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Winds of change

Filed under: — group @ 11 June 2009

Gavin Schmidt and Michael Mann

There was an interesting AP story this week about possible changes in wind speed over the continental US. The study (by Pryor et al (sub.)), put together a lot of observational data, reanalyses (from the weather forecasting models) and regional models, and concluded that there was some evidence for a decrease in wind speeds, particularly in the Eastern US. However, although this trend appeared in the observational data, it isn’t seen in all the reanalyses or regional models, leaving open a possibility that the trend is an artifact of some sort (instrumental changes, urbanization etc.). If the effect is real though, one would want to see whether it could be tied to anything else (such as forcing from greenhouse gas or aerosol increases), and indeed, whether it had any implications for wind-generated electricity, water evaporation etc.

Amusingly, both of us were quoted in the story as having ostensibly conflicting views. Mike was quoted as finding the evidence for a trend reasonably convincing, while Gavin was quoted as being unconvinced of the evidence for an anthropogenic climate change signal (note that the two statements are not in fact mutually inconsistent). As one should expect in any news story, these single lines don’t really do justice to the longlonger interviews both of us gave the reporter Seth Borenstein. So what is the bigger context?

First some background. It’s important to note that ‘windiness’ is not a globally uniform field, and that changes will occur in different regions for very different reasons. Also, note that mean wind speed is not the same as storminess*.

Winds in the mid-latitudes are a function of the jet stream and of the ‘baroclinic instability’ that we see as low-pressure systems. In the tropics, winds locally depend strongly on convective activity and on a larger scale, the Hadley circulation. In monsoonal regions (West Africa, India etc.), winds are a function of the temperature contrasts over land and sea during the warm seasons. Winds can be affected by the ozone hole in the Southern Ocean, a change in the orbit of the Earth in the tropics, or by the presence or absence of an ice sheet. So the concept of winds changing in a general sense is not unusual or unexpected. However, because of the many distinct influences you wouldn’t expect all winds to increase or decrease together.

In the free atmosphere off the equator, wind is essentially ‘geostrophic’ which means that it’s driven by the (predominantly north-south) gradients in air pressure, and follows contours of constant pressure (’isobars’). Near the surface, friction slows the winds, and causes them to cross the isobars from high to low pressure (hence we get ‘convergence’ in the center of surface low pressure regions). Nonetheless, changes in surface winds will follow approximately from the associated change in the surface pressure field.

The business-as-usual projections show a general poleward shift of the current subtropical surface high pressure belt into the mid-latitudes, especially during summer (a poleward shift of the descending branch of the so-called “Hadley Cell”). The high pressure belt is a region of low pressure gradient, and hence low wind. A northward shift displaces the region of maximum westerly surface winds poleward, from the U.S. into, say, southern Canada. A decrease in the mean strength of the surface westerlies over the U.S. would therefore appear to be consistent with projected changes in large-scale circulation. However, it’s not that simple. The average wind speed at these latitudes depends as much on the day-to-day variance (driven primarily by mid-latitude storms) as it does on the mean strength of the climatological westerly surface winds. The gradient in temperature between subtropics and pole tends to decrease with global warming (due to the ‘polar amplification’ of warming) and this, in turn, diminishes the “baroclinicity” of the atmosphere, and thus, the degree of storminess. So both a decrease in baroclinicity and a poleward shift in the extratropical band of westerly surface winds would therefore seem to work in the direction of decreasing wind in mid-latitudes.

But even this reasoning is somewhat questionable, as wind anomalies over a region as small as the U.S. are unlikely to be representative of the trend for the entire latitude band on the whole. Factors such as El Nino, and the “Northern Annular Mode” have an important role on wind patterns over the U.S., and changes in the behavior of these phenomena could easily overwhelm the average trend for the mid-latitude band. So in short, the observations of decreasing wind speeds over the U.S. are in a rough sense consistent with these ideas, but given the uncertainties in factors that are important in determining wind patterns over the scale of the U.S. continent, it’s hard to say precisely what would be expected.

Figure 1. The trends in the station winds and in the N. American reanalysis (from fig.4 in Pryor et al.)

In the specific case of the GISS-ER model, we can easily see what the model suggests. The picture below gives the annual mean wind speed change for a business-as-usual scenario out to 2100 (we picked this just because the changes are large, but a picture for simulated trends over the last 50 years is similar).

The first thing to note is that the expected changes are complex. There is a clear increase in the Southern Oceans (related to changing temperature trends in the lower stratosphere associated with both the ozone hole and greenhouse gas increases). There is also a change near the equator associated with increases in convective activity and a shift in the Hadley Cell. Note also that changes over land are very small, and in particular, over the US no significant changes are seen. The situation might be different in different models (or different seasons, or in the day-to-day variance), and so one wouldn’t want to read to much into this single figure, but it makes clear that a change in US windiness is not a strong ‘a priori’ expectation from global warming. This doesn’t of course shed any light on whether the observed trends are real, but it does speak to the attribution part of the discussion.

Indeed, you would need a careful detection/attribution analysis to see if the observed changes in wind speeds are consistent with the multi-model climate change projections. This has been done for surface temperature, precipitation, and sea level pressure changes, and there is no obvious reason it can’t be done for wind speeds if the data holds up.

Regardless of the cause of the indicated decline, is this likely to have a direct impact on wind power generation? There is a study by Archer and Jacobson that explores the potential for wind power over the US, and the results can be seen in this graph:

Wind speed class 3 (usable for power generation) and above (dark blue, green, yellow, red and black dots) are not that widespread, and are concentrated over the plains and offshore. Comparison to the trend map in the Pryor et al study (figure 1 above) shows only a limited overlap, so even if all these sites were being used, it’s not clear the trends would hamper wind-power generation much. However, this is highly speculative and will need to be looked at much more carefully in future.

Whether the wind of change is truly blowing through this continent remains to be seen…

Note that an apparent quote from David Deming that the possibility of decreased wind speed over the Eastern US is somehow in contradiction with the possibility of increased tropical storm intensity in the tropical Atlantic is embarrassing in the inappropriateness of the comparison.

180 Responses to “Winds of change”

  1. 101

    99 David. You have to find it, then chase it!

    and moving the power lead and string could be a bit involved! Next!

  2. 102

    Re #16 Martin Vermeer,

    You sum up correctly the OTEC result, though I am surprised that you say there are “a number of small installations in operation.”

    Many years ago I talked to a person involved in the Lockheed OTEC project in Hawaii about that Lockheed system. As I recall, it got quite complicated, even involving a working fluid other than sea water. If memory serves me, the person reported that the system worked only to the point that it could keep itself going, but produced no meaningful energy for external use. Lockheed put quite a lot of R and D money into it, but the economics of that system at that scale did not seem to work.

    But then you went on to speak of the effect that such systems on a large scale could “rob tropical cyclones of the energy they feed on.” Of course the “large scale” is not defined here, but it seems hard to imagine this sort of man made equipment ever beginning to compete with the energy of cyclones, or even just wind, as a vertical mixing driver in the oceans. This brings us around to a question of several months ago about whether the vertical mixing action due higher winds caused by warmer ocean surfaces would tend to moderate those same winds since the vertical mixing would bring up some of the deep cold ocean water.

    As far as I could take this, it seemed that the climate modeling did not adequately consider this kind of effect.

    As I reason it through, it seems that the predicted catastrophic weather effects will be slower in coming than other problems such as sea level rise. Further, it seems possible that the near surface ocean temperatures might not increase all that much, first because polar ice melting will delay this effect and then the vertical mixing will further delay it. The thermohaline circulation would couple with the vertical mixing to make the problem hard to model, but as a general trend, it seems there could be such a sequence.

    I tend to think this sequence better explains why the ocean temperature data (discussed some time back) did not seem to make sense than the explanation that the Navy bathythermograph instruments were miscalibrated. (They were not even designed to be that accurate for absolute temperature measurement. Recalibrating them on a hunch does not lead to a solid validation that oceans are warming as some people seem to think.)

    Of course, sea level will rise regardless of surface temperature. Warming of the deep ocean will have the same thermal expansion effect.

  3. 103
    Richard Steckis says:

    Ray Ladbury:

    “Very good, Steckis. Maybe your learning curve does have a positive slope. We’ll find out if you quit arguing for the cessation of climate change based on 8 years of data.”

    Thank you Ray. However, you are wrong on a couple of points. Firstly I never argued that climate change has ceased. It never ceases. The only constant about climate is that it changes. Secondly, as to 8 years of data being evidence of such, you will have to prove to me that I said it because I can’t recall saying it.

    Given that, I am not a strong believer in the 30 year time scale for climate signal to emerge from noise. I do recall that I asked you to provide a peer-reviewed reference that provided statistical evidence that that time scale is appropriate. You have yet to do so.

  4. 104
    Anders Valland says:

    In #33 Seth Borenstein actually refutes two of the major claims made by the authors of this post. There were no “long interviews”, and the views presented by the post authors were actually opposite. Borensteins report is accurate.

    In #33, Michael Mann even admits this and says that his and Gavin Schmidts wording in this article is poor.

    [Response: Please do not twist our words. In no conceivable honest reading of what I wrote did I in any way contradict the point that Gavin and I did not give opposite views. One of us was talking about the reality of the observed trends, the other was talking about whether the trends are tied to anthropogenic forcing. Do you really not understand this? Take your nonsense elsewhere, it won’t be tolerated on this site. -mike]

    Even so, the poor wording is still there. I would think that removing that poor wording and conceding that you actually gave opposing views would be the better thing to do. As it now stands you give the impression of making a complaint in the headline, and then deep in the story admitting that you have no complaint.

    When will the post be changed?

    [Response: I think you may be a little confused. This post was not a complaint about the AP story, nor was it a criticism of Seth Borenstein’s reporting. Our point was to give more context to the story than appeared in the mainstream press, but not to imply that they were not doing their job properly. There are very real constraints on what can get into a newspaper piece (length, assumptions of prior knowledge etc.). The point is not that Seth should have quoted us more fully – that would be unreasonable. But it is valid to point out that we gave longer interviews that rounded out our comments as paraphrased by Seth. For instance, some people read my comment as implying I thought the study flawed *because* climate models did not suggest a large change in US winds. This is not what I believe and this was explicitly stated in my email to Seth and in the post above. Extra context therefore allows people to amend their initial misreading to something closer to the actual intent. The only ‘poorly worded’ issue is whether our interviews with Seth were ‘long’ – that is of course relative, and for clarity I have amended it to ‘longer’ which should not be as confusing. – gavin]

  5. 105
    Mark says:

    “It never ceases. The only constant about climate is that it changes. ”

    But surely then that must change…

    “Given that, I am not a strong believer in the 30 year time scale for climate signal to emerge from noise.”

    Well, what you could do is take a best fit polynomial to the temperature line and calculate what the single-reading variation from that line is. Then, using statistics, define how many readings you need to get the temperature readings noise below the signal level of AGW.

    If you find that turns out to be ~30 readings (thereby reducing the error from the actual mean from the partial sampling by sqrt(30) or about 2/11ths) then you now will believe the figure.

    Go on, educate yourself.

  6. 106
    Ray Ladbury says:

    Steckis, there are de jure standards and de facto standards. The 30 year standard is of the latter type and so doesn’t require justification so much as validation. You can validate it yourself:
    Go look at climate data and see how long it takes for a trend to emerge with what confidence. Looking at the past 120 years of climate data, how many times would you have been fooled looking at 8 year trends? Now how many times would you have been fooled looking at 30 year trends?
    The only 30 year period where you might not have seen rising temperatures was the period 1944-74, and as we’ve seen that was a period dominated by aerosols. That was in fact a trend we needed to know about, so even there the 30 year trend is telling us something.

    As far as I know, there is no peer-reviewed study establishing Celsius as the standard for temperature, either. It just works.

  7. 107
    L. David Cooke says:

    RE: 101

    Hey Nigel,

    As of the time frame the NCDC data has been published it would be reasonable to say that Jet Stream drift can be strongly related to ENSO, PDO and NAO effects. The movement as related to your link describing long wave and short wave Jet Stream deviation phenomena does not seem to hold up in light of the most recent La Nino event.

    Classically the multimodal range of short period and long period phenomena would best describe the balance of your link. When we now go back and review the data in relation to the ENSO things begin to change. For one there is nothing in the classic observation that supports the definition of the variations in the period of positive or negative ENSO variation. Hence, the observations provided are more of secondary observations of what appears to be primary drivers. This gets us back to the actual subject of this thread.

    What drives the ENSO and other large scale atmospheric patterns? Is it the surface temperatures in the ITCZ moving to escape at the poles? Is it instead the build up or trapping of energy in the ITCZ by zonal events? I can suggest to you that from my layman’s observations it appears that the Jet Stream deviations may be related to the energy content in cross zonal flow patterns. Meaning it depends on the energy content in the North to South flow within the Hadley bordered regional cell. Hence, if the cross zonal flow drives the Jet Stream deviations, then they also drive most of the observed deviations in Rossby waves. ( 6/17/09)

    The end result is that is is more likely that the energy contained in a cross latitude region may be trapped by the convection/radiation limitations due to either a mid-altitude temperature inversion (in the case of convection) or increased atmospheric CO2 content (in the case of radiation) in the 300-500mb region. Given this the current paper leaves the pursuit of the primary driver of Jet Stream deviations from it’s elliptical path between 40 and 60 Degrees unanswered and hence it only addresses a part of the picture.

    Then again I am not an expert, so we will let the experts define the science. I can say that based on my observations; convection and not radiation has the greatest energy transport potential. Given this we need to be trying to define the participants of the mid-altitude Tropospheric Temperature Inversion a little better. Now, I will quit here rather then swallow both feet whole.

    Dave Cooke

  8. 108
    L. David Cooke says:

    RE: 102

    Hey Jim and Martin,

    Actually Jim you have the OTEC conclusion correct; but, the issue of abandonment may suggest further research. ( )
    The attempt off Hawaii to extract the differences in temperature between the surface and up to 1700 meters below just could not insulate the water traveling through the pipes sufficiently the get the necessary temperature differential to be effective.

    Plus it seems even if you ran the pumps on Solar power the amount of energy potential extracted was much less then the energy input to the system. (Funny though, the Sunlight was not very expensive and could still be used to pump nearly 33,000 gallons of water/day (roughly 145,000 liters for our metric cousins).)

    Did you also read about the use of the giant sea going turbine being tested near the same time? There were several discussion in Popular Science about both of these projects in the late 70’s.

    Even the sea turbine had it’s issues. One of the biggest drivers for using the giant sea going ocean current energy extraction type devices was that the current is not bounded. Hence, if there is too much impediment, the current simply diverts around the object. This leads to reducing the greatest extraction potential downward from the near 62% potential to around a humble 23%. Meaning it was not going to be cost effective, either. As they had to pitch the blades to less then 45 degrees to get sufficient flow of the working fluid (The optimum angle is generally between 12 and 22 degrees, similar to a close reaching sail boat sail).

    I am afraid that the folks in the UK, specifically Scotland, may be jousting at Tidal Stream Windmills at this time. I am concerned that similar experiments being done in relation to open stream tidal flow experiments, being attempted in Europe and China, will eventually fail. It was due to the energy extraction efficiency that drove the application of the Tidal Barrage designs. If you were to install a large turbine in the Florida Straights there is a greater potential to raise the energy extraction; however, now you have two issues, first the ocean depth in this region and secondarily tropical storms.

    Hence, for this reason I have favored Vertical Axis devices along coastlines near estuaries in the higher latitudes. First, they seem more conducive to energy extraction without providing a point source impediment. The effect is that though slowed the current continues to move through the sweep area without bypassing the device. Secondarily, since they employ impact lift/drag they do not suffer tip speed deterioration as do most Horizontal Axis devices. Yes, the efficiency per device is lower; however, they are generally much better suited for the application. What it comes down to is using the right tool for the job. Sometimes efficiency is not the best indicator of Return of Investment.

    Dave Cooke

  9. 109
    L. David Cooke says:

    RE: 104

    Hey Nigle,

    So sorry wrong David. The kite idea and the idea in a 1980 copy of Science and Mechanics of a atmospheric ionic charge extracting 100 meter fence were both discarded as impractical; however, in theory they were possible.

    Dave Cooke

  10. 110
    Douglas Wise says:

    re 106: Ray, you point out that the failure to observe increasing STs between 1944 and 1974, despite rising CO2, can be explained by aerosols. I think we, in the developed world, then removed many of the aerosols, unmasking the warming trend. I would be interested in what’s happening to aerosols now. Wouldn’t one expect them to be as high as they were earlier as a result of increased industrial activity and deforestation, primarily in Asia? I appreciate that 1998 temperatures were especially high due to el Nino and that some doubters, not allowing for this, have been unimpressed with subsequent warming despite the trend still being up. What I would be interested to know is how much the trend has been squashed by developing country aerosols – a quantitative rather than qualitative answer would be particularly useful. For example, are cooling atmospheric aerosols now lower, similar to or higher than they were in the late 1960s?

  11. 111
    Mark says:

    re 110, why would you expect them to be higher?

    Burning wet leaves creates LOTS of smoke. Burning charcoal produces more heat and less smoke.

    So to get more useful stuff out doesn’t lead to more useless stuff, does it.

    Maybe if you tell us why you would expect aerosols to be higher after more of the world has a clean-air act, we could discuss it.

  12. 112
    Marion Delgado says:


    It’s true most disagreements aren’t public and those that are aren’t free-for-alls. Part of the reason for that is the belated recognition by the scientific communities that they’re being watched by anti-science people with agendas, frankly.

    Actual science is a fairly rude and confrontational process, in my experience.

  13. 113

    Re #108 L. David Cooke,

    Hi Dave,

    Your favored scheme would have a large volume flow rate to work with but the pressure side of the equation would not leave you with much to work with.

    “Low head” power generation can be made to work, but the machinery cost is hard to justify for what you get out of it. Doing this in rivers and streams seems at least conceivable. The Gulf Stream represents plenty of energy, but it is also a fairly big thing to harness. Better to leave the mixing to hurricanes?

  14. 114
    Jim Norvell says:

    If I have it right, we have something like 800 GW (800e9 watts) installed electric capacity. The proposal is to replace that with low or non carbon energy. Just how do you propose to do this? Our (US) current production of green energy is 40 GW or 5% of the total.

  15. 115
    L. David Cooke says:

    RE: 110

    Hey Douglas,

    Here are a few references. Though the data set is short, the combination of the wiki published MODIS and the Mauna Loa observations offer some insights as to trends over the past couple of decades.

    (I left out the NOAA reference, as the Optical Depth data was not formated in an appropriate public reference. If you are looking for additional aerosol data you may need to keep in mind that prior to around 2005 they were generally called atmospheric particulates.)

    Dave Cooke

  16. 116
    L. David Cooke says:

    RE: 113

    Hey Jim,

    If you look to this site:
    and click on the Enermar image it will take you to a cyclo-turbine that was being experimented with in Italy. There are even a few videos on the site that talk about the operation of the device though most of them are in Italian. Another option would be the Blue Energy site here:

    Kind of amazing that these have been operational for several years and are only being considered for developing countries…

    Dave Cooke

  17. 117

    Re # 116 L. David Cooke,

    Hi Dave,

    Thanks for the links.

    For the Italian project, we can only guess at what they mean with, “22,000 Kilowatts per hour of useful energy can be extracted each year” but it sounds like 22,000 Kilowatt hours per year. My usage is about 5000 Kilowatt hours per year. Myself and three or four neighbors would probably not be good for the cost of their system.

    Of course this is an experimental project and it could well scale into something more meaningful. But for now, it seems like a little skepticism is ok.

    The Blue Energy device would be good for the “remote domestic consumer,” if he lived near a big enough river. I will be happy to be convinced that this will amount to a significant alternative.

    Cheers, Jim

  18. 118
    Richard Steckis says:

    Ray Ladbury:

    “Go look at climate data and see how long it takes for a trend to emerge with what confidence.”

    Well Ray. The RSS figures show that there has been a statistically significant (linear model p=0.1). So, the satellites say a significant decline and the surface record shows a change from a significant increase (linear model p

  19. 119

    116 LDavid. Both of these turbines are of the modified Salvonius type. These are characterised by higher torque, but quite poor efficiency compared with the ‘conventional’ wind mill type.

    While in crude installations they have the advantage of being able extract useful power for small pumping or grinding tasks using rag sails, with any bigger installation there has to be a major site, structural or environmental constraint for them to come out ahead of a normal rotating airfoil.

    The efficiency of a normal airfoil wind turbine is at its best using a single counter-weighted blade with the tip rotating at seven times the wind speed. In terms of designing a good system for extracting energy from a passing fluid stream all you have to remember is: One Blade and Seven to One. Every blade you add after that merely increases the drag, hence reduces the achievable tip speed and hence pulls the turbine design further away from optimum.

    Quite why such sub-optimum designs as you mention get foisted onto ‘developing countries’ is a mystery, or a crime.

  20. 120
    Mark says:

    Jim 114, we do it by making 800GW of renewable energy available. By building power stations, like you did to get the 800GW in the first place.

  21. 121
    Nick Gotts says:

    “The RSS figures show that there has been a statistically significant (linear model p=0.1” – Richard Stekis

    Well Richard, p=0.1 would not be considered statistically significant by any scientific journal I know of.

  22. 122
    Nick Gotts says:

    Douglas Wise #110, Mark #111:
    Science 13 March 2009:
    Vol. 323. no. 5920, pp. 1468 – 1470
    DOI: 10.1126/science.1167549

    Clear Sky Visibility Has Decreased over Land Globally from 1973 to 2007
    Kaicun Wang* Robert E. Dickinson Shunlin Liang

    Visibility in the clear sky is reduced by the presence of aerosols, whose types and concentrations have a large impact on the amount of solar radiation that reaches Earth’s surface. Here we establish a global climatology of inverse visibilities over land from 1973 to 2007 and interpret it in terms of changes in aerosol optical depth and the consequent impacts on incident solar radiation. The aerosol contribution to “global dimming,” first reported in terms of strong decreases in measured incident solar radiation up to the mid-1980s, has monotonically increased over the period analyzed. Since that time, visibility has increased over Europe, consistent with reported European “brightening,” but has decreased substantially over south and east Asia, South America, Australia, and Africa, resulting in net global dimming over land.

  23. 123
    Ray Ladbury says:

    Steckis, a significance presumes a model. Yours was? Now go back and apply said model to past data. How many times would you have been fooled? I count about 3 “cooling trends” in the past 35 years that would have looked as significant at the time.
    It astounds me how you guys want to draw conclusions based on 8 years data, but utterly ignore the past 35 years. Mighty selective.

  24. 124
    L. David Cooke says:


    Hey Nigel,

    Actually, these designs do not abide by the basic premise of the Savonius design, drag. The Savonius or 55 gallon drum version promoted by Michael Hackleman in the late 1970’s had a rough efficiency in the range of 13-18%. The primary benefit for poorer countries was through the use of waste oil drums and belt-pulley or bike chain-sprocket it was possible to harness wind energy where high level funding was not available.

    The Darrieus design; however, employs lift similar to the horizontal axis device with efficiencies ranging in the 28 to 42% region. The Modified Darrieus or gyromill or cyclo-turbine employed straight airfoils with some using articulating blades that required extensive mechanical control. (The blade articulation controls are really not much different then the use of the tail and cutout function in horizontal designs.) The efficiency limitation of Darrieus was that for roughly 18-20% of it’s rotation that a blade could not provide energy meaning the theoretical limit of 63.5% was reduced to approximately 50%.

    This leads to the other implied issues of structure and complexity. First structure, a properly balanced cyclo-turbine can be erected on a single pylon similar to a horizontal axis. Secondly, the complexity for blade articulation has been vastly over stated by opponents. The simple arrangement of centripetal weights as suggested in the wiki link were an example. Another, and one I have been experimenting with for over 30 years, is rather then use a blade hinge I use a set of perpendicular mounted eye bolts.

    By interlocking the two eyes and mounting the support arm bolt at a 45% angle with the top towards the axis, it is possible to limit the rotation of the blade to 45 Deg. (To be effective it actually does not have to close anymore then 23 Deg. to perpendicular to the support arm to be effective. Secondly, by tipping the blade mounted eyebolt outer side downward by 12 Deg. you prevent the blade from opening anymore then 12 Deg. there by reducing the idle rotation drag induced by the flat spinning blade.

    Finally, design for the task is what is important. With a cyclo-turbine unit as designed above you can extract up to 42% of the energy in the wind employing a simple box frame with a couple of flat panels bolted on the end. (As a general rule of thumb you size the blades and blade count according to the load and wind.) Where as a horizontal axis can rotate with one blade a vertical axis works best with two. (However, you could employ a fly wheel to rotate through the dead zone.) By the same token with a little air foil and springs it is possible to reduce the dead zone to less then 25 Deg. of rotation allowing you to realize a extraction efficiency of nearly 48%.

    The main advantage is the startup or operating wind speed of vertical axis devices. Since they are not dependent on lift they can start up and operate in winds as low as 5 mph or roughly 1.7-2.5 mps. As to building components, the Chinese used these for irrigation as far back as 2000 years ago constructing them from bamboo and reed mats. With modern materials the costs can be comparable to horizontal axis with the benefit of increasing the sites that can potentially be used, due to lower average windspeeds.

    As to blade count, though the Germans in 1978 proposed a one bladed horizontal axis unit you will notice that most systems now employ 3 blades. And where a vertical axis can run with as few as two blades the slip stream and down wind lift optimize their operation with a three blade configuration, (though a five blade version runs a little smoother). By mounting the cantilever support via a central hub disk the ability to experiment what best suits your installation is available.

    As to a final design consideration is the blade size, this depends primarily on the startup energy required, if you stair step your energy extraction a narrow blade can be used; however, as these are primarily designed for low wind conditions, a blade to support arm ratio of 1:3 is recommended.

    Sorry for getting so detailed, though you are correct that efficiency is not as high, the effectiveness and expansion of installation siting is greater with vertical axis devices in my humble opinion.

    Dave Cooke

  25. 125
    Douglas Wise says:

    re #110 and 122. Dave Cooke amnd Nick Gotts.

    Many thanks for the aerosol links. From the information I gleaned from reading them, I have learned that:

    1) Only 10% of aerosols have an anthropogenic origin.
    2) The apparent pause in the global warming trend noted between 1944 and 1974 is ascribed to global dimming caused by fossil fuel combustion in the absence of emissions controls.
    3) There has been a net global increase in dimming (over land) from 1973-2007 but this hasn’t apparently resulted in a masking of the warming trend (if one discounts the claims of sceptics).

    Could anyone explain? I appreciate that some aerosols (eg sulphates) cause negative forcings while others (eg black carbon) act in the opposite direction. I also realise that ghg positive forcing is getting progressively larger over time. Throw in the odd Pinatubo- type volcano, El Nino, La Nina and Uncle Tom Cobley and things get complicated.

    I suppose that I would really like to know where global surface temperatures would be now if the developing world had imposed the same emission controls at the same time as the developed world. I would also like to know whether the climate modellers have already factored in the increase in aerosol negative forcing reported in the 2009 paper cited by Nick Gotts.

  26. 126
    Richard Steckis says:

    Ray Ladbury Says:

    “Steckis, a significance presumes a model. Yours was? Now go back and apply said model to past data. How many times would you have been fooled? I count about 3 “cooling trends” in the past 35 years that would have looked as significant at the time.
    It astounds me how you guys want to draw conclusions based on 8 years data, but utterly ignore the past 35 years. Mighty selective.”

    Ray. My apologies. Unfortunately, for some reason, the whole of my comment did not get posted. Internet glitch I would say. In that I said that the 8 year measurement is preliminary (amongst other things). I am not being selective as I did mention the significant increase in temperatures between 1975 and 2000 (again, in the mangled part of the comment). I also stated that more time is needed for observation. The model was a linear model.

    As for celcius beig selected as the standard temperature, the celsius scale was accepted primarily because Anders Celsius conducted exhaustive experiments on the essential fixed points (melting point of ice and the boiling point) as well as the need to account for atmospheric pressure in the determination of the melting point. His published paper on the subject was titled “Observations of two persistent degrees on a thermometer” in 1742. The moral is that Celcius was selected because of extensive emprical published research and not on a de facto “that seems about right” expert opinion.

    Nuff said.

  27. 127
    J. Bob says:

    118 – Richard Steckis

    Get to the East Anglia data from 1659

    And the Skockholm GML (STOCKH-GML) data from

    Select Sweden – Stockh-GML. This gives continous temp recordings from 1755 tp 2005.

    This will give you two very long term temp trends. Doing a simple linear least sq. fit, both graphs seem to stay in a band with no major explosions at the end. Rimfrost has a lot of long term temp data available to look at.

  28. 128

    #124 L. David Cooke

    Hi Dave,

    Please do not apologize for a note that actually explains some things. Yes, it has to be a bit longer than a ‘— twitter’ (expletive deleted).

    Perhaps you would clarify how efficiency is defined for these wind devices? Is the reference energy the kinetic energy of the flow through the full area swept out by the blades? Or is it just the blade projected area?

    Cheers, Jim

  29. 129
    Save Gaia says:

    Stable ancient atmosphere underscores current greenhouse spike
    “Despite vast changes in climate since the early Pleistocene, 2.1 million years ago, carbon dioxide levels have stayed pretty stable until lately, according to a study published online today in Science.

    All of that consistency, in which CO2 levels averaged 280 parts per million, makes today’s concentration—385 parts per millions, which is 38 percent higher—all the more stunning, the authors report. Previous work showed stable CO2 levels going back about 650,000 years.

    For the new estimate, the researchers analyzed ancient plankton shells beneath the Atlantic Ocean floor, rather than relying on data from polar ice cores, which can only give readings for the past 800,000 years. The tiny shells provided info on CO2 levels as well as temperature and ocean acidity.

    The findings suggest that previous ice ages may have had more to do with other forces, such as changes in the Earth’s orbit, than with plummeting levels of carbon dioxide in the atmosphere. But, spikes in CO2 levels did match up with periods of warming.

    “Our data continues to suggest that greenhouse gases and global climate are intimately linked,” lead study author Bärbel Hönisch, a geochemist at Columbia University’s Lamont Doherty Earth Observatory, said in a statement. ”

  30. 130
    Jim Galasyn says:

    According to this analysis from Munich Re, wind damage is increasing:

    Graph of the Day: Losses from Floods, Windstorms, and Earthquakes, 1980-2005

  31. 131
    L. David Cooke says:

    RE: 128

    Hey Jim,

    The measure is related to sweep area taken in profile. Betz Law limits maximum energy extraction to approximately 59.3%. Subsequent work demonstrates a dual actuator cross flow turbine system seems to point to a 64% limit.

    (Newman, B.G. Actuator-disk theory for vertical-axis wind turbines. J. Wind Eng. And
    Industrial Aerodynamics, 15/3, 1983, p.347-355.)

    Dave Cooke

  32. 132

    #131 L. David Cooke,

    Sounds like you know about this stuff.

    You must also know the significance of a drag coefficient of .05 for the basic airship form compared to the drag coefficient of our best production cars.

    For wind and waterflow systems, there seems to be something real to work with, but the cost of these things seems to be the main question. Up to now, it looks like the wind folks are coming up short on being able to do it in an economically “sustainable” way.

  33. 133
    Rick Brown says:

    Re: # 125 Douglas Wise

    Perhaps this has some relevance to your questions:

    Published Online June 18, 2009
    Science DOI: 10.1126/science.1174461

    Consistency Between Satellite-Derived and Modeled Estimates of the Direct Aerosol Effect

    The direct aerosol effect has a radiative forcing estimate of –0.5 Wm–2 in the IPCC AR4, offsetting the warming from CO2 by almost one-third. The uncertainty range, however, ranges from –0.9 to –0.1 Wm–2, largely due to differences between estimates from global aerosol models and observation-based estimates, with the latter tending to have stronger (more negative) radiative forcing. This study demonstrates consistency between a global aerosol model and adjustment to an observational-based method, giving a global and annual mean radiative forcing weaker than –0.5 Wm–2 with a best estimate of –0.3 Wm–2. The physical explanation for the earlier discrepancy is that the relative increase in anthropogenic black carbon (absorbing aerosols) is much larger than the overall increase in the anthropogenic abundance of aerosols.

  34. 134
    L. David Cooke says:

    RE: 132

    Hey Jim,

    As to knowledge, no more then the average bear in the industry…

    As to economic systems, that is open for debate. The issue comes to establishing the break-even points for a single versus separate systems. Overall the main cost drivers are the foundation and engineered stress-strength for the weather that might occur over the lifetime of a system. As to the primary limitation, tip speed is likely going to be the main issue for horizontal systems. Once the tip speed reaches near the 500mph limit the potential for blade stresses to form stress fractures in the blade.

    (Another reason I like vertical axis devices is the blade tip speed ratio rarely exceeds 4, meaning it would require 125 mph winds before stress fractures would be a question. Whereas axial devices usually have a TSR of around 7 limiting maximum peak wind subjection to less then 70mph.)

    In relation to your reference regarding drag coefficients, there were extensive experiments carried out by GM and Ford in the early 1980’s. The primary findings were; one, the undercarriage and flow through of the engine compartment had a large detrimental effect. Secondly, the laminar air flow separation was the greatest issue of all. When you look at most vehicles the “chord” of the air flow versus the breadth of the airflow are the primary cause of the problem.

    The idea of the lifting body such as the X-24/X-33/M2, or the Space Shuttle and Dynalifter airship designs talk to this issue a lot. Even though they suffer a similar chord to width ratio as a motor vehicle, the designs take all surfaces into account. (BTW, if you notice not many air ships employ chopped off ends.) The point being if you wish to maintain laminar air flow you have to create drag to reduce de-lamination at the posterior of the object. At the same time you need to not create so much drag that you increase the turbulence. Of question is at what speed do aerodynamic forces start to become critical? (I can share that the point that they become an issue is as soon as the impact lift has a positive buoyancy effect on the object.)

    As to blade coefficients, my preference is a flat blade as I do not like the symmetrical foil design, it adds too much drag. When you employ an asymmetrical foil you are introducing another potential stress factor. To me a flat blade with just a slight curvature to it, is preferred. (Slight defined as less then 3% deviation from flat over the chord of the blade.) With the apex of the curvature to occur forward of the CG by roughly 33%. (In essence, on a 36 inch/1 meter blade a curvature not to exceed 1 inch/2.54 cm, positioned about 12 inches/30 cm back from the leading edge.) Placing the curvature towards the axis of rotation allows for strengthening stress to be placed in the rolled metal or graphite/epoxy shell reducing the tendency of the surface to “oil can”. (“Oil canning” is similar to the sound of the hull of a Jon boat or Airboat on a plane.)

    Dave Cooke

  35. 135

    Re #134

    Thanks Dave,

    Yes, the chord to breadth ratio is the main problem with automobile drag. Generally, the auto industry accepts that they are stuck with “bluff” bodies. This made sense for most of automobile history, where energy supplies were not so limited as we now know they need to be.

    A fairly complete representation of the entire automobile industry efforts is in Huchco, SAE, from the “torpedo” of Jenatsy, 1899, the Alpha Romeo “air ship” of Count Ricotti, 1914, “tear drop” of Rumpler, 1922 and so on.

    The “boxfish” work by Daimler recently revisited the subject, and showed that even for fairly short bodies the drag coefficient could be .07. However, the conditions were that it had to be in free flow conditions. When that body was brought close to the road the number increased to .11 (if I remember right). Then they adapted it with wheel wells, wheels, and what they considered absolute requirements for people, and the number went to about .20. Details were a bit sketchy but the final result looked like it would be headed for the .26 range ( the Prius Cd ).

    In a paper of 1982, Morelli showed that a specially formed variation of the teardrop shape could be brought close to the ground without causing Cd to degrade. (The Aptera looks very much like this shape.) Morelli claimed Cd of .047 in ground proximity, which is the same as the ideal teardrop in free flow that he started with. Aptera started off claiming .07, then .11, and lately it is .15. That is very good.

    However, the teardrop is not really optimum since its volume is reduced by that shape, compared with the ideal airship shape.

    In 1906 Fuhrman, student of Prandtl, developed the ideal airship. It set the standard of nearly perfect laminar flow while maximizing volume (important for airships and anything else that needs to carry stuff). German, British, and Americans polished that shape until 1933 when the USS Akron was emerging, and a scale model was measured in the NACA (now NASA) wind tunnels. An extremely thorough set of measurements were made in several sets, but the most useful was the set published by Freeman, 1933 (see NASA reports server, or quicker, see the main one at You might appreciate the old papers that are now available at the NASA reports server.

    While Freeman used a different Cd formulation, it converts to slightly less than .05 in the modern formulation. The scale used for this USS Akron, ZRS-4 model turns out to be close to actual size for an automobile application, so we do not have to worry about Reynolds number to scale the answer.

    The only thing left was to adapt the car to this form. The main thing was to enable free flow aerodynamics and to keep the same body of revolution form, including the shape that maintains laminar flow. It can be done while preserving the important functions of the automobile.

    This could turn out to be a better way to make cars. If that became the standard, USA emissions of CO2 would be cut by 30% to 40% from this action alone. And, the cost would be less than the normal replacement cost of the automobile.

  36. 136
    Mark says:

    Jim, #135, one way to solve it is to travel less quickly.

    Or not individually.

  37. 137

    Re #136

    Right you are Mark.

    We only differ in the value we put on personal time.

    Even traveling in groups might seem to be a way to get around quickly, but it seems to end up making travel time substantially longer.

    Sure, we can all move to high rises over train stations.

    The problem with transportation is that the ideal forms that are trains are linear and if people choose to live in the two dimensional arrangements, linear fails in distribution.

    I try to solve the problem in a way that lets people live as they have chosen. Uh, well, they need to at least adapt to a new kind of car.

  38. 138
    Douglas Wise says:

    re#133: Rick Brown

    Many thanks for the information. It is interesting that dimming appears to be less than one might have expected because of the relative preponderance of black carbon in anthropogenic emissions.

    David Benson (#570 on Groundhog thread) refers to a report in which Schellnhuber claims that we would already be 2.5 deg C warmer were all SO2 to be filtered out of the atmosphere

  39. 139
    Mark says:

    “I try to solve the problem in a way that lets people live as they have chosen. Uh, well, they need to at least adapt to a new kind of car.”

    Well, not really. They have to use your car for a start.

    And I’m sure you won’t let them walk into your home if they feel like it.


    Heck, we have speed limits. That people break them shows that people don’t want to live that way.

    The difference in approach we take on “letting people live their lives the way they want” is nowhere near as big as you make out.

  40. 140
    Jim Norvell says:

    Slightly off topic but is anybody working on a GCM from first principles? Form a first look there seems to be only 3 variables: pressure, temperature and humidity. As an old ME who chased heat transfer problems in various industries over the years, it is just another large radiation, natural circulation model. Admittedly there is a lot of the physics that is not well defined. Like cloud physics or the dynamics of the natural circulation flow. Other than that and the fact that you need several million grid cells, it should be easily solvable.

  41. 141
    Brian Dodge says:

    Will global warming cause changes in the balance of latent versus sensible heat transport in the atmosphere, and thus cause changes in wind and weather patterns?

  42. 142
    KW says:

    Your beliefs in climate change are likely for the sake of the safety of humanity. And I highly respect your committment and dedication to the subject matter involved. You belief deftly in your ideas and are unwavering in your studies. That I applaud. Bravo Realclimate and all the climatologists and scientists who study our earth sciences.

    But I still disagree that our climate changing will be all negative. You fail to list or research any positive effects of climate change. Why all the negative stories? Why all the negative human welfare aspects? Why not include some positives? Warmer or colder? More or less GHGs? Why does it all have to be bad? Is it truely only motivated by fear? Why cant it be motivated and funded moreso by the principle of science instead….aka curiosity? Why can’t there be a distinct seperation between science and government? There is between religion and state! Actually, you know already know the answer to these questions. It is because you are afraid or unwilling to accept the fact that your view point may have an element of flaw…or rather…flaw by association. Association with the belief that all that man does to exist is by default – bad.

  43. 143
    Mark says:

    “Slightly off topic but is anybody working on a GCM from first principles?”

    Uh, all physical models do.

    There was a thread on this a few months ago about it.

    Looks like it didn’t stick, Gavin.

  44. 144
    Mark says:

    “But I still disagree that our climate changing will be all negative”

    Who has said this?

    I’m pretty sure that cockroaches will love the loss of most competing lifeforms.

    I’m pretty sure our Lizard Alien Overlords will love the hot dry temperatures too.

    Heck, having dengue isn’t all negative. If you survive you will have antibodies against similar diseases. Which is a bonus, is it not?

    And where is your diatribe against those who say that mitigation will be expensive? Or do you think that is right? If so, why? And why do you think that changing the climate and flooding the earth will be only a good thing?

  45. 145
    Jim Eager says:

    Jim Norvell @140 asks “is anybody working on a GCM from first principles,” thereby demonstrating that he has no clue what GCMs are or how they are constructed.

    Not at all surprising, really.

    He then goes on to arrogantly state “it is just another large radiation, natural circulation model… it should be easily solvable,” when in fact it has already largely been solved, but he simply does not accept the solution derived from said first principles.

  46. 146

    KW @ 142:

    But I still disagree that our climate changing will be all negative. You fail to list or research any positive effects of climate change. Why all the negative stories? Why all the negative human welfare aspects? Why not include some positives? Warmer or colder? More or less GHGs?

    Because in order to have all those greenhouse gases, we have to burn a lot of natural resources that are not renewable.

    Even if you think that global warming isn’t going to be a bad thing, how are you going to feel when your car is costing you as much to operate as your mort-gage?

  47. 147

    KW, if you look at the Summary report from Copenhagen, on p.16 you will note in the columns labeled “Distribution of Impacts” and “Aggregate Impacts” the words, “Positive impacts.” You will also note that positive impacts disappear as temperature increases past +2 C.

    So some positive impacts are acknowledged (and have been since at least the 3rd IPCC report.) However, the “goods” aren’t going to continue with temperature increases beyond the relevant limits; and the “bads” keep getting worse. I trust the reasons are fairly clear if you reflect a bit.

  48. 148

    KW writes:

    But I still disagree that our climate changing will be all negative. You fail to list or research any positive effects of climate change. Why all the negative stories? Why all the negative human welfare aspects? Why not include some positives?

    Because both positives and negatives have been analyzed and the negatives dominate overwhelmingly.

    Global warming will mean more droughts in continental interiors. The Australians have lost a third of their agricultural production to drought in the last few years, and that kind of thing is going to spread. If we do nothing, I fully expect human agriculture to crash in the next 50 years or so, and our civilization with it.

    Global warming will also remove the main source of fresh water — rivers fed by glacier melt — for a billion people in Asia in Latin America.

    Those two effects, plus more violent weather along coastlines, and eventually, sea-level rise, will create hundreds of millions of “climate refugees.” Continuing how much Americans welcome the few million Mexican immigrants we get, how do you suppose the rest of the world will handle that? In a world where a dozen nations now have nukes, one of them Kim Jong Il’s North Korea?

    Global warming is going to be a disaster. More so because people like you still control public opinion, and that means nothing helpful will be done in time.

  49. 149
    Mark says:

    “The Australians have lost a third of their agricultural production to drought in the last few years”

    That’s unpossible, BPL!!! CO2 is a ***plant food***.

    Ergo, the plants MUST be growing!!!

    I heards it on the internets!!!

    (I would use the sarcasm tags, but this is partly desperation, so sarcasm doesn’t really cut it…)

  50. 150
    G. Karst says:

    As far as I can figure, whenever observational data is studied, evidence indicates warming moderates severe weather.