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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."
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
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.
evil math within Nature's Cubic Creation!
Not at all. The problem these days is not quantity of food, but lack of effective distribution thereof.
Hokey statistics and ancient misconceptions are no match for a good thought in your head, kid!
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.
Galileo: "The Earth revolves around the Sun!"
Score: -1 100% Flamebait
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.
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.
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The internet is the greatest source of biased information in the history of mankind.
Yes it is. You haven't actually read the article, have you?
It states -
Sorry to be sarcastic, but you could at least have searched the text for, say, 'violet' before commenting.
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
Sustainable Farming Connection
FarmFolk/CityFolk
The Ram's Horn
World Resources Institute
WorldWatch Institute
Pesticide Action Network
Sustainable Agriculture Network
Permaculture
ETC Group
There, that should get you started. You want evidence? there's plenty out there.
Damn those pesky terrorists
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
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.
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.