Only dirty coal can save the Earth

In summary: We need to see if this matches the data."In summary, the conversation between the forum members discussed the relationship between global warming and global dimming, as well as the impact of clean air regulations and aerosols on the warming of the Arctic. It was noted that the NASA study in the initial post was related to the concept of global dimming, which is not mutually exclusive or contradictory to the theory of global warming. The potential masking effect of global dimming on global warming was also mentioned, as well as the suggestion of using aerosols as a geoengineering measure to combat warming. A link to a 1922 Monthly Weather Review article discussing changes in Arctic conditions was also
  • #1
mgb_phys
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http://www.nasa.gov/topics/earth/features/warming_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.

nasa_arctic_temp.jpg
 
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  • #2
Interesting, that would explain why there is climate change that doesn't correlate to the amount of CO2.
 
  • #3
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.
 
  • #4
jostpuur said:
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.
 
  • #5
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.
 
  • #6
" 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 [Broken]. ... review.png

http://wattsupwiththat.com/2008/03/16/y ... ergs-melt/
 
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  • #7
jostpuur said:
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. :wink:

Please find an official source for your link.
 
  • #8
nucleus said:
" 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 [Broken]. ... 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.
 
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  • #9
Evo said:
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.
 
  • #10
Ivan Seeking said:
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.
 
  • #11
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. http://www.nature.com/ngeo/journal/v2/n4/full/ngeo473.html, 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. http://www.nature.com/ngeo/journal/v2/n4/full/ngeo486.html, in Nature Geoscience 2, 243 - 244 (2009). doi:10.1038/ngeo486​

Cheers -- Sylas
 
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  • #12
Evo said:
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
 
  • #13
sylas said:
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.
 
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  • #14
Evo said:
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 http://www.giss.nasa.gov/staff/dshindell/; 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
 
  • #15
Evo said:
But wikipedia is not an acceptable source in this forum. Don't worry, I'm not giving you a penalty. I'm nice. :wink:

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.
 
  • #16
jostpuur said:
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 let's 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 [Broken]
 
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  • #17
sylas said:
(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.
 
  • #18
Bystander said:
---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 http://www.gats-inc.com/linepak.htm [Broken] 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.
1239405112.png

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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  • #19
Bystander said:
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.

OK... I've taken a bit of time to clarify guidelines with the mentors here. I think your suggestion is a very good one.. The reply I give above is focused simply on the calculation of radiative forcing, since that is the integration you focused upon; but there's more involved in getting to temperature effects.

This is now getting beyond the issue of Arctic warming, and really needs a new thread. I'm just making public acknowledgment here that I think you have made an excellent suggestion, and I will try to take it up. I'll put together a post for a new thread where we can do just that.

Cheers -- sylas
 
  • #20
sylas said:
...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
That would require a different rate of diffusion to the Arctic between man made CO2 and man made aerosols. Is this the case? Then should we not also be seeing the same effect in in the Antarctic? Antarctic ice has been increasing.
 
  • #21
mheslep said:
That would require a different rate of diffusion to the Arctic between man made CO2 and man made aerosols. Is this the case? Then should we not also be seeing the same effect in in the Antarctic? Antarctic ice has been increasing.

There is indeed a different rate of diffusion; or more particularly, a different extent of diffusion. But that's why you don't see the same thing in the Antarctic.

The Northern Hemisphere has most of the emissions of anthropogenic aerosols, black carbon, and greenhouse gases. The gases, CO2 especially, are well mixed into the atmosphere, and spread fairly well over the whole planet. They contribute to warming in the Antarctic, which is warming at rates somewhat below the global average.

Aerosols and black carbon (eg: soot) tends not to distribute so well, and tend to wash out of the atmosphere over large distances. Black carbon in particular has its effect by dropping out of the atmosphere and making the surface a bit darker. Dirty snow is much less reflective than clear snow. The paper is proposing that these factors are driving the Arctic temperature trend well above the global trend. Aerosols and black carbon don't get far enough south to have the same impact in the Antarctic.

You simply don't get the aerosols and black carbon from the Northern hemisphere distributing all the way down south, and that's why they make so much sense as the cause of a difference between the north and the south.

Changing levels of sea ice cover is a whole new ball of wax. Ice cover is affected by temperatures, by precipitation, by currents and maybe other factors. In the Arctic, with the large changes in temperature, temperature stands out as a major reason for steadily reducing cover. However, isolated extremes may reflect other causes; much like the the regional extreme reflects other causes to a global trend.

For example, the exceptional low in Arctic sea ice last year was not because of an exceptional high in temperatures that year, but mainly a result of ocean currents. Rising temperatures drive the long term trend of steadily reducing sea ice over several decades, but for individual seasons you have to look also at other causes of variations above and below the main trend.

In the Antarctic, you don't have as strong an effect from rising temperatures, and so here the impact of changing currents and precipitation are proportionally as important for sorting out the sea ice trend over several decades. As you note, the trend there, if anything, is for a slight increase in cover.

Cheers -- Sylas
 
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  • #22
Thanks for the clear and coherent response.
sylas said:
There is indeed a different rate of diffusion; or more particularly, a different extent of diffusion. But that's why you don't see the same thing in the Antarctic.

The Northern Hemisphere has most of the emissions of anthropogenic aerosols, black carbon, and greenhouse gases. The gases, CO2 especially, are well mixed into the atmosphere, and spread fairly well over the whole planet. They contribute to warming in the Antarctic, which is warming at rates somewhat below the global average.

Aerosols and black carbon (eg: soot) tends not to distribute so well, and tend to wash out of the atmosphere over large distances. Black carbon in particular has its effect by dropping out of the atmosphere and making the surface a bit darker. Dirty snow is much less reflective than clear snow.
I'm being slothful and not reading the paper, but this makes sense for particulates, though I had thought SO2 was a primary aerosol and would diffuse much like CO2?

The paper is proposing that these factors are driving the Arctic temperature trend well above the global trend. Aerosols and black carbon don't get far enough south to have the same impact in the Antarctic.

You simply don't get the aerosols and black carbon from the Northern hemisphere distributing all the way down south, and that's why they make so much sense as the cause of a difference between the north and the south.
Yes indeed, if we don't see the aerosols/particulates in the south, then why don't we see the same lack-of-aerosols warming in the S. hemisphere that is being credited for the Arctic, because it lacks aerosols? Scratch 'warming', I'm aware there are too many other variables; CO2 minus aerosols 'forcing' is more precise I expect.

For example, the exceptional low in Arctic sea ice last year was not because of an exceptional high in temperatures that year, but mainly a result of ocean currents.
Yes saw that, here for instance from Son Nghiem, JPL:
http://www.nasa.gov/vision/earth/lookingatearth/quikscat-20071001.html
 
  • #23
mheslep said:
Thanks for the clear and coherent response.
I'm being slothful and not reading the paper, but this makes sense for particulates, though I had thought SO2 was a primary aerosol and would diffuse much like CO2?

SO2 is one of the most important aerosols, and also a major contributor to acid rain, which is why it was such a great idea to clean it up.

The issue is not so much diffusion as lifetime. Just suppose, for example, CO2 emissions somehow stopped dead. The atmospheric concentrations would go into a gradual decline, as CO2 is flushed out of the atmosphere and comes back to an equilibrium -- mainly with oceanic carbon. This would take a long time; on the scale of many centuries; maybe a thousand years or two. We don't actually know the carbon cycle well enough to be definite on this.

SO2 is much more reactive, and it flushes out of the atmosphere much more quickly. Hence, when emissions were cut back, atmospheric concentrations fell very rapidly as well.

Technically, CO2 is a "well mixed" gas in the atmosphere, meaning that differences in concentration around the planet are relatively small. SO2 is not well mixed. The regional differences are enormous.

Just reading the paper may not help all that much; it doesn't go into this kind of background. These kinds of questions help make the technical details more comprehensible. It's been useful for me to sort through the answers for myself as well.

Yes indeed, if we don't see the aerosols/particulates in the south, then why don't we see the same lack-of-aerosols warming in the S. hemisphere that is being credited for the Arctic, because it lacks aerosols? Scratch 'warming', I'm aware there are too many other variables; CO2 minus aerosols 'forcing' is more precise I expect.

There are indeed a lot of variables. But this is one that can be answered. We don't see a "lack of cooling" in the south nearly so much, because there never was as much cooling to start with. When SO2 emissions were cut back, there was not as much difference in the south as a result, because SO2 was never much of a factor down here.

There are more variables involved, of course, and SO2 is not the only aerosol that can have a cooling effect. But as far as SO2 is concerned, I think it is expected that cutting emissions has a much stronger effect in the north by comparison with the south.

Yes saw that, here for instance from Son Nghiem, JPL:
http://www.nasa.gov/vision/earth/lookingatearth/quikscat-20071001.html

Good link. In fact, you've corrected an error in my previous post. I said "currents", but your link indicates I would have been better to say "winds". On checking further, I agree. Thanks muchly!

Cheers -- Sylas
 
  • #24
Bystander said:
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.

As I said previously, I think this is a great idea, but it is beyond the scope of this thread. I have started a new thread at [post=2162699]Estimating the impact of CO2 on global mean temperature[/post], which takes up this suggestion.

Cheers -- Sylas
 
  • #25
In answer to the question, "What stopped global cooling?", changes in Earth's orbit were cited. If this is correct, then this must also be the cause of global warming.
 
  • #26
Peter Watkins said:
In answer to the question, "What stopped global cooling?", changes in Earth's orbit were cited. If this is correct, then this must also be the cause of global warming.

Peter, that is a non-sequitur. It's not at all clear what you even mean by "stopped global cooling". If you mean the end of the ice age -- which is where charges in Earth's orbit are implicated as a trigger mechanism -- then note this was 12,000 years ago. It's completely absurd to say that what ever caused the end of the last ice age must also be the cause of every other warming episode.

Climate changes associated with the "ice ages", or cycles of repeating glaciations over the last couple of million years, do have a strongly suggestive link with orbital variation.

The current episode of globally increasing temperatures over the recent decades has nothing whatsoever to do with orbital variation.

Cheers -- sylas
 
  • #27
Quite the reverse! Despite having vast ice-sheets that reflected the sun's heat, the cooling stopped and the process reversed. As the ice melted the expectation would be that the globe would heat up at an ever increasing rate. And this is precisely what has happened, and is happening. With so little ice left it's rate of disappearence should increase at an exponential rate. The temperature graphs, both up and down, will not be precisely linear, but will be "saw-toothed" to reflect mini warm and cold periods. With polar ice-sheets thought to have existed for only 10% of Earth's history, it would seem that the globe is simply returning to it's "normal" state. So there is little about which to get excited, or be done.
 
  • #28
Peter Watkins said:
Quite the reverse! Despite having vast ice-sheets that reflected the sun's heat, the cooling stopped and the process reversed. As the ice melted the expectation would be that the globe would heat up at an ever increasing rate. And this is precisely what has happened, and is happening. With so little ice left it's rate of disappearence should increase at an exponential rate. The temperature graphs, both up and down, will not be precisely linear, but will be "saw-toothed" to reflect mini warm and cold periods. With polar ice-sheets thought to have existed for only 10% of Earth's history, it would seem that the globe is simply returning to it's "normal" state. So there is little about which to get excited, or be done.
Here is a graph of the Holocene.http://www.globalwarmingart.com/images/b/bb/Holocene_Temperature_Variations_Rev.png

Note that temperatures have been declining for ~7000 years, which how these cycles normally develop. Slow warming then an accelerated rise, then gradual cooling as the snow and ice begins to accumulate year round at lower latitudes and GHG's become sequestered.

Your hypothesis is far to simplistic. It seems as if you are searching for confirmation of your belief.
 
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  • #29
Haven't yet read the paper by Shindell or the discussion in this thread, but I would like to say that I found the figure in the NASA report (also pasted in the OP) to be dangerously bordering on misleading, as shown. After all, the point when the so-called aerosol regulations kicked in in the early '70s is also the point of time when the AMO and the PDO were at local minima and began upward swings immediately after.
 
  • #30
Gokul43201 said:
Haven't yet read the paper by Shindell or the discussion in this thread, but I would like to say that I found the figure in the NASA report (also pasted in the OP) to be dangerously bordering on misleading, as shown. After all, the point when the so-called aerosol regulations kicked in in the early '70s is also the point of time when the AMO and the PDO were at local minima and began upward swings immediately after.

The PDO when positive in the late 70's but the AMO was in it's cool phase from 1970 to 1995 and is currently in a warm phase.

pdo_latest.png


672px-Amo_timeseries_1856-present.svg.png
 
  • #31
Skyhunter said:
The PDO when positive in the late 70's but the AMO was in it's cool phase from 1970 to 1995 and is currently in a warm phase.
Not sure I understand the point here. Does any part of that contradict my statement?

Gokul43201 said:
...the early '70s is also the point of time when the AMO and the PDO were at local minima and began upward swings immediately after.

Perhaps I should have been more careful to mention "local minima" without saying anything about the timescale/algorithm I am using for smoothing out minima in the raw data.
 
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  • #32
These oscillations have long term cycles which is why they have such a strong influence on climate. It appeared to me that you were suggesting the two cycles synchronized at that same time as the clean air act. True, they were both at a minima when the clean air regulation kicked in, but they did not rise together. The AMO remained negative for two decades and the PDO is currently in a cool phase while AMO is positive.
 
  • #33
Gokul43201 said:
Haven't yet read the paper by Shindell or the discussion in this thread, but I would like to say that I found the figure in the NASA report (also pasted in the OP) to be dangerously bordering on misleading, as shown. After all, the point when the so-called aerosol regulations kicked in in the early '70s is also the point of time when the AMO and the PDO were at local minima and began upward swings immediately after.

What I found ... bizarre ... was the comment "dangerously bordering on misleading". What the..?

The figure shows zonal temperature anomalies. The paper -- which I have read -- makes a strong case for aerosol and black carbon effects being behind a strong regional warming effect in the Arctic, which is running well above the global trends.

The diagram includes an arrow, which neatly shows one of the features of the record that their hypothesis explains quite nicely; a strong kink in the Arctic temperature record at about the time of a sharp change in aerosol emissions.

You, evidently, have a different hypothesis. Bully for you; there's nothing wrong with that, in principle.

Is it "dangerous" or "misleading" for anyone else to present a case for a different hypothesis from yours? I can't make any other sense of the remark.

I think you SHOULD read the paper before declaring it "dangerous". It's specifically about the Arctic, which is treated as a zone above 60 North in the paper.

Skyhunter has already pointed out that the timing of these indicies don't actually fit very well with the particular trend THIS paper is exploring. He might have added... neither does the location! The AMO is defined by Atlantic sea surface temperatures from latitude 0 to latitude 70. The PDO is a defined as a shift in temperatures from East to West and back again, in the Pacific, from about latitude 20 to 60 or so.

Such oscillations are important factors for global weather patterns in mid latitudes, but they are pretty much dead in the water for explaining such a strong Arctic excess over the global trends. I suspect you have a hammer, and are now seeing everything as a nail. It gets comical when you actually call it "dangerous" to discuss screws.

Cheers -- sylas
 
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  • #34
Evo said:
Interesting, that would explain why there is climate change that doesn't correlate to the amount of CO2.
Could you please explain this statement? I don't understand it.
 
  • #35
Gokul43201 said:
Could you please explain this statement? I don't understand it.

I'm going to take a quick stab here. Evo may mean something different, but if Evo doesn't mind (or even if he does; it's too late :wink:) I'll give my spin.

Evo is quite right to say there is climate change that doesn't correlate to the amount of CO2. Put another way... there's more to climate than CO2.

No scientist anywhere has ever said that CO2 is all that matters. It stands out pretty clearly as the largest single global scale forcing, but to give any kind of credible account of climate you still need to consider:
  1. Lots of other global scale forcings, many of which are also pretty significant in their own right.
  2. A whole heap of regional forcings and redistributions of energy. It's a big planet, and although a global temperature anomaly is a very useful diagnostic number for a big picture, this tells you little about what's going on where you live. Some of the regional forcings can easily exceed the general global trend.

Popular discussion focuses a lot on a single diagnostic number: a global anomaly. And it's a useful indicator. But if you look, every single actual global temperature anomaly being produced by any research group turns out to be a data product that gives "gridded" results distributed over the surface; and these grids are what are actually used in research and model comparisons and so on. The single value global mean, for any given month or year, is just a handy statistic for a much larger dataset.

---

Here's an anecdote, relating directly to the research described in this thread.

The research described here focuses on aerosols and black carbon. The work was conducted at NASA, under James Hansen's research group. Hansen is probably the most prominent climatologist in the world today, and he justly stands as a pioneer of work on anthropogenic greenhouse warming. So if you think AGW is a scam, you'll peg James Hansen as a fraud.

Shortly after the paper being discussed here was published, a well known contrarian website speculated that Drew Shindell (the author of the Arctic warming paper) must now be in a difficult position, what with his boss being all gung-ho for carbon dioxide.

When the guys as NASA heard this, they just laughed... because James Hansen has recently been very active in emphasizing the importance of aerosols and black carbon as well. (It's on the realclimate blog, which is largely an educational outreach by NASA climatologists.)

It seems to be a solidly entrenched myth in some circles that the IPCC and scientists generally are fixated on CO2 to the exclusion of all other considerations, unlike the open minded contrarians who have all kinds of alternative suggestions.

That is, of course, nonsense. Pretty much all the real progress on other factors is done by the same scientists who recognize the importance of CO2. All those effects work together. It's the people who think they can actually replace the CO2 elephant-in-the-room with something else who are being naive.

Aerosols don't replace greenhouse as a theory; they add on to it. The author of this Arctic report, for example, makes no bones about the fundamental importance of CO2 for global climate. That doesn't alter in the slightest his inference of the importance of aerosols and black carbon, both globally and as a particularly strong regional Arctic forcing. See, for example, this interview. It was pretty funny: Shindell doesn't like the term "global warming". He thinks it sounds too cosy, and suggests instead "climate meltdown".

Cheers -- Sylas
 

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