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Aerosol formation and climate, Part I

Filed under: — group @ 13 April 2009 - (Italian)

Guest post by Bart Verheggen, Department of Air Quality and Climate Change , Energy research Institute of the Netherlands (ECN)

The impacts of aerosols on climate are significant, but also very uncertain. There are several reasons for this, one of which is the uncertainty in how and how fast they are formed in the atmosphere by nucleation. Here, in part I, I’ll review some of the basic processes that are important in determining the climate effects of aerosols, focusing in particular on their formation. This is also relevant in order to better understand –and hopefully quantify- the hypothetical climate effects of galactic cosmic rays which I’ll discuss in a follow-up post.


Aerosols are liquid or solid particles suspended in the atmosphere (but not including water droplets or ice crystals). They can either be directly emitted into the atmosphere (primary aerosols like dust), or they can be formed in the atmosphere by condensation (secondary aerosol like sulfates). Almost all of their properties, and thus effects, are size dependent: The particle size governs the rate at which they fall out (and thus atmospheric lifetime), their interaction with radiation, their impact on clouds, or even their health effects. And they come in very different sizes, ranging from a few nanometers to tens of micrometers. Some sites with good introductory explanations to aerosols and their climate effects are here, here and here (German). RC also had some posts on the same generic topic here and here.

Climate effects of aerosols

Aerosol particles can influence climate in several ways: They scatter and absorb (in the case of black carbon) solar radiation (direct effects). They also act as cloud condensation nuclei (CCN) around which clouds can form, and thereby influence cloud reflectivity and cloud lifetime (indirect effects). Black carbon can have another indirect effect by changing the albedo of snow and ice, but that’s not the topic of this post. The aerosol indirect effects are the greatest source of uncertainty in assessing the human impact on climate change (reviewed here. The main idea is that more CCN causes liquid clouds to consist of more, but smaller, droplets. The resulting cloud is more reflective (first indirect effect). Due to the smaller size of cloud droplets, the formation of precipitation may be suppressed, resulting in a longer cloud lifetime and larger cloud cover (second indirect effect).

The mass of a freshly nucleated aerosol particle is more than 100,000 times smaller than that of an ‘aged’ aerosol of a size optimal to affect climate. As a rule of thumb, particles have to grow past 100 nm (1 nm = 10-9 meters) in order to become climatically active; below this size they are not easily activated into a cloud droplet and they don’t scatter solar radiation very efficiently. It is thus not immediately obvious that the climate effects of aerosols will depend very strongly on nucleation; the dependence is likely considerably damped, because a lot can happen to the aerosol particle as it comes of age.

Aerosol formation

The most prevalent trace gases do not generally nucleate new aerosols (or even condense onto existing ones), because they are too volatile (i.e. they have a high saturation vapor pressure and thus evaporate readily). They first have to be oxidized (usually under the influence of sunlight) to produce a compound with a lower vapor pressure. The prime example of this is the oxidation of sulfur dioxide (SO2) into sulfuric acid (H2SO4), which has a very low vapor pressure. The H2SO4 can then condense together with water vapor (and perhaps organic compounds and/or ammonia) to form a stable cluster of molecules: A new particle is typically 1-2 nanometers in diameter. Ions can also play a role, by lowering the energy barrier that needs to be overcome: The attractive forces between the molecules are stronger when one of them is charged. See here and here for a review of atmospheric nucleation processes.

Instead of nucleating into a new particle, H2SO4 could also condense on an existing aerosol particle, making it grow in size. Because of this competition for the vapor, nucleation is more likely to happen when there is only a little aerosol present.

Aerosol growth

Condensation of more vapor onto the nucleated aerosol makes it grow in size. However, other processes hamper its possibility to grow large enough to substantially influence the climate: Two aerosols can collide together, in a process called coagulation. Coagulation is particularly efficient between very small nano-particles and larger particles (of a few hundred nanometers). It causes the bigger one to grow in size, whereas the smaller (recently nucleated) one disappears. When there are a lot of very small aerosols around (i.e. after a nucleation event), they can also coagulate together. This causes them to grow in size, but decreases their number concentration. The loss processes for the number of aerosols (deposition and coagulation with bigger particles) are stronger when they’re very small.

Figure 1: Different factors influence the extent to which nucleation contributes to the number of cloud condensation nuclei (CCN). (Figure partly based on AGU presentation by Jeff Pierce)


New particle formation has been observed all over the globe, from the Poles to the Tropics, from urban to remote areas, and from surface sites to the upper troposphere (see here for a review of such observations). Of these locations, only nucleation in the free troposphere and in the vicinity of clouds seems to agree with theoretical predictions. In most other cases the number of aerosol particles produced is under-predicted. This has led to the development of semi-empirical approaches to describe nucleation. Laboratory studies have typically found much stronger dependencies on H2SO4 than atmospheric measurements. A confounding factor is that newly formed particles of 1 to 2 nanometers can not be directly measured by commercially available instrumentation (though there are new developments in this area). Nucleation takes place in a kind of no-man’s land between the gas and the liquid phase, about which we know surprisingly little.

Figure 2: Measurements of an atmospheric nucleation and growth event in the Lower Fraser Valley, Canada. The color gives the (normalized) number concentration, where the red color indicates the enhanced concentration of nucleated particles, growing into the CCN size range. (from Mozurkewich et al.)

So what is needed for nucleation to occur? Favorable conditions include a strong source of condensable vapor; high UV radiation intensity; low aerosol surface area; high relative humidity; low temperature; presence of ions; and atmospheric mixing processes. Under different environmental conditions, different nucleation mechanisms may be at work. For example, in industrial plumes and over urban areas enough sulfuric acid may be present to form new particles and have them grow to a stable size. Ammonia may neutralize the acidic cluster, and thereby help stabilizing it. Over forested areas, the relative role of organic compounds is expected to be much larger (though a strong correlation of nucleation events with sulfuric acid remains). In coastal areas, iodine compounds are likely involved in the nucleation process. In the upper troposphere, the ion density is usually larger, whereas the sulfuric acid concentration is lower. The relative role of ion induced nucleation may therefore be larger up there. The dominant role of sulfuric acid has remained a steady conclusion over the years, whereas the potential roles of organic compounds and ions are still hotly debated.

In part II, I’ll discuss the potential importance of nucleation and of galactic cosmic rays for climate change.

81 Responses to “Aerosol formation and climate, Part I”

  1. 51
    Mark says:

    “For a pittance of free conference travel,”

    Oddly enough, people like Monkton get to go to lecture circuits for bigwigs and not only get free nosh, travel and board, but they can get paid a wodge with it too.

    So if you subscribe to the “scientists just want the grant money”, then you can’t believe Monkton, Lindzen, Evans et al. either.

    Pity that doing their own thinking is too much work for them.

  2. 52
    Jim Bouldin says:

    Damn, sorry for veering off topic, my bad. Let’s talk aerosols not airheads.

  3. 53
    Ike Solem says:

    Marcus and twuth, the discussion of the Cornell study on soil carbon has little to do with aerosol topics, and everything to do with the response of the carbon cycle to warming temperatures – something that climate models do not attempt to take into account. Instead, climate models using CO2 forcing scenarios chosen by researchers – educated guesses about future human behavior and carbon cycle responses. (These are the IPCC scenarios).

    Soil carbon trends are due to a balance between photosynthesis, respiration, and burial. A leaf falls to the floor, and is largely digested back to CO2 by fungi and microorganisms – but some fraction ends up residing in soil for thousands of years before finally making its way back to the atmosphere.

    What the Cornell study shows is that in Australia, much of the soil carbon is built up due to wildfire activity, rather than microbial activity. This kind of charcoal-based soil carbon is remarkably stable relative to leaf-fungal humus, and as the planet continues to warm, such soils should be fairly stable and there should be little positive feedback effect.

    This area of science is called “biogeochemical modeling”, and involves more than just carbon. For example, there is a nitrogen cycle that continually interacts with the carbon cycle, and often determines the rate of the carbon cycle – along with temperature and many other variables.

    It is a good example of how denialists are trying to distort scientific research, however. Here is the original news release on the Cornell Paper:

    Nov. 18, 2008 Soil study suggests future climate change models should be revised – By Krishna Ramanujan

    As a result of global warming, soils are expected to release more carbon dioxide, the major greenhouse gas, into the atmosphere, which, in turn, creates more warming. Climate models try to incorporate these increases of carbon dioxide from soils as the planet warms, but results vary greatly when realistic estimates of black carbon in soils are included in the predictions, the study found.

    The story was then picked up by the website, which respun it:

    Global warming predictions are overestimated, suggests study on black carbon

    The paper says nothing about the ability of modern climate models to produce realistic predictions, despite what that headline implies. The site put on a new title, removed the first two sentences, and stuck in a new header:

    ( — A detailed analysis of black carbon — the residue of burned organic matter — in computer climate models suggests that those models may be overestimating global warming predictions.

    Again, those would be climate models that attempt to do biogeochemical predictions – a whole new subject, with the largest uncertainty being future human behavior – and there are no reliable equations for that one. They are not talking about how modern climate models treat aerosol forcing.

    Just a tad bit misleading, isn’t it? is owned by a technology consulting company, Omicron Technology Ltd. “We get people talking”, is part of their advertising line.

    We now get back to the link cited by “truth”, which directs readers to

    That link points us to the misleading and re-spun version, not the Cornell press release. It also includes the following dishonest claim:

    “The findings are significant because soils are by far the world’s largest source of carbon dioxide, producing 10 times more carbon dioxide each year than all the carbon dioxide emissions from human activities combined. Small changes in how carbon emissions from soils are estimated, therefore, can have a large impact.”

    In fact, the biosphere is thought to exchange as much as 100 gigatons of carbon in either direction each year – photosynthesis and respiration – compared to the 6 gigatons of fossil fuel CO2 added each year. The key difference is that the 6 gigatons of carbon is fossil carbon – it is not part of the normal carbon cycle, but rather lifts the level of all pools – more CO2 in the atmosphere and in the oceans.

    Thus, one could say that plants and soils are also the biggest sink of carbon dioxide on the planet, as they absorb at least ten times as much CO2 each year as is emitted by all human activity. Thus, there is no problem – all the CO2 is sucked up… or is it?

    The soil absorbs and emits vast amounts of CO2 each year, but is in steady state overall – a thousand years ago, the situation was much the same as it was a hundred years ago. The argument being made is similar to one claiming that evaporation isn’t balanced by precipitation, so the oceans will eventually evaporate away. X billion tons evaporate every year, so if you divide ocean mass by X you see that they will soon be gone…

    The actual paper is part of the very active scientific effort to understand potential feedbacks in the carbon cycle – soil carbon is a big one, as is permafrost, and possible ocean circulation changes. It in no way alters current scientific consensus on climate model reliability.

    Practically, what the paper says is that biochar amendments to soil are very stable – and so far, biochar is the only realistic carbon sequestration and storage program out there.

  4. 54


    Thank you for your response. I’m sorry I used the word belief, I didn’t mean anything by it. I should perhaps have said view.

    I don’t have access to Nature Geoscience, just Nature. So I guess I was wondering if you could summarize how Dr. Shindell’s study updates what can be found in the TAR.

  5. 55
    Hank Roberts says:

    > MikeB, 13 April 2009 2:35 PM, Shindell 2007 NYT, Nicolas, TAR ….
    Could y’all _please_ move a conversation about tha telsewhere? This is
    “Aerosol formation and climate, Part I” –we have a reading list at the top, we have the scientist here to teach, for now. Digress-> egress?
    “be Clonin” says ReCaptcha. Like, copy yours somewhere else.

  6. 56
    Hank Roberts says:

    Trying myself; Ike brought up the new Shindell paper. Okay, yeah, it agrees aerosols are the big uncertainty. But the topic is about what the factors are.

    Dr. Verheggen, you gave us a great many factors in the first post that affect what becomes an aerosol, how long the stuff stays in the air, how fast it grows from its original size (if it does), how big it has to get to change how it behaves.

    The first three links are to the introductory stuff. I’m trying.
    Gee, climatology is hard ….. (third paper is German language — anyone able to translate? Anything unique there that’s not in the first two introductory papers?)

    Then you pointed to the discussion of uncertainty, with the link to the PDF copy of Atmos. Chem. Phys., 5, 715–737, 2005
    Global indirect aerosol effects: a review; U. Lohmann, J. Feichter.
    (Ike, did you compare Shindell to that paper, for Nicolas’s question?)
    I’m just starting to try to read this.

    You know, this reminds me of hearing performance majors talk about learning music at college — how for the first few years they could no longer just enjoy music, because they were starting to learn to notice elements and how they fit together and changed over time, and it was as though the music was falling apart (this was before pixels …).

    I realize you’ve given us basic introductory reading here — and it’s dense, complicated, new, and amazing. And it is making just looking at the blue sky a little difficult right now. It’s full of stuff!

    Dr. V. — of the factors you listed, or the introductory papers you gave us listed — do you have grad students building the instruments to detect this kind of thing? Are you using off the shelf gear? Is there anything you “know is there but can’t measure” in the air? And are you working with any of the sediment/coring people to figure out how what’s in the air becomes whatever they find in mud or ice cores?

    I imagine as you’ve showed us it changes for weeks while floating around, that it continues to change after it falls into ice and freezes, or salt or fresh ice or water, and eventually sinks and ends up in mud layers.

    Does anyone do experimental work putting material into air (maybe in a big Zeppelin hangar or something?) and waiting a few weeks without any air movement and looking at the layers that fall out, say?

    Do you have any good radioactive tracers, say from the surface bomb tests, that help identify ‘airborne’ aerosols with whatever they become by the time a stratigrapher finds them in the mud or ice?

    Whew. ….

  7. 57

    Heinrich Schmid (33),
    I’m not aware of any estimates to what extent these mid-century wars contributed to climate changes, but I suspect it’s less than you’d estimate from the enormous destruction. Aerosol emissions from industrial sources are likely to be dominant in terms of climate.

    Hank Roberts (56),
    The prime thing relevant here that we “know is there but can’t measure” are the conglomerates of molecules leading up to a stable aerosol particle. Both their number concentration as a function of size, and their chemical composition (which is only being measured from a much larger size, say 20 nm). There are interesting developments in this area though, eg the AIS (air ion spectrometer), measuring the number size distribution of charged ions and clusters between 0.5 and 40 nm. I’m not working on instrument development myself, although that is an active area of R&D in the group I work at. As yet, we don’t collaborate with ice core/sediment researchers. An active area of research is based on simulating atmospheric reactions in so-called smog chambers. Waiting a few weeks is hardly possible tough, since most particles will have been lost to the walls of the chamber by then. It’s only recently that groups started to look at longer timescales of eg 60 hours, to look at chemical transformations that occur over those timescales, relevant for atmospheric aging processes.

  8. 58
    Marcus says:

    #53: Ike Solem: Fascinating! I am 99% sure that at the time I wrote my email (Nov 20th) the title of the Cornell news release was in fact “Global warming predictions are overestimated, suggests study on black carbon”: in fact, if you look at websites that picked the story up they cite the original title.

    Therefore, the author must have changed the title at some point after I wrote my email. It is nice to see that press offices do fix things when alerted to possible miscommunications (not saying that it was due to my email alone – I wouldn’t be surprised if other people wrote to them too).

  9. 59
    Ike Solem says:

    Note to Marcus: No, the author did not change the title or had the deceptive header – that was done by the editors of the web sites who picked up the story and respun it. Journalists don’t get to pick headlines – that’s the editor’s perogative – or that of the public relations agency, I suppose. For a recent example of how this works, see this story on Hill&Knowlton and Burson-Marstellar.

    Hank, you say:

    “Trying myself; Ike brought up the new Shindell paper. Okay, yeah, it agrees aerosols are the big uncertainty.”

    Hmmm… “Duae Quartunciae” brought up the topic, I thought. The Shindell paper reduces the uncertainty regarding the aerosol effect in the Arctic, and helps close gaps between models and observations. It’s not the only plausible explanation of the observed trends, but so far seems the most likely.

    However, it is worthwhile to compare and contrast the Shindell & Faluvegi paper with another recent aerosol paper:

    The Role of Aerosols in the Evolution of Tropical North Atlantic Ocean Temperature Anomalies, Evan et al. Science Mar 26 2009

    Here, we elucidate this question by using 26 years of satellite data to drive a simple physical model for estimating the temperature response of the ocean mixed layer to changes in aerosol loadings…

    Which is more reliable, and why? Are their conclusions similar, or mutually exclusive? Notice that Evan et al are saying that aerosol changes over the tropical Atlantic have a warming, not a cooling influence… Apparently, the only factor in the warming oceans in the Atlantic is a reduction in dust from Africa over the past ? years…

    To better determine the extent to which aerosols have contributed to the evolution of this tropical North Atlantic temperature anomaly, we subtract our monthly estimates of the oceanic cooling by dust and stratospheric aerosols from the observed tropical North Atlantic SST and plot the anomaly of the residual (Fig. 3). This is our estimation of variability in northern tropical Atlantic SST that is not directly driven by local changes in aerosols, which we will refer to as the residual SST. The trend in the residual SST time series is 0.08°C/decade (Table 1 and Fig. 3), 0.17°C/decade weaker than the trend in observed SST (Fig. 2B) and not statistically significant (23). These calculations suggest that 69% of the recent upward trend in northern tropical Atlantic SST is due to changes in aerosols

    There is a rather obvious ongoing effort to blame global warming on aerosols, as seen in Australia:

    “The Sahelian drought may be due to a combination of natural variability and atmospheric aerosol. Cleaner air in the future will mean greater rainfall in this region,” Leon Rotstayn, an Australian government researcher, said in a recent report – Washington Times, 2002

    CSIRO has a long record of supporting coal industry propaganda:

    The Shindell paper seems far more reliable than the Evans paper, overall – and the reason is that they use a complete global coupled model, not a “simple physical model”. The Evans et al. “estimate of the direct effect of dust radiative forcing on the upper-ocean heat budget” doesn’t seem very reliable for that reason alone. Their simplistic treatment of aerosols also doesn’t help much (they assume two types only with very specific optical properties (“sulfuric acid” and “dust”), and zero black carbon).

    It’s pretty surprising that a paper that used such simplistic approaches was selected for ScienceExpress publication, isn’t it?

    As far as uncertainties, the big one is not aerosols, but future human behavior. That will be the single largest factor in future climate outcomes.

  10. 60
    Marcus says:

    Ike: My recollection was that at the time, that was the title used on the Cornell website, as well as by all the sites that picket it up. I don’t know that I have any evidence of that, not having taken a screenshot at the time, but like I said, I’m 99% sure that the “deceptive” title was the original title at the time I wrote my email (November 20th). And therefore, I am presuming that the Cornell news office has changed the title, but all the sites that link to it are still using the original title.

  11. 61
    CTG says:

    There definitely seems to be a campaign in the media to use any aerosol research as “proof” that CO2 is not the principal cause of AGW. The Shindell paper was reported at The Register with the headline: “NASA: Clean-air regs, not CO2, are melting the ice cap”.

    I tried posting a comment asking for the headline to be changed, but it got nixed, and I also complained to the editor, but got no response. It might be an idea for Shindell or someone else at Goddard to drop a line to The Register asking them to correct their inaccuracies.

  12. 62
    Lawrence Brown says:

    Today’s New York Times has a front page article by Elisabeth Rosenthal about the effects of Soot from third world stoves on AGW.
    It reads in part:”While carbon dioxide may be the No. 1 contributor to rising global temperatures, scientists say, black carbon has emerged as an important No. 2, with recent studies estimating that it is responsible for 18 percent of the planet’s warming, compared with 40 percent for carbon dioxide. Decreasing black carbon emissions would be a relatively cheap way to significantly rein in global warming — especially in the short term, climate experts say. ”

  13. 63
    truth says:

    Jim Bouldin and Doug Rostram: [47] [50]
    You really have lost it completely, haven’t you.
    The implication from your attack seems to be that the only people in the world who are above questioning are the scientists and the true believers of AGW—that any other citizen of this world who just raises findings [ by other credible scientists] that you see as a threat to the firewall, —-must be verbally annihilated —it’s pathetic.
    I am just an Australian who wants the correct decisions made on the best possible evidence, for the sake of my children.
    Ike Solem:[53]
    You say the models don’t attempt to take into account the feedback response—

    ‘the response of the carbon cycle to warming temperatures – something that climate models do not attempt to take into account.’

    But later , you cite the Cornell paper —
    ‘Climate models try to incorporate these increases of carbon dioxide from soils as the planet warms, but results vary greatly when realistic estimates of black carbon in soils are included in the predictions, the study found.’

    You blame for the ‘over-estimating climate predictions ’ quote—–but the actual press release from Cornell begins with the following statement:
    ‘A detailed analysis of black carbon – the residue of burned organic matter – in computer climate models suggests that those models may be overestimating climate change predictions.’
    The statement from, that you call dishonest , also comes straight from the Cornell press release, below:
    ‘The findings are significant because soils are by far the world’s largest source of carbon dioxide, producing 10 times more carbon dioxide each year than all the carbon dioxide emissions from human activities combined. Small changes in how carbon emissions from soils are estimated, therefore, can have a large impact.’
    In your attack on the CSIRO, and on Evans et al , in [ 59], you appear to be saying that any researchers who do any research, or come up with any findings that suggest new factors,or that soften the alarmist rhetoric , or seek to find ways to use coal more cleanly, are just purveyors of blame and ‘propaganda’.
    The CSIRO, that you accuse of being a propagandist for the coal industry, is firmly on your side of this issue—but the crime in your view seems to be that they would have the temerity to seek to find ways to cut the CO2 emissions from coal-burning , or eliminate them—which is the subject of the two links you provided.
    How realistic is that attitude, when China is still commissioning coal-fired power stations on a weekly basis—Obama is now agreeing that coal will be with us for decades—and Germany [ even or especially its Greens party] is planning at least 12 new coal-fired power stations?

  14. 64
    Ike Solem says:

    Interesting, Lawrence – the NYT persists in insisting that black carbon is from wood stoves, and has nothing to do with ship emissions or diesel truck emissions or perhaps more frequent wildfires.

    In Asia and Africa, cookstoves produce the bulk of black carbon, although it also emanates from diesel engines and coal plants there. In the United States and Europe, black carbon emissions have already been reduced significantly by filters and scrubbers.

    In reality, studies show about a 50-50 split between fossil and biomass sources of black carbon, although data collection is quite poor. For biomass burning to be the culprit, there must have been quite the explosion in biomass use recently as compared to past eras. India’s population has roughly doubled in the past half-century, but it’s not clear that this would double biomass-sourced black carbon emissions. On the other hand, records show that India has increased fossil fuel use by a factor of at least 10, possibly 20, in the past half-century. And yet, we are informed by the NYT that the culprit is poor people burning dung.

    It certainly plays a role in the total black carbon aerosol load over India and the Indian Ocean – but fossil fuels are responsible for the vast majority of the addition – just look at the numbers.

    The other thing is that black carbon emissions from diesel trucks and shipping in the United States have not been reduced (much) or eliminated, as the NYT claims:

    Large Cargo Ships Emit Double Amount of Soot Previously Estimated, ScienceDaily (July 11, 2008)

    Commercial Ships Spew Half As Much Particulate Pollution As World’s Cars, ScienceDaily (Feb. 27, 2009)

    I’m not sure why the NYT is so insistent on ignoring shipping and blaming poor people for the atmospheric aerosol clouds, other than that it fits standard practice for diehard boosters of the “uncontested benefits of global trade”. Resource extraction is not responsible for environmental destruction, we learn, poor people are. What is particularly nauseating is how they try and use Ramanathan’s quote to push the PR agenda – ask yourself why they didn’t instead use the lead sentence from Ramanathan’s 2005 paper:

    South Asian emissions of fossil fuel SO2 and black carbon increased 6-fold since 1930, resulting in large atmospheric concentrations of black carbon and other aerosols.

  15. 65
    Lawrence Brown says:

    I agree,Ike, that the Times article could have ( and should have) put more emphasis on other sources of black carbon. Though I don’t believe that the Times has any bias against the poor. They don’t rely on the shipping industry to remain solvent.

    I’m not too familiar with this writer’s work,but Andy Revkin, who also covers global warming and related topics for the Times has had an objective approach.

    In any case Dr. Ramanathan considers the reduction of black carbon from this source to be serious enough that he returned to his homeland to deal with the problem.

  16. 66
    Ike Solem says:

    For a quick review of Ramanathan’s work, see:

    “More recently, Ramanathan showed that South Asian “brown clouds” caused by the burning of fossil fuels could lower ocean temperatures, slowing down monsoon circulation and reducing seasonal rainfall. In a pioneering study with agricultural economists, he linked the phenomenon to a significant decrease in the Indian rice harvest. He has also linked the combined heating effect of greenhouse gases and brown clouds, which contain soot, trace metals and other particles, to the recent retreat of Himalayan glaciers that supply drinking water to billions of people.”

    In particular, he’s known for the use of UAVs to sample atmospheric clouds, which was done in Beijing recently.

    It’s true that providing clean energy for cooking is necessary for India’s rural poor, but so is the replacement of diesel-powered transport with solar-powered transport.

    I must admit I do not find Andrew Revkins reporting to be very objective as of late. Compare the above Tyler prize report with Revkin’s blog on the topic:

    “The smoke is rising mainly from cooking fires fueled with firewood or dried dung.”

    That looks like respinning the press release to change the emphasis from fossil fuels to wood and dung fires, not like objectivity.

    Now, for the truest of the true:

    1) There are weather models which use sea surface temperatures and other climate variables as input for one-week forecasts

    2) There are climate models based on weather models, and they are driven by external forcings: greenhouse gases, for example

    3) There are biogeochemical models which attempt to estimate the rates of carbon cycling, nitrogen cycling, sulfur cycling, and so on. This is the kind of model that the paper addresses.

    Our current estimates of climate sensitivity are based on climate models that use CO2 emission profiles which are set by researchers.

    By far, the largest uncertainty in carbon cycle modeling is future human behavior.

    Another uncertainty is what will happen to carbon stored in permafrost and in soils as the temperatures warm – will much of it be converted to CO2, or not? The paper in question shows that biochar is a very stable form of carbon, unlikely to be converted back to CO2 as the climate warms. Thus, biochar is the leading candidate for effective carbon burial over geological time periods – which is the only way to reduce atmospheric CO2 concentrations (assuming you’ve already replaced fossil fuel combustion).

    Clearly, the web sites in question distorted the meaning of the original article in a transparent attempt to cast doubt on climate model conclusions – although it is true that the original author could have been a little more clear about what kind of models were being discussed.

  17. 67
    Lawrence Brown says:

    In his white paper on the subject of elemental carbon Ramanathan says:
    “Biomass burning and biofuel cooking are the major sources of EC emissions in India and other developing nations. The current international emphasis in global warming mitigation is on carbon dioxide, whereas the main focus of Surya is on EC, for reasons given in the next few sections.”

    The paper goes on to say:
    “……..75% of households in India, use biofuels and biomass, including wood, charcoal, crop residues and dung, to prepare food and heat their homes.9 More than 70% of India’s population lives in rural areas. Cooking accounts for about 60% of the overall energy and 80% of the non-commercial energy used in rural India. More than 90% of the cooking is done with fire wood and bovine dung, i.e, cow-dung10”
    “Soot and other particles in ABCs lead to a large reduction of sunlight at the ground and, in addition, lead to large atmospheric solar heating.”

    It appears that Revkin is correct in saying that the smoke and soot are mainly from cooking stoves in this area.

  18. 68
    Wili says:

    How much warming from GHG’s is being offset by the cooling effects of aerosols? Less than one degree? More? How much more or less?

    Another question I have is when gavin (I think it was) says that industry emits 7GtC/yr does he mean CO2, CO2 equivalent, or actual carbon? If the latter, what is the conversion factor to get annual tonnage for CO2? Does this ignore non-CO2 sources of GHG’s with carbon like methane?

    Thanks ahead of time for any light anyone sheds on my dimness.

  19. 69
    David B. Benson says:

    Wili (68) — Since it is carbon inthe active carbon cycle which matters, these emissons figures are typically stated in terms of C. But it is, of course, mostly CO2; 7 GtC = (44/12)X7 = 25.7 GtCO2. Methane contributions of carbon are rather small, but I haven’t the figures. Try the Carbon Dioxide Information Analysis Center at ORNL for more.

  20. 70
    Jim Eager says:

    Wili (68), 7Gt/yr would be only the carbon in the CO2.
    The molecular weight of carbon is 12, that of the O2 is 16×2, so CO2 is 44. Multiply the carbon weight by 44/12 to get to the weight of CO2.

  21. 71
    Lawrence Brown says:

    Re#68 by Wili: This is in partial answer to your questions

    “Based on records of activity in the energy and transportation sectors of the economy and on correlations with
    economic growth about 7 GtC (carbon) per year were injected into the atmosphere from 1995 to 2005 . Additionally,roughly 1 GtC/yr was injected” from forest burning.(the quoted part is from “Climate Change-Picturing the Science”by Gavin Schmidt and Joshua Wolf, page 146)

    This represents actual gigatons of carbon. To get the the tonnage for CO2 multiply the carbon tonnage by 44/12 or ~3.67. This is because carbon has an atomic weight of 12 and oxygen has an atomic weight of 16.Then the weight of a CO2 molecule is 12 + 2×16=44.
    Ergo the weight of C02 released into the atmosphere by burning fossil fuels = 7×44/12=~26Gt.

    I’ll have to leave it to the more knowledgeable to respond to the effects of aerosols on forcings or temperature. Though,I believe,the numbers on this are still (sorry about this) up in the air.

  22. 72
    Mark says:

    LAwrence, how much of the CO2 from world production is NOT from India?

    Given the US is #1 and doesn’t tend to use ANY dung for their cooking fires, I would suggest that “in this area” means “in india”.

    But most of the CO2 production is in the developed world.

  23. 73
    Lawrence Brown says:

    Mark, the ABC refers to the Asian Brown Cloud which is mainly made up of soot aerosols from polluted air in China and India. Note to the current administration- Don’t propose changing to dung cooking as an alternate fuel. :)

  24. 74
    Lawrence Brown says:

    Mark, The ABC stands for Asian Brown Cloud which is mostly composed of soot aerosols from India and China.

  25. 75
    Wili says:

    Thanks, guys, for the info on CO2 and references.

    Does anyone have any ideas on the aerosol issue. I thought this would be a central component of the thread, but I have not seen it discussed. Surely to know where we stand right now we need to know how much “current” GW is being masked by daily inputs of these aerosols. Is there know way to come up with even a back-of-the-envelope approximation?

  26. 76
    t_p_hamilton says:

    “Surely to know where we stand right now we need to know how much “current” GW is being masked by daily inputs of these aerosols. Is there know way to come up with even a back-of-the-envelope approximation?”

    Here you go:

  27. 77
    Lawrence Brown says:

    In addition to the site given by t_p_ figure
    SPM.2 ,of the Summary for Policy Makers of the 2007 report of the Intergovernmental Panel on Climate Change (IPCC)shows radiative forcings of black carbon on snow,as well as direct and cloud albedo effect of aerosols.

  28. 78
    Wili says:

    Thanks again. t_p’s figure seems to indicate that direct and indirect (what might those be, I wonder) effects of aerosols add up to more negative forcing than all the positive forcing of CO2 and methane combined since 1770! Can that be right? Am I missing something.

    Laurence, I couldn’t get your link to work.

    Thanks again. I am always impressed by the high level of expertise exhibited here.

  29. 79
    Hank Roberts says:


    > add up to more negative …. Am I missing something?

    Wili, what you’re missing is the right hand bar, in the first two graphs — the “sum” — where they add up.

    And the (b) graph in the second pair, also showing where they add up.

  30. 80
    Mark says:

    “Mark, the ABC refers to the Asian Brown Cloud”

    Well, see, CO2 is quite well known for being “transparent” rather than “brown”.

    So again, I ask:

    How much of the CO2 is NOT INDIA


    Would the answer you’re avoiding be “almost all of it”?

  31. 81
    Lawrence Brown says:

    Wili, with regard to the link I referenced above, pdf files, at least on my computer, are slow to appear. It takes patience on my part before anything shows up on the screen.