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Global Dimming and climate models

Filed under: — group @ 17 April 2006

Guest posting from Beate Liepert (LDEO)

On April 18th PBS will air the NOVA documentary “Dimming the Sun” which stirred up lively discussions among scientists and non-scientists when originally shown by BBC in the UK (under the name ‘Global Dimming’ – see our previous posts). [The NOVA version has been thoroughly re-edited and some of the more controversial claims have apparently been excised or better put into context [and we look forward to seeing it! - Ed.].

Global dimming is the phenomena of an observed reduction (about 1-2% per decade since ~1960) of sunlight reaching the surface of the Earth caused by air pollution (aerosols – small particles) and cloud changes. Some of this solar energy is reflected back out to space and this cooling effect is believed to have counteracted part of the greenhouse gas warming. The original version of the film focused mainly on the observational recognition of global dimming, but one aspect did not receive much attention in the film – namely the oft-claimed lack of global dimming in climate models. This led some to assume that climate modelers were ignoring air pollution other than greenhouse gases emissions from fossil fuel burning. Another implication was that climate models are not capable of adequately simulating the transfer of sunlight through the atmosphere and the role of clouds, sunlight extinction of aerosols and aerosol effects on clouds etc, and therefore model projections should not be trusted. The NOVA version will address this issue more prominently by adding an interview with Jim Hansen from NASA Goddard Institute for Space Studies. Along this line, I’d like to elaborate on aerosols in climate models in more detail.

It is indeed true that the first climate change simulations were predominantly concerned with greenhouse gas forced climate change. Albeit very early papers argue that man-made aerosol changes might cause a cooling (Rasool and Schneider, Science 1971 and Bryson, Science 1974). And already in 1990, J. Hansen and A. Lacis (Science 1990) published a paper where they explicitly discuss the importance of anthropogenic aerosol forcing: “Sun and Dust versus Greenhouse Gas Forcing”. The authors list direct effects of increasing concentrations of light scattering sulfate aerosols, light absorbing carbonaceous aerosols like soot and even aerosol effects on cloud properties (indirect aerosol effects). Finally they conclude that “… solar variability will not counteract greenhouse warming and that future observations will need to be made to quantify the role of tropospheric aerosols … ”. The surface dimming effect was not yet considered an important climate factor. Back then, state-of-the-art climate models changed the reflectivity at the top of the atmosphere to account for the climate effect of increases in man-made aerosol emissions. Using cloud properties from independent climate simulations and weather forecast models to provide monthly mean water vapor and temperature fields, Kiehl and Briegleb (Science 1993) estimated a top of the atmosphere global mean human-related sulfate aerosol forcing of -0.3 W/m2 in contrast to the a +2.1 W/m2 greenhouse gas forcing. A year later, Jones, Roberts and Slingo (Nature 1994) added the indirect aerosol effect – the impact of increasing sulfate aerosol concentrations on cloud droplet sizes – which make look cloud darker. They used empirical relations to link the number of aerosol particles and number of cloud droplets to cloud droplet radii for their estimates. Other groups as well, started testing new prognostic cloud schemes for general circulation models that were able to capture the microphysical processes of cloud formation (e.g. MPI in Hamburg – Lohmann and Roeckner, Climate Dynamics 1996). These climate-modeling developments were compared (Wild et al., JC 1995) with the then available observational data of the surface solar radiation (incidentally the same data sets were used by Russak (Tellus 1990), Stanhill and Moreshet (Climatic Change 1992) and myself (Liepert et al., Contr. Atm. Physics 1994) to reconstruct the history of global dimming). One conclusion was that then-current models did not include enough aerosol absorbtion in the atmosphere (and Wild and I (GRL, 1998) wrote a paper on the “Excessive Transmission of Solar Radiation Through the Cloud-free Atmosphere in GCMs”). Note that at the end of 1990s these more complex climate models with a more physically based prognostic cloud scheme were run as equilibrium experiments hence transient 20th Century changes could not be used directly for comparison. But is has always been clear that anthropogenic aerosols are so temporally and spatially variable that long-term means are not adequate in assessing the actual aerosol forcing.

Several publications on model validations and improvements based on surface solar radiation records followed and I was involved in two of these studies. We analyzed the simulated multi-decadal changes in the direct tropospheric aerosol forcing in the NASA GISS GCM and utilized global dimming time series of the United States and Germany to assess the temporal change prognosed in the model (Liepert and Tegen, JGR 2002). Ina Tegen’s aerosol model was one of the first that added time variations in carbonaceous aerosol components (including black carbon – an absorbing aerosol). We concluded that increasing absorption might actually play a stronger role than expected.

Climate simulations are the primary tools for explaining and understanding observations that might otherwise seem counterintuitive. For instance, how global dimming can go hand in hand with global warming. In 2004, at the MPI in Hamburg my coauthors and I (Liepert et al. GRL 2004) analyzed output data from a brand new version of the ECHAM general circulation model (GCM) that incorporated a fully interactive aerosol module and aerosol-cloud-scheme. This model interactively calculates aerosol chemical transformation, aerosol transport, rainout and fallout processes and even aerosol formation for some species (e.g. sulfate). We showed that, in the model, global warming caused changing rainfall patterns that fed back on aerosol distribution and composition supressing the water cycle (i.e. evaporation) as had been observed. The key to explaining the apparent contradiction was that the surface forcing changes can be very large without affecting the top-of-the-atmosphere radiation as much.

All major climate models now have some representation of aerosol physics though they range in their complexity – e.g. from top of the atmosphere aerosol forcing to highly interactive aerosol-cloud modules. The role that aerosols play in issues like the Sahel drought (Rotstayn and Lohmann, JC, 2002) or the Asian Brown Clouds (Ramanathan et al., PNAS 2005) is starting to be understood (and both these examples are featured in the documentary), but we do not as yet have a clear picture of exactly how aerosols and the other human-related forcings have affected climate.

More recently, many modeling groups ran 20th Century climate simulations in support of the Intergovernmental Panel on Climatic Change 4th Assessment Report (IPCC AR4) that include representations of the aerosol direct, indirect and semi-direct aerosol effects. The models show a global dimming effect of between 1 to 4 W/m2 over the 100 years with simultaneous global warming between 0.4 and 0.7°C (Romanou et al, under revision) which match the observational dimming quite well.

Overall, in the fifteen years from the 1990 Hansen and Lacis paper to the IPCC AR4, major steps forward have been made in implementing aerosols in climate models and hence matching observations of global dimming. However, it would be misleading to claim that the new appreciation for the surface energy balance changes implied that modelers a few years back were ignorant about the role of aerosols in other aspects of climate change. It is indeed a very complex problem.


92 Responses to “Global Dimming and climate models”

  1. 51
    Beate says:

    In my opinion Jim Hansen and Peter Cox simplified that global dimming masks global warming to a 2-1=1 problem (light bulbs). This is surely the right approach for a five minute statement on TV but would not hold in the scientific debate.

    Jim Hansen’s light bulb illustration is correct at the top of the atmosphere. The aerosol dimming affects the surface of the Earth and is very important for the water cycle more than greenhouse gas warming. The surface energy budget is much more complicated than the top of the atmosphere energy budget. Our model results show that global dimming energy loss equals greenhouse gas forcing energy gain at the surface but this is not true for the top of the atmosphere.

    We think that the surface energy loss by global dimming is mainly compensated by reduced evaporation and reduced turbulence over oceans and land. These spatially varying changes lead to changes in winds and in moisture transport not only in regions where the aerosols are present (note the shown reduction in pan-evaporation in Australia).

    The interactions between global warming and dimming are very important and subject of ongoing research (we have an animation on the Lamont web site http://www.ldeo.columbia.edu).

    Beate

  2. 52
    alisa brooks says:

    RE:49
    Thanks Hank. My error…but please be patient withe me… I guess I should have asked:
    Is Dr. Hansen is trying to say that we need to look at the consequences of REDUCING Air Polution?

    onsequences of REDUCING GHG

  3. 53
    Robichaud says:

    Did anyone had a Peak at this today?

    http://www.climateprediction.net/board/viewtopic.php?t=4759

    [Response: Peek? But anyway (just to quash the misinterpretations I've seen enthusiastically indulged in elsewhere...) this refers to an ongoing experiment, *not* to any published results. It means they have to start again, but doesn't call into question anything you read elsewhere... - William]

  4. 54

    Re #33 (comment):

    Raypierre, I hope (and expect) that water vapor hasn’t changed its absorption bands, that was why I asked for trends. If there is any influence of other absorbing (and partially reflecting) items in the atmosphere, this should be seen as a change of ratio between water absorption bands and total insolation. For SO2 there is a very strong decrease since 1975 in Europe. NOx also decreased, but far less than SO2.

    This is of course only for the primary effect (with open skies). But the huge change in SO2 emissions should be visible in the European stations which have long-term trends in both one or more specific absorption band(s) and in total insolation…

  5. 55
    Hank Roberts says:

    48
    see the actual paper, but to greatly oversimplify (I’m not a climate scientist)
    — clouds make for warmer nights (at night) by blocking some heat that gets radiated into space when the night sky is clear.
    — clouds make for cooler days (in the daytime) by blocking some heat that gets radiated from the sun to Earth when the daytime sky is clear.

    In the absence of contrails for that period of time, some heat was not blocked. They observed “changes in diurnal temperature range, mostly from increased daytime high temperatures” during that span of day/night time.

    52
    Alisa, soot and dust and sulfates fall out of the air fairly quickly, so as soon as pollution control or dust storm plantings succeed, the particles decrease. So to whatever extent pollution is blocking some heat, that will change fast when pollution is better controlled.

    Google +diesel +coal +respiratory +cardiac for the reasons it’s still a good idea to reduce air pollution at the same time as reducing carbon dioxide production.

  6. 56
    pat neuman says:

    re 48.

    In my reply (39.) to your question about the cause of the (apparent) cold spell in the 1960s, I wrote that the average overnight minimum temperatures (even in winter) followed the same warm 30s-40s/cool 50s-60s pattern as the average daily means and global temperatures. It is unlikely that aerosols cooling would have had a large effect overnight.

    Thus, I doubt aerosols were the reason for the dip in temperatures during the 60s. I also discussed this in my comments to RC in January, at:
    http://www.realclimate.org/index.php/archives/2006/01/polar-amplification/

    Also see average minimum temperatures at climate stations in the U.S., a few plots are at:
    http://pg.photos.yahoo.com/ph/patneuman2000/my_photos

  7. 57
    Bryn Hughes says:

    Further to 48
    http://www.pbs.org/wgbh/nova/sun/contrail.html
    “These results suggest that contrails can suppress both daytime highs (by reflecting sunlight back to space) and nighttime lows (by trapping radiated heat). That is, they can be both cooling and warming clouds. But what is the net effect? Do they cool more than they warm, or vice versa? “Well, the assumption is a net warming,” Travis says, “but there is a lot of argument still going on about how much of a warming effect they produce.”
    Is evidence that Global dimming causes Global warming

  8. 58
    Bryn Hughes says:

    Pat
    Theoretically, water vapour in the higher atmosphere is cooled (at night) forming cirrus clouds which prevent a higher proportion of the heat absorbed by the earth during the day from escaping.
    However theoretically in the 60s sulphate pollution formed more clouds during the the day making the earth colder.
    A cold cloudy day is generally followed by a cold night (clear or cloudy)

  9. 59

    Re #51:

    Beate, are there indications of changes in wind/moisture content for the SH? As my understanding of aerosol transport is that there is little exchange from the main sources in the NH to the SH, how do changes in NH aerosols and consequent NH changes in wind/moisture affect wind/moisture in the SH?

  10. 60
    amy quint says:

    Saw “Dimming the Sun” on Tuesday night. Have we passed the point of no return? If not, what actions could advert this catastrophe given less than a decade to act? Could the USA draft the necessary brainpower into a sort-of public works project? Does the USA have the will to act?

  11. 61
    BG says:

    Quick question: In the show ‘Global Dimming’ there were many shots of the pan evaporation apparatus. Also shown sometimes around those shots were shots of a clear glass globe on a stand of some sort. They one time showed a focused spot of sunlight burning a record of something into a thin metal strip. It seemed to me the glass globe was acting as a 360 degree magnifying glass, concentrating the suns rays on the thin metal, sheet or tape wasn’t clear in the shot I saw, to burn the record of something (declination of the sun perhaps) into the recording material.

    Does anyone know what sort of measuring device this was and what its function is?

    Best Wishes,
    Blake

  12. 62
    Gareth says:

    #61: It sounds like a means of recording sunshine hours. Used to be a standard instrument (I remember my father changing the strips on a daily basis for his met reports), but I suspect it may have been superseded by solid state equivalents.

  13. 63
    Adam says:

    Re 61: Sounds like Campbell Stokes sunshine recorder.

  14. 64
    david Iles says:

    I saw the PBS show and have been very taken with the need for action, regarding the implications of global dimming on global warming. I am an artist and early childhood care provider. The one to three year olds that I work with deserve a life. Your discussion is very academic and I understand you are fulfilling your role as scientists. However I have been looking over a great deal of polling data recently and it is clear that Americans are very ill informed on science issues. I am sure this is not news to you. Here is an example:

    “Do you think most scientists agree with one another about whether or not global warming is happening, or do you think there is a lot of disagreement among scientists on this issue?” Most Agree 35% A Lot of Disagreement 64% Unsure 1%
    ABC News/Time/Stanford University Poll. March 9-14, 2006. N=1,002 adults nationwide
    .
    I understand there is near unanimity among scientist on the broad aspects of global warming and its causes. This information is obviously not getting to the public. And as you must know certain industries are doing all they can to increase the perception of disagreement. I believe this problem is somewhat better in Europe.

    If I understand the issue correctly we have maybe twenty years to do an almost complete turn around on emission into our environment. (?) This would require a world wide and very intense campaign to get peoples attention so we can change individual, corporate, and governmental behavior. It is obvious that our present government and corporate structure is not going to collaborate much in this. We need to cross over from a scientific discussion to one that all people can understand. This PBS show was a good example, but I see that the BBC did a show on this topic a couple of year’s back that made a tiny stir and then faded away. The problem is that given bad news people want either to deny it or they become fatalistic, either of these will result in inaction.

    This is an issue that has the potential to connect a whole host of organizations and individuals, because of its implications to life here on earth. It requires all of us to put aside our individual pursuits and interests to join a greater cause. We have done this in the past to fight wars, and 30 million people worldwide came out to protest against invading Iraq. So there is some precedent of large-scale interaction in a single cause.

    What climate scientists need to do is write a clear statement about Global Warming, Global dimming and what can reasonable be predicted of there effects on life on earth, and then get every scientist in the field to sign it and then distribute it to every media outlet in the world. The misperceptions must be set aside, so every one of us can face this problem.
    My suggestion for a statement is as follows.

    We the undersigned are reasonably convinced that the problems presented by emissions from automobiles and industry will become obvious and acute within the next twenty years. We are also convinced that without a significant change in these human behaviors we will severely limit the possibilities of human survival beyond this century, and will certainly all life on earth. Of all the problematic effects presented by human behavior on the earth’s environments and climates, global warming is the most life threatening.

    Earths climate is very complex and many things could happen to steeply shift the gradual warming trend that we have been experiencing over the last fifty years, these include but are not limited to: the thawing of tundra world wide, the death of forests and their subsequent burning, the melting of ice sheets, the reduction of aerosols that cause the “global dimming” effect, and the release of the methane hydrates frozen in our oceans. Anyone of these could rapidly increase global climate change and sharply escalate its dangers to humanity, and a combination of them may prove disastrous.

    We also believe it is within humans capabilities to respond to the challenges presented by global warming by reducing the emissions going into the environment and implementing technologies that fill human energy needs without the heavy costs associated with fossil fuel use. However we will have to focus attention on these issues and encourage innovation, understanding, and cooperation across many disciplines and among all humanity in order to provide a reasonable chance that our children and grand children will have a healthy world to live in.

    Obviously any way you whish to change or use this suggestion is fine with me. We must all of us work to inform and inspire people to the greater possibilities open to us if we concentrate our actions on this issue. As scientist you have a unique role to play.

    I apologize for using so much of your time.

  15. 65

    Re #64 That sounds like a good idea to me. Perhaps the RC team could set up a web page where scientists could log in and sign up. I would keep the wording more or less the same as above, with spelling and punctuation corrected :-) If the text is changed then note that the more people involved in the changes then the less readable and understandable it will become :-(

  16. 66
    Jerry Steffens says:

    I’m still puzzled by the notion that there could be a decrease in surface evaporation (as highlighted in the program) and an increase in atmospheric water vapor content (required for operation of the water vapor feedback). This would seem to imply that there has been a decrease in global precipitation which is greater than the decrease in evaporation. Has such a decrease in global precipitation been observed?

    [Response:Not really. On any long time scales > a few weeks, precip is equal to total evaporation. The amount of water in the atmosphere is a statement about the residence time of the water vapour which can change independently of the evap/precip, and in fact goes like the temperature. - gavin]

  17. 67
    Jerry Steffens says:

    Follow-up to #66:

    But, isn’t it true that, absent an internal source, the rate of change of the mass of a given substance in a reservoir is equal to the net flux of that substance into the reservoir? So shouldn’t this equation be true: rate of increase of water vapor = evaporation – precipitation?

    [Response: The amount of water vapor in the air is very small, and the amount in the radiatively important mid troposphere is yet smaller. Though there is almost certainly a secular increase in water vapor in the air, the E-P budget is a difference of two large quantities and I am certain you would never be able to detect the net moisture source to the atmosphere by monitoring E-P. --raypierre]

  18. 68

    Re #65 & #66 Of course you are correct. This does imply that global rainfall should decrease, and that is what we are seeing locally in the south of England!

    However, the pan evaporation is not being measured globally. It is only being measured at sites on land. Most of the evaporation which feeds the rain is coming from the oceans. I am not sure how you measure ocean (as opposed to pan) evaporation :-) If the oceanic air blown onto the continents is more humid than before, then that would cause less pan evaporation. In other words, if the continental relative humidity is increasing then that would explain less pan evaporation, but AFAIK it is not happening.

    The original reports highlighted less sunshine as the cause. And their investigations pointed to thicker cloud, and cloud forming earlier in the day as the cause. This does not fit with the current climate models! Hence the attempt to grab at the straw of contrails in order to show that the models are correct.

  19. 69
    rinconj says:

    From what I read, something like 2/3 of CO2 in the air is converted to O2 by algae in the oceans. But ever since industrial revolution, most industrial waste has been dumped to rivers/lakes/oceans or buried in the ground but gradually released to the water after rainfalls. So eventually much of the solid and most of the liquid form waste ends up in the oceans. The environmental changes in the oceans by humans obviously have significant impact on global climate too.

    I’m a mathematician/digital signal processing engineer, so I feel excited reading all the statistical models. But the more I read, the more apparent it becomes that the changes in the oceans are at least as important as any other factor. The release of methane hydrates is also directly linked to ocean temperature.

    The first article I found about the changes in the oceans is the dead zones in
    the Gulf of Mexico were growing:

    http://oceanservice.noaa.gov/products/pubs_hypox.html

    I’ve also read quite a few news that fishermen all over the world witnessed dramatic decrease in their catches over the decades.

    It’ll be interesting to find any recent observations and prediction/errors from the statistical models.

  20. 70
  21. 71
    Bronwen Lu says:

    My high school environmental science class should see “Dimming the Sun”. They have been focusing on energy issues since September and global climate change specifically since January, and though they are all non-native speakers of English, I think they could understand it quite well. (They have also been doing a lot research on heating and energy conservation in our building.) They are ideal students to watch this film. But half the class is from Ethiopia. How will they respond to the part about the droughts in the Sahel and their likely cause? The whole film was jaw-dropping for me but that part was by far the most chilling. I don’t see discussion of it here. I’d like to get some sense of how strong the evidence is of a link beween those droughts and particulate pollution.

  22. 72
    jack fletcher says:

    we need a 60% – 80% reduction in CO2 in the next 10 yrs to impact global warming. i really would like to see a serious plan to achieve this goal. insulating your home, adjusting the thermostat, driving a smaller car and becoming a vegetarian will make a trivial impact. please list real actions and the corresponding percentage reduction that would result from those actions to achieve the stated goal.

    [Response: This overstates what is needed. What we really need to do is more like reduce the global emisssions by 10% in the next ten years, with steeper drops thereafter. Don't discount what individual choices can do. Building energy use accounts for roughly a third of US CO2 emissions, and that's a big chunk. Replacing your furnace and refrigerator with state of the art energy efficient models, adding home insulation and double-pane argon filled glass, driving a Prius instead of an SUV (or better biking, walking or taking public transit) all can make a huge difference. Support energy-efficient buiding codes in your town. Support natural gas cogeneration plants wherever feasible. There are lots of productive steps. --raypierre]

  23. 73
    Hank Roberts says:

    Bronwen, the BBC transcript is online; it doesn’t have footnotes but points to CSIRO.

    BBC – Science & Nature – Horizon
    NARRATOR: Rotstayn has found a direct link between Global Dimming and the Sahel drought. If his model is correct, what came out of our exhaust pipes and …
    http://www.bbc.co.uk/sn/tvradio/programmes/horizon/dimming_trans.shtml BBC –

    From memory, somewhere in the NASA spaceflight archives you can find astronauts who flew early and late saying that their 1960s flights saw the Earth’s atmosphere much clearer (before the second half of the carbon to date was burned); after those early years Earth’s air has appeared more and more translucent rather than transparent when viewed “sideways” from low Earth orbit — dirtier.

    Reminds me of this lyric:

    ‘Before Believing’ by Emmylou Harris (Danny Flowers)

    “How would you feel if the world was falling apart around you
    Pieces of the sky were falling in your neighbor’s yard
    But not on you.
    Wouldn’t you feel just a little bit funny
    Think maybe there’s something you oughta do.
    Solutions that never lay down before you
    The answers are all around….

  24. 74
    jack fletcher says:

    big chunk? huge difference? what percentage reduction in total CO2 produced would each of those changes make? while each action suggested may make economic sense, i don’t see a significant impact on total CO2 reduction to change global warming. you are the first i’ve heard say only 10% reduction in 10 yrs. kyoto’s target is a 30% reduction in the U.S. how long until you think a larger (60%) reduction is needed? and then what other changes must be made to reach that target? we need a plan of action to tell our elected officials what to do.

  25. 75
    pat neuman says:

    re: 72

    Excerpts from – Interview: Straight talk about climate change.
    Jerry Mahlman on dealing with your grandkids’ problem.
    Posted: April 2006

    Jerry Mahlman … Formerly the head of NOAA’s Geophysical Fluid Dynamics Laboratory, he’s now a senior researcher at the National Center for Atmospheric Research. …

    Mahlman: There’s a colossal misperception that if you bike to work
    once a week and recycle your garbage, then global warming will be
    fixed up. The problem is that, even if everyone did that, the attempt
    to stop global warming would fail by a factor of, oh, roughly of 100,
    from what we really need to be doing.

    For example, I was in Al Gore’s office when he was vice-president.
    And he asked me the question, “If we could hold the emissions of
    carbon dioxide into the atmosphere constant, would global warming go
    away?”

    And I said, “If you were to hold the emissions constant, you would
    get up to eight times the carbon dioxide, or CO2, that there was
    before the Industrial Revolution. You would still be in a heck of a
    mess.”

    http://www.earthsky.org/shows/observingearth_interviews.php?id=49567

  26. 76

    I agree with Pat]’s post #75. I think it is bordering on the criminal for Ray to write that “What we really need to do is more like reduce the global emisssions by 10% in the next ten years, …” The US has increased its CO2 emissions by 20% since Al Gore’s day. A 10% reduction would not take them back to 1990s levels which Jerry Mahlman was saying were too high.

    Ice is melting in the Arctic, in Greenland, on tropical mountain tops, and in the Himalayas. That will change global albedo and provide a positive feedback on greenhouse gas warming. This is not alarmism, it is fact. We have already raised CO2 too high. The longer we delay doing anything about it, the worse the consequences will be.

    [Response: Note I said "global" emissions. It would be fair and feasible for the developed world to do more than 10% while the developing world did a bit less. If we can get a 10% reduction in GLOBAL emissions, including India and China, in the next 10 years that will be doing well. It's a worthwhile target, and one that is probably achievable. How much CO2 emissions reduction we "need" in the next decade is dependant on your target CO2 level, and there is no one magic number on that. Take a look at the discussion following "Climate Sensitivity, Plus ca Change" and play around with Archer's model. Look at the difference between doing a 10% reduction in ten years with steeper reductions afterword, vs. starting a crash-program of reduction earlier. In my view, it's not sharp reductions we need IMMEDIATELY, but policies that prevent building of a lot of coal plants with 60 year capital life. If we build those in the next decade, we really will have a much harder time reducing emissions in the out-years. That's where we most need IMMEDIATE action. --raypierre]

  27. 77
    jack fletcher says:

    thanks pat#75. i’m glad to see a leading expert expressing my concerns. i heard recently that if all U.S. households would switch to Fluorescent lights, it would be equivalent to removing 8 million cars from the road. that’s an impressive number and they match the best numbers i could find. i have made the switch in my home to save $84/yr on a $12 investment that lasts 5 yrs. but if all americans did the same, the total impact on CO2 production in the U.S. would be 2/3 of 1%. there are lots of quick fixes and scapegoats – none are significant. all of Ray’s suggestions in #72, would result in less than a 10% reduction in U.S. CO2 production. crush all the SUV’s and drive a hybrid. and yet it gets warmer. we have an interested and concerned group here willing to take action, but i cannot find a plan that will make any impact on global warming. i would like to see a plan by someone knowledgeable and experienced. can anyone point me to RealSolutions.org? ;-)

    [Response: Nonsense. You're being defeatist without cause. Wind only gives you 5% of your energy? Fine, get five percent of your energy from wind. Another 5% from solar. Figure in 20% reductions from energy efficiency. Cut transportation in half by driving Prius and replacing short-haul flights with trains. Add another 10% of capacity in the form of nuclear energy. Biodiesel (maybe from algae) to fuel those priuses. Maybe do a little carbon sequestration from new IGCC coal fired power plants. Natural gas cogeneration. Sheesh, we're over 100% already. Mahlman is right that if you just hold emissions constant forever we'll hit 8x Co2 or more, but that's not what I was proposing. I said that if we make a start on getting the right market signals in, the really sharp reductions can be postponed for a decade or two. The saddest thing is that we've already wasted 20 years without doing anything. Defeatism will only result in wasting another 20 years. --raypierre]

  28. 78

    Re #77 There is no workable plan that would not hurt. For instance, we could ban all combustion engined vehicle globally and that would save 33% of the all CO2 produced. But even that would not meet the 60% reduction some people say is neccessary.

    Don’t forget that here in the UK we are using twice as many resources per head as is sutainable and in the US it is five times. If GWB manages to export the American way of life to China and India then we will soon all be starving.

    There is only one quick fix and that is to create a parasol by injecting water vapour into the stratosphere, ie more contrails. No, I don’t think that would work either :-(

  29. 79
    Pekka Kostamo says:

    Some musings about the impacts of an increasing dustiness….

    There should be some impact on the cloud processes. It is not uncommon that the saturation vapor is exceeded inside clouds (i.e. 100 – 105 %RH is still a realistic measurement). This occurs when there are relatively few condensation nuclei around and the air is rising. More condensation nuclei should generate more and smaller liquid water droplets, at a lower altitude. This would mean that the latent energy is released at a lower altitude as well, and within a narrower altitude range.

    The same would happen at higher altitude when the droplets freeze and continue collecting vapor from their surroundings. Over a wide temperature range the clouds contain a mix of liquid droplets, ice crystals and vapor. Ice forms around icing nuclei, which are different from the condensation nuclei forming liquid droplets. (Liquid water droplets may exist down to -38 degC temperatures). As the saturation vapor pressure with respect to ice is lower than the saturation with respect to liquid water, there is also a process of transfer via vapor phase (evaporation from droplets, accredition on crystals). More nuclei makes for lower altitude latent energy release also in this case.

    Another aspect yet is that the evaporation rate is dependent on droplet diameter. For reasons I do not understand, in the micrometer world of cloud droplets the evaporation is less efficient than that from large water surfaces.

    More dust in the atmosphere probably changes the cloudiness, as well as the precipitation. This is the cornestone of the murky art of weather modification, but it is also behind the observation that hurricanes are seldom generated during the sandstorm outbursts from Sahara into the Atlantic.

    The impacts of these changes on the cloud formation proces in general and the radiation properties in particular are a question mark for me.

  30. 80

    I find it difficult to stay on topic, especially when the topic is “Global dimming and climate models”, and I have been banned from discussing climate models :-(

    [Response: Come come, Alastair, don't be glum. You haven't been banned from discussing climate models, only from making certain claims about Kirchoff's laws. I'm very glad you decided to stay with us anyway. --raypierre]

    Anyway, rather than my views, here are some new pages about climate models produced by NASA only two days ago.
    * Earth’s Big Heat Bucket
    http://earthobservatory.nasa.gov/Study/HeatBucket/
    The Earth now absors more energy than it emits back into space, and the excess heat is hiding in the ocean.

    They say that the oceans are warmming, and that they will continue warm even if CO2 is stabilised:

    Hansen remarks, â??Weâ??re putting in the pipeline additional change that will occur over the next several decades, and which will be difficult if not impossible to avoid.â?? By his estimates, the current energy imbalance is likely to produce an additional 0.5 to 0.6 degrees Celsius of warming in global average surface temperature on top of the 0.7 degrees that occurred between 1880 and 2000.

    What I argued in #76 is that with the Greenland ice already melting, then with another 0.5 C rise in global temperature (at least 1C in Greenland temperatures due to polar amplification) then it is now inevitable that the Greenland ice sheet will melt and that sea level will rise by 7 metres (over 20 feet.) A point which is often ignored is that as the Greenland ice melts the altitude of the ice surface will decrease. Since the temperature of the atmosphere falls with altitude, then the reduction of the altitude of the ice surface will mean that it will warm. In other words, there is a positive feedback which will mean that the melting of the Greenland ice will accelerate. Moreover, since the surface of melting ice is wet the enhanced greenhouse effect from water vapour will also accelerate the melting. Oh, sorry! The idea that surface effects could overide those at the tropopause was disposed of in “A busy week for water vapour” http://www.realclimate.org/index.php/archives/2005/11/busy-week-for-water-vapor/

    Moving swiftly on, in the NASA article, it mentions the danger of the West Antarctic ice shelves being melted by the warmer ocean. May I point out that as they thin the grounding line will retreat, and the mass of ice that is grounded will decrease. This will reduce the friction that is holding back the ice shelves, and they will accelerate towards the ocean also causing sea level rise.

    Presumably if I praise the models that will be acceptable, so I would just like to repeat what NASA have to say about the work of their man James Hansen:

    He developed three-dimensional models of global climate. In 1988 Hansen testified before Congress, describing how different levels of greenhouse gases might affect future temperatures. Over the next 17 years, observed temperatures closely agreed with Hansenâ??s 1988 predictions.

    They also show a diagram where the agreement is clear:
    http://earthobservatory.nasa.gov/Study/HeatBucket/Images/ocean_heat.gif

    I just wonder how clear it would be if the start date had been 1995 rather than 1993, or if the end date had been 2005 rather than 2003?

  31. 81
    jack fletcher says:

    re: 77 response: defeatist? never! what the cited article and i are saying is the solution is greater than the usual suspects. you are a numbers guy. run the numbers and see how much those horrible suv’s really contribute to the co2 footprint. i’ll counter your statement that defeatism is delaying action with naivety is delaying action. if people feel that the solution is just implementing the often stated easy fixes, there’s no need for them to act now. looking at co2 generation by sector, green electric power will have to be major component of the solution. that will need to start now to clear regulations and public objections to be available 10 yrs from now. are energy efficient cars, appliances, and home improvements part of the solution? do we want to wait until individuals can afford this or do we offer incentives? we need a coordinated plan to present to those in authority that this is what a bloc of voters want to do to achieve stated results.

  32. 82
    Javier says:

    Hey Im very interested about the topic of Global Dimming. Are there books published about Global Dimming?Because where I live;Baldwin Park,CA in the library there dont have any books about the topic or anything related. I got to go to class.

  33. 83
    Hank Roberts says:

    Javier, you’re within the Los Angeles Public Library system. I just checked the Baldwin Park online library collection search via the Net and was able to find fifty-odd likely references fairly easily. Being local, you’ll want to narrow that down a bit.

    You will probably get best results quickest if you can actually physically go there, meet and talk to the person at the Reference Desk about how to find things there, and then how to branch out via Interlibrary Loan.

    Also use the Periodicals Index, which I know they have available — that will get you newspaper and magazine articles in addition to the books available.

  34. 84
    Vince Ready says:

    If contrails are a significant contributor to the global dimming phenomenon, wouldn’t it make sense to mandate the use of cleaner-burning jet fuels for commercial aircraft? Or to require cleaner burning engines that more fully combust the fuel and reduce the particle emmissions?

    This seems like a very practical and attainable step in the right direction if such improvements are technological possible.

  35. 85
    danny says:

    I m very interested in the topic of Global dimming. THe global environment is changing constantly with the melting of ice in Himalayas,in Arctic and in the tropical greenlands. THis is changing the face of climate models. All this is due to the increase of CO2 in the air. Something has to be done for this as the consequences could be harmful.

  36. 86
    Steve Sadlov says:

    RE: #76 “The US has increased its CO2 emissions by 20% since Al Gore’s day.” Show me your data. That is a very wild claim especially considering the general movement offshore of heavy industry, the ongoging transition away from oil fired power plants and the trends in fuel costs.

    [Response: Not wild at all. CO2 emission up 19.6% since 1990, all GHGs up 21%. See the latest EPA report. - gavin]

  37. 87
    Steve Sadlov says:

    RE: #80. Based on considerations of the energy required to promote a solid – liquid or solid – gsas phase change, what would you think may be the least and greatest amoounts of time required to completely melt the mass of ice on Greenland? (others welcome to present their own data and views here …)

  38. 88

    RE: #80, 87. Thanks Steve for this question, for the estimates of sea level rise on which storm surges will ride are the most urgent question in my opinion for those of us with an urban planning-environmental policy bent.

    My understanding of working group conclusions preliminary to #4 has been that climate models have converged nicely or perversely, depending whether you come from a primary research or policy application standpoint, to approach a temperature increase curve unavoidable through about 2040 regardless of contemporary actions/BAU. Please correct me if this is outdated information.

    I wondered whether a corresponding sea level rise curve now exists, properly accounting for expansion and acceleration due to feedbacks from albedo and aerosols on down, and what that curve might imply for direct-hit major-hurricane surges in low-lying metropolitan coasts through the 2040s. I’d like some idea how much time we may have left to move Miami and major parts of Houston-Galveston out of harm’s way! (And are there other urban candidates over 5.5 million population at the seashore that I should guide these considerations toward?)

  39. 89
    Aubrey E Banner says:

    Energy and global warming

    Renewable forms of energy such as wind, wave and solar energy are the only realistic ways to meet the worldâ??s long term energy requirements. Since these forms of energy already exist, and will continue to do so, they do not add to the worldâ??s total energy, and this is important because of considerations of global warming.

    The current climate change/global warming debate has become highly political, with some people maintaining that the warming over the last 150 years is due to the enhanced greenhouse effect caused by anthropogenic emission of carbon dioxide and other gases from the burning of fossil fuels. However, there is some scientific opinion that the claimed increase in the concentration of carbon dioxide in the atmosphere is based on flawed data obtained from ice core measurements in samples from the Antarctic, with some alleged preferential selection of values having occurred, although this has been strongly disputed.

    The principal argument for the enhanced greenhouse effect seems to be that climate models can be made to reproduce the observed warming only if the expected effects of the extra carbon dioxide are included in the models. If the carbon dioxide is removed, the models fail.

    However, amid these claims and counter-claims, one fundamental consideration seems to have been omitted, and this is the effect of the vast amount of energy currently being generated by mankind. I believe that IT IS THIS ENERGY ITSELF WHICH IS CAUSING THE GLOBAL WARMING. It is derived mainly from the chemical energy of fossil fuels, but whatever the source, the energy eventually ends up in the form of heat and as a change of state in melting ice into water.

    Greenhouse gases are emitted, but this is simply a side effect which correlates with the amount of energy produced.

    Energy consumption data was obtained from the website of the Energy Information Administration of the United States Department of Energy, which go back to 1970 and give figures for the whole world. From this data the quantity of ice which can currently be melted in one year is calculated to be 1200 Gigatons, where 1 Gigaton is one thousand million metric tons. This is about twice the amount estimated from practical observations for the whole world.

    On the basis of a simple â??total energyâ?? hypothesis, good agreement has been obtained with the reports of five sets of practical observations, namely the Arctic sea ice, the Greenland ice cap, the rise in temperature of the atmosphere in the Northern hemisphere, the melting of the Antarctic ice sheet, and the rise in temperature of the Antarctic troposphere. Further details can be provided if generally required.

    No consideration has been given in this hypothesis to anthropogenic greenhouse gases and so no reduction of these gas emissions will be able to solve the problem of global warming, which, indeed, must be occurring as evidenced by the melting of the worldâ??s ice.

    It also follows that no benefit can be gained by switching to nuclear or geothermal energy because the problem is simply one of the very energy being produced by mankind.

    Therefore, the only way to solve the global warming problem is by changing completely to the use of “renewables”, solar energy, wind energy and possibly energy from the waves. Since this energy is not “new energy”, its use does not add to the total world energy, and so has no net warming effect.

    Aubrey E Banner, Manchester, England

    [Response: Total energy use by humans is equivalent to 0.03 W/m2, much much smaller than the impact of GHG forcing and completely negligible except in localised environments like cities. - gavin]

  40. 90
    Hank Roberts says:

    Aubrey, you write
    >Further details can be provided if generally required.

    Please do provide details — if you have references/cites to published science with the numbers.

    Yes, there will be a visible similarity between graphs of fossil fuel use and warming — but such claims need numbers to deal with the science involved.

    As Gavin points out the total heat energy released by human use is tiny compared to the excess solar energy that is and will be captured by the increased atmospheric CO2.

  41. 91
    Edward Greisch says:

    We are causing global warming by burning coal because people are afraid of nuclear power. I have been surveying my neighbors. So far, only my family doctor had ever heard of background radiation. Nobody in my neighborhood had ever heard of any natural source of radiation. It is clearly the ignorance of the public that is the problem. A copy of the following paper possibly modified by a George W. Bush political appointee is available at:
    http://www.ornl.gov/ORNLReview/rev26-34/text/coalmain.html

    [full text of link deleted]

  42. 92
    Steve Sadlov says:

    RE: #88. But you did not answer the actual question I posed. Many people make statements to the effect of “the Greenland Ice Cap is going to melt.” What does that mean? Does it mean that it will lose some of its mass? Melt completely away, exposing the land underneath? Or something in between? If it loses some of its mass, only, how long will that take? And is it possible that some larger effect, such as the end of the interglacial, will completely obviate that with a crisis of epic proportions in a quite different direction?


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