global dimming

December 19, 2003 4:47 AM

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 an extraordinary thing that for some reason this hasn't penetrated even into the thinking of the people looking at global climate change. It's actually quite a big deal and I think you'll see a lot more people referring to it."
posted by stbalbach (15 comments total)

We have accurate measurements of this spanning 50 years?
posted by RavinDave at 5:16 AM on December 19, 2003

Interesting article, thanks stbalbach. I guess I was wrong when I said my future's so bright I've got to wear shades.

RavidDave, read the article. At least one scientist does question the accuracy of the historical data. The apparatus is simple enough though. A black plate is placed in the sun and it's temperature is recorded. I would think that you could apply math to determine the amount of sunlight from the temperature difference. Sources for inaccuracy would be your temperature measuring device, the properties of your black plate, the blackness of your black and the thermal junction coefficient between the black material and the plate itself.
posted by substrate at 5:30 AM on December 19, 2003

This is all fear-mongering. You and the people who created this study are just Chicken Littles. We need to do nothing about this, since doing anything at all might inconvenience me. This country was built on freedom, and you have no right to stop me from turning the planet into an inhospitable shit hole.

And a few years later, if it looks like these folks are right, I'll become more resolute and argue that light is actually bad for you. It says so in the bible. It says a lot of stuff, so it must say that.
posted by Mayor Curley at 5:51 AM on December 19, 2003

This strikes me as very strange. If this is an issue of more clouds due to pollution, that should have easily been noticed from satellites and radar over the past twenty years. If it's in clear air, the magnitude is so huge it should be easy to put up some more sophisticated instrumentation and run it for a couple of years to see if this is real.
posted by cameldrv at 6:08 AM on December 19, 2003

This doesn't bode well for people suffering from Seasonal Affective Mood Disorder. People are getting crankier and meaner - it wasn't just my imagination - it's the light!

Mayor Curley - You're pushing that art form to new heights. Does it have a name? It should.

cameldrv - It wasn't more clouds but darker ones. This is a great article, stbalbach. The important point, to me, is that - the article notes - the solar radiation hitting the Earth is believed to have increased over the past 150 years - "...The global dimming effect is much, much larger and the opposite of what would be expected given there has been a general increase in overall solar radiation over the past 150 years. " It's just that the composition of the atmosphere has changed and is blocking out more light. Still, it is odd. You would have thought more people would have noticed.

This raises the following point - if a giant, grotesque, faint but distinct visage of Osama Bin Laden were to appear in the sky over North America, mocking us, would people even notice that? Or do we notice sudden changes, even minor ones, but completely miss gradual changes - even if these add up to to major shifts over time? I haven't heard many people talk about the new "Kudzu of the Northeast", Japanese Knotweed, but the damn stuff is everywhere - enveloping trees and hedges, practically unkillable (unless uprooted and burnt). I live smack in the bulls-eye of the epicenter. My backyard is starting to resemble Kudzu-covered Georgia.

As soon as I saw this article, I thought : particulates. soot. Indeed, I was right - mostly - but this raises an interesting question. The article notes that the dimming trend seems to have reversed itself, at least over northern latitudes, probably in response to reduced pollution from pollution control legislation. Cleaner cars and cleaner stacks.

So...umm - China?.....India?.....Mexico?.....What effect will 2 billion rapidly industrializing, coal burning Chinese and Indians have? They could just stop Global Warming in it's tracks, I suppose (until they get tired of the dirty air, that is). Except - this process has been ongoing, and the Earth still seems to be warming.

I guess this means that - although less solar radiation is reaching the ground overall - atmospheric muck and increased levels of Greenhouse gasses are trapping more of that heat energy.

One of the ironies of this story is the fact that it just might be one of the most significant missing factors explaining the divergence between warming predicted by computer climate models and warming actually observed - pollution serves as a partial "self quenching mechanism" in the equation [ quick - Call Jerry Lindzen over at MIT! ]. Until humans get tired of breathing in dirty air and pass pollution control laws, at any rate. Then the Greenhouse really kicks in.

I'd be willing to guess that the campaign to discredit global climate modelling - in the decade from the early 1990's to the present and led by a handful scientists financed by petrochemical dollars - made the climate modelling researchers shore up the ramparts a little too aggressively. Did they reject the "Global Dimming" factor for fear that it would advance the contrarian/skeptic agenda of "disproving" (in the public mind anyway) Global Warming?
posted by troutfishing at 7:26 AM on December 19, 2003

MetaTalk.
posted by Slithy_Tove at 7:51 AM on December 19, 2003

It's not at all clear that this is caused by human activity. For one thing, if humanity was increasing the planet's albedo, we'd be worried about global cooling, not warming. Furthermore, natural vulcanism puts more gunk in the air than we do. To give a recent example, Mount Pinatubo had more effect in two years than humanity has (possibly) had in a half-century of CO₂ production.

The role of solar variation in climate modeling is unclear, or not even considered in many models. The interplay between CO₂ concentrations, atmospheric particulate concentrations and solar variation is far more complex, I think, than the simple CO₂ emissions==warming equation that is current.

The planet is undeniably warming, but I don't think the models are good enough yet for us to really understand why. It's always struck me as simple human arrogance to assume that we are the sole cause, or even a major factor in climate change.

Here is a nice backgrounder on other levers on the climate other than "greenhouse" warming.
posted by bonehead at 7:55 AM on December 19, 2003

bonehead - I agree that there are lots of levers on climate besides "Greenhouse" gasses. But the article doesn't actually say anything about humans increasing the planet's albedo. I don't think that's the mechanism at all. Most clouds are translucent, to an extent. So what happens if they are "seeded" by darker particulates which make them a little less translucent? - Well, those particulates absorb the solar radiation and warm up, and then release it. Since that radiation is being released higher up in the atmosphere, more of it can escape into space. In the Earth's overall "heat budget" - the ratio of incoming solar radiation to the rate at which that radiation is released back into space - an increase in cloud particulates would tend to increase that rate. So - cooling, but not from an increased albedo. The issue at stake is the ability of sunlight to penetrate cloud cover and reach the ground.

Anyway - sure, vulcanism puts more junk in the air than humans - and sometimes spectacularly so. Indeed, the Pinatuba eruption coincides perfectly with an observed decline in the earth's average temperatures - for between five and ten years. BUT.....if the average, background level of vulcanism holds steady but anthropogenic pollution increases, it will still exert a significant effect. I've heard it estimated that global human C02, NOx, particulate emissions, and so on, amount to something on the order of the eruption of a mid-sized volcano per year. OK - but we do it year after year after year.......

We are indeed now a major factor in climate processes - not that there aren't other major factors, of course there are - but that's exactly the point of the article - we're at least partially responsible, for example, for a significant decrease in ground level sunlight.
posted by troutfishing at 8:30 AM on December 19, 2003

...the article doesn't actually say anything about humans increasing the planet's albedo. I don't think that's the mechanism at all. Most clouds are translucent, to an extent.

Not at all. Clouds are a major component of the planet's reflectivity. See here for a discussion of the role clouds play in the the earth's radiation budget. Clouds can have a warming or cooling effect depending on their altitude and the surface they cover, but generally the low-lying, high particulate clouds caused by polution (such as the yellow haze currently over the parts of the Indian Ocean and the South China Sea) are net coolers.
posted by bonehead at 8:59 AM on December 19, 2003

bonehead - Of course they are. As I said, this is about where the solar radiation is absorbed and then re-emitted - in clouds, or at the ground level.

"generally the low-lying, high particulate clouds caused by polution (such as the yellow haze currently over the parts of the Indian Ocean and the South China Sea) are net coolers." - Exactly.
posted by troutfishing at 9:23 AM on December 19, 2003

Bonehead - Thanks for the link. OK - I figured out what is going on here. We're talking about two different mechanisms at play I think, Reflection vs. Absorbtion. What stbalbach's linked story doesn't make clear though is whether the enhanced cooling is from a low-cloud or a high cloud mechanism. And - is it about my hypothesis that cloud albedo is decreasing so that clouds - high or low - suck up more solar energy and then radiate it back out to space? Or are there just more clouds!

*slow drum roll*
posted by troutfishing at 9:59 AM on December 19, 2003

What stbalbach's linked story doesn't make clear though is whether the enhanced cooling is from a low-cloud or a high cloud mechanism.

That's really my point.

I work on the edge of the modeling community and have seen the struggles they go through. Getting a model right is really, really hard, particularly if you don't have great data. Until recently, for instance, hurricanes were not really predicable with macro climate models. Ocean convection has only just been put into climate models. Much of this has to do with computing power and how many grid points modelers can include. We are still in early days, believe it or not.

One of the key points of stbalbach's link was that no one knows the effects that this will have on climate models. There's only minimal data (stuff from even a decade ago can be suspect), and no good model of cause.

One of the key things to do when looking it things like these is to keep an open mind about them and evaluate them on their merits alone. We simply don't know right now enough to do that. That isn't to say that the Kyoto accord isn't a good idea, but don't be too surprised if, in humpty-dump years time we get told that CO₂ isn't the main problem after all, but H₂O, or particulates or solar variation, or something else.
posted by bonehead at 10:47 AM on December 19, 2003

Since accurately modelling climate is such a hard thing to do, why not focus on local climate issues like air pollution? Everyone can agree this is a bad problem and an immediate threat to health.

For example, one quarter of the world cooks its food in poorly ventilated huts using animal manure or scavaged wood from rapidly shrinking local forests. The implications for lung health are horrible in such conditions. Imagine a 30 something year old, who has survived by beating the odds against disease, over work, and exploitative social systems, but whose capacity to work and live is never the less destroyed by years of inhaling cook fumes.

At the same time rich world farmers are paid huge subsidies to overproduce grains that are dumped on these very same third world markets, destroying their native food producing economies.

Why not pay rich world farmers to grow woody crops (willow, cottonwood, alder, etc.) that can be converted to charcoal and them 'dumped' on third world markets? This charcoal (being pure carbon) would burn much more cleanly than any locally scavenged fuel sources, thereby preserving lung health AND displacing third world deforestation, not food prodcuers.

Everybody wins - politically powerful rich world farmers get to keep their subsidies, third world famers' grain markets are not disrupted, lung health for the world's most vulnerable improves greatly, some of the pressure is taken off tropical forests, and you preserve a sustainable, non fossil fuel economy. Oh, and forest cropping is vastly better for the environment and wildlife than monoculture cropping.

Nobody looses anything that they have now, and everyone wins.

Well, there's one drawback: greenies and capitalists would be working together instead of demonizing each other, which often seems to be a motivator for both groups.

It's just an idea, but if we put just a part of the effort we spend on arguing about future climate into finding solutions for today's pollution just think of what we could do.
posted by Jos Bleau at 12:53 PM on December 19, 2003

Jos Bleau - That.....that...that.....Sounds like a Bjorn Lomborg point. nooo, demon spawn spewed up from fiery HELLL...nooooo....

Actually, I think those are brilliant ideas. Sometimes practical solutions are just so.....practical. And if they come out of Lomborg's mouth (or whoever's) they're still good.

"....greenies and capitalists would be working together instead of demonizing each other" - That would be great, especially because of lot of brilliant ideas are being bypassed for the stigma (to some in the business community) of being "green" (cut to Kermit the Frog song "It's hard to be green")

"That isn't to say that the Kyoto accord isn't a good idea, but don't be too surprised if, in humpty-dump years time we get told that CO2 isn't the main problem after all, but H2O, or particulates or solar variation, or something else." - Bonehead, or maybe we'll be attempting to fight off an impending ice age, frantically feeding vast herds of cows to make them belch out more methane....Who knows?

The modelling community is often in a tight spot, I sense - from one side they get criticized for the validity of their models, and of course the science is in it's infancy......but Global Warming seems pressing to many......Would you be inclined to say that some modellers you've known would be more reticent about current drawbacks in modelling (or modelling's very prelimary state) because of outside criticism?.......I'm curious what you think.
posted by troutfishing at 5:00 PM on December 19, 2003

Jos Bleau - BTW, I didn't mean to suggest that those weren't your ideas.
posted by troutfishing at 5:04 PM on December 19, 2003