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Only dirty coal can save the Earth

by mgb_phys
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mgb_phys
#1
Apr9-09, 12:09 PM
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http://www.nasa.gov/topics/earth/fea..._aerosols.html

Apparently global warming is due to clean air regulations reducing the amount of acid rain in the artic and so the amount of sunlight absorbing smog.

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Evo
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Apr9-09, 12:22 PM
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Interesting, that would explain why there is climate change that doesn't correlate to the amount of CO2.
jostpuur
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Apr9-09, 01:42 PM
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http://en.wikipedia.org/wiki/Global_dimming

Interactions between the two theories for climate modification have also been studied, as global warming and global dimming are not mutually exclusive or contradictory.
There's no need to declare incorrectness of mainstream global warming science yet.

Evo
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Apr9-09, 02:15 PM
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Only dirty coal can save the Earth

Quote Quote by jostpuur View Post
http://en.wikipedia.org/wiki/Global_dimming

There's no need to declare incorrectness of mainstream global warming science yet.
That's a wiki article. The NASA study in the OP's post is what we are discussing.
jostpuur
#5
Apr9-09, 03:12 PM
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The NASA's study is very much related to the global dimming, so the link to the Wikipedia's article was very well justified.

The title of the NASA's article is "Aerosols May Drive a Significant Portion of Arctic Warming".

The description of the causes of global dimming in the Wikipedia begins with a sentence
It is thought that global dimming was probably due to the increased presence of aerosol particles in the atmosphere caused by human action.[2]
You cannot seriously insist that these would be unrelated topics.

My instinct tells me that it might also be relevant to point out that the conclusion about the dimming effect is usually this:

Some scientists now consider that the effects of global dimming have masked the effect of global warming to some extent and that resolving global dimming may therefore lead to increases in predictions of future temperature rise.[17] According to Beate Liepert, "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."[42] The magnitude of this masking effect is one of the central problems in climate change with significant implications for future climate changes and policy responses to global warming.[43]
The idea "Only dirty coal can save the Earth" is not completely disconnected from reality IMO, since there are thoughts like this out there:

Some scientists have suggested using aerosols to stave off the effects of global warming as an emergency geoengineering measure.[46] In 1974, Mikhail Budyko suggested that if global warming became a problem, the planet could be cooled by burning sulfur in the stratosphere, which would create a haze.[47][48]
But ignoring the greenhouse effect and using more greenhouse gases for more dimming doesn't sound very smart IMO.
nucleus
#6
Apr9-09, 03:15 PM
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" The Arctic ocean is warming up, icebergs are growing scarcer and in some places the seals are finding the water too hot, according to a report to the Commerce Department yesterday from Consul Ifft, at Bergen, Norway.

Reports from fishermen, seal hunters and explorers, he declared, all point to a radical change in climate conditions and hitherto unheard-of temperatures in the Arctic zone. Exploration expeditions report that scarcely any ice has been met with as far north as 81 degrees 29 minutes. Soundings to a depth of 3,100 meters showed the gulf stream still very warm.

Great masses of ice have been replaced by moraines of earth and stones, the report continued, while at many points well known glaciers have entirely disappeared. Very few seals and no white fish are found in the eastern Arctic, while vast shoals of herring and smelts, which have never before ventured so far north, are being encountered in the old seal fishing grounds. "

~Monthly Weather Review for November 1922
http://wattsupwiththat.files.wordpress. ... review.png

http://wattsupwiththat.com/2008/03/16/y ... ergs-melt/
Evo
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Apr9-09, 03:32 PM
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Quote Quote by jostpuur View Post
The NASA's study is very much related to the global dimming, so the link to the Wikipedia's article was very well justified.
But wikipedia is not an acceptable source in this forum. Don't worry, I'm not giving you a penalty. I'm nice.

Please find an official source for your link.
Evo
#8
Apr9-09, 03:33 PM
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Quote Quote by nucleus View Post
" The Arctic ocean is warming up, icebergs are growing scarcer and in some places the seals are finding the water too hot, according to a report to the Commerce Department yesterday from Consul Ifft, at Bergen, Norway.

Reports from fishermen, seal hunters and explorers, he declared, all point to a radical change in climate conditions and hitherto unheard-of temperatures in the Arctic zone. Exploration expeditions report that scarcely any ice has been met with as far north as 81 degrees 29 minutes. Soundings to a depth of 3,100 meters showed the gulf stream still very warm.

Great masses of ice have been replaced by moraines of earth and stones, the report continued, while at many points well known glaciers have entirely disappeared. Very few seals and no white fish are found in the eastern Arctic, while vast shoals of herring and smelts, which have never before ventured so far north, are being encountered in the old seal fishing grounds. "

~Monthly Weather Review for November 1922
http://wattsupwiththat.files.wordpress. ... review.png

http://wattsupwiththat.com/2008/03/16/y ... ergs-melt/
Nucleus, the link is broken and is not an allowable source anyway. Please read the postings guidelines sticky at the top of the Earth forum.
Ivan Seeking
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Apr9-09, 05:12 PM
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Quote Quote by Evo View Post
Interesting, that would explain why there is climate change that doesn't correlate to the amount of CO2.
It has been suspected for some time that particulates have helped to mask GW.
Evo
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Apr9-09, 06:16 PM
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Quote Quote by Ivan Seeking View Post
It has been suspected for some time that particulates have helped to mask GW.
Yes, but was pushed aside in preference of the C02 theory.
sylas
#11
Apr9-09, 06:30 PM
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This looks interesting. I'm not going to comment yet on my own behalf; but here are what seem to be the relevant peer reviewed articles, which I think brings things back into line with forum guidelines. First, the main research article:
Shindell, Drew, and Faluvegi, Greg. Climate response to regional radiative forcing during the twentieth century, in Nature Geoscience 2, 294 - 300 (2009). Published online: 22 March 2009 | doi:10.1038/ngeo473
Second, a commentary in the same issue:
Keenlyside, Noel. Atmospheric science: Clean air policy and Arctic warming, in Nature Geoscience 2, 243 - 244 (2009). doi:10.1038/ngeo486
Cheers -- Sylas
sylas
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Apr9-09, 06:58 PM
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Quote Quote by Evo View Post
Yes, but was pushed aside in preference of the C02 theory.
OK. This is now my own comment. Evo, you seem to have misunderstood what is meant by masking. You've just agreed with the comment from Ivan Seeking that:
It has been suspected for some time that particulates have helped to mask GW.
But that IS the CO2 theory! Nothing has been pushed aside. CO2 theory (which is simply basic thermodynamics of radiation transfer in the atmosphere) is the physical basis for the effects of CO2 on temperature.

The problem is, of course, that accounting for all the causes impacting temperature on Earth gets really really complicated and involves heaps of different effects. Sorting that out is hard and there are many many legitimate and wide open research questions.

Unfortunately, the popular debate gets side tracked into irrelevant nonsense about whether CO2 has a major role. Of course it does. That's fundamental physics.

As for masking... we know that aerosols can have a cooling effect. That's seen directly in strong effects following a big volcanic eruption. Unfortunately, the role of aerosols is not that simple. Under some circumstances they can also increase temperature. Their impact is a combination of changes to albedo and changes to thermal opacity. (Loosly, interactions with shortwave and longwave radiation.) In some cases the thermal absorption can be more significant and let aerosols actually help have a warming contribution. But overall, cooling seems to win out in most cases.

The role of industrial emissions is similarly mixed, and complex. Industrial emissions include both aerosols, and CO2, and lots of other stuff. There is no credible doubt at all that human emissions are the driving factor for rapid increases in atmospheric CO2 concentrations. Neither is their any credible doubt at all over the basic physics of how IR absorption characteristics of CO2 contributes significantly to surface temperature. Calculating the details gets tricky, but the limits of confidence on the effect of CO2 in isolation are actually pretty small, and the net effect is large.

Where it gets difficult is that CO2 is NOT acting in isolation. There are other factors; natural feedbacks from the other features of Earth's climate, and the fact the emissions themselves are a lot more than just CO2. In particular... there are the aerosols as well.

If industrial aerosol emissions are contributing a cooling effect, then this can be considered as "masking" the CO2 effect. We put it that way around (rather than CO2 masking the aerosols) because in fact it is much much easier to manage aerosols in emissions than to manage CO2. Aerosols can get cleaned up fairly easily. CO2 can't.

So when we say particulate are masking CO2, that IS the CO2 theory at work. The comment about masking makes no sense unless you recognize the basic physics of the impact of CO2.

This is part of the paradox with so-called "clean coal". You can clean out the aerosols, and that's good because their effect on health is dreadful. But you can't clean out the CO2. It's the basic part of the underlying chemical reactions that are why we bother to burn coal at all. Cleaner coal is healthier in immediate terms, but it's climatic impact can be greater.

On my first glance at the cited paper, a part of the effect being described is that the Arctic has LESS masking of the CO2 effect. The question at issue is: why is the Arctic warming more than the most of the rest of the planet?

The major difference between the Arctic and the rest of the world is not that there's more greenhouse or CO2 up there. (That's obvious.) This paper is suggest the difference is because there are less aerosols. It's cleaner. And hence, there is less masking of the basic CO2 effect that is the major driver of increasing global temperatures.

Does that make sense?

Cheers -- Sylas
Evo
#13
Apr9-09, 09:31 PM
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Quote Quote by sylas View Post
OK. This is now my own comment. Evo, you seem to have misunderstood what is meant by masking. You've just agreed with the comment from Ivan Seeking that:
It has been suspected for some time that particulates have helped to mask GW.
But that IS the CO2 theory! Nothing has been pushed aside. CO2 theory (which is simply basic thermodynamics of radiation transfer in the atmosphere) is the physical basis for the effects of CO2 on temperature.
Thank sylas, that was an excellent explanation. No, my comment was from my viewpoint as a layman that sees media articles that claim C02 from burning fossil fuels as the only contributing factor and the conspiracy of oil companies to cover it up. If you ask anyone on the street what is causing "global warming". C02 will be the response. To me, discussion of everything else has been "pushed aside" in favor of harping on C02 from burning fossil fuels.
sylas
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Apr10-09, 01:08 AM
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Quote Quote by Evo View Post
Thank sylas, that was an excellent explanation. My comment was from my viewpoint as a layman that sees media articles that claim C02 from burning fossil fuels as the only contributing factor and the conspiracy of oil companies to cover it up. If you ask anyone on the street what is causing "global warming". C02 will be the response. To me, discussion of everything else has been "pushed aside" in favor of harping on C02 from burning fossil fuels.
I sympathize. It's not particularly surprising that you get something of a cartoon view from non-experts.

If you do simply ask what is causing "global warming", then the correct answer is "greenhouse gases". That is mostly CO2, with smaller additional contributions from gases like CH4, N2O, O3, and the halocarbons. The people on the street you mention are pretty close to the mark here.

On the other hand, if you ask what is causing Arctic warming, then greenhouse gases is not a good answer. The street talk, even from supporters of conventional science, will be misleading. That's what this research addresses.

Don't get me started on oil companies. It would be off topic in this thread, but I'll sign on in a heartbeat to the proposition that there is a deliberate campaign at work to distort the scientific literature and foster confusion over points that are not actually in any credible dispute at all, and this is in part supported from certain oil companies. It's a big problem, and by no means limited to oil companies. Whenever science has a potential of impacting the bottom line at some industry, there are folks who'd like to distort the process. I'm keen to get hold of the book Doubt is their Product, which focuses on the area of health and substance regulation; though apparently there's a bit on global warming also. I've a long standing interest on bad science in the popular culture. This is much more my driving obsession than any special concern with climate in particular.

Sorry; I'll climb down off that high horse and get back on topic.

Most of the factors you could invoke for the global warming trend, other than a strengthening greenhouse effect, are either masking the warming (like the aerosols) or else are far too small to any meaningful impact or (worse) simply don't align at all the major warming trend people are asking about. (The widely invoked notion of increased solar activity is in this category.) One factor -- poorly understood -- that could reasonably be given a credible role is natural changes to ocean heat transport, with changes in currents or overturning. It's not an alternative to greenhouse driven warming, but rather a possible short term shift that displaces the major overlying trend up, or conversely down.

The effect of greenhouse gases is not a guess or a correlation based argument. It's a necessary consequence of the thermodynamics of radiation in the atmosphere. You can calculate the effect from first principles, if you make a whole pile of simplifying assumptions (no cloud, nice simple lapse rate, etc) and have the necessary computer to integrate through all the different bands of the spectrum of light.

There are still plenty of wide open questions, of course, and the paper in this thread helps to address two of them. One is the magnitude of climate response to forcing (any forcing). This is called "sensitivity". But mainly, this research is about the causes for regional variation.

That is, this paper is not addressing the cause of "global warming". It is addressing the cause of "regional warming"… and it does so by looking at the difference between trends of increasing temperatures at different bands of latitude. You can't explain that by looking at a cause of the global trend, because it isn't the global trend that they are seeking to explain.

And – just to underline the point – check out the first author. He's Drew Shindell; and you can google more. He works directly with James Hansen, in the NASA climate group, on climate models. That is, he could hardly be in any deeper with the whole main thrust of scientific work that the denialists love to hate. In fact, this whole paper is a good example of what climate models are really used for. It's not "prediction". That's a kind of secondary sideline, of legitimate public interest but of limited immediate use to scientists. What climate models are really important for is running virtual experiments to test out competing theories of causes and effects.

Drew Shindell has a special interest in atmospheric physics and modeling, especially with ozone. But his research covers a lot of ground. He doesn't seem to write much about how CO2 is the major cause of global warming; but he doesn't need to. That is simply not an interesting scientific question any more. We know it’s the major cause of the current warming episode. Measuring the magnitude of the impact of greenhouse gases is an open question – but it's not the question Shindell and Faluvegi are addressing here.

There is one way in which his research is a good caution for the supporters of conventional AGW science, like myself. The warming in the Arctic really stands out from warming elsewhere. It's tempting then, as a kind of rhetorical ploy, to focus on the Arctic as indicative of global warming. But the Arctic is not the whole planet, and what goes on there is not the same as what goes on everywhere else. The graph in the first post of the thread shows this nicely.

Warming of the Arctic is a part of global warming, but the actual temperature rise, which is something like 1.5 C per decade over the last several decades, is not a good quantification of global warming. It is far greater than what should be predicted as a global trend from increasing greenhouse gas levels. The global trend is about 0.2C/ decade.

It means, of course, that most of the absolute temperature increase in the Arctic is not directly caused by greenhouse gas increases.

I'm expecting, with some dismay, that all the usual suspects in the media who love to trash conventional AGW science will spin this as evidence against greenhouse driven global warming. It isn't, although the confusion is understandable.

Cheers -- Sylas
jostpuur
#15
Apr10-09, 04:29 AM
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Quote Quote by Evo View Post
But wikipedia is not an acceptable source in this forum. Don't worry, I'm not giving you a penalty. I'm nice.

Please find an official source for your link.
If somebody writes an equation [itex]F=ma[/itex] in some post here, moderators are not going to attack him or her by demanding official sources. And are not going to discuss how nice they are, if they allow Wikipedia, despite it not being a peer-reviewed journal.

If somebody suddenly claims some very unusual claim, possibly in violation with mainstream scientific world view, I understand that moderators can start demanding sources. It is absurd to start demanding sources for every simple thing too. If you don't know anything about some field, wouldn't it be smarter to not moderate posts of that field then, instead of demanding sources for every possible claim?

The trouble with Wikipedia starts if somebody starts writing their own theories up there, or their own interpretations. Fortunately this usually results in some warning signs appearing in the beginning of the article, and "citation needed" marks appearing behind some specific sentences. In this particular article there is no trouble with citations.

If I was a fanatic climate enthusiast, I could start going through the sources of the Wiki article, and then continue the battle here with more convincing citations.

Alternatively, I could be lazy, and just copy paste some sources from there to here.

But actually I think I'm merely going to make the remark that the Wiki-article is full of sources, and hope that it is now clear that the Wiki-article is ok.
Evo
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Apr10-09, 09:27 AM
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Quote Quote by jostpuur View Post
If somebody writes an equation [itex]F=ma[/itex] in some post here, moderators are not going to attack him or her by demanding official sources. And are not going to discuss how nice they are, if they allow Wikipedia, despite it not being a peer-reviewed journal.
Actually, the rules here were recently changed so that members are not allowed to make up their own equations, graphs etc... even if it is from verified data. And wikipedia is not allowed as a source either. The rules in the Earth forum are a bit stricter than in other forums. I agree with you though, I think it's very limiting, but there is a reason for it. We do not have anyone on staff that is a climate scientist, and people that post here are not climate scientists, I do know one, and actually got him to register here, but he was too busy writing grant proposals to post. The decision was between shutting down the earth forum or creating very strict guidelines for posting. If the data is peer reviewed or similary qualified, it is much easier for the mentors to monitor. Wikipedia is not an accepted source in the Earth forum.

And this blurb is the extent of what most people think when they think AGW.

How does carbon dioxide cause global warming?

(Lansing State Journal, August 31, 1994)

Fossil fuels such as gasoline, methane and propane contain mostly carbon. When these fuels are burned, they react with oxygen and produce carbon dioxide.

Because of our heavy use of fossil fuels, the amount of carbon dioxide in the atmosphere has been increasing since the industrial revolution. The destruction of forests which use carbon dioxide also contributes to the increase in carbon dioxide.

<snip>
Carbon dioxide doesn't absorb the energy from the sun, but it does absorb some of the heat energy released from the earth. When a molecule of carbon dioxide absorbs heat energy, it goes into an excited unstable state. It can become stable again by releasing the energy it absorbed. Some of the released energy will go back to the earth and some will go out into space.

So in effect, carbon dioxide lets the light energy in, but doesn't let all of the heat energy out, similar to a greenhouse.

Currently, the amount of carbon dioxide in the atmosphere is increasing at the rate of about one part per million per year. If this continues, some meteorologists expect that the average temperature of the earth will increase by about 2.5 degrees Celsius. This doesn't sound like much, but it could be enough to cause glaciers to melt, which would cause coastal flooding.
http://www.pa.msu.edu/sciencet/ask_st/083194.html
Bystander
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Apr10-09, 03:47 PM
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Quote Quote by sylas View Post
(snip)The effect of greenhouse gases is not a guess or a correlation based argument. It's a necessary consequence of the thermodynamics of radiation in the atmosphere. You can calculate the effect from first principles, if you make a whole pile of simplifying assumptions (no cloud, nice simple lapse rate, etc) and have the necessary computer to integrate through all the different bands of the spectrum of light.
(snip)
---annddd --- have the emissivities and concentration data necessary for the integration.

That "whole pile of assumptions" is where there is a whole lot of room for discussion --- and, given the guidelines for earth sciences posting, can be regarded as "speculative."

This has been suggested before, and ignored, but why not again? Let's take the "pile" apart, one assumption at a time, discuss bases, possible tests, and uncertainties in resulting calculations.
sylas
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Apr10-09, 06:18 PM
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Quote Quote by Bystander View Post
---annddd --- have the emissivities and concentration data necessary for the integration.
The calculation I refer to is of the radiative forcing from changes in atmospheric composition. It uses emissivities for the various gases you might include, and you can also add here that it uses profiles of pressure, concentration and temperature; all up and down the atmospheric column. The change from CO2 concentrations depends also on the concentrations of other gases in the atmosphere.

That "whole pile of assumptions" is where there is a whole lot of room for discussion --- and, given the guidelines for earth sciences posting, can be regarded as "speculative."
That's a bad misuse of the term "speculative". It's flatly wrong to speak of "speculative" when what you really mean are bounded uncertainities based on measurement uncertainties of the quantities involved. Furthermore, as we are calculating a forcing, many uncertainities have only a small impact. The result of doubled CO2 concentrations is a forcing, or a change of about 3.7 W/m2 in the energy balance, and that holds over a range of atmospheric composition, temperature and pressure profiles.

The net energy flux can differ quite a lot, while the change in flux from change in CO2 may remain about the same or vary only slightly.

Calculation of a radiative forcing

Concentrations of gases and changes in pressure and in temperature up and down the atmosphere are not "speculative". They are measured, and they have uncertainties, and that constrains the accuracy of results.

The emissivity of gases is not "speculative". It's based thoroughly on theory and observation. This calculation requires you to look in very fine detail at the absorption spectrum of a gas, and at line broadening effects with pressure and temperature, and there are well established tools for doing this.

The consequent implications for radiative balance are not "speculative". They are grounded solidly in measurement and basic physics, and the results are definite. Like any complex measurement in science they have an associated error term. From this you can get as basic data that a doubling of CO2 levels will lead to about 3.7 W/m2 change in the energy balance of the Earth. The relation is approximately logarithmic, which is why it is given in terms of doublings. Increase by a factor of 1.414 and you get half the effect. The word "about" is needed partly from measurement errors, but more importantly because of natural variations in conditions that impact the calculation, of cloud and temperature and so on. The number has an accuracy of about 10%.
Reference: Myhre, G, Highwood, EJ, Shine, KP. "New estimates of radiative forcing due to well mixed greenhouse gases", in Geophysical Research Letters, Vol 25, No 14, pp2715-2718. July 15 1998.
This reference gives the result in natural logarithms rather than log base 2. The forcing is 5.35 W/m2 per natural log CO2. This is a basic reference for the calculation. There are other calculations since, giving about the same numbers, but this is the key reference for the subject.

This is only a matter of "discussion", in the usual sense for a forum like this. There's lots of scope for useful educational discussion against a background of science that all of us are trying to learn about, for clarifying details, learning more about it, and understanding it better.

It is not a matter for debate over whether temperature or pressure or emissivity unknowns might invalidate the whole result – because physicsforums is not intended to be dealing with fringe or crank science. The unknowns in temperature, pressure and emissivity are all already a part of the calculation I refer to, and they show up as part of the 10% uncertainty on the number 5.35 W/m2 per Ln(CO2).

Emissivity and transmittance spectra

If you want know more of the fine details, there is an excellent on-line tool used by researchers involved in radiative transfer calculations for gases. See: Spectral Calculator, an on-line tool supplied for use by researchers and other interested parties. This is a very heavy duty calculation and full use requires a subscription, but there's a lot a visitor can do for free. It's making available the LINEPAK suite of algorithms for spectra in a whole range of cases, from an atmosphere to gas cells in a laboratory. This is a basic tool for a working scientist.

To give you an idea of why you really want a supercomputer for this, here is a bit of a spectrum. It's taken from the on-line calculator, using N2O in a gas cell 1 meter long, held at 1 atm pressure and 296K temperature, and it corresponds to a small part of the whole spectrum, from wavenumber 2300 cm-1 to 2400 cm-1.

Note the fine details of the absorption lines in the spectrum. They will broaden with pressure and temperature. Unfortunately I gen't get a graph for the full spectrum, but it is full of bumps and dips; this graph zooms in and shows the fine details at higher spectral resolution.

The full calculation of radiative forcing integrates over the whole spectrum, line by line, and over the whole atmospheric column, at least up into the levels where the remainder is optically thin. It uses all the various gases, and a profile of temperature and pressure. And it repeats this for different latitudes and times of day. Then you do it all again, but with a change in the CO2 level. Repeat as required with different temperature and pressure profiles, to get a mean impact for a given change in CO2 concentration.

If that sounds arduous… it is. But it is not speculative. The result has an associated uncertainty, of course. It's about 10%. If you think the radiative forcing for doubled CO2 might be 2.5 W/m2, or 5 W/m2, then you are in basic conflict with fairly fundamental physics.

The "debate"

Bottom line. There are lots of people out there who, for whatever reason, don't accept that CO2 has a strong impact on climate and temperature, and who apparently think that the widespread acceptance of this impact in the scientific literature is because of some hoax, or because of a bias by scientific publishers as to what they'll accept, or because the critic simply has no idea of what actually appears in the literature and thinks there's still some big scientific debate over the matter.

There is certainly lots of real scientific debate going on. The impact of a forcing on temperature, for example, is not nearly so well known as the radiative forcing number for doubled CO2.

But you are flatly incorrect to think that the point I raise here, on the calculation of CO2 radiative forcing, is "speculative". It's basic physics.

The real debate is over the climate response in temperature to forcings, over regional variations in forcings and temperatures, and most especially over the forcings for other factors – like aerosols, for example – where we don't have nearly so good an idea of the numbers. Globally, however, greenhouse effects stand out as the major forcing for global climate changes over recent decades.

Shindell and Faluvegi

The paper by Shindell and Faluvegi is solid science, all in the context of the above data. Indeed, these guys are particularly expert in the kinds of atmospheric modeling that is required for the calculations I'm talking about above.

Their paper is talking about the difference between the Arctic and other latitudes. Over recent decades, the Arctic has been warming at about 1.5C/decade, where the global trend is more like 0.2C/decade. A crude back of the envelope calculation indicates that the effects of increasing CO2 is in the ball park of the global trend, but not the Arctic trend. That calculation relies upon the numbers I've quoted above, and sensitivity numbers such as Shindell and Faluvegi use in their paper (which are pretty bog-standard magnitudes).

Taking other greenhouse gases into effect doesn't change things all that much. So it makes good sense to me that the rate of warming in the Arctic cannot possibly be explained as a direct greenhouse effect. The global warming trend is mainly a greenhouse effect, but on top of that there's something else going on in the Arctic. Shindell and Faluvegi make a persuasive case that aerosols and black carbon may be the major contributor to the 1.5C/decade Arctic temperature trend.

Cheers -- Sylas


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