Only dirty coal can save the Earth

[mgb_phys]

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.

 

[Evo]

Interesting, that would explain why there is climate change that doesn't correlate to the amount of CO2.

 

[jostpuur]

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]

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]

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]

" 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]

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]

" 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]

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]

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]

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

 

[sylas]

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]

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]

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

 

[jostpuur]

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 F=ma 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]

If somebody writes an equation F=ma 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

 

[Bystander]

(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]

---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 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

 

[sylas]

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

 

[mheslep]

...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.

 

[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.

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

 

[mheslep]

Thanks for the clear and coherent response.

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

 

[sylas]

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

 

[sylas]

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

 

[Peter Watkins]

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.

 

[sylas]

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

 

[Peter Watkins]

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.

 

[Skyhunter]

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.

 

[Gokul43201]

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.

 

[Skyhunter]

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.

 

[Gokul43201]

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?

...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.

 

[Skyhunter]

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.

 

[sylas]

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

 

[Gokul43201]

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.

 

[sylas]

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 ) 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

 

[Gokul43201]

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.

1. This arrow is not present in the original paper; only in the NASA article cited in the OP.

2. The arrow is positioned at 1967. The (US) Clean Air Act regulating SO2 emissions was passed in 1970. The kink in the Arctic temperature anomaly appears at 1967.

3. There is yet a stronger kink in the Arctic anomaly at about 1915 (coincidentally, another low point in the AMO). So, the 1967 kink is not the only distinct (let alone most distinct) kink in the anomaly record plotted in that figure.

4. As I understand it, the actual figure 2 in Shindell (2009) is primarily meant to show the large divergences in the correlation coefficient between global anomalies and different regional anomalies; not to "show" that the effect of aerosol forcings can be "seen" in the Arctic anomalies.

5. Was there a "sharp change in aerosol emissions" around 1967? From the little digging I've done, I've seen plots that say things between (a) there was a sharp decrease in US sulfur emissions around 1970, and (b) there wasn't much of a decrease in North American + European + East Asian sulfur emissions until late in the '70s, but there was a slow down in the increase starting around 1970. Most of the figures I looked at didn't cite the original sources, so I'm not sure how accurate they are. (Example: http://adamant.typepad.com/seitz/images/clip_image002.jpg ).

You, evidently, have a different hypothesis.

Where did you get that idea? If there is one thing I am aware of, it is that I am by no means qualified to contradict most anything published in refereed papers in Climate Science, least of all, the overall model itself. My only complaint here is with the manner of presentation of one particular figure on the NASA page, and not with the hypothesis of the Shindell-Faluvegi paper. Do you find it inconsistent that I can completely accept the regional aerosol forcings determined by Shindell and Falugevi and also doubt that these forcings can be eyeballed out of the regional anomaly curves (as suggested by the modified figure in the NASA page)?

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 must not have made myself very clear then, since I, in no way objected to the hypothesis, nor even presented a different hypothesis. And I certainly didn't attempt to make the point that any hypothesis different from mine (if I were to present one), became "dangerous" or "misleading" because I disagreed with it (if I were to disagree, and in this case, I don't).

I think you SHOULD read the paper before declaring it "dangerous".

I did no such thing (should I ask you to read my post again, before mischaracterizing it?). I specifically limited my comment to the figure in the webpage, and I didn't even call that "dangerous". I said that I found it "dangerously bordering on misleading". Furthermore, having read the paper now, I see that the figure (as presented on the NASA page, with the arrow) and the figure caption (this, I expected) are different from those in the paper.

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.

Thanks for the discussion. Let me stress that I am not proposing any kind of alternate hypothesis that disagrees with the conclusions of the Shindell paper. I am not even saying that the AMO is a dominant factor in explaining the Arctic anomalies. All I am saying is that the NASA page gives the impression that the 1967 kink is essentially due to cuts in aerosol emissions, while, I believe that (i) the kink itself (not the overall excess in the Arctic trend, which the paper makes clear is due largely to aerosols) may be an artifact of several coincident events (of which, off the top of my head, I named the AMO and the PDO, which you explain are irrelevant in this case), and (ii) unless there is a strong mathematical case for it, eyeballing kinks, even if it seems to make a rather pleasing visual statement, should not serve as a surrogate for the results of a pretty complex model involving several interacting factors.

But as a layperson, I have a question relating to your above paragraph:

From a rough estimate, I would guess that about 5/9 (or about 56%) of the Arctic latitudes (i.e., lats above 60N) lie below 70N lat, which you mention is the upper boundary for the AMO data. This looks like a large fraction to a casual observer like me. Is this number irrelevant (or insignificant due to its value, contrary to its appearance to me) to a statement (not exactly yours) that the AMO is essentially inconsequential to Arctic climate (which I assume includes the area weighted anomalies shown in Fig 2)? If such a statement is true, is there a reasonably accessible-to-layperson explanation for why this is so?

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.

Can we keep the pop-psychology out of this thread?

 

[Gokul43201]

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".

Ha ha. That's priceless!

 

[sylas]

Can we keep the pop-psychology out of this thread?

You're right. I was more snarky than necessary. Sorry. Just posting this quickly to acknowledge and apologise; and I'll followup on the specifics later tonight with any luck.

By the way. We're all lay amateurs here. I'm a novice with an appetite for physics and too much time on my hands. I've learned a lot by reading and playing around for myself, to the point where I feel pretty comfortable talking with experts, but not as an equal. I am an egg.

Cheers -- Sylas

 

[sylas]

1. This arrow is not present in the original paper; only in the NASA article cited in the OP

Quite so. The press release included the arrow as a good way to describe for a popular audience the nature of the hypothesis advanced in the paper. It works pretty well, IMO. The idea of a press release is short, simple, comprehensible accounts of key ideas.

2. The arrow is positioned at 1967. The Clean Air Act regulating SO2 emissions was passed in 1970. The kink in the Arctic temperature anomaly happened in 1967.

The data does not admit that level of precise identification. It's a nine year running average. There's no attempt in the paper to explain kinks at a year to year resolution.

A general reader is likely to over interpret the graph and see things in terms of one particular year. I did it myself when I first saw the graph, even without the arrow. There's no great damage done as a result. The shift is pretty abrupt, even if you can't really use the data to pin it to a single year. The key point is that there is a definite shift in trend associated with changes to aerosol emissions. That is the hypothesis, well argued in the paper.

The arrow points to a time where there is a plain shift in the trend, that the paper associates with a shift in historical trends for aerosol emissions, of which the clean air act is an important part. One of the major points in the paper is that this indicates some possible ways to mitigate Arctic warming. Hence the indicated shift is actually pretty fundamental to the paper.

To show what I mean about over interpreting a smoothed average, I picked up a time series for latitude 64 and north, based on the same NASA data used by Shindell and Faluvegi. (Zonal timeseries available here). Shindell and Faluvegi plotted latitude 60 and North. Here is latitude 64 and North, both the data and a 9 year average, as applied in the paper. Note that the actual analysis work uses the underlying gridded product, which divides up the planet with a grid and gives separate anomalies to each cell.

The paper itself identifies three distinct phases, as 1880-1930, 1931-1975, and 1976-2007. If I am following this correctly, the middle period was selected to be large enough to include the shifts, rather than trying to pick out a specific year of change.

In the analysis of the historical record, setting the middle time period to 1931-1975 was based on the clear shifts in temporal trends around 1930 and 1975. However, it also has the advantage of allowing us to avoid the influence of spurious trends that are thought to have been introduced around the time or World War II, whose influence gradually faded out by the mid-1960s. […]

-- Shindell and Faluvegi 2009, supplementary information​

4. As I understand it, the actual figure 2 in Shindell (2009) is primarily meant to show the large divergences in the correlation coefficient between global anomalies and different meridianal anomalies; not to "show" that the effect of aerosol forcings can be "seen" in the Arctic anomalies.

The paper is saying the effect of aerosol forcings is clearly seen in the meridinal anomalies. The purpose of the paper is to derive aerosol forcings from the anomalies.

Where did you get that idea? …

From your repeated mention of AMO and PDO as possible explanations. It did not occur to me that you might want to explain the kink only, rather than the trend. You don't need to explain short term kinks in noisy data. They're there all the time; and smoothing is applied in order to hide them away and reveal the main trends which are the focus for explanations.

… Do you find it inconsistent that I can completely accept the regional aerosol forcings determined by Shindell and Falugevi and also disagree that these forcings can be eyeballed out of the meridianal anolamy curves (as suggested by the modified figure in the NASA page)?

I can't see how you manage to both agree with Shindell and Faluvegi about forcings while not also seeing the clear association with the merididial anomaly upon which their forcings are based. It's rather odd.

The forcings they derive are inferred from those curves. After some detailed consideration of how this derivation works, they then see if their inference from the anomaly curves can be matched with historical emissions. The inference from the anomaly is first. They are not basing their argument upon the historical data, but rather using the data as a check on their model based argument. In fact, the historical data is in some respects not adequate for making this inference. The authors go on to make speculations for aspects of the history that are rather unclear.

It's a neat piece of work; and much stronger that merely taking historical emissions as the basis for forcings.

Thanks for the discussion. Let me stress that I am not proposing any kind of alternate hypothesis that disagrees with the conclusions of the Shindell paper. I am not even saying that the AMO is a dominant factor in explaining the Arctic anomalies. All I am saying is that the NASA page gives the impression that the 1967 kink is essentially due to cuts in aerosol emissions, while, I believe that (i) the kink itself (not the overall excess in the Arctic trend, which the paper makes clear is due largely to aerosols) may be an artifact of several coincident events (of which, off the top of my head, I named the AMO and the PDO, which you explain are irrelevant in this case), and (ii) unless there is a strong mathematical case for it, eyeballing kinks, even if it seems to make a rather pleasing visual statement, should not serve as a surrogate for the results of a pretty complex model involving several interacting factors.

In my opinion, it is very helpful for press release to have a suitable surrogate for a complex model, so that the main idea can be conveyed to a popular audience without all the technical detail of the paper.

Any graph of a comparatively abrupt transition is likely to have a local minimum that will draw the eye, and no additional explanation is needed beyond this for "kinks". The paper itself definitely identifies the shift in aerosol emissions as the cause for that shift in the anomaly that you can see at a glance when you look. Given noisy data there are random variations that might make one year or another stand out as the minimum in the graph. It's your prerogative to speculate, of course; but temperature timeseries show heaps of natural short term variation that is always present along with any other longer term trends.

But as a layperson, I have a question relating to your above paragraph:

From a rough estimate, I would guess that about 5/9 (or about 56%) of the Arctic latitudes (i.e., lats above 60N) lie below 70N lat, which you mention is the upper boundary for the AMO data. This looks like a large fraction to a casual observer like me. Is this number irrelevant (or insignificant due to its value, contrary to its appearance to me) to a statement (not exactly yours) that the AMO is essentially inconsequential to Arctic climate (which I assume includes the area weighted anomalies shown in Fig 2)? If such a statement is true, is there a reasonably accessible-to-layperson explanation for why this is so?

My point was that the AMO extends a long way beyond the Arctic, down to latitude 20 and the tropic. Therefore it is unlikely to be the cause of trends not seen also down in the middle latitudes.

Furthermore, most of the Arctic is landlocked behind Siberia and Canada. The polar amplification of warming extends right across the whole Arctic, not just the bit adjacent to the Atlantic, whereas we should expect any AMO influence to be more localized.

It is quite possible that the AMO will have some impact on the Arctic, but I would expect any impact to be localized.

Cheers -- sylas

 

[sylas]

Breaking news!

Drew Shindell has just put up a fairly lengthy guest post at the realclimate blog, specifically to talk about his research.

Guest post from Drew Shindell, NASA GISS

Our recent paper “Climate response to regional radiative forcing during the twentieth century”, has generated some interesting discussion (some of it very 'interesting' indeed). So this post is an attempt to give a better context to the methods and implications of the study. [...]

-- realclimate: Yet more aerosols: Comment on Shindell and Faluvegi​

This is not peer reviewed comment so it is technically not a legitimate reference for this forum, which is amusing. I think the physicsforum rule is a very sensible one and has obvious advantages. On the other hand, this is written by the first author of the study we are discussing here, and it is specifically intended to give the kind of background context that interested amateurs like most of us here really need.

So here's the link, which is useful if you want to know how the authors of the peer reviewed article would explain it at a more accessible level. We'll continue to refer to the peer reviewed article as a basis for discussion, but I think it is fair enough to have a link to Drew's own comments as a resource and aid to understanding of the article in question. I beg the indulgence of mentors.

Cheers -- Sylas

 

[Gokul43201]

Quite so. The press release included the arrow as a good way to describe for a popular audience the nature of the hypothesis advanced in the paper. It works pretty well, IMO. The idea of a press release is short, simple, comprehensible accounts of key ideas.

That arrow would have never gotten past peer review. I disagree with your opinion: sexying up the science at the cost of rigor, in my opinion, more often does more damage than good.

The data does not admit that level of precise identification. It's a nine year running average. There's no attempt in the paper to explain kinks at a year to year resolution.

Then why center the arrow at 1967 instead of 1970? Or any other year. It's plain to see that the arrow was positioned not at some supposed starting point of "clean air regulations" but at the nearest convenient kink.

In fact, the analysis in the paper is not particularly well suited to pinpointing even a single decade during which aerosol emission changes may be inferred from the difference between observed regional trends and modeled results of warming from GHGs + Natural forcings + Ozone since it only analyzes correlations for the linear trends over three multidecadal periods (Fig 4 and related discussion).

A general reader is likely to over interpret the graph and see things in terms of one particular year. I did it myself when I first saw the graph, even without the arrow. There's no great damage done as a result.

You think not? Let me get back to this in my closing. ;)

The shift is pretty abrupt, even if you can't really use the data to pin it to a single year.

Then why create the impression that you can? Moreover, the abruptness of the shift in the observed data is not something the analysis in the paper is even capable of addressing (not saying that it ought to be; in fact, I'd be pretty surprised if someone said that). All they can say is that aerosol forcings (when added to the "composite" forcing of 20 different climate models) explain the difference in trend over two consecutive 40-ish year periods. Whether that difference appears as an abrupt change in slope over only year or two or as a continuous - but lot less abrupt - increase over two or three decades is not something the analysis can tell.

The key point is that there is a definite shift in trend associated with changes to aerosol emissions. That is the hypothesis, well argued in the paper. The arrow points to a time where there is a plain shift in the trend, that the paper associates with a shift in historical trends for aerosol emissions, of which the clean air act is an important part. One of the major points in the paper is that this indicates some possible ways to mitigate Arctic warming. Hence the indicated shift is actually pretty fundamental to the paper.

What do you mean by "indicated"? Nowhere in the paper is there a reference, directly or indirectly to the indicator (the arrow placed at 1967) in the NASA figure. The indication given by that indicator goes a lot further than the paper is capable of going.

From your repeated mention of AMO and PDO as possible explanations. It did not occur to me that you might want to explain the kink only, rather than the trend. You don't need to explain short term kinks in noisy data. They're there all the time; and smoothing is applied in order to hide them away and reveal the main trends which are the focus for explanations.

I agree that it might be wise to give short term kinks in noisy data (noisy, that is, at the timescale relevant to the size of the kink) little or no attention, which adds to my chagrin that such a convenient kink was chosen to finesse a statistically unmakeable point (in the NASA figure).

As for my mention of the AMO/PDO, it was partly based on (my now somewhat foggy) memory of a paper I had read in the context of another thread ( linked here ). I was therefore only mildly surprised when, upon reading the Shindell paper, I got to this part in the concluding section (emphasis mine):

Our results suggest that aerosols have had a large role in both global and regional climate change during the twentieth century. Both these results and forward modelling^24–26 indicate that Arctic climate is especially sensitive to Northern Hemisphere short-lived pollutants. Arctic trends may also be related to internal atmosphere–ocean dynamics^27–29.

Reference 27: Schlesinger & Ramankutty, Nature (2004) is the paper I mentioned above. And the sentence in bold make almost exactly the kind of admission that I was pointing to sort of naively: that there may be some significant contribution to the warming trends from these atmosphere-ocean interactions that could possibly factor into the observed variations in the timeseries.

I can't see how you manage to both agree with Shindell and Faluvegi about forcings while not also seeing the clear association with the merididial anomaly upon which their forcings are based. It's rather odd.

Of course I see the association and raise no objections to it (that is the extent to which I "agree", given that I don't consider myself particularly qualified to disagree). The only thing I raised an objection to is the presentation of the graph with the arrow.

The forcings they derive are inferred from those curves. After some detailed consideration of how this derivation works, they then see if their inference from the anomaly curves can be matched with historical emissions. The inference from the anomaly is first. They are not basing their argument upon the historical data, but rather using the data as a check on their model based argument.

Correct (at least, that is how the analysis is presented in the published form). But the inference is only upon the trend over a 30-40 year period and has no ability to make predictions over much smaller timescales. And in the paper, they make no such insinuations.

In my opinion, it is very helpful for press release to have a suitable surrogate for a complex model, so that the main idea can be conveyed to a popular audience without all the technical detail of the paper.

Any graph of a comparatively abrupt transition is likely to have a local minimum that will draw the eye, and no additional explanation is needed beyond this for "kinks". The paper itself definitely identifies the shift in aerosol emissions as the cause for that shift in the anomaly that you can see at a glance when you look.

The paper never attempts to make the case that aerosol emissions should give rise to a sharp increase in the Arctic trend around 1967. And, as you explain, the analysis is clearly a lot more complicated than (and a lot different from) eyeballing sudden changes in temperature anomalies and looking for historical records that coincide with those eyeballed "events", but that is the kind of impression the press release risks creating with the lay reader. And it is this kind of overreach for the sake of visual "voila"ness that I'm objecting to here. I strongly believe there is a greater disservice done to the public when you provide an oversimplified explanation that does not carry the kind of scientific merit that it appears to possesses than when you tell them something like: There's not a simple explanation; it takes a lot of careful mathematical analysis, but in this graph, there is a relatively larger trend in the Arctic temperatures over the last few decades that correlates well with what would be expected from the decrease in aerosol emissions resulting from recent Clean Air acts in the US and Europe.". If you are going to make an oversimplification for the sake of audience penetration, I believe you have a responsibility to put out this disclaimer clearly.

Creating the impression that one can easily eyeball correlations (to say nothing of causation) in a complex many-variable system is a bad idea. It's just the kind of thing, in my opinion, that has resulted in the gazillions of climate blogs penned by Tom, Dick & Harry, who have overnight become armchair climate scientists because they have easy access to historical data. It is what I think has led to a gross misrepresentation of climate science, to the extent that every T, D & H now feels qualified to referee and refute the work of professionals.

PS: That took too long. I don't have the time or energy to keep this debate up. I imagine we will likely disagree on the broader point here. I will be happy to read any response you have (if you wish to write one), but if I do not follow up, it is not out of disrespect or disregard.

 

[sylas]

PS: That took too long. I don't have the time or energy to keep this debate up. I imagine we will likely disagree on the broader point here. I will be happy to read any response you have (if you wish to write one), but if I do not follow up, it is not out of disrespect or disregard.

No problem, I understand and sympathize. We disagree on how trivial/dreadful it is to use an arrow in a press release to point out a shift in the trend, given the potential for over-interpretion, and that's fine. I'm glad to have your view expressed, and am content to leave it there. Thanks for the exchange.

Moving on, there are other aspects of this research that can be usefully emphasized.

Can dirty coal help save the Earth??

The title of this thread is funny, but it is directly in conflict with the research being described. I'm guess it was intended as a joke, and not as a serious inference. One could only think that dirty coal can save the Earth if they looked at one graphic alone, and not the caption, or the rest of the press release, or the other diagrams. In fact, dirty coal is just as likely to increase the Arctic aerosol warming effect being described.

In the press release, and in the associated paper, there's a consistent parallel recognition of two major aspects of the aerosol impact: warming from black carbon, and cooling from sulfates.

Though there are several varieties of aerosols, previous research has shown that two types -- sulfates and black carbon -- play an especially critical role in regulating climate change. Both are products of human activity.

Sulfates, which come primarily from the burning of coal and oil, scatter incoming solar radiation and have a net cooling effect on climate. Over the past three decades, the United States and European countries have passed a series of laws that have reduced sulfate emissions by 50 percent. While improving air quality and aiding public health, the result has been less atmospheric cooling from sulfates.

At the same time, black carbon emissions have steadily risen, largely because of increasing emissions from Asia. Black carbon -- small, soot-like particles produced by industrial processes and the combustion of diesel and biofuels -- absorb incoming solar radiation and have a strong warming influence on the atmosphere.

-- NASA press release on publication of Shindell and Faluvegi (2009)​

The main research paper concludes by looking specifically at ways that Arctic warming can be mitigated. This is a consistent thread through all Shindell's research. He's not only interested in describing the science, but seeing how it can be applied. The concluding paragraph of the main text in the paper takes up this theme.

Our calculations suggest that black carbon and tropospheric ozone have contributed ~0.5 - 1.4 C and ~0.2 - 0.4 C, respectively, to Arctic warming since 1890, making them attractive targets for Arctic warming mitigation. In addition, they respond quickly to emissions controls, and reductions have ancillary benefits including improved human and ecosystem health.

-- Shindell and Faluvegi (2009), concluding paragraph, p298​

Sulfates are not mentioned here, because they are NOT an attractive target for Arctic warming mitigation. You'd have to increase sulfates, and that's a dreadful idea. The associated damage to health and ecosystems is appalling. Think acid rain. This is why we have the clean air policies in the first place!

The simplest mitigation step is to help clean up the dirty combustion processes that generate black carbon. Most especially this arises from inefficiently combusted diesel fuels, the extensive use of biomass (like wood) as fuel, and small scale and domestic use of inefficient coal burners. Dirty coal also contributes to this load of black carbon. The best approach is moving to cleaner combustion technologies, which also brings additional benefits of health and standard of living for people living in the highly polluted urban centers in Asia, especially.

Sources of misunderstanding

Sometimes misunderstanding arises just from careless reading. It's always possible to improve the presentation of a press release; but some responsibility lies also with a reader for basic common sense; even with a complete novice.

The figure we've been talking about has a labeled arrow for the clean air act, and nothing about black carbon. The text in the caption is as follows:

Since the 1890s, surface temperatures have risen faster in the Arctic than in other regions of the world. In part, these rapid changes could be due to changes in aerosol levels. Clean air regulations passed in the 1970s, for example, have likely accelerated warming by diminishing the cooling effect of sulfates.

-- Caption to a graph: NASA press release​

Read in isolation, someone might skip over the word "example" and get the incorrect impression that this is mostly about reducing sulfates with the clean air act; but even a complete novice reader should be expected to see more than just the last diagram of the press release in isolation. The diagram above it, and the main text, all explains the dual impact plainly.

… While black carbon absorbs radiation and contributes to warming, sulfates reflect it and tend to cool Earth.

-- Caption to images of aerosol and black carbon particles: NASA press release for publication of Shindell and Faluvegi (2009)​

At the risk of being controversial, the wider response to this paper online and in popular media shows a more serious problem than novices failing to pick up the whole picture at first glance.

There is strong popular objection to the notion that human influences are driving the trend of global warming, and to the idea that carbon dioxide or other greenhouse gases are the major factor involved. This is fostered by a steady stream of material from various pundits and bloggers and social commentators, ranging from scientifically dubious to demented pseudoscience.

In fact, the primacy of anthropogenic greenhouse gases as the major global forcing in the modern era is basic physics. There's plenty of room to investigate other impacts; but it is nonsense to say that anthropogenic greenhouse gases are unimportant. Their central role in global trends is taken for granted by Shindell and Faluvegi. Indeed, Drew Shindell in particular is a major figure in the development of modeling for climate and atmosphere, which shows the global greenhouse impact clear as daylight.

The level of misunderstanding in popular debate goes well beyond misreading a press release. The speed at which Shindell and Faluvegi's work has been picked up and passed around by the usual suspects in this game, as if it was some kind of refutation of conventional climatology and greenhouse warming, shows more than mere misunderstanding.

Masking global warming

The paper argues that most of the temperature increase in the Arctic arises from a regional aerosol impact. It does not mention the clean air act directly; but there is one mention of "clean-air policies" in Europe and the USA, in a single sentence that also speaks of black carbon.

During 1976-2007, we estimate that aerosols contributed 1.09 +/- 0.81 C to the observed Arctic surface temperature increase of 1.48 +/- 0.28 C. Hence, much of this warming may stem from the unintended consequences of clean-air policies that have greatly decreased sulphate precursor emissions from North America and Europe (reducing the sulphate masking of greenhouse warming) and from large increases in Asian black carbon emissions.

-- Shindell and Faluvegi (2009) p298​

From the numbers, Shindell and Faluvegi are obviously not saying it is all up to aerosols and black carbon; there's still a substantial contribution from a mix of other effects, including the global greenhouse impact and internal regional variability. The method applied in the paper is to take the general global trend, which is a mix of greenhouse, natural and ozone forcings, (G+N+O in the paper) and then identify the local regional impact that drives any local difference from the global trend.

I'll give the last word here to Drew Shindell himself:

It’s also worth considering how to interpret the effects of decreasing sulfate during the past 3 decades. To try to make sure that the complex role of aerosols wouldn't be misunderstood, when referring to the recent warming due to aerosols at Northern Hemisphere mid-latitudes and in the Arctic, we stated in the conclusions of the paper:

"much of this warming may stem from the unintended consequences of clean-air policies that have greatly decreased sulfate precursor emissions from North America and Europe (reducing the sulfate masking of greenhouse warming) and from large increases in Asian black carbon emissions."​

So it is incorrect, or at least quite incomplete, to say that that controls on air pollution such as those created under the Clean Air Act in the US have caused the recent warming. In the absence of increasing greenhouse gases, our large historical emissions of sulfate precursors would have led to substantial cooling from sulfate, and the subsequent reduction in emissions would have brought temperatures back towards their previous level. So reduced sulfate does not cause warming in an absolute sense, only relative warming compared to a time when emissions were larger.

-- Drew Shindell, in Yet more aerosols: Comment on Shindell and Faluvegi, April 21 2009​

Cheers – Sylas

 

[Gokul43201]

(Regarding the controversy issue you raised) I don't see why a novice skeptic of AGW would care for anything in this paper. After all, the analysis is based on a composite of some 20-odd climate models, most of which presumably attribute a sensitivity of somewhere between 1.5C to 4.5C per doubling of CO2. If you ("you" being the skeptic) believe the real number is closer to zero, then you are essentially rejecting the starting point of the paper. Fig 1 in the paper ought to make you stop reading right away, as you doubtless will have noticed that the (1 sigma) error bars on the response per unit forcing from CO2 are way smaller than the error bars from the other types of forcing.

So what is in this paper that it has the skeptics all interested? Why not simply pooh-pooh it in the same way that you'd pooh-pooh any other paper that uses a significant sensitivity to CO2?

 

[Skyhunter]

(Regarding the controversy issue you raised) I don't see why a novice skeptic of AGW would care for anything in this paper. After all, the analysis is based on a composite of some 20-odd climate models, most of which presumably attribute a sensitivity of somewhere between 1.5C to 4.5C per doubling of CO2. If you ("you" being the skeptic) believe the real number is closer to zero, then you are essentially rejecting the starting point of the paper. Fig 1 in the paper ought to make you stop reading right away, as you doubtless will have noticed that the (1 sigma) error bars on the response per unit forcing from CO2 are way smaller than the error bars from the other types of forcing.

So what is in this paper that it has the skeptics all interested? Why not simply pooh-pooh it in the same way that you'd pooh-pooh any other paper that uses a significant sensitivity to CO2?

Because the anti-AGW psuedo media need to fill their blog pages and op-ed columns every day with something new.

Anything they can cherry pick in order to form a specious argument is fair game. They know that their audience in general will ignore the contradictions in logic.

I know that most men — not only those considered clever, but even those who are very clever and capable of understanding most difficult scientific, mathematical, or philosophic, problems — can seldom discern even the simplest and most obvious truth if it be such as obliges them to admit the falsity of conclusions they have formed, perhaps with much difficulty — conclusions of which they are proud, which they have taught to others, and on which they have built their lives.

 

[mheslep]

I know that most men — not only those considered clever, but even those who are very clever and capable of understanding most difficult scientific, mathematical, or philosophic, problems — can seldom discern even the simplest and most obvious truth if it be such as obliges them to admit the falsity of conclusions they have formed, perhaps with much difficulty — conclusions of which they are proud, which they have taught to others, and on which they have built their lives.

Among the scientific community, of which side is it more correct to say they have 'built their lives' and careers around their position on AWG? Even among the pundits, which side?

 

[Skyhunter]

Among the scientific community, of which side is it more correct to say they have 'built their lives' and careers around their position on AWG? Even among the pundits, which side?

Scientists from both sides, to one degree or another have all built their careers around their beliefs.

You are suggesting a causal link with no statistical basis.

 

[mheslep]

Scientists from both sides, to one degree or another have all built their careers around their beliefs.

No doubt, but my casual observation of, say, the 100s of Nobel peace prizes handled out to the IPCC members, and the punditry income and Academy Awards from 'Inconvenient Truth' all lead me to believe its a rather lopsided investment on the part of AWG proponents.

You are suggesting a causal link with no statistical basis.

Yes, in response to the Tolstoy quote. What was the basis for originally posting that?

 

[Gokul43201]

Among the scientific community, of which side is it more correct to say they have 'built their lives' and careers around their position on AWG? Even among the pundits, which side?

Among the scientific community, I don't believe there really is this clear distinction that let's one classify all of its members as belonging in one side or another. I believe this is, for the most part, a false dichotomy created by politicians, the press and the blogosphere.

And Al Gore is NOT a member of the scientific community. Neither is the IPCC Chairman.

Edit: I notice this is now drifting away from the science in the paper cited in the OP and getting into a discussion of sociological and/or political issues, neither of which belong in this thread and if continued, could well lead to its locking.

 

[misgfool]

The carbon capture and storage technology might increase coal usage by up to 40% (for the equivalent energy produced) and cut down CO2 emissions leaked to the atmosphere by 90%. So it would increase the global dimming effect and dampen global warming effect.

 

[mheslep]

Edit: I notice this is now drifting away from the science in the paper cited in the OP and getting into a discussion of sociological and/or political issues, neither of which belong in this thread and if continued, could well lead to its locking.

Yes, apologies for my role in that.