Supreme irony: wind farms can cause atmospheric warming, finds a new study?

What is it about GW that brings out such levels of stupidity in so many people?

Lets start with the easy bit. There’s a paper Impacts of wind farms on land surface temperature by Zhou et al.. It isn’t very exciting, but it made into Nature Climate Change, probably because of the inevitable stupidity it would arouse. What it says is Our results show a significant warming trend of up to 0.72 °C per decade, particularly at night-time, over wind farms relative to nearby non-wind-farm regions. This isn’t ironic or even particularly surprising: the effect is due to mixing down of warmer air on nights with an inversion. At least, that’s what I expect, not having read the paper, and its what Black of the Beeb wrote, having talked to Zhou: At night, air above ground level tends to be warmer than the ground. Dr Zhou and his colleagues believe the turbine blades are simply stirring up the air, mixing warm and cold, and bringing some of the warmth down to ground level.

But if you’re silly, like the Torygraph, you find yourself obliged to headline your story Wind farms can cause climate change, finds new study. The actual article itself isn’t too bad – it correctly notes this is a local effect, largely night-time only, and it permits itself a little speculation that if done on a large enough scale this might just be noticeable regionally. And, being generous, you could call this “climate change” – though to most people, “climate change” will mean global climate change, which this isn’t.

However, you then get people who really should know better repeating Windmills cause climate change! Timmy manages the oh-how-I-wish-it-was unusual feat of having nothing useful to say, whilst quoting the worst bits of the article and suppressing the useful bits. This is global cooling come again – people just can’t resist the “counter intuitive” stuff. He has another go at Forbes but gets it even wronger there – now its explicitly become Wind Farms Cause Global Warming!

But the funny thing is to look at the comments. Like:

I had a good laugh about that, it’s fairly obvious really you convert kinetic energy into electricity and get heat as a bi product. Silly eco mentalists


Think it through & you’ll realise there’s no climate warming effect whatsoever. The energy is in the wind. The bird shredders remove some of the energy as electricity but the process of doing so isn’t 100% efficient so it also creates heat

These are wrong – they are fairly typical of the “I know nothing about climatology, but rather than trying to find something out I’ll just speculate and call it truth” sort of commentator. But they have absolutely no excuse for being wrong, because even the Torygraph got it right, in the first few paragraphs of its article: “Usually at night the air closer to the ground becomes colder when the sun goes down and the earth cools. But on huge wind farms the motion of the turbines mixes the air higher in the atmosphere that is warmer, pushing up the overall temperature.”

Since its Timmy’s blog, and he is often rude to people, I get to call him and his commentators idiots. Which he (in this instance) and they (oh so often) richly deserve. Which brings me neatly on to…

WUWT, which is where I stole my headline from. That too reports the same study, and in the same sensationalist terms. What is, again, funny is that the commentators there completely miss the point and run off down the same inefficient-conversion-leads-to-heat rabbit-hole (and they even find some new ones), even though Watts has half-said it in the very top paragraph. I tell them the truth, but they aren’t grateful. In fact Watts is very ungrateful indeed – but that is after the inevitable degeneration of the dicussion into a pointless demonstration of their lack of knowledge of wikipedia.


* Potential Climatic Impacts and Reliability of Very Large Scale Wind Farms – Chien Wang and Ronald Prinn

25 thoughts on “Supreme irony: wind farms can cause atmospheric warming, finds a new study?”

  1. I tell them the truth, but they aren’t grateful. In fact Watts is very ungrateful indeed – but that is after the inevitable degeneration of the dicussion into a pointless demonstration of their lack of knowledge of wikipedia.

    Well, Watt’s proud proclamation that he authored a Wikipedia article made me curious and I dug up the original version. Despite his assertions the article does not contain links to his sources. The article was actually a verbatim cut and paste from two sources with a single sentence actually written by Watts.

    Color coded texts are nice, so here you can assess the effort Watts put into “writing” his article.

    [Thanks. I’d assumed that AW was talking about, which also exists. But you’re right, its probably the other. They should be merged; I shall see to it. I’ve left a comment on his blog explaining his error, it will be fun to see if it got published -W]


  2. because even the Torygraph got it right, in the first few paragraphs of its article: “Usually at night the air closer to the ground becomes colder when the sun goes down and the earth cools. But on huge wind farms the motion of the turbines mixes the air higher in the atmosphere that is warmer, pushing up the overall temperature.”

    The newspaper did reflect the quote from Zhou, and normally I would expect that to be “getting it right”. But this time I’m not so sure. AFAICT, Zhou et al did not study the fluid mechanics involved, and it’s not clear that it is their expertise.

    As RGB at WUWT noted, the cooling of air near ground is mostly a calm night thing, and on calm nights, wind turbines aren’t doing anything. But on any night, the primary thing isn’t the air close to the ground becoming colder, but the ground itself. What then happens to the air is a boundary layer thing. And in uninterrupted flow, the boundary layer is at its thinnest. The warm air is closest to the ground. Turbulence thickens the boundary layer, pushing the mixed air further away.

    Turbulence does convert kinetic energy to heat, and this is on a scale which is large enough to account for the effect. Efficiency is probably less than 50%; it makes more heat than electricity. The electricity is enough to power a small town and create an urban heat island. There’s no reason why the waste couldn’t have that effect at the farm.

    Of course, none of this creates any global warming. The wind KE was always going to end up as heat; the turbines just shift the location. And it’s all tiny compared with GHE.

    [I’m sticking with my story, and Zhou’s. However the point about still nights is a good one: to make my story right, the effect has to be in light winds; inversions won’t break up until the wind strengthens, so that is OK. Here I regret not having the paper; I’d expect Zhou et al to have stratified their analysis based on differing wind speeds. They don’t mention that, though, so they may not have thought of it -W]


  3. The limits for windmill efficiency have little to do with thermo. You are converting work (motion of the air in a specific direction) to work (rotation of the blades) to work (electricity generated by the turbine through the gearbox). Mechanical losses in the last two steps would have to be low, otherwise there would be enormous heat sinks hanging off the turbine housing

    The major limit is the fact that the wind does not stop after exiting the blades of the windmill, otherwise you would have to move it away for the device to continue working. This is determines the maximum energy that can be pulled out of the wind of to ~60-70% depending on wind speed for winds fast enough to be worth letting the blades spin.


  4. @Eli: The limit for how much energy you can pull out of the wind is 16/27 (about 59%). This is the Betz limit. But you are right that it is a consequence of the fact that for the blades to keep turning you need to have some wind moving past the blades. The power available to be extracted from the wind by the turbine is modeled as the rate of change of kinetic energy of the wind, so you can’t take all of the energy else you stop the wind and stop your turbine (probably not actually possible but well cartoons…). So the Betz limit is related to the optimum amount of “slowing of the wind” for maximum power extraction. The actual amount of power a wind turbine can extract from the wind is determined by it’s power coefficient and this is typically less than the Betz limit.


  5. I know I’m being nasty here, but the wikipedia article is lifted verbatim from NOAA. While that information is in the public domain, NOAA’s copyright notice does read as follows (emphasis added)

    As required by 17 U.S.C. 403, third parties producing copyrighted works consisting predominantly of the material produced by U.S. government agencies must provide notice with such work(s) identifying the U.S. Government material incorporated and stating that such material is not subject to copyright protection within the United States. The information on government web pages is in the public domain and not subject to copyright protection within the United States unless specifically annotated otherwise (copyright may be held elsewhere). Foreign copyrights may apply.
    You are more versed in these copyright issues than I am, so can the article stay as it is or does it have to be rewritten? Should the links to the original documents I posted upthread be included as sources?

    [Actually I gave up caring about copyright minutae on wiki some time ago, though I still remove clear copyvio’s. There are people who do care about the details, though. The principle I’d apply is, “is the world a better place with this info there, or not?” In this case, i’d say it is, so all is well.

    But yes, it does need to be re-written by someone who cares -W]


  6. Why bother trying to condemn wind turbines with such obtuse arguments, when their actual performance is so abysmal? Wind turbine proponents always quote figures in terms of averages, percentages or totals; we never get an account of how they actually perform.

    Well over here in the UK, a report has used actual figures from the National Grid of the amount of electricity delivered by wind farms and periods of time over which that electricity was contributed:

    It is a shameful disgrace that our politicians can be so beguiled by the false claims of the industry’s snake-oil salesmen and their gullible supporters into spending such vast sums of our hard-earned taxes on such a useless technology.


  7. Colin, whilst Eli may not disagree about the need for nuclear power in the mix of solutions, what you point to is more a measure of installed base than of potential use, and as such for somebunny, most bunnies, who do not follow the links, misleading. Better to say that currently wind is not playing a huge role (although, in places like Spain where it is hitting 20% it is).

    As to the power coefficient, well yes, but the mechanical part of the loss in the drive train is small. The Betz limit, of course, scales with wind velocity.


  8. What made me chuckle was Watts’ comment to WC:

    Hey Connolley, read the first paragraph before you say “not one”. I’m really growing weary of your condescension. Since you think we are all “stupid”, as you stated publicly, why not go back to your Stoat blog and rant there. I don’t disagree with your explanation, but saying “not one of the “skeptics” here had the slightest idea what the effect was” is a condescending assumption on your part, and is dead wrong. – Anthony

    Really, if Watts himself agrees with WC’s explanation – which is what “I don’t disagree” means – then Watts should himself be commenting loudly and conspicuously in order to halt the river of thermodynamic Stupid that continues to flow through the thread.

    I can think of only one reason why he permits the continued misrepresentation/misinterpretation of the Zhou et al paper, and that is that he wants to promulgate and perpetuate yet another invalid, pseudoscientific challenge to real physics and climatology. Which is, no doubt, why he originally posted the thread in the first place…

    [Its odd. Part of it is that, of course, if he simply described the paper accurately it would be obvious there was nothing exciting, surprising, or ironic about it. In which case, what would he be writing about?

    But more than that, I can’t recall ever seeing him correct anyone’s errors: he will make interjections against people he dislikes, and “correct” them; but never to those on “his side”. This may be because he doesn’t really understand the science: in this case, his first para, which he is relying on to prove he knows what is going on, is more observational than understanding: he’s just thought of something similar. I’m not really convinced he understood the mixing point until I explained it -W]


  9. @Eli no.11: An expression for the power coefficient (Cp) of a wind turbine can be derived via axial momentum theory. This gives Cp = 4a(1-a)^2. ‘a’ is the axial flow induction factor. If ‘a’ is 0.2, then the wind is slowed as it passes the turbine by 20%. By differentiation you can find the value of ‘a’ that produces the maximum possible Cp for a wind turbine. This occurs when a = 1/3 and means that the max Cp for a wind turbine is 16/27. This is the Betz limit and it doesn’t scale with wind velocity.

    I don’t dispute that mechanical and electrical conversion losses for wind turbines are small. Some turbines, such as those manufactured by Enercon, do away with gearboxes altogether.


  10. I think Tony needs a number of posts a day to attract funding. As Pete revealed, ( and Tony has loudly denied) he gets money from places like Heartland. This type ofcash scrounge necessitaes a quantity not quality philosophy.

    [I think it is more eyeballs than cash. He has a number of people who treat it as their daily comic; if they aren’t regularly thrown fresh meat, they’ll get into the habit of finding it elsewhere -W]


  11. 17 John,

    Watts says exactly that in his opening para. Does anyone know if that was there from the beginning?


  12. Found an online copy of the complete paper, given the “tmp” in the link it may not be up for long:

    [Thanks! I’ve taken a copy. Now I just have to read it… -W]

    [OK, I’ve read it. Overall, the impression I get is that this is kind-of interesting, but crying out to be done properly: you need in-situ measurements, preferably through the boundary layer, in affected areas and adjacent unaffected ones -W]


  13. This “new study” of the effect of local air mixing at the site of a wind farm says nothing about wind energy and global climate, and casts no doubt on all the other studies that find wind power is one of the best ways to address climate change. Local air mixing has nothing to do with climate, because no heat or heat-trapping gases are being added to the atmosphere.

    To clarify the facts:

    -Wind plants do not contribute to climate change, and in fact they are one of the leading technologies preventing climate change by avoiding fossil fuel use and the emission of greenhouse gases
    -All studies have found that any impact wind plants may have on local weather is trivially small.

    Read our full fact check on the Into the Wind Blog at


  14. re: 18 TrueSkeptic
    I don’t know if comment was there from beginning, since I rarely look at WUWT. Given the wineries around Watts’ area, I’m sure he’d know that, so my comment was actually addressed to others.

    It only takes tiny rotors to ameliorate frost, so the effects of large turbines are unsurprising.


  15. John Mashey, good call.

    Citrus orchards in both CA and FL also have electric-powered fans to cause the kind of mixing on cold, typically windless, nights when freezing air settles. Mixing it up causes the ground temps to rise.

    Of course, windmills won’t do this on cold, *windless* nights, but it’s no surprise they do so when the wind blows.

    [Yes, but be careful. Too much wind destroys the inversion, and hence the effect -W]

    The importance of this study would lie on the fact that windfarms often are built in agricultrual areas. The wind-mixing effects with warming average night-time temps might be important to the farmer who’s leased land for a wind farm. They should have better information on how the windfarm might impact their ag productivity (possibly positive, which they’d hold close to the vest when negotiating; possibly negative, in which case they would not).


  16. Foxx had this and I took a peek as it came up in a gadget on my Google home page. There reporting wove in, “The warming could hurt local farmers, who have already suffered through a killer drought over the past few years. Texas agriculture contributes $80 billion to the state’s economy, second only to petrochemicals…. West Texas is a dry area that uses irrigation to grow wheat, cotton and other crops, as well as raise cattle.”

    I was struck by the inundation of falsity.

    1st, mention the total value of Texas ag contrasted the area south and east of Sweetwater, the area I bothered to checked on Google Earth, where the my prior understanding of the affected geography was confirmed. An admittedly a limited sample reveals not much irrigation, rather grazing scrubland. Some evidence there of hay grown in the bottoms between low hilly ridges with wind generators on the higher elevations that extend slightly into level plains type terrain in grass.

    2nd, the focus on temp as the governing factor in the co-located agriculture, rather the persistent low humidity wind coupled with low precipitation that limits soil moisture. The energy extracted in electrical generation, by slowing slightly the velocity of the prime soil dying factor, should help.

    The embedded video clip with Morano fibbing at near light speed, abetted by some Foxx gibbering head agrees with company policy.

    The text article was interestingly off message in that it did note the rather sizable amount of wind power, “10,000 megawatts … enough to power three million average American homes”, being generated throughout Texas in contrast to the pointed belittlement by Morano. I do question the amount quoted, but see that the American Wind Energy Association sources 6.4% of Texas’ 2010 electricity as wind generated and claims only a 2.7 million home metric. The side bar in the video does credit wind’s penetration in the US, quite a contrast to Morano’s spin.

    [The bit about warmth and farmers… the warmth is only likely to kick in on cold nights, and is likely to be a benefit in preventing frost -W]


  17. [The bit about warmth and farmers… the warmth is only likely to kick in on cold nights, and is likely to be a benefit in preventing frost -W]

    Not really. Preventable frosts affecting crops occur under clear sky, windless conditions.

    [They occur with stable inversions. Which are the conditions under which the wind farms will warm the surface. It isn’t necessary for the wind to be zero -W]

    They happen when radiant cooling of the surface is strong enough to lower the bottom bit of the stationary boundary layer’s temperature via conduction. If there is terrain relief, drainage from higher elevations and pooling in sumps develops. Horizontal air movement, strong enough to turn a blade, would have already produced turbulent mixing for frost prevention.

    The temperature gradient of the air in contact with and immediately above the surface under such condition is relatively large but only because its depth is quite shallow. The 1.25–2 m standard mounting height of surface air thermometers removes a good part of this “micro climate” effect. I’ve personally seen differences of less than a foot in height reflected in frost sensitive plants in a sloping garden. Alternatively, frosts with noticeable horizontal air movement occur when the overall air mass in below freezing not just a shallow few meters at the bottom of boundary layer.

    Again, I’d speculate the largest effect on farming (in the area covered by the study, and likely true where it’s the factor limiting plant growth) is through soil moisture. The area is open forest with little apparent brush or grass on low hills, the type of location where root systems areas produce quite regular tree spacing. The windfarms straddle annual precipitation bands that meet at 18 inches yearly. Abiline, a bit to the east has 24.5 inches with April (almost) through October at 2 inches or more, but markedly less in winter. Sweetwater, just north of the north easternmost aggregation has sunshine on 327 days a year, and also 24 annual inches. This is about the southern fringe of the 1930’s dust bowl.

    Understandably, the English may have a bit of a problem with the concept of aridity.

    I’d be interested in someone doing a back of the envelope estimate of the kinetic energy extracted and the partitioning of that between spinning generators and aerodynamic drag (heat). The mechanical loss is small but the blade area adds up and the tip vortexes convert much otherwise laminar flow into turbulence.


  18. Well color me stoopid, that is why they call me stoopid.

    Alas, Anthony Watts and some of his friends, are truly are showing their complete ignorance of the science of aerodynamics and the laws of thermodynamics.

    Now, a well known phenomena in the aerospace industry, is called “tip vortex”, where all rotating blades and aerofoils(wings), show a rotational wave mixing pattern.

    This youtube video shows the simulated effect of a two blade unit.


    This is a NASA youtube video of a jumbo jet, on landing approach with full flaps down, where the effect is quite severe and can be very dangerous for any aircraft following closely behind. Any disruption of air flow over an aircraft wings, will result in both loss of lift and control at the same time. This is why all landing aircraft have very strict separation rules, due to wake turbulence caused by wing tip vortex and short range hot engine exhaust.


    This a wikipedia short form article on the subject :-

    This is a picture of rotating blade vortex from the article in question. link :-

    A simulation of wind turbine wake vortex


    Vestas V52 wind turbine simulation of wake turbulence.


    Thus, there are no mysterious reasons why this is so and electric windmills do not break any of the laws of thermodynamics in the real world.

    And why do engineers carefully spread the electric windmills, on land in a careful dispersal pattern again? And the answer is, they know about the disruptive effect of down wind blade tip vortices.

    As usual, the supreme irony, is this is just another cherry picked piece of deliberate misinformation by denialati in chief Anthony Watts. One of spreading ignorance around, from the complete lack of understanding of basic aerodynamics and the laws of thermodynamics.


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