn't totally natural. It's the warming rate that we're more concerned about.

"More aerosols emitted into the atmosphere may lead to cooling," Allen continued. "But if these aerosols are able to combine with other compounds and ultimately form clouds, it could have a warming effect. There's a complex balance between warming and cooling."

This work was funded by the National Science Foundation and the Natural Sciences and Engineering Research Council of Canada.

[BigBunny]

4 March 2002
Aerosol Pollution May Defeat Greenhouse Effect
Atmospheric scientists have long suspected that microscopic aerosol particles from industrial processes increase the brightness of clouds, resulting in greater reflection of sunlight and cooling of Earth's climate. However, this supposition is based on model calculations rather than observations, and these model calculations are very uncertain.

Now, scientists at the U.S. Department of Energy's Brookhaven National Laboratory and Purdue University have combined satellite measurements of cloud brightness, water content, and other variables with model calculations of atmospheric aerosols to demonstrate the brightening effect. This effect, described in the February 19, 2002 issue of the Proceedings of the National Academy of Sciences, should be accounted for in assessing the magnitude of global climate change, the researchers say.

"We're not saying that aerosols can counteract the greenhouse effect," said lead scientist Stephen Schwartz, an atmospheric chemist at Brookhaven, "but rather that we need to know how much of a cooling effect they have so we have a clearer picture of the greenhouse effect. To whatever extent aerosols are offsetting greenhouse warming, then the offset is the unseen part of the greenhouse 'iceberg,'" he said.

One difficulty in measuring the effect of aerosols is knowing their concentration. Aerosols such as sulfur compounds result from emissions by fossil-fuel-burning power plants and other industrial processes. They are typically found in the lowest three to four kilometers above Earth's surface and precipitate out of the atmosphere, typically in about a week. "Because of this short residence time, aerosols are highly variable as a function of location and time, which makes it tough to measure their concentrations on a global scale," Schwartz said.

Schwartz's team has been working for more than a decade to develop and refine a "chemical transport model" to calculate aerosol distribution. The model uses archived weather data and weather prediction models to track the distribution of aerosols from industrial sources to various parts of the atmosphere. "This model is the key to knowing where and when to look for the aerosol effect," Schwartz said.

By analyzing data from the model, the Brookhaven-Purdue team identified two one-week episodes during April 1987 when the modeled concentration of sulfate aerosol over the North Atlantic Ocean — far from any local sources of aerosol emissions — increased significantly and then decreased over the course of each week. These large variations in aerosol concentration and the fact that there were no high-atmosphere (obscuring) clouds during these events made them ideal episodes for studying the effect of aerosols on cloud brightening.

The next challenge was to get the data on cloud brightness for that area over the same time period. For this, the scientists retrieved satellite measurements of radiance (how much light the clouds reflect) and optical depth (a value related to how much light is transmitted through the cloud), and used these measurements to calculate the size of the cloud droplets and the liquid water path (the amount of liquid water in the cloud). They were also able to analyze how these variables were related to one another.

The findings show that, for a given liquid water path, cloud reflectivity was indeed higher on the days with higher aerosol content than on the days with lower aerosol levels. "If the effect is as widespread as we think it is, it would produce quite a substantial cooling effect on climate," Schwartz said. "This new study," he added, "provides a method of quantifying the phenomenon globally over the past 15 years using archived satellite data. Once this is done, we will have a much better idea of the true magnitude of the greehnouse effect."

Could aerosols be deliberately employed to offset the greehnouse effect? "This is an attractive thought," Schwartz said, "but it cannot work in the long run — because aerosols are so short-lived in the atmosphere, whereas greenhouse gases accumulate over time. An ever increasing amount of aerosols would be required. We'd never solve the long-term problem."

Also, says Schwartz, the aerosol effect may have a different geographical distribution from the greenhouse effect, and "the consequence of this mismatch is unknown." One key to assessing the overall impact of aerosols, he said, will be further development of the satellite-based measurements.


www.scienceagogo.com/news/20020204005723data_trunc_sys.shtml

[BigBunny]

Global Dimming

Programme transcript.

NARRATOR (JACK FORTUNE): This is a film that demands action. It reveals that we may have grossly underestimated the speed at which our climate is changing. At its heart is a deadly new phenomenon. One that until very recently scientists refused to believe even existed. But it may already have led to the starvation of millions. Tonight Horizon examines for the first time the power of what scientists are calling Global Dimming.

NARRATOR: September 12th 2001, the aftermath of tragedy. While America mourned, the weather all over the country was unusually fine. Eight hundred miles west of New York, in Madison, Wisconsin a climate scientist called David Travis was on his way to work.

DR DAVID TRAVIS (University of Wisconsin, Whitewater): Around the twelfth, later on in the day, when I was driving to work, and I noticed how bright blue and clear the sky was. And at first I didn't think about it, then I realised the sky was unusually clear.

NARRATOR: For 15 years Travis had been researching an apparently obscure topic, whether the vapour trails left by aircraft were having a significant effect on the climate. In the aftermath of 9/11 the entire US fleet was grounded, and Travis finally had a chance to find out.

DR DAVID TRAVIS: It was certainly, you know, one of the tiny positives that may have come out of this, an opportunity to do research that hopefully will never happen again.

NARRATOR: Travis suspected the grounding might make a small but detectable change to the climate. But what he observed was both immediate and dramatic.

DR DAVID TRAVIS: We found that the change in temperature range during those three days was just over one degrees C. And you have to realise that from a layman's perspective that doesn't sound like much, but from a climate perspective that is huge.

NARRATOR: One degree in just three days no one had ever seen such a big climatic change happen so fast. This was a new kind of climate change. Scientists call it Global Dimming. Two years ago most of them had never even heard of it, yet now they believe it may mean all their predictions about the future of our climate could be wrong. The trail that would lead to the discovery of Global Dimming began 40 years ago, in Israel with the work of a young English immigrant called Gerry Stanhill. A trained biologist, Gerry got a job helping to design irrigation schemes. His task was to measure how strongly the sun shone over Israel.

DR GERALD STANHILL (Agricultural Research Organisation, Israel): It was important for this work to measure solar radiation, because that is the factor that basically determines how much water crops require.

NARRATOR: For a year Gerry collected data from a network of light meters; the results were much as expected, and were used to help design the national irrigation system. But twenty years later, in the 1980s, Gerry decided to repeat his measurements to check that they were still valid. What he found, stunned him.

DR GERALD STANHILL: Well I was amazed to find that there was a very serious reduction in sunlight, the amount of sunlight in Israel. In fact, if we compare those very early measurements in the 1950s with the current measurements, there was a staggering 22% drop in the sunlight, and that really amazed me.

NARRATOR: A 22% drop in solar energy was simply massive. If it was true surely Israelis should be freezing. There had to be something wrong. So when Gerry published his results they were ignored. DR GERALD STANHILL: I must say the publications had almost no effect whatsoever on the scientific community.

NARRATOR: But in fact Gerry was not the only scientist who had noticed a fall in sunlight. In Germany a young graduate climatologist called Beate Liepert found that the same thing seemed to be happening over the Bavarian Alps too. DR BEATE LIEPERT (Lamont-Doherty Earth Observatory): I was the same, I was as sceptical as any other climatologist. But then, um, I, I saw the same results er in Germany, so um I believed him.

NARRATOR: Germany, Israel, what about the rest of the world? Working independently of each other, Liepert and Stanhill began searching through publications, journals and meteorological records from around the world. And they both found the same extraordinary story. Between the 1950s and the early 1990s the level of solar energy reaching the earth's surface had dropped 9% in Antarctica, 10% in the USA, by almost 30% in Russia. And by 16% in parts of the British Isles. This was a truly global phenomenon, and Gerry gave it a suitable name - Global Dimming. But again, the response from other scientists was one of sheer disbelief.

DR GERALD STANHILL: The scientific community was obviously not ready to deal with the fact that there was a Global Dimming phenomena.

NARRATOR: Of course, there was a good reason for the scepticism. Less energy from the Sun should be making the world cooler. Yet scientists knew the Earth was getting hotter. As the carbon dioxide and other greenhouse gases we emit trap ever more heat in the Earth's atmosphere and cause Global Warming.

DR BEATE LIEPERT: My friends' reaction actually to Gerry's and to my work at the same time too was, oh my God this is really extreme, you are um contradicting global warming. Er do you know how many billions of dollars was spent on global warming research and you and this old guy er are contradicting er us.

NARRATOR: So Liepert and Stanhill's work was widely dismissed. But Global Dimming was not the only phenomenon that didn't seem to fit with Global Warming. In Australia two more biologists, Michael Roderick and Graham Farquhar were intrigued by another paradoxical result - the world-wide decline in something called the pan evaporation rate.

PROF GRAHAM FARQUHAR (Australian National University): It's called pan evaporation rate because it's evaporation rate from a pan. Every day all over the world people come out in the morning and see how much water they've got to add to a pan to bring it back to the level it was the same time the morning before. It's that simple.

NARRATOR: In some places agricultural scientists have been performing this rather dull daily task for more than a hundred years. PROF GRAHAM FARQUHAR: The long-term measurements of pan evaporation are what gives it its real value.

DR MICHAEL RODERICK (Australian National University): And the fact that they're doing the same thing day in day out with the same instrument.

PROF GRAHAM FARQUHAR: Yeah, they deserve a medal. Each of them.

DR MICHAEL RODERICK: Yeah.

NARRATOR: For decades, nobody took much notice of the pan evaporation measurements. But in the 1990s scientists spotted something very strange, the rate of evaporation was falling.

PROF GRAHAM FARQUHAR: There is a paradox here about the fact that the pan evaporation rate's going down, an apparent paradox, but the global temperature's going up.

NARRATOR: This was a puzzle. Most scientists reasoned that like a pan on the stove, turning up the global temperature should increase the rate at which water evaporated. But Roderick and Farquhar did some calculations and worked out that temperature was not the most important factor in pan evaporation.

DR MICHAEL RODERICK: Well it turns out in fact that the key things for pan evaporation are the sunlight, the humidity and the wind. But really the sunlight is a really dominant term there.

NARRATOR: They found that it was the energy of the photons hitting the surface, the actual sunlight, that kicks the water molecules out of the pan and into the atmosphere. And so they too reached an extraordinary conclusion.

DR MICHAEL RODERICK: You know, if the pan is going down then maybe that's the sunlight going down. NARRATOR: Was the fall in pan evaporation in fact evidence of Global Dimming? Somewhere in the journals, they felt, must be the hard numbers that could tie the two things together.

DR MICHAEL RODERICK: And then one day, just by accident, I had to go to the library to get an article out Nature. As you do, I couldn't find it. And I just glanced at a, through the thing, and there was an article called Evaporation Losing Its Strength. Which reported a decline in pan evaporation over Russia, United States and Eastern Europe. And there in the, in the measurements, they said that the, the pans had on average, evaporated about a hundred millimetres less of water in the last thirty years.

NARRATOR: Mike knew how much sunlight was needed to evaporate a millimetre of water. So he put the two sets of figures together - the drop in evaporation with the drop in sunlight.

DR MICHAEL RODERICK: And so you just do the sum in your head. A hundred millimetres of water, less a pan evaporation, two and a half mega joules, so two and a half times a hundred is two hundred and fifty mega joules. And that is in fact what the Russians have measured with the decline in sunlight in the last thirty years. It was quite amazing.

NARRATOR: It was the same with Europe and the USA. The drop in evaporation rate matched exactly the drop in sunlight reported by Beate Liepert and Gerry Stanhill. Two completely independent sets of observations had come to the same conclusion. Though it seemed incredible, there was no doubting Global Dimming now.

DR BEATE LIEPERT: All of a sudden you see, oh my God the world is dimming, and then you, all of a sudden you see oh my God this really has a tremendous impact.

PROF GRAHAM FARQUHAR: There had to be dimming in Europe in America and in Russia, this is on a global scale. And we thought, this is really important because the amount of dimming was enormous. So this is BIG on a global scale.

NARRATOR: But what was causing it? Scientists knew that there was nothing wrong with the sun itself. The culprit had to be here on Earth. And as they searched for clues, they would make another startling discovery. Global dimming is a killer. It may have been behind the worst climatic disaster of recent times, responsible for famine and death on a biblical scale. And Global Dimming is poised to strike again.

NARRATOR: The Maldives: a nation of a thousand tiny islands in the middle of the Indian Ocean, so recently battered by the Asian tsunami. It was here that Veerabhadran Ramanathan, one of the world's leading climate scientists first began to unravel the mystery of what's causing Global Dimming. He had first noticed declining sunlight over large areas of the Pacific Ocean in the mid-1990s.

PROF VEERABHADRAN RAMANATHAN (University of California): But we didn't know at that time it was part of a much larger global picture, but I knew we had to find out what was causing that.

NARRATOR: Ramanathan was certain of one thing, the big drop in sunlight reaching the ground had to be something to do with changes in the Earth's atmosphere. There was one obvious suspect.

PROF VEERABHADRAN RAMANATHAN: Almost everything we do to create energy causes pollution.

NARRATOR: Burning fuel doesn't just produce the invisible greenhouse gases which cause global warming. It also produces visible pollution, tiny airborne particles of soot and other pollutants. These produce the haze which shrouds our cities. So Ramanathan wondered: Could this pollution be causing Global Dimming? The Maldives were the perfect place to find out. The Maldives seem unpolluted, but in fact the northern islands sit in a stream of dirty air descending from India. Only the southern tip of the long island chain enjoys clean air coming all the way from Antarctica. So by comparing the northern islands with the southern ones, Ramanathan and his colleagues would be able to see exactly what difference the pollution made to the atmosphere and the sunlight. Project INDOEX, as it was called, was a huge multinational effort. For four years every possible technique was used to sample and monitor the atmosphere over the Maldives. INDOEX cost twenty-five million dollars, but it produced results - and they surprised everyone.

PROF VEERABHADRAN RAMANATHAN: The stunning part of the experiment was this pollutant layer which was three kilometre thick, cut down the sunlight reaching the ocean by more than 10%.

NARRATOR: A 10% fall in sunlight meant that particle pollution was having a far bigger effect than anyone had thought possible.

PROF VEERABHADRAN RAMANATHAN: Our models led us to believe the human impact on the dimming was close to half to one per cent. So what we discovered was tenfold.

NARRATOR: INDOEX showed that the pollution particles were blocking some sunlight themselves; but far more significant was what they were doing to the clouds. They were turning them into giant mirrors. Clouds are made of droplets of water. These only form when water vapour in the atmosphere starts to condense on the surface of naturally occurring airborne particles, typically pollen or sea salt. As they grow, the water droplets eventually become so heavy they fall as rain. But Ramanathan found that polluted air contained far more particles than the unpolluted air, particles of ash, soot and sulphur dioxide.

PROF VEERABHADRAN RAMANATHAN: We saw ten times more particles in the polluted air mass north of the Maldives compared with what we saw south of the Maldives which was a pristine air mass.

NARRATOR: In the polluted air billions of man-made particles provided ten times as many sites around which water droplets could form. So polluted clouds contained many more water droplets, each one far smaller than it would be naturally. Many small droplets reflect more light than fewer big ones. So the polluted clouds were reflecting more light back into space, preventing the heat of the sun getting through. This was the cause of Global Dimming.

PROF VEERABHADRAN RAMANATHAN: Basically the Global Dimming we saw in the North Indian Ocean, it was contributed on the one hand by the particles themselves shielding the ocean from the sunlight, on the other hand making the clouds brighter. So this insidious soup, consisting of soot, sulphates, nitrates, ash and what have you, was having a double whammy on the Global Dimming.

NARRATOR: And when he looked at satellite images, Ramanathan found the same thing was happening all over the world. Over India. Over China, and extending into the Pacific. Over Western Europe... extending into Africa. Over the British Isles. But it was when scientists started to investigate the effects of Global Dimming that they made the most disturbing discovery of all. Those more reflective clouds could alter the pattern of the world's rainfall. With tragic consequences.

NEWS REPORT - MICHAEL BUERK VOICE OVER: Dawn, and as the sun breaks through the piercing chill of night on the plain outside Korum it lights up a biblical famine, now in the 20th Century. This place say workers here is the closest thing to hell on earth.

NARRATOR: The 1984 Ethiopian famine shocked the world. It was partly caused by a decade's long drought right across sub-Saharan Africa - a region known as the Sahel. For year after year the summer rains failed. At the time some scientists blamed overgrazing and poor land management. But now there's evidence that the real culprit was Global Dimming. The Sahel's lifeblood has always been a seasonal monsoon. For most of the year it is completely dry. But every summer, the heat of the sun warms the oceans north of the equator. This draws the rain belt that forms over the equator northwards, bringing rain to the Sahel. But for twenty years in the 1970s and 80s the tropical rain belt consistently failed to shift northwards - and the African monsoon failed. For climate scientists like Leon Rotstayn the disappearance of the rains had long been a puzzle. He could see that pollution from Europe and North America blew right across the Atlantic, but all the climate models suggested it should have little effect on the monsoon. But then Rotstayn decided to find out what would happen if he took the Maldive findings into account.

DR LEON ROTSTAYN (CSIRO Atmospheric Research): What we found in our model was that when we allowed the pollution from Europe and North America to affect the properties of the clouds in the northern hemisphere the clouds reflected more sunlight back to space and this cooled the oceans of the northern hemisphere. And to our surprise the result of this was that the tropical rain bands moved southwards tracking away from the more polluted northern hemisphere towards the southern hemisphere.

NARRATOR: Polluted clouds stopped the heat of the sun getting through. That heat was needed to draw the tropical rains northwards. So the life giving rain belt never made it to the Sahel.

DR LEON ROTSTAYN: So what our model is suggesting is that these droughts in the Sahel in the 1970s and the 1980s may have been caused by pollution from Europe and North America affecting the properties of the clouds and cooling the oceans of the northern hemisphere.

NARRATOR: Rotstayn has found a direct link between Global Dimming and the Sahel drought. If his model is correct, what came out of our exhaust pipes and power stations contributed to the deaths of a million people in Africa, and afflicted 50 million more. But this could be just of taste of what Global Dimming has in store.

PROF VEERABHADRAN RAMANATHAN: The Sahel is just one example of the monsoon system. Let me take you to anther part of the world. Asia, where the same monsoon brings rainfall to three point six billion people, roughly half the world's population. My main concern is this air pollution and the Global Dimming will also have a detrimental impact on this Asian monsoon. We are not talking about few millions of people we are talking about few billions of people.

NARRATOR: For Ramanathan the implications are clear.

PROF VEERABHADRAN RAMANATHAN: There is no choice here we have to cut down air pollution, if not eliminate it altogether.

NARRATOR: Fortunately, tackling air pollution needn't be too difficult. It wouldn't mean giving up on oil and coal altogether. We'd just have to burn them more cleanly. And in Europe we've already made a start: scrubbers in power stations, catalytic converters in cars and low sulphur fuels, though they do nothing to reduce greenhouse gases, have already begun to cut down visible air pollution. This should be good news for the Sahel, and in recent years the droughts have been nothing like as bad. But there's a terrible catch. Because while Global Dimming is itself a major threat to humanity, it now appears it has been protecting us from an even greater threat. Which means that as we reduce the dimming, we may find ourselves faced by something even worse.

[BigBunny]

NARRATOR: It was David Travis who first caught a glimpse of what the world could be like without Global Dimming. It happened in those chaotic days following the tragedy of 9/11. For fifteen years, Travis had been studying the vapour trails, or contrails, left behind by high-flying aircraft. Though each individual contrail seems small, when they all spread out, they can blanket the sky.

DR DAVID TRAVIS: Here are some examples of what we call outbreaks of contrails. These are large clusters of contrails. And here's a particularly er good one from Southern California. Here's the west coast of the United States. And you can see here this lacing network of contrails er covering at least fifty per cent, if not seventy five per cent or more of the sky in that area. It doesn't take an expert to er realise that if, if you look at the satellite picture and see this kind of contrail coverage that they've got to be having an effect on temperature at the surface.

NARRATOR: But the problem Travis faced was to establish exactly how big an effect the contrails were actually having. The only way to do that was to find a period of time when, although conditions were right for contrails to form, there were no flights. And, of course, that never happened. Until September 2001. Then, for three days after the 11th virtually all commercial aircraft in the US were grounded. It was an opportunity Travis could not afford to miss. He set about gathering temperature records from all over the USA.

DR DAVID TRAVIS: Initially data from over 5,000 weather stations across the 48 united states, the areas that was most dominantly affected by the grounding.

NARRATOR: Travis was not looking just at temperature - that varies a lot from day to day anyway. Instead he focused on something that normally only changes quite slowly: the temperature range. The difference between the highest temperature during the day and the lowest at night. Had this changed at all during the three days of the grounding?

DR DAVID TRAVIS: As we began to look at the climate data and the evidence began to grow I got more and more excited. The actual results were much larger than I expected. So here we see for the 3 days preceding September 11th a slightly negative value of temperature range with lots of contrails as normal. Then we have this sudden spike right here of the 3 day period. This reflects lack of clouds, lack of contrails, warmer days cooler nights, exactly what we expected but even larger than what we expected. So what this indicates is that during this 3 day period we had a sudden drop in Global Dimming contributed from airplanes.

NARRATOR: During the grounding the temperature range jumped by over a degree Celsius. Travis had never seen anything like it before.

DR DAVID TRAVIS: This was the largest temperature swing of this magnitude in the last thirty years.

NARRATOR: If so much could happen in such a short time, removing just one form of pollution, then it suggests that the overall effect of Global Dimming on world temperatures could be huge.

DR DAVID TRAVIS: The nine eleven study showed that if you remove a contributor to Global Dimming, jet contrails, just for a three day period, we see an immediate response of the surface of temperature. Do the same thing globally we might see a large scale increase in global warming.

NARRATOR: This is the real sting in the tail. Solve the problem of Global Dimming and the world could get considerably hotter. And this is not just theory, it may already be happening. In Western Europe the steps we have taken to cut air pollution have started to bear fruit in a noticeable improvement in air quality and even a slight reduction in Global Dimming over the last few years. Yet at the same time, after decades in which they held steady, European temperatures have started rapidly to rise culminating in the savage summer of 2003.

Forest fires devastated Portugal. Glaciers melted in the Alps. And in France people died by the thousand. Could this be the penalty of reducing Global Dimming without tackling the root cause of global warming?

DR BEATE LIEPERT: We thought we live in a global warming world, um but this is actually er not right. We lived in a global warming plus a Global Dimming world, and now we are taking out Global Dimming. So we end up with the global warming world, which will be much worse than we thought it will be, much hotter.

NARRATOR: This is the crux of the problem. While the greenhouse effect has been warming the planet, it now seems Global Dimming has been cooling it down. So the warming caused by carbon dioxide has been hidden from us by the cooling from air pollution. But that situation is now starting to change.

DR PETER COX (Hadley Centre, Met Office): We're gonna be in a situation unless we act where the cooling pollutant is dropping off while the warming pollutant is going up, CO2 will be going up and particles will be dropping off and that means we'll get an accelerated warming. We'll get a double whammy, we'll get, we'll get reducing cooling and increased heating at the same time and that's, that's a problem for us.

NARRATOR: And that's not all. Climatologists like Peter Cox have begun to worry that Global Dimming has led them to underestimate the true power of global warming. They fear that the Earth could be far more vulnerable to greenhouse gases than they had previously thought.

DR PETER COX: We've got two competing effects really, that we've got the greenhouse effect, which has tended to warm up the climate. But then we've got this other effect that's much stronger than we thought, which is a cooling effect that comes from particles in the atmosphere. And they're competing with one another. And we know the climate's moved to a warmer state by about point six of a degree over the last hundred years. So the whole thing's moved this way. If it turns out that the cooling is stronger than we thought then the warming also is a lot stronger than we thought, and that means the climate's more sensitive to carbon dioxide than we originally thought, and it means our models may be under sensitive to carbon dioxide.

NARRATOR: The models that everyone has been using to forecast climate change predict a maximum warming of 5 degrees by the end of the century. But Cox and his colleagues now fear those models may be wrong. Temperatures could rise twice as fast as they previously thought with irreversible damage just twenty-five years away.

DR PETER COX: If we don't do anything by about twenty thirty we could have a global warming of exceeding two degrees, and at that point it's believed the Greenland ice sheet would start to melt in a way that you wouldn't be able to stop it once it started it, it would melt. Take a long time to melt but ultimately it would lead to a sea level rise of seven or eight metres.

NARRATOR: Once the Greenland ice cap begins to melt, nothing will stop it. Many of the world's major cities will be living on borrowed time. Decade by decade, the risk of catastrophic flooding would increase inexorably. But unless action is taken it won't stop there. Because after Greenland, the world's tropical rainforests will start to wither in the heat.

DR PETER COX: 2040 it could be four degrees warmer, the climate change could have led to big drying particularly in the Amazon Basin, that would make the forest unsustainable, we'd expect the forest to catch fire probably, turn into savannah and maybe ultimately even desert if it gets really really dry as our model suggests.

NARRATOR: And as the rainforest burnt away, it would release vast amounts of carbon dioxide into the atmosphere, driving global warming still further. Cox calculates that in just a century, the world could be 10 degrees hotter, a warming more rapid than any in Earth history. If this were to happen, the landscape of England would be utterly transformed.

DR PETER COX: We're talking about a change from er a lush, moist climate, environment like this, to a North African climate in just a few decades or a hundred years.

NARRATOR: Most British plant species could not survive a North African climate. With vegetation dying everywhere, soil erosion would become a severe problem. From a green and pleasant land, England would become a country of extremes, with winter flooding giving way to summer dust storms. And it will be far worse elsewhere.

DR PETER COX: You can imagine ten degree warming in the UK in a hundred years is catastrophic. Ten degree warming in a hot country already makes it essentially uninhabitable.

NARRATOR: And just when one might think things could get no worse in the far North a ten degree warming might be enough to release a vast natural store of greenhouse gas bigger than all the oil and coal reserves of the planet.

DR PETER COX: We will be in danger of destabilising these things called methane hydrates which store a lot of methane at the bottom of the ocean in a kind of frozen form, ten thousand billions tons of this stuff, and they're known to be destabilised by warming.

NARRATOR: At this point, whatever we did to curb our emissions, it would be too late. Ten thousand billion tons of methane, a greenhouse gas eight times stronger than carbon dioxide, would be released into the atmosphere. The Earth's climate would be spinning out of control, heading towards temperatures unseen in four billion years. But this is not a prediction - it is a warning. It is what will happen if we clean up pollution while doing nothing about greenhouse gases. However, the easy solution - just keep on polluting and hope that Global Dimming will protect us - would be suicidal.

DR PETER COX: If we carried on pumping out the particles it would have terrible impact on human health, I mean particles are involved in all sorts of respiratory diseases, that's why they're being brought under control, and of course they effect climate anyway. If you, if you fiddle with the, the balance of the planet, the radiative balance of the planet, you affect all sorts of circulation patterns like monsoons, which would have horrible effects on people. So it would be extremely difficult, in fact impossible, to cancel out the greenhouse effect just by carrying on pumping out particles, even if it wasn't for the fact that particles are damaging for human health.

NARRATOR: Instead we have to take urgent action to tackle the root cause of both global warming and Global Dimming - the burning of coal, oil and gas. We may have to make very difficult choices, about how we live and how we generate our electricity. We have been talking about such things for 20 years. But so far very little has been done in practical terms. The discovery of Global Dimming makes it clear that we are rapidly running out of time.

DR PETER COX: One of the real driving forces is that you leave an environment that is comfortable for your children. And we carry on going the way we're going, we're not going to do that, we're going to leave an environment that's much worse than the environment we lived in; and it will be down to what we did when we were using that environment, and that would be, um, tragic really, if that happened.

www.bbc.co.uk/sn/tvradio/programmes/horizon/dimming_trans.shtml

[BigBunny]

If you are really interested in this subject consider the following:

Global Dimming Bibliography

Abakumova, G. M. (2000). "Trends of long-term changes in atmosphere transparency, cloudiness, solar radiation, and surface albedo in Moscow." Meteor. i Gidrol. 9: 51-62.

Abakumova, G. M., E. M. Feigelson, et al. (1996). "Evaluation of long-term changes in radiation, cloudiness, and surface temperature on the territory of the former Soviet Union." Journal of Climate 9(6): 1319-1327.

Allen, M. R. and W. J. Ingram (2002). "Constraints on future changes in climate and the hydrologic cycle." Nature 419: 224-232.

Anderson, T.L., Charlson, R.J., Schwartz, S.E., Knutti, R., Boucehr, O., Rodhe, H. and J. Heintzenberg (2003), "Climate forcing by aerosols - a hazy picture." Science 300: 1103-1104.

Angell, J. K. (1990). "Variation in United States cloudiness and sunshine duration between 1950 and the drought year of 1988." Journal of Climate 3: 296-308.

Angell, J. K., J. Korshover, et al. (1984). "Variation in United States cloudiness and sunshine, 1950-1982." Journal of Climate and Applied Meteorology 23: 752-761.

Asanuma, J. and H. Kamimura "Long-term trend of pan evaporation measurements in Japan and its relevance to the variability of the hydrological cycle." alpine.suiri.tsukuba.ac.jp/~asanuma/research/publications/pdf/epochal.pdf.

Ball, R. J. and G. D. Robinson (1982). "The origin of haze in the central United States and its effect on solar radiation." Journal of Applied Meteorology 21: 171-188.

Brutsaert, W. and M. B. Parlange (1998). "Hydrologic cycle explains the evaporation paradox." Nature 396: 30.

Chameides, W. L., H. Yu, et al. (1999). "Case study of the effects of atmospheric and regional haze on agriculture: An opportunity to enhance crop yields in China through emission controls?" Proceedings of the National Academy of Sciences 96: 13626-13633.

Changnon, S. A. (1981). "Midwestern cloud, sunshine and temperature trends since 1901: Possible evidence of jet contrail effects." Journal of Applied Meteorology 20: 496-508.

Charlson, R.J., F.P.J. Valero and J.H. Seinfeld (2005) “In search of Balance.” Science 308: 806-807.

Chattopadhyay, N. and M. Hulme (1997). "Evaporation and potential evapotranspiration in India under conditions of recent and future climate change." Agricultural and Forest Meteorology 87: 55-73.

Chen, D., G. Gao, et al. (2005). "Comparison of the Thornthwaite method and pan data with the standard Penman-Monteith estimates of reference evapotranspiration in China." Climate Research 28: 123-132.

Cohen, S., A. Ianetz, et al. (2002). "Evaporative climate changes at Bet Dagan, Israel, 1964-1998." Agricultural and Forest Meteorology 111: 83-91.

Cohen, S, Liepert, B.and G. Stanhill (2004)." Global dimming comes of age". Eos 85 (38): 362-363.

Cohen, S. and G. Stanhill (1996). "Contemporary climate change in the Jordan Valley." Journal of Applied Meteorology 35: 1051-1058.

De Bruin, H. A. R., B. J. J. M. van den Hurk, et al. (1995). "A series of global radiation at Wageningen for 1928-1992." International Journal of Climatology 15: 1253-1272.

Dutton, E. G., A. Farhadi, et al. (2004). "Long-term variations in the occurrence and effective solar transmission of clouds as determined from surface-based total irradiance observations." Journal of Geophysical Research 109: D03204, doi: 10.1029/2003JD003568.

Dutton, E. G., R. S. Stone, et al. (1991). "Recent interannual variaitons in solar radiation, cloudiness, and surface temperature at the South Pole." Journal of Climate 4: 848-858.

Farquhar, G. D. and M. L. Roderick (2003). "Pinatubo, diffuse light, and the carbon cycle." Science 299: 1997-1998.

Feichter, J., E. Roeckner, et al. (In press). "Nonlinear aspects of the climate response to greenhouse gas and aerosol forcing." Journal of Climate.

Gilgen, H., M. Wild, et al. (1998). "Means and trends of shortwave irradiance at the surface estimated from global energy balance archive data." Journal of Climate 11: 2042-2061.

Goldberg, B. and W. H. Klein (1971). "Comparison of normal incident solar energy measurements at Washington, DC." Solar Energy 13: 311-321.

Golubev, V. S., J. H. Lawrimore, et al. (2001). "Evaporation changes over the contiguous United States and the former USSR: A reassessment." Geophysical Research Letters 28(13): 2665-2668.

Gorley, B. (2005) "Global Dimming" Weather 60 (6): 174.

Hansen, J., T. Bond, et al. (2002). "Carbonaceous aerosols in the Industrial Era." EOS: (in press).

Hatch, D. J. (1981). "Sunshine at Kew Observatory 1881-1980." Journal of Meteorology UK 3: 101-113.

Henderson-Sellers, A. (1992). "Continental cloudiness changes this century." Geo-Journal 27(3): 255-262.

Husar, R. B. and D. E. Patterson (1986). Haze climate of the United States. Research Triangle Park, North Carolina, Atmospheric Studies Research Laboratory, USEPA.

Idso, S. B. (1972). "Solar radiation measurements augment air pollution studies." Journal of Air Pollution Control Association 22: 364-365.

Jauregui, E. and E. Luyando (1999). "Global radiation attenuation by ari pollution and its effects on the thermal climate in Mexico City." International Journal of Climatology 19: 683-694.

Jones, P. A. and A. Henderson-Sellers (1992). "Historical records of cloudiness and sunshine in Australia." Journal of Climate 5: 260-267.

Joseph, J. H. and A. Manes (1971). "Secular and seasonal variations of atmospheric turbidity at Jerusalem." Journal of Applied Meteorology 10: 453-462.

Kaiser, D. P. and Q. Yun (2002). "Decreasing trends in sunshine duration over China for 1954-1998: Indication of increased haze pollution." Geophysical Research Letters 29(21): 2042.

Kane, R. P. (1997). "Interannual variability of global irradiation at Wageningen." International Journal of Climatology 17: 1487-1493.

Kimball, H. H. (1918). "Volcanic eruptions and solar radiation intensities." Monthly Weather Review 46((August)): 355-356.

Kimball, H. H. (1924). "Variation in solar radiation intensities measured at the surface of the Earth." Monthly Weather Review 6((November)): 527-529.

Lawrimore, J. H. and T. C. Peterson (2000). "Pan evaporation trends in dry and humid regions of the United States." Journal of Hydrometeorology 1(6): 543–546.

Lelieveld, J. and e. al. (2002). "Global air pollution crossroads over the Mediterranean." Science 298: 794-799.

Li, X.W.,W.L.Li and X.J. Zhou (1998). "Analysis of the solar radiation variation of the China in recent 30 years" Quart. J. Appl. Meteor. 9(1): 24-31 ( In Chinese with abstract in English).

Li, X., X. Zhou, et al. (1995). "The cooling of Sichuan Province in recent 40 years and its probable mechanisms." Acta Meteorologica Sin. 9: 57-68.

Liepert, B. G. (1997). "Recent changes in solar radiation under cloudy conditions in Germany." International Journal of Climatology 17: 1581-1593.

Liepert, B. G. (2002). "Observed reductions of surface solar radiation at sites in the United States and worldwide from 1961 to 1990." Geophysical Research Letters 29(12): DOI 10.1029/2002GL014910.

Liepert, B. G., P. Fabian, et al. (1994). "Solar radiation in Germany - Observed trends and an assessment of their causes. Part 1. Regional approach." Contr. Atm. Physics 67: 15-29.

Liepert, B. G., J. Feichter, et al. (2004). "Can aerosols spin down the water cycle in a warmer and moister world?" Geophysical Research Letters 31: doi: 10.1029/2003GL019060.

Liepert, B. G. and G. J. Kukla (1997). "Decline in solar radiation with increased horizontal variability in Germany between 1964-1990." Journal of Climate 10: 2391-2401.

Liepert, B. G. and U. Lohmann (2001). "A comparison of surface observations and ECHAM4-GCM results relevant to the indirect aerosol effect." Journal of Climate 14: 1078-1091.

Liepert, B. G. and I. Tegen (2002). "Multi-decadal solar radiation trends in the United States and Germany and direct troposheric aerosol forcing." Journal of Geophysical Research 107: 10.1029/2001JD000760.

Linacre, E. T. (in press). "Evaporation trends."

Liu, B., M. Henderson, et al. (2004). "A spatial analysis of pan evaporation trends in China, 1955-2000." Journal of Geophysical Research.

Lohmann, G., N. Rimbu and M. Dima (2004). " Climate signature of solar irradiance variations: Analysis of long-term instumental, historical, and proxy data" Int.J. Climatol. 24:1045-1056.

Luo, Y., D. Lu, et al. (2001). "Characteristics of the spatial distribution and yearly variation of aerosol optical depth over China in last 30 years." Journal of Geophysical Research 106(D13): 14501-14513.

MacWilliams, S. (1973). Atmospheric turbidity at Valencia Observatory. Dublin, Irish Meteorological Service: Vol 36.

Manes, A., Y. Goldreich, et al. (1975). Inadvertant modification of the solar radiation climate at Bet Dagan. Sixth Sci. Conference of the Israel Ecological Society, Tel-Aviv.

Moonen, A. C., L. Ercoli, et al. (2002). "Climate change in Italy indicated by agrometeorological indices over 122 years." Agricultural and Forest Meteorology 111: 13-27.

Morawska-Horawska, M. (1985). "Cloudiness and sunshine in Cracow, 1861-1980, and its contemporary tendencies." Journal of Climatology 5: 633-642.

Nunez, M. (1993). "The development of a satellite-based insolation model for the tropical western Pacific ocean." International Journal of Climatology 13: 607-627.

Ohmura, A. and M. Wild (2002). "Is the hydrological cycle accelerating?" Science 298: 1345-1346.

Palle, E. and C. J. Butler (2001). "Sunshine records from Ireland, cloud factors and possible links to solar activity and climate." International Journal of Climatology 21(6): 709-729.

Palle, E. and C. J. Butler (2002). "Comparison between sunshine records and synoptic cloud observations: A case study for Ireland." Physics and Chemistry of the Earth 27: 405-414.

Palle, E. and C. J. Butler (2002). "The proposed connection between clouds and cosmic rays: Cloud behaviour during the past 50-120 years." Journal of Atmospheric and Solar-Terrestrial Physics 64(3): 327-337.

Palle, E., P. R. Goode, et al. (2004). "Changes in the Earth's reflectance over the past two decades." Science 304: 1299-1301.

Peterson, T. C., V. S. Golubev, et al. (1995). "Evaporation losing its strength." Nature 377: 687-688.

Philipona, R., B. Durr, et al. (2004). "Radiative forcing - measured at Earth's surface - corroborate the increasing greenhouse effect." Geophysical Research Letters 31: L03202, doi: 1029/2003GL018765.

Pinker, R.T., B. Zhang and E.G. Dutton. (2005). "Do satellites detect trends in surface solar radiation." Science. 308: 850-854,

Power, H. C. (2003). "Trends in solar radiation over Germany and an assessment of the role of aerosols and sunshine duration." Theoretical and Applied Climatology 76(1-2): 47-63.

Power, H. C. and A. Goyal (2003). "Comparison of aerosol and climate variability over Germany and South Africa." International Journal of Climatology 23: 921-941.

Power, H. C. and D. M. Mills (In press). "Solar radiation climate change over South Africa and an assessment of the radiative impact of volcanic eruptions." International Journal of Climatology.

Power, H. C. and C. J. Willmott (2001). "Seasonal and interannual variability in atmospheric turbidity over South Africa." International Journal of Climatology 21: 579-591.

Przybylack, R. (1999). "Influence of cloudiness on extreme air temperatures and diurnal temperature range in the Arctic in 1951-1990." Polish Polar Research 20: 140-173.

Raju, A. S. N. and K. K. Kumar (1982). "Comparison of point cloudiness and sunshine derived cloud cover in India." Pure and Applied Geophysics 120: 495-502.

Ramanathan, V., Crutzen, P.J., Kiehl, J.T. and D. Rosenfeld (2001). "Aerosols, Climate and the Hydrological Cycle." Science 294: 2119-2124.

Rimmer, W. B. (1937). "The depletion of solar radiation by volcanic dust." Betr. Geophys. Leipzig. 50: 388-93.

Roderick, M. L. and G. D. Farquhar (2002). "The cause of decreased pan evaporation over the past 50 years." Science 298: 1410-1411.

Roderick, M. L. and G. D. Farquhar (in press). "Changes in Australian pan evaporation from 1970-2002." International Journal of Climatology.

Roderick, M. L., G. D. Farquhar, et al. (2001). "On the direct effect of clouds and atmospheric particles on the productivity and structure of vegetation." Oecologia 129(1): 21-30.

Rotem Schwarzbard, A. (2004). The effects of various aerosols and clouds on the recent climatic variations in the surface insolation. Tel-Aviv, Tel-Aviv University: 83.

Russak, V. (1990). "Trends of solar radiation, cloudiness and atmospheric transparency during recent decades in Estonia." Tellus 42B: 206-210.

Satheesh, S. K. and V. Ramanathan (2000). "Large differences in tropical aerosol forcing at the top of the atmosphere and Earth's surface." Nature 405: 60-63.

Schiermeier, Q. (2005). "Clearer skies leave global warming forecasts uncertain." Nature 435: 135.

Schiffer, R. A. and W. B. Rossow (1985). "ISCCP global radiance data set: A new resource for climate research." Bulletin of the American Meteorological Society 66: 1498-1505.

Sekihara, S. (1973). "Some aspects of radiation climate of Tokyo as observed by the eleven year measurement of spectral global radiation." Journal of the Meteorological Society of Japan 51: 119-132.

Stahle, D. W., M. K. Cleaveland, et al. (1991). "Tree ring reconstructed sunshine duration over central USA." International Journal of Climatology 11: 285-295.

Stanhill, G. (1992). "Accuracy of global radiation measurements at unattended, automatic weather stations." Agricultural and Forest Meteorology 61: 151-156.

Stanhill, G. (1995). "Global irradiance, air pollution and temperature changes in the Arctic." Philosophical Transactions of the Royal Society of London A 352: 247-258.

Stanhill, G. (1997). "Physics and stamp collecting: Comments arising from "The NOAA integrated surface irradiance study (ISIS) - a new surface radiation monitoring program."" Bulletin of the American Meteorological Society 78: 2872-2873.

Stanhill, G. (1998). "Long term trends in, and spatial variation of, solar irradiances in Ireland." International Journal of Climatology 18: 1015-1030.

Stanhill, G. (1998a). "Estimation of direct solar beam irradiance from measurements of the duration of bright sunshine." International Journal of Climatology 18: 347-354.

Stanhill, G. (2000). The future of irrigation: The role of climate trends and uncertainties. Theory and Practice of Water Saving Agriculture. H. Guanhua. Beijing, China Water Power Press: 8-17.

Stanhill, G. (2002). "Is the class A evaporation pan still the most practical and accurate meteorological method for determining irrigation water requirements?" Agricultural and Forest Meteorology 112: 233-236.

Stanhill, G. (2003). "Through a glass brightly: Some new light on the Campbell-Stokes sunshine recorder." Weather 58: 3-11.

Stanhill, G. (2005). "Global Dimming: A new aspect of climate change." Weather 60 (1): 11-14.

Stanhill, G. and S. Cohen (1997). "Recent changes in solar irradiance in Antarctica." Journal of Climatology 10: 2078-2086.

Stanhill, G. and S. Cohen (2001). "Global dimming: a review of the evidence for a widespread and significant reduction in global radiation with discussion of its probable causes and possible agricultural consequences." Agricultural and Forest Meteorology 107: 255-278.

Stanhill, G. and S. Cohen (2005). "Solar radiation changes in the United States during the twentieth century: Evidence from sunshine duration measurements." Journal of Climate. 18: 1503-1512.

Stanhill, G. and A. Ianetz (1996). "Long term trends in, and spatial variation of, global irradiance in Israel." Tellus 49B: 112-122.

Stanhill, G. and J. D. Kalma (1994). "Secular variation of global irradiance in Australia." Australian Meteorological Magazine 43: 81-86.

Stanhill, G. and J. D. Kalma (1995). "Solar dimming and urban heating at Hong Kong." International Journal of Climatology 15: 933-941.

Stanhill, G. and S. Moreshet (1992). "Global radiation climate changes in Israel." Climatic Change 22: 121-138.

Stanhill, G. and S. Moreshet (1992). "Global radiation climate changes: the world network." Climatic Change 21: 57-75.

Stanhill, G. and S. Moreshet (1993). "The cooling of Lake Kinneret: A result of solar dimming?" Biosphere 25(8/9): 27-30.

Stanhill, G. and S. Moreshet (1994). "Global radiation change at seven sites remote from surface sources of pollution." Climatic Change 26: 89-103.

Steif, G. (1992). "Pianeta azzuro o pianeta grigrio? Sine sole silet. Le conseguenze dell'inquinamento atmosferico su clima e biosfera ca particolare reguardo al traffico aereo." Ministero Agriccoltura e Foreste, Roma Collana Verde 90: 150pp.

Sun, B. and P. Y. Groisman (2000). "Cloudiness variations over the Former Soviet Union." International Journal of Climatology 20: 1097-1111.

Suraqui, S., H. Tabor, et al. (1974). "Solar radiation changes at Mt. St. Katherine after forty years." Solar Energy 16: 155-158.

Szilagyi, J., G. G. Katul, et al. (2001). "Evapotranspiration intensifies over the conterminous United States." Journal of Water Resources Planning and Management 127(6): 354-362.

Thomas, A. (2000). "Spatial and temporal characteristics of potential evapotranspiration trends over China." International Journal of Climatology 20: 381-396.

Travis, D.J., Carleton, A.M. and R.G. Lauritsen (2002). "Contrails reduce daily temperature range." Nature 418: 601.

Wagner, G., D. M. Livingstone, et al. (2001). "Some results relevant to the discussion of a possible link between cosmic rays and the Earth's climate." Journal of Geophysical Research 106(D4): 3381-3387.

Wielicki, B.A., T. Wong, N. Loeb, P. Minnins, K. Priestley and R. Kandel (2005). "Changes in Earthy’s albedo measured by satellite." Science. 308: 825.

Wild, M., H. Gilgen, et al. (2005). "From dimming to brightening: decadal changes in solar radiation at Earth's surface." Science. 308: 847-854.

Wild, M. and B. G. Liepert (1998). "Excessive transmission of solar radiation through the cloud-free atmosphere in GCM's." Geophysical Research Letters 25: 2165-2168.

Wild, M., A. Ohmura, et al. (2004). "On the consistency of trends in radiation and temperature records and implications for the global hydrological cycle." Geophysical Research Letters 31: L11201, doi: 10.11029/2003GL091188.

Xu, J. (2001). "An analysis of climatic changes in Eastern Asia using the potential evaporation." Journal of Japan Society of Hydrology and Water Resources 14: 141-170.

Zhang, Y. L., B.Q.Qin and W.M. Chen (2004). " Analysis of 40 year records of solar radiation data in Shanghai, Nanjing and Hangzhou in Eastern China." Theor. Appl. Climatol. 78: 217-227.

Zhitorchuk, Y. V., V. V. Stadnyuk, et al. (1994). "Study of linear trends of temporal series of solar radiation. Izvest. Akad. Nauk (Ser. Phys. Oceans)." 30: 389-396.

submit further references for this bibliography to: [e-mail]

(Last modified 1/09/05)

www.greenhouse.crc.org.au/crc/research/c2_bibliog.htm

[BigBunny]

Earth's Albedo in Decline



On average, the Sun shines on Earth 341 watts of energy per square meter of surface area. The Sun beams more energy to our planet every hour than humanity uses in a whole year. This energy provides the fuel needed to support most of our world’s life forms, and it keeps our world warm enough to sustain them. Sunlight also provides the energy that powers Earth’s climate system.

The image above shows Earth’s average albedo for March 2005, measured by the Clouds and Earth’s Radiant Energy System (CERES) instrument aboard NASA’s Terra satellite. Albedo is the fraction of incoming sunlight that our planet reflects back to space. If Earth was covered in ice like a giant snowball, its albedo would be about 0.84, meaning it would reflect most (84 percent) of the sunlight that hit it. On the other hand, if Earth was completely covered by a dark green forest canopy, its albedo would be about 0.14, meaning most of the sunlight would get absorbed and our world would be far warmer than it is today. Satellite measurements made since the late 1970s estimate Earth’s average albedo to be about 0.30.

In the albedo image above, white shows areas where Earth reflected the highest percentage of shortwave solar radiation. Dark blue shows areas where Earth reflected the lowest percentage of shortwave solar radiation. Notice how the highest albedo values are in regions where Earth is mostly covered by snow and ice, or clouds, or both. The lowest albedo values occur in forest-covered landscapes or open ocean.

There are factors in Earth’s climate system that influence how much sunlight our world reflects back to space versus how much it catches and stores in the form of heat. Any significant changes in the brightness of the land surface or in the extent of clouds and aerosols in the atmosphere affect how much sunlight Earth reflects, which, in turn, affects the climate system. A drop of as little as 0.01 in Earth’s albedo would have a major warming influence on climate—roughly equal to the effect of doubling the amount of carbon dioxide in the atmosphere, which would cause Earth to retain an additional 3.4 watts of energy for every square meter of surface area.

In the May 6, 2005, issue of the journal Science, the CERES Science Team reported Earth’s shortwave albedo has been steadily declining since the Terra CERES instrument began making the measurement in February 2000. Over the 4-year span (2000 through 2004), the CERES instrument measured an albedo decrease of 0.0027, which equals 0.9 watt of energy per square meter retained in the Earth system. The CERES Team is currently unsure what caused this decline in albedo. The team says future research will focus on comparing CERES data to data from other space-based sensors to see if there are any significant changes in Earth’s climate system during that time that could account for the change in albedo.

[Editor’s note: Glancing at the headlines, it may seem as if this caption disagrees with the U.S. Department of Energy’s news release, titled Earth Lightens Up. However, a more careful read of that press release reveals that this caption is in agreement. That DOE press release refers to brightness at surface, or the amount of sunlight that penetrates all the way down through the atmosphere, whereas this caption refers to the fraction of incoming sunlight that gets reflected. Researchers suspect that an overall reduction in aerosol in the air is allowing more sunlight to penetrate to the surface, thus causing the brightening, which could also explain why Earth’s albedo is in decline.]

NASA image by Jesse Allen, Earth Observatory Team, using data courtesy the CERES Science Team at NASA’s Langley Research Center

earthobservatory.nasa.gov/Newsroom/NewImages/images.php3?img_id=16905

[BigBunny]

May 5, 2005
EARTH LIGHTENS UP

Earth’s surface has been getting brighter for more than a decade, a reversal from a dimming trend that may accelerate warming at the surface and unmask the full effect of greenhouse warming, according to an exhaustive new study of the solar energy that reaches land.

Ever since a report in the late 1980s uncovered a 4 to 6 percent decline of sunlight reaching the planet’s surface over 30 years since 1960, atmospheric scientists have been trying out theories about why this would be and how it would relate to the greenhouse effect, the warming caused by the buildup of carbon dioxide and other gasses that trap heat in the atmosphere.

Meanwhile, a group led by Martin Wild at the Swiss Federal Institute of Technology in Zurich, home of the international Baseline Surface Radiation Network (BSRN) archive, had gone to work collecting surface measurements and crunching numbers.

“BSRN didn’t get started until the early ‘90s and worked hard to update the earlier archive,” said Charles N. Long, senior scientist at the Department of Energy’s Pacific Northwest National Laboratory and co-author of a BSRN report in this week’s issue (Friday, May 6) of the journal Science.

“When we looked at the more recent data, lo and behold, the trend went the other way,” said Long, who conducted the work under the auspices of DOE’s Atmospheric Radiation Measurement (ARM) program.

Data analysis capabilities developed by ARM research were crucial in the study, which reveals the planet’s surface has brightened by about 4 percent the past decade. The brightening trend is corroborated by other data, including satellite analyses that are the subject of another paper in this week’s Science.

Sunlight that isn’t absorbed or reflected by clouds as it plunges earthward will heat the surface. Because the atmosphere includes greenhouse gasses, solar warming and greenhouse warming are related.

“The atmosphere is heated from the bottom up, and more solar energy at the surface means we might finally see the increases in temperature that we expected to see with global greenhouse warming,” Long said.

In fact, he said, many believe that we have already been seeing those effects in our most temperature-sensitive climates, with the melting of polar ice and high altitude glaciers.

The report’s authors stopped short of attributing a cause to the cycle of surface dimming and brightening, but listed such suspects as changes in the number and composition of aerosols—liquid and solid particles suspended in air—and how aerosols affect the character of clouds. Over the past decade, the ARM program has built a network of instrumentation sites to sample cloud characteristics and energy transfer in a variety of climates, from tropical to polar.

“The continuous, sophisticated data from these sites will be crucial for determining the causes,” Long said.

Long also pointed out that 70 percent of the planet’s surface is ocean, for which we have no long-term surface brightening or dimming measurements.

PNNL (www.pnl.gov) is a DOE Office of Science laboratory that solves complex problems in energy, national security, the environment and life sciences by advancing the understanding of physics, chemistry, biology and computation. PNNL employs more than 4,000 staff, has a $650 million annual budget, and has been managed by Ohio-based Battelle since the lab’s inception in 1965.

###
Contact:

Bill Cannon
DOE/Pacific Northwest National Laboratory
509-375-3732
[e-mail]

This text derived from www.pnl.gov/news/2005/05-33.htm

[BigBunny]

Source: Brookhaven National Laboratory

Posted: March 1, 2002
Atmospheric Aerosols Found To Brighten Clouds; Higher Reflectivity May Result In Global Cooling, Partially Offsetting Greenhouse Effect

UPTON, NY -- Atmospheric scientists have long suspected that microscopic aerosol particles from industrial processes increase the brightness of clouds, resulting in greater reflection of sunlight and cooling of Earth's climate. However, this supposition is based on model calculations rather than observations, and these model calculations are very uncertain.

Now, scientists at the U.S. Department of Energy's Brookhaven National Laboratory and Purdue University have combined satellite measurements of cloud brightness, water content, and other variables with model calculations of atmospheric aerosols to demonstrate the brightening effect. This effect, described in the February 19, 2002 issue of the Proceedings of the National Academy of Sciences, should be accounted for in assessing the magnitude of global climate change, the researchers say.

"We're not saying that aerosols can counteract the greenhouse effect," said lead scientist Stephen Schwartz, an atmospheric chemist at Brookhaven, "but rather that we need to know how much of a cooling effect they have so we have a clearer picture of the greenhouse effect. To whatever extent aerosols are offsetting greenhouse warming, then the offset is the unseen part of the greenhouse 'iceberg,'" he said.

One difficulty in measuring the effect of aerosols is knowing their concentration. Aerosols such as sulfur compounds result from emissions by fossil-fuel-burning power plants and other industrial processes. They are typically found in the lowest three to four kilometers above Earth's surface and precipitate out of the atmosphere, typically in about a week. "Because of this short residence time, aerosols are highly variable as a function of location and time, which makes it tough to measure their concentrations on a global scale," Schwartz said.

Schwartz's team has been working for more than a decade to develop and refine a "chemical transport model" to calculate aerosol distribution. The model uses archived weather data and weather prediction models to track the distribution of aerosols from industrial sources to various parts of the atmosphere. "This model is the key to knowing where and when to look for the aerosol effect," Schwartz said.

By analyzing data from the model, the Brookhaven-Purdue team identified two one-week episodes during April 1987 when the modeled concentration of sulfate aerosol over the North Atlantic Ocean -- far from any local sources of aerosol emissions -- increased significantly and then decreased over the course of each week. These large variations in aerosol concentration and the fact that there were no high-atmosphere (obscuring) clouds during these events made them ideal episodes for studying the effect of aerosols on cloud brightening.

The next challenge was to get the data on cloud brightness for that area over the same time period. For this, the scientists retrieved satellite measurements of radiance (how much light the clouds reflect) and optical depth (a value related to how much light is transmitted through the cloud), and used these measurements to calculate the size of the cloud droplets and the liquid water path (the amount of liquid water in the cloud). They were also able to analyze how these variables were related to one another.

The findings show that, for a given liquid water path, cloud reflectivity was indeed higher on the days with higher aerosol content than on the days with lower aerosol levels. "If the effect is as widespread as we think it is, it would produce quite a substantial cooling effect on climate," Schwartz said. "This new study," he added, "provides a method of quantifying the phenomenon globally over the past 15 years using archived satellite data. Once this is done, we will have a much better idea of the true magnitude of the greehnouse effect."

Could aerosols be deliberately employed to offset the greehnouse effect? "This is an attractive thought," Schwartz said, "but it cannot work in the long run -- because aerosols are so short-lived in the atmosphere, whereas greenhouse gases accumulate over time. An ever increasing amount of aerosols would be required. We'd never solve the long-term problem."

Also, says Schwartz, the aerosol effect may have a different geographical distribution from the greenhouse effect, and "the consequence of this mismatch is unknown." One key to assessing the overall impact of aerosols, he said, will be further development of the satellite-based measurements.

This work was funded by the U.S. Department of Energy, which supports basic research in a variety of scientific fields, and the National Aeronautics and Space Administration (NASA).

The U.S. Department of Energy's Brookhaven National Laboratory (http://www.bnl.gov) conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies. Brookhaven also builds and operates major facilities available to university, industrial, and government scientists. The Laboratory is managed by Brookhaven Science Associates, a limited liability company founded by Stony Brook University and Battelle, a nonprofit applied science and technology organization.

www.sciencedaily.com/releases/2002/03/020301071814.htm