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A simple -- yet interesting -- model for the greenhouse effect
realclimate.org — So how simple can you make a model that contains the basic greenhouse physics? Pretty simple actually. You need to account for the solar radiation coming in, the longwave radiation coming from the surface, and some absorption/radiation of longwave radiation in the atmosphere. There will be mathematics, but hopefully it won't be too painful.
burkinaboy- 265 diggs
- digg it
- mtb167, on 10/12/2007, -5/+11Where are all the fancy pictures, and animations of the earth sizzling like a strip of bacon?
- snapneck, on 10/12/2007, -2/+8They've been substituted by all the cool math.
- Fordi, on 10/12/2007, -2/+5Ah, the article doesn't state anything definitive about the effects of global warming; it's just a beautiful example of the simplest form of climate model, using global warming as a pertinent example.
- adsoftheworld, on 10/12/2007, -3/+4No need to worry! Michelin's road of tomorrow will save us: http://www.michelinman.com/forward/
And animals will evolve: http://adsoftheworld.com/media/print/whale_and_dolphin_conservation_society_pollution?size=_original- Twango, on 10/12/2007, -0/+2First, from what I've read, catching 20% of the world's wind energy would provide the energy for all human activities, not just electricity. If that much wind were captured, 80 percent of the winds would remain.
Second, the theoretical max for wind energy extraction is said to be 59 percent. Today's mills capture about 50 percent.
The energy in oceans (tides, currents) is much greater. Water is 1000 times denser than air, so it has much more energy at the same speed.
There's no one solution; it's a matter of finding the right mix. In some places (Demark, >20 percent; Germany, 14 percent) wind is already a significant part of the mix.
- Twango, on 10/12/2007, -0/+2First, from what I've read, catching 20% of the world's wind energy would provide the energy for all human activities, not just electricity. If that much wind were captured, 80 percent of the winds would remain.
- adragons, on 10/12/2007, -16/+6Too bad it doesn't include things like
forest fire smoke polution
volcano ash,
wind farms slowing down the wind
space cooling down the outer atmosphere
cows/methane etc... etc...
And thats why I don't think anyone has 'proved that we cause global warming'.- GrahamStw, on 10/12/2007, -6/+10"wind farms slowing down the wind"
Errrr... what now? - Lyph4, on 10/12/2007, -7/+4Wind farms actually do slow down the wind a LOT. Wind farms actually do a LOT of harm to the environment.
Lets just go with some pebble bed reactors and get this ***** over with. - SEMW, on 10/12/2007, -2/+8> And thats why I don't think anyone has 'proved that we cause global warming'.
Ummm...
The article wan't trying to "prove global warming". It was about the construction of a basic mathematical model in order to illustrate certain principles of mathematical modelling.
Obviously the model they constructed wasn't anywhere near advanced enough to make a prediction on global warming. Forget wind farms, they didn't even model convection. It was a tutorial. - Fordi, on 10/12/2007, -0/+6@Lyph4:
A wind farm must, by sheer physics, slow down wind what passes through it. I would be interested in knowing how much kinetic energy is available in the wind at a given windspeed, what the losses are in a horizontal-axis / vertical axis wind turbine, and how to calculate the energy-transfer curve between the wind and wind turbine.
If we're going to show environmental damage from an energy source considered innocuous, the burden of proof is on us. - SEMW, on 10/12/2007, -1/+6On a lighter note:
Adragons' Physics teacher: "And now, we're going to model the Earth and the sun as particles of constant mass, neglecting relativistic effects, and show how even this simple model can explain the circular orbit of the Earth."
Adragon: "What? But you've neglected the effect of wind farms constantly slowing down the wind, which will mean that by E=mc^2 the Earth's mass is constantly decreasing! You're results are useless! I don't think you've proved relativity at all!"
Adragon's Physics teacher: "Ummm... What?" - duhblah, on 10/12/2007, -1/+3Surely trees slow the wind down as well. Lets chop them all down.
- GrahamStw, on 10/12/2007, -1/+5I'm not arguing that wind farms don't slow winds, they must cause some effect, but are people actually claiming that this is causing significant environmental damage?
Surely the speed of wind is also changed when it hits other obstructions like trees, cliffs, mountains, houses etc? - SEMW, on 10/12/2007, -1/+5The wikipedia article on wind power (http://en.wikipedia.org/wiki/Wind_power) is nicredibly detailed and comprehensive, including long writeups of criticism of wind power (seperate paragraphs on Ecological footprint, Land use, Impact on wildlife, Aesthetics...); and there's nothing there about any environmental impact from them slowing down wind -- and I can't imagine how there would be any.
- Manhigh, on 10/12/2007, -1/+3I've thought about the wind farms slowing down the wind issue...
Now I'm not so sure its such a big deal, for two reasons:
1.) Planting trees would have a similar affect, removing wind energy via drag. AFAIK more trees was never noted to be a bad thing.
2.) Wind is driven by thermal differences. It would seem that the wind will continue to blow until equilibrium is achieved. So it may take longer for that to happen, but probably not much. - ajkrik, on 10/12/2007, -0/+1The point of the wind comment is that if you took advantage of 20% or the world's wind (gotta laugh) to produce energy, it would have to have some impact on the flow of air and that kind of stuff . . . temp distribution. It's really not such a bizarre theoretical question.
- GrahamStw, on 10/12/2007, -6/+10"wind farms slowing down the wind"
- chingy1788, on 10/12/2007, -0/+3Ahh!!! Physics, thermo dynamics
the things I just got a hairline Pass in... - DaveV, on 10/12/2007, -2/+6unfortunately, simple models of complex interactions are often wrong.
- magicjava, on 10/12/2007, -4/+12Quotes from the article...
Quote - "Note that this is just going to be a qualitative description and can't be used to quantitatively estimate the real world values."
Quote - "Again, I should stress that this is not an estimate for the real Earth!"
Quote - "In this example it's cooler because of the radiative balance, while in the real world it's cooler because of adiabatic expansion (air cools as it expands under lower pressure) modified by convection."
Quote - "While this is just a simple model that is not really very Earth-like "
Unfortunately, while the author makes it clear his simplified presentation cannot represent the real climate, he never mentions the complex models can't represent the real climate either.- SEMW, on 10/12/2007, -2/+7I'm glad you've reiterated that TFA wasn't intended to be an accurate, predictive model -- a surprising number of posters have seemingly failed to realise this (e.g. adragon) -- but I'll have to disagree with you regarding your assertion that "complex models can't represent the real climate either."
Obviously, a model of highest possible complexity (i.e. one that models every particle as a single particle, and models all the forces on it from every other particle) would be completely accurate, because it would be identical to reality. Obviously, such a model is impossible; not just practically (for obvious reasons) but theoretically as well (by Heisenberg we could never know the exact position and velocity of even a single particle, let alone all of them).
Thus, the question becomes: what simplifications can we apply to that model that will result in the least reduction of accuracy?
Obviously, the biggest simplification is to draw a distinction between weather and climate. This is an extremely useful distinction, because weather is extremely chaotic, in the mathematical sense (i.e. it takes x times more information and computing power to predict the weather y+1 days in advance as y -- exponential growth) in a relatively short period of time. Climate, on the other hand, is much, much less chaotic -- I may not know what the weather will be next month, but I know that next summer will be warmer than next winter. Seperating weather and climate also allows you to consider the Earth as an energy system -- which is essentially what they've done in TFA -- and make progressive refinements to that simple model in order to gain accuracy.
In other words, as long as you bear in mind the limitations of whatever model you are using, and the more fundamental ones imposed by chaos theory; climate modelling is a very, very useful tool; and the assertion that "complex models can't represent the real climate either" is frankly a load of crap. - andyd273, on 10/12/2007, -0/+5You just have to remember to check your models against the real world every once and a while.
Dang, it was supposed to be sunny today! Stupid TV5...
The further ahead you try to predict, the more mistakes appear from your simplifications.
And you have to take all models with a grain of salt. - magicjava, on 10/12/2007, -1/+1semw, could you provide a list of climate models that are capable of modeling thunderstorm cells?
- Isidore, on 10/12/2007, -1/+3A quantitative model is a quantitative hypothesis. We have observed historical climate data over the last 150 years which we can test against climate models/hypotheses. A climate model which 'simulates' (fits) past observations better than another is more likely to be true. There are too many variables so some approximation is inevitable.
The climate debate is about whether there is a significant human cause of current global warming.
- Climate skeptics no longer doubt that the earth is warming, they claim the causes are purely natural eg sunspots and volcanoes.
- The IPCC does not doubt that there are natural causes of recent global warming but they claim 90% certainty that this warming has a significant human cause.
These competing hypotheses can be tested by quantitative models see UK Met Office Climate Change Myths.
http://www.metoffice.gov.uk/corporate/pressoffice/myths/index.html
The two graphs next to Myth 2 show that natural causes alone cannot explain the increase in earths temperature since about 1975. But If human factors are added to natural causes we get a much better fit to the observed data.
AFIK climate skeptics have not been able to provide a quantitative model of natural-only causes which fit the observed data so well. Please correct me if I'm wrong.
This is the key data the climate skeptics on Digg and other places ignore, instead they attack the straw man that ALL climate change is man-made. - magicjava, on 10/12/2007, -1/+2isidore:
Quote - "care should be taken not to over-interpret good agreement between climate models and past observed global mean warming, with large uncertainties in climate forcings, especially that due to aerosols, agreement when models include all the most important anthropogenic and natural forcings could be obtained fortuitously as a result of, for example, balancing too much (or too little) greenhouse gas warming by too much (or too little) aerosol cooling."
Stott, P.A., Mitchell, J.F.B., Allen, M.R., Delworth, T.L., Gregory, J.M., Meehl, G.A. and Santer, B.D. 2006. Observational constraints on past attributable warming and predictions of future global warming. Journal of Climate http://www.gfdl.noaa.gov/reference/bibliography/2006/pas0601.html
The question then becomes, can these models predicte climate they weren't built from, such as the beginning or end of an ice age. The answer is, as I'm sure you know, they can't. - magicjava, on 10/12/2007, -1/+2andyd273, I agree with you completely. Unfortunately, the models aren't taken with a grain of salt. These speculative models are combined with speculative models of economics and speculative models of biology, ecosystems, and evolution, and cast 100 to 500 years into the future and the result is treated with grim seriousness.
- Isidore, on 10/12/2007, -1/+2magicjava
you make a valid point - as-yet-unknown or under-estimated factors may also be contributing. I agree that the models cannot conclusively prove human-caused climate change, that is why the IPCC are only 90% certain of a human cause. We would need to do many repeatable experiments on hundreds of identical planets and suns over centuries to establish this with full 'scientific certainty'. In the mean time we need to test as many factors as possible and refine the models to take account of say aerosols.
The models seem to falsify the view that natural factors alone can explain recent climate change.
Modeling the past is a separate matter from extrapolating future trends, which I agree are more complicated. The range of outcomes seem to range from bad to terrible.
The warning bells are ringing loudly enough for the precautionary principle to apply. - Arrhenius, on 10/12/2007, -0/+2@magicjava
"could you provide a list of climate models that are capable of modeling thunderstorm cells?"
As I'm pretty sure you know, climate models operate on too coarse a resolution to be able to model individual thunderstorm cells. A more interesting question is how much does this matter? An individual storm has little impact on the total heat in the combined ocean-atmosphere system - weather does serve to transport heat both vertically and horizontally and that in turn influences how efficiently the Earth cools due to radiational cooling. Thus they need to is estimate average level of storminess in order to estimate heat transport. In the end, its all about total energy in vs total energy out and individual weather events don't matter very much.
"The question then becomes, can these models predicte climate they weren't built from, such as the beginning or end of an ice age. The answer is, as I'm sure you know, they can't."
Its true that models are designed around today's world and naturally won't do as well when conditions are much different. You can't do the ice ages without handling the ice sheet issues and resulting ice albedo feedback. My understanding is that is an active area of current research.
Going in the other direction, the models currently don't attempt to handle feedbacks such as the release of CO2 or methane from thawing permafrost. I don't understand why this should be used an excuse to do nothing about GHG emissions - virtually all of the "known unknowns" point in the direction of greater warming, not less. Skeptical scientists (the few that are left) have been trying to identify negative feedback mechanisms for 15-20 years now - with a notable lack of success. - magicjava, on 10/12/2007, -1/+2isidore, that study I linked to isn't saying there are unknowns. It's saying, in English, that on a computer model you can twiddle the numbers any way you want until you get the results that match your dataset. That doesn't mean you've modeled the actual climate. I just means you've twiddled numbers until you've gotten a match. The way to test if you've actually done a model or just twiddled numbers is to test against other datasets. When we do those tests, the models fail.
Arrhenius, clouds will affect the models. More low level clouds means less energy enters the system. Less of these clouds means more energy enters the system. Vegetation, ice cover, and oceans are more examples of things we can't accurately model. When you look at a picture of the Earth, you'll see that the portion covered in clouds, oceans, ice, or vegetation is basically the entire planet. - Arrhenius, on 10/12/2007, -0/+2Our modeling of ocean currents may be imperfect, but I don't see that how that would have an impact on ocean albedo. Not much trend in overall cloud cover has been noticed in the last 30 years of warming. If anything, the observed trend has been negative, but that has been recently disputed as an artifact of satellite viewing angles. Any error in modeling ice cover is overwhelmingly considered to be on the conservative side. I think you're right about vegetation changes not being modeled, but is there any reason to believe that this is going to be a large net effect?
- SEMW, on 10/12/2007, -2/+7I'm glad you've reiterated that TFA wasn't intended to be an accurate, predictive model -- a surprising number of posters have seemingly failed to realise this (e.g. adragon) -- but I'll have to disagree with you regarding your assertion that "complex models can't represent the real climate either."
- billlyboobs34, on 10/12/2007, -2/+3Plus there's that tiny little bit of information that says the greenhouse effect will cause a higher rate of warming in the middle of the troposphere and yet here in the real world we aren't seeing a greater rate of temperature increase. Every model of greenhouse effect, while they may be true, are basically proving that global warming is not being caused by the greenhouse effect.
- Arrhenius, on 10/12/2007, -0/+2Greenhouse gas theory predicts that the LOW troposphere will warm, but the MID troposphere will stay about the same. The warming in the low troposphere has been observed in the satellite data.
The satellite data also shows stratospheric cooling, which is predicted by greenhouse gas theory and is totally incompatible with theories based on the (unobserved) warming of the Sun.
- Arrhenius, on 10/12/2007, -0/+2Greenhouse gas theory predicts that the LOW troposphere will warm, but the MID troposphere will stay about the same. The warming in the low troposphere has been observed in the satellite data.
- GrizzWolf, on 10/12/2007, -7/+2It's April 11 and there is anywhere from 1 to 6 inches of snow here on the ground. (Chicago area).
Coldest April ever.
To hell with your greenhouse and global warming theories.- Lyph4, on 10/12/2007, -4/+6The funny thing is, if we have an odd-ball 60 degree day (I'm in New England) everyone's ranting about global warming and all that *****, but the next day when it's back to the normal 20-30 degrees, nobody says anything.
Also, check your historical documents about hottest and coldest records. Western MA was in the 80s a few days back in 1949 during April.
Short term stuff doesn't mean ***** to the climate. Just because it's hot now doesn't mean it's a warming trend.
Even if global warming WAS real, you wouldn't be seeing 80 degrees in April, you'd be seeing a global temperature of +1 degree above normal in 100 years.
Seriously, look at the crazy ***** you people quote out of context. +1 degree in 100 years is a lot, yeah, but who's to say it's not a normal warming/cooling trend?
Guess work and black magic is all you guys have to go on.
And no, I'm neither a Republican nor a Christian. I'm an atheist anarcho-capitalist. - Fordi, on 10/12/2007, -0/+4@lyph:
My girlfriend's mom has a theory: The seasons are shifting forward, and no one seems to notice. And I'm inclined to agree, at least from personal experience; we have summer-like fall, fall-like winter, winter-like spring, and spring-like summer for a good month before each season really gets going.
Apply CO2 as an insulator, and this makes sense; temperatures don't rise, they just linger.
I'd love to see a study done on this.
Meanwhile, my fellow atheist, are you a rational anarchist? - davesbrain, on 10/12/2007, -0/+3@Lyph4
Could be the overall warming trend over the last hundred years has caused the jet-streams to shift and what we're seeing is the radical changes in temperatures resulting from the quick influx of arctic air from Canada, or warm humid air from the southern USA. - SEMW, on 10/12/2007, -0/+5@ Lyph4:
You're absolutely correct that short term hot weather trends are, of course, in no way "proof" of (or even evidence for) global warming. But unless I've seriously misunderstood you, seem to be somehow taking the fact that people are trying to do this as some sort of proof that (manmade) global warming is not true, which is just as bad as those you (rightly) criticise. - bidness, on 10/12/2007, -0/+1I don't think that 1 degree in 100 years is a big deal, what is a big deal is the millions and millions of tons of greenhouse gases we are dumping into our atmosphere. We do know that the concentrations of gases like CO2 have increased in the atmosphere because of us. If that translates into global warming is the debate. And it looks like people Al Gore are winning that debate.
So what should we do?
#1 alternative today: conserve energy and diversify energy sources (nuclear, wind, solar, wave)
- Lyph4, on 10/12/2007, -4/+6The funny thing is, if we have an odd-ball 60 degree day (I'm in New England) everyone's ranting about global warming and all that *****, but the next day when it's back to the normal 20-30 degrees, nobody says anything.
- viggity, on 10/12/2007, -6/+6Yeah, because the Earth is a "Simple" heterogeneous system. The "Average" temperature of earth is as meaningful as finding the "Average" phone number in the phone book
- ssam, on 10/12/2007, -1/+6whatever makes you think that?
a temperature is by definition an average. the temperature of a cup of tea is an average over all the molecules in the cup. the same for the temperature of the atmosphere.
phone numbers are just labels that happen to use numbers (on a computer one would store a phone number as a string rather than an integer). you can't average over names or labels or strings.
- ssam, on 10/12/2007, -1/+6whatever makes you think that?
- CromCruach, on 10/12/2007, -1/+2I could be wrong, but it seems the author and those commenting on the story at the bottom of the page place to much emphasis on the models themselves. I believe there is a danger in considering model generated data as "truth", or proof of something in and of itself. There is only one criteria in evaluating a model, and that is whether it behaves in the same way as a the true physical system. Additionally, I believe one must recognize the inherent stochastic nature of the Earth's climate and the processes that effect it. Its not a simple deterministic system, its nonlinear and very complex.
- SEMW, on 10/12/2007, -0/+3FFS, the author states, clearly, several times, "Note that this is just going to be a qualitative description and can't be used to quantitatively estimate the real world values." It's not intended to be an accurate model of the Earth, it was a tutorial about the construction of a basic mathematical model in order to illustrate certain principles of mathematical modelling.
- davesbrain, on 10/12/2007, -2/+2Maybe this is why Ted Kasinski lost his marbles. Reality cannot be boiled down to the simplest mathematical equation.
- Schmitty, on 10/12/2007, -0/+3Where's the orange on a stick and blow-torch? Oh wait, that's if the Earth's electromagnetic field fails. It's hard telling one bloody useless simile from another.
- lizardking7112, on 10/12/2007, -0/+4Real nice and pretty get back to me once they can accurately predict weather a week in advance.
- Y2Krieger, on 10/12/2007, -0/+2Don't worry folks, it'll all balance itself out. See, if we continue emitting CFCs into the atmosphere, we'll deplete the amount of ozone there is to protect us from harmful UV radiation. Since there will be a huge gaping hole in the ozone-layer, there's less ability for the Earth to form and hold any greenhouse gases. So, perhaps we'll all end up dying from freezing cold winters instead! So, keep your refrigerator running before heading into town with your 8-cyclinder gas-guzzling SUV!
- caponumen, on 10/12/2007, -3/+3Yet more useless non-sense.
This simple model is just as accurate as any other model.
They are all just academic toys. - veersite, on 10/12/2007, -0/+1Models must "account for the solar radiation coming in..."
At least this article allows for variables OTHER than Man's terrible misuse of the Earth. I'm all for conservation and alternative energy... but mostly just for gernaeral principals and political reasons (let's get weaned off Middle Eastern oil NOW.)
These articles make me cringe - I expect an irate tirade on "Global Warming," etc. This wasn't too bad, tho. - tedc, on 10/12/2007, -0/+3Interesting article, but I have a couple of recommendations on improving it.
First, to make it more accessible to the layman, they could have included a spreadsheet with all the formulae entered into it already. Then you could play around with the inputs and see immediate results. Having your own little climate model "toy" in a spreadsheet can be a lot of fun. I came up with several of them with varying levels of complexity when I was taking climatology.
Second, this article stays focused on the final results, but to me, at least, the feedbacks are much more interesting to watch as they occur over time. I love seeing how climate shifts towards a new equilibrium after the greenhouse gases have been added. Again, the spreadsheet is your friend. You can have each column represent one year, say, and let the energy fluxes gradually balance each other out as you fill to the right and extrapolate the timeline. We live in a transitional period, after all, so the way the system changes is, in many ways, more relevant than its final state. - hobbified, on 10/12/2007, -0/+2Simple? Yeah, definitely simple. Far too simple, in fact. Convection is _way_ too important of an effect to leave out. Various "feedbacks" are brought up, but only a couple, and the fact that we don't even have very good _guesses_ for the values of the feedback constants is left out. The whole particulates/industrial revolution thing is likewise left out.
The point, I assume, was to establish a simple model to point out some basic facts in how a thermodynamic equilibrium works, and to shoot down some of the stupidest arguments that are out there. But please take note of the article's warning that the model is "not really very earth-like". You're not supposed to draw any grand conclusions from it. - moxfdg, on 10/12/2007, -1/+2I had a professor who would have referred to this article as using "the OZ effect." It looks authoritative because it uses mathematical generalizations about something so idiots run it up on a flag pole and salute it as gospel. Just like people tend to blindly believe results that are spit out of a computer using "complex algorithms," etc... I could have my computer flash "9 out of 10 complex algorithms agree that you're an idiot," but then all the idiots would argue that I had invalidated my point, and hence miss my point entirely.
- SEMW, on 10/12/2007, -1/+3I don't usually like to copy/paste my comments, but FFS, RTFA. IT'S NOT SUPPOSED TO BE AN ACCURATE, AUTHORITATIVE MODEL OF THE EARTH. the author states, clearly, several times, "Note that this is just going to be a qualitative description and can't be used to quantitatively estimate the real world values." It's not intended to be an accurate model of the Earth, it was a tutorial about the construction of a basic mathematical model in order to illustrate certain principles of mathematical modelling.
- lordchronos, on 10/12/2007, -1/+2if the hippies hadn't made us install catalytic converters in 1975 we would have continued with global cooling instead of global warming...just think of all the extra C02 in the atmosphere since that ill thought out program got started.;-)
- SEMW, on 10/12/2007, -0/+1...You would rather "all the extra CO2 in the atmosphere" was CO instead? CO2 may be a greenhouse gas, but CO is pretty damn toxic.
Not to mention that CO oxidizes into CO2 in the upper atmosphere eventually, so it wouldn't really reduce global warming in the long term. All the downsides of CO2, with the added effect of widespread carbon monoxide posioning in big cities. Fun!
- SEMW, on 10/12/2007, -0/+1...You would rather "all the extra CO2 in the atmosphere" was CO instead? CO2 may be a greenhouse gas, but CO is pretty damn toxic.
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