Only dirty coal can save the Earth

[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.