Global Dimming

wiredog writes "The Guardian reports on research which shows that the amount of sunlight reaching the Earth's surface has decreased by 10% in 30 years. This has implications for global warming models and, especially, agricultural output."

Full Text

[jhouserizer]

Goodbye sunshine

Each year less light reaches the surface of the Earth. No one is sure what's causing 'global dimming' - or what it means for the future. In fact most scientists have never heard of it. By David Adam

Thursday December 18, 2003
The Guardian

In 1985, a geography researcher called Atsumu Ohmura at the Swiss Federal Institute of Technology got the shock of his life. As part of his studies into climate and atmospheric radiation, Ohmura was checking levels of sunlight recorded around Europe when he made an astonishing discovery. It was too dark. Compared to similar measurements recorded by his predecessors in the 1960s, Ohmura's results suggested that levels of solar radiation striking the Earth's surface had declined by more than 10% in three decades. Sunshine, it seemed, was on the way out.

The finding went against all scientific thinking. By the mid-80s there was undeniable evidence that our planet was getting hotter, so the idea of reduced solar radiation - the Earth's only external source of heat - just didn't fit. And a massive 10% shift in only 30 years? Ohmura himself had a hard time accepting it. "I was shocked. The difference was so big that I just could not believe it," he says. Neither could anyone else. When Ohmura eventually published his discovery in 1989 the science world was distinctly unimpressed. "It was ignored," he says.

It turns out that Ohmura was the first to document a dramatic effect that scientists are now calling "global dimming". Records show that over the past 50 years the average amount of sunlight reaching the ground has gone down by almost 3% a decade. It's too small an effect to see with the naked eye, but it has implications for everything from climate change to solar power and even the future sustainability of plant photosynthesis. In fact, global dimming seems to be so important that you're probably wondering why you've never heard of it before. Well don't worry, you're in good company. Many climate experts haven't heard of it either, the media has not picked up on it, and it doesn't even appear in the reports of the Intergovernmental Panel on Climate Change (IPCC).

"It's an extraordinary thing that for some reason this hasn't penetrated even into the thinking of the people looking at global climate change," says Graham Farquhar, a climate scientist at the Australian National University in Canberra. "It's actually quite a big deal and I think you'll see a lot more people referring to it."

That's not to say that the effect has gone unnoticed. Although Ohmura was the first to report global dimming, he wasn't alone. In fact, the scientific record now shows several other research papers published during the 1990s on the subject, all finding that light levels were falling significantly. Among them they reported that sunshine in Ireland was on the wane, that both the Arctic and the Antarctic were getting darker and that light in Japan, the supposed land of the rising sun, was actually falling. Most startling of all was the discovery that levels of solar radiation reaching parts of the former Soviet Union had gone down almost 20% between 1960 and 1987.

The problem is that most of the climate scientists who saw the reports simply didn't believe them. "It's an uncomfortable one," says Gerald Stanhill, who published many of these early papers and coined the phrase global dimming. "The first reaction has always been that the effect is much too big, I don't believe it and if it's true then why has nobody reported it before."

That began to change in 2001, when Stanhill and his colleague Shabtai Cohen at the Volcani Centre in Bet Dagan, Israel collected all the available evidence together and proved that, on average, records showed that the amount of solar radiation reaching the Earth's surface had gone down by between 0.23 and 0.32% each year from 1958 to 1992.

This forced more scientists to sit up and take notice, though some still refused to accept the change was real, and instead blamed it on inacc

Re:Agricultural output

[Malc]

The global population of people has also multiplied and skyrocketed over the years, no thanks to technology. It rather cancels out the gains in agricultural production.

Re:Global Cooling Theories

[tiled_rainbows]

If you read the article, global dimming does not equal global cooling. It is, in fact, compatible with global warming. The theory is either that (as stated above) atmospheric pollutants are blocking sunlight, or that global warming is resulting in more water vapour being carried in the air - in other words, it's getting cloudier.

Re:Agricultural output

[JPelorat]

Not at all. The problem these days is not quantity of food, but lack of effective distribution thereof.

Re:So instead

[100lbHand]

nope, according to the article only infrared and visable light is getting blocked, UV still gets to the ground

Re:How will H usage affect this?

[mschaffer]

No, it is not more efficient.

Most H2 generated today comes from hydrocarbons. It takes energy to reform the hydrocarbons to make H2 (with CO, CO2, etc. as the usual byproducts). This extra energy produces more H2O (and CO2).

The net result is more H2O from H2 fuel compared to the hydrocarbon fuel used directly.

Author of Article Got it Wrong?

[StarWreck]

Ohmura's results suggested that levels of solar radiation striking the Earth's surface had declined by more than 10% in three decades.

Not a reduction in actual light, but in "Solar Radiation". Solar Radiation includes UV which has been going steadily down since CFC's were banned (in the 60's?). The hole in the ozone is even starting to repair itself!!!!

Re:So instead

[Glock27]

No. The amount of sunlight reaching earth is still the same. The amount reaching the ground is what is decreasing. It is being absorbed elsewhere or being reflected.

Not quite right either. The amount of sunlight reaching the top of the Earth's atmosphere is still the same. The amount reaching the ground is over 10% less than during the 60's. It is not clear how much of the sunlight is being absorbed and then re-emitted as IR within the atmosphere, and how much is being reflected back into space. Snow and clouds both reflect a lot of energy back out of the atmosphere. You mention reflection, but you don't seem to think it could result in net energy loss.

What I'm trying to get at is that if some factor (say cloud seeding from aircraft exhaust, a known phenomenon) is causing more cloud cover, it could well be that the total solar energy absorbed by the ground+atmosphere is substantially less than it used to be. The article wasn't clear on this point.

Re:yeah right

[dhovis]

a lot of pollution comes from Third World countries that have no pollution laws, or don't enforce the ones they have

Don't kid yourself. The US is responsible for a very large chunk of the greenhouse gas output of the world. It is something like 40%. That is despite the fact that the US has around 5% of the world's population.

But through the Nineties, air quality started to get worse again, and we're now just about back to where we were when the laws came into effect. Halve the average emissions, double the population ... the math ain't hard.

Don't forget that average fuel economy of cars sold in the US is at its lowest level in 20 years. Think about that for a moment. The average car sold today has roughly the same fuel economy as a car sold in 1983! Why? Looser resrtictions on "light trucks", because they were used for work purposes. Then the automakers realized they could make glorified station wagons and call them SUVs and sell them as "light trucks", as though they were being used for work. Heck, the Chevy Suburban is so big that it isn't even considered a "light truck" and is therefore not subject to fuel economy regulations at all. For fuel economy purposes, a Suburban is treated as though it were the same type of vehicle as a dump truck.

Re:So instead

[Hittite Creosote]

Whether this is true of IR (which causes the majority atmospheric / planetary heating) and UV (cancer / tanning) spectrum is not touched upon

Yes it is. You haven't actually read the article, have you?

It states -

The missing radiation is in the region of visible light and infrared - radiation like the ultraviolet light increasingly penetrating the leaky ozone layer is not affected.

Sorry to be sarcastic, but you could at least have searched the text for, say, 'violet' before commenting.

Re:Agricultural output

[gobbo]

What evidence is there that modern farming methods are unsustainable?

Good question, though not too hard to research as there's a volume of data and it's a hot issue. Of course, it's controversial, since much of the research is influenced by agribusiness (esp. here in Canada -- AgCan is in industry's pocket) and that means that research is overly reductionist or just plain skewed.

Keywords to look for in your reference search: loss of topsoil in green revolution scenarios (effects of tilling, bare soil, industrial watering, monocrops, heavy feeding crops, pesticides); dependence of farming on chemical inputs; loss of seed sovereignty; crop diversity reduction; the effects of large-scale monocropping on the environment; water usage; permaculture; loss of local knowledge (microclimates, local pest management, seed varieties --again--, plant companions, etc); misguided pest management (overused pesticides etc.); distribution and ownership models that reduce local food security; and so on.

Some good places to start looking outside of google:
Institute for Agriculture and Trade Policy [iatp.org]
Sustainable Farming Connection [ibiblio.org]
FarmFolk/CityFolk [ffcf.bc.ca]
The Ram's Horn [ramshorn.bc.ca]
World Resources Institute [wri.org]
WorldWatch Institute [worldwatch.org]
Pesticide Action Network [panna.org]
Sustainable Agriculture Network [sare.org]
Permaculture [ibiblio.org]
ETC Group [etcgroup.org]

There, that should get you started. You want evidence? there's plenty out there.

The science behind contrails

[G4from128k]

I'm no climate scientist, or climate engineer, but it seems to me that dark |= cold. A greenhouse can be dark but hot. The gasses keep in the heat, yet keep out the light. Venus springs to mind.

Scientists have been debating this one quite a bit -- whether cloud's reflection of the sun light creates more cooling than the cloud's night-time heat-trapping abilities. The suspension of airtravel around 9-11 gave scientists a chance to study this [sciencenews.org]. They found that the absence of contrails created pronounced higher daytime highs and slightly lower nighttime lows. At least for contrails, the net effect seems to be a reduction in average temperture.

Admittedly, this is only a single study. The point is that intuitions about clouds reflecting energy vs. greenhouses retaining energy only provide insight into potential qualititive outcomes. The real quantitative answer may be different depending on the numerical balance of all the effects.

Re:Interesting Statistic

[grgyle]

No, finding the size of area required to supply the US energy needs is a common text problem in almost any college astronomy or phsics course. Here is a link to a calculation example. Assuming 10% efficiency, the area required to power the US would require an installation half the size of Colorado . This is vastly larger than 200 sq miles. http://www.colorado.edu/GeolSci/courses/GEOL3520/T opic6/Topic6.html

Re:The unintended benefits of pollution

[Azghoul]

Any 3 year old wouldn't have a clue.

Clear skies generally indicate high-pressure systems, usually coming from northern areas over land.

Cloudy skies generally indicate the approach of a differently-pressured system.

Come to the Washington, DC area. Cloudy days mean cooler weather, and usually rain.

If you are speaking of night-time effects, you are right that clear skies will indicate cooler temperatures than cloudy skies, but there is no "INCREASES" going on. The cloudy skies simply trap more of the daytime heat, letting less escape into the upper atmosphere.

Re:Interesting Statistic

[Skim123]

It's been a while since high school physics, but isn't there a loss in the energy when transmitting electricty over long distances? That is, it wouldn't be plausible to build one huge-ass power plant in the middle of the US and have it serve as a power source for all of North America. If this assumption is correct then it's quite clear why we can't just appropriate the bottom half of New Mexico for one giant solar cell.

Re:So instead

[cev]

I AM an optical scientist, so I'll fill in a few gaps that are not covered in the article, and are often misrepresented. The phenomenology of propagation through the atmosphere is very different for longwave infrared, visible (& shortwave infrared), and ultraviolet (UV). That is why it is possible to have global warming with decreasing sunlight, and increasing UV.

NOTE: when I say 'atmosphere,' I mean the part where most of the air is, i.e., just the stratosphere and troposphere. Don't be a snot about the "exosphere".

1. Most of the energy reaching the earth from the sun is in the visible and near IR wavelengths. The atmosphere is nearly transparent to these wavelengths, so a lot of the sun's energy reaches the surface of the earth. Scattering from particulates (e.g. pollution, volcanic material, water particles, etc.) is the primary loss mechanism for sunlight. Most of these particulates are close to the ground, or well-distributed through the atmosphere. Therefore, nearly all of the sunlight gets close to the earth.

2. Dangerously short wavelengths (cosmic rays, x-rays, gamma rays, hard UV) are scattered and absorbed at the cusp of earth's atmosphere. Almost none reaches even the lower atmosphere. Soft UV is predominantly absorbed by ozone. The atmosphere itself scatters short wavelengths very well (thus, blue sky).

3. Excepting a few 'windows', the atmosphere is opaque to longwave infrared light. Earth emits long-wave IR light due to its low temperature. Longwave IR light from is absorbed in the atmosphere, preventing the earth from cooling itself. This is the 'greenhouse effect.' Since the atmosphere is so opaque to longwave-IR, the greenhouse 'panes' are pretty much at the edge of the atmosphere.

4. The article presents research which raises the possiblity that increased pollution (possibly) is causing more solar energy to be absorbed in the lower atmosphere. Global warming is still possible since the lower atmposphere is still 'inside' the greenhouse, so the extra abosrbed energy is still contributing to heating. UV light is being absorbed by the particulates as well, but not enough to offset the damage done to the ozone layer.

6. Do I believe the article? A little bit. The main point is that a previously crazy idea was corroberated very well by a second, independent measurement (evaporation). Two improper experiments are much less likely than one. Still, 10% seems pretty big.

CV

Re:Not enough data

[barakn]

Until we have thousands of years worth of data, observed from outside the atmosphere, we can't prove that solar radiation is a constant.

It's not constant [noaa.gov], and so it only took several decades to prove it.

Nuclear decay == Remains of a supernova

[penguinoid]

No, the radioactive elemants in the earth's core did not come from the sun. They formed from the same cloud of gas as the sun did (from the remains of a supernova IIRC).

As to saying that radioactive decay is non-renewable, that is rediculous. It will always be there (unless you're looking at millions/billions of years in the future, and you might as well be worried about the sun burning out or exploding by then. You might as well consider the sun to be non-renewable on that timescale, as well.

Re:Interesting Statistic

[FJ]

My apoligies for a blanket statement. Next time I'll do more research. I always thought that the same thing that made the hydrogen a good fuel made it more dangerous (I could have sworn I heard this in high school chemestry, but I'm old).

I did a quick google search & found this. Very informative.

http://www.e-sources.com/hydrogen/safety.html

Thanks for catching me on this. I can say I learned something new today.

Re:Interesting Statistic

[I8TheWorm]

Except it's been decided that the cause was not the hydrogen, but rather the prevailing atmospheric conditions and the unorthodox method of landing at Lakehurst [hydrogenus.com].

Observations of the incident show evidence inconsistent with a hydrogen fire: (1) the Hindenburg did not explode, but burned very rapidly in omnidirectional patterns, (2) the 240-ton airship remained aloft and upright many seconds after the fire began, (3) falling pieces of fabric were aflame and not self-extinguishing, and (4) the very bright color of the flames was characteristic of a forest fire, not a hydrogen fire (hydrogen makes no visible flame). Also, no one smelled garlic, the scent of which had been added to the hydrogen to help detect a leak.

Or were you being sarcastic and I missed it?

Re:Driving a Truck Through This One

[PrionPryon]

The premise of nuclear winter is that the atmosphere absorbs all incoming solar radiation. The surface and the atmosphre then reach a radiative equilibrium through long wave emission. The equilibrium temperature of the surface is then the same as the planet's (as a whole) measured emission temperature from space. That is, 255 K. Average surface temp today is ~288 K. Increase atmospheric absorbption leads to decreased surface temps.

Re:Interesting Statistic

[Firethorn]

Huh, recently I saw an article about the Australians putting up a new 200MW solar plant [bluefish.org]. This plant was expected to produce 650GW/h a year. Out of curiosity, I looked up the power production of the US, and did some calculations. It came out to replace US power production with solar like the proposed plant would require 83k square miles (2% of the USA's area). Note: This is a reflective plant, that directs solar energy to a central tower, that then uses the heat to drive a standard steam cycle generator. The cost would be about 3 trillion dollars for the number of plants required. Don't forget that you'd still need to figure out a way to power places during the night/cloudy days.

I also figured it out for the south african pebble bed reactors. Replacing the entire US power generation system with these plants would only cost 500bil-1tril(figuring 2x cost from south africa). It was something like 2.5k plants to produce this much power, but they don't cost that much per MW.

I think that the best use for nuclear waste is recycling to reclaim useful isotopes, then glassification of the true waste, then burying it in a subduction trench.

Re:Interesting Statistic

[rossifer]

Actually, the fact that the skin doping was a highly flammable lacquer, akin to gasoline, seems to have had more to do with the flammability of the Hindenburg's fabric envelope than the hydrogen inside.

They painted the entire fabric skin of the ship with explosively flammable paint/sealant and they were suprised when it burned so readily.

Helium in the envelope wouldn't have saved the Hindenburg. But it was a convenient explanation at the time.

Regards,
Ross

Venus - No Direct Sunlight But Hottest Planet

[meehawl]

It's interesting to note that Earth's closest twin planet in terms of position and size is Venus, where a runaway Greenhouse Effect keeps surface temperatures around Venusian a toasty 480C (894F) but the entire planet is mired in a perpetual twilight gloom (verified by the Russian landers [google.com]) due to the extraordinarily thick atmosphere (around 9000 kPa or around 90 times Earth's atmospheric pressure). Venus's oceans long ago boiled away in this runaway Greenhouse Effect [google.com]. The oceanographic runaway Greenhouse Effect begins to occur over large bodies of water at around 27C (80F) [google.com]. Even ignoring current human-directed climate change, the increasing solar output of the Sun as it moves along a typical Main Sequence stellar evolutionary path [google.com] means that sooner or later the Earth's oceans will also vaporise and temperatures soar quickly to Venusian levels. Strange days indeed lie ahead of us...