Wind farms affect local nighttime temperatures, not global warming

On April 29, a paper about how wind farms affect surface temperatures was published online by the journal Nature Climate Change. The authors of the paper found that wind farms increase the nighttime surface temperature within and immediately downwind of the wind farm because the turbines mix up cold surface air with warmer air from up higher off the ground. What the authors did not find, however, was that wind farms were having any global effect on climate disruption. But if you only read articles and blogs from Forbes, Fox News, The Star Ledger, the UK’s Daily Mail, The National Review‘s Planet Gore blog, The Free Republic, etc., you’d never know that.

In fact, if those were your only sources of information, you’d believe that the paper was all about how wind farms were yet another cause of global warming, when in fact it says nothing of the sort.

The fundamental point of the paper is shown in the figure above (Figure 2a from the paper) – there’s a high degree of correlation between areas of increased nighttime surface temperatures (red blotches) and the location of large wind farms (black “plus” symbols). Looking closely at the figure reveals that the red areas are very tightly associated with the turbines and extend only a small distance downwind (north in this case) of the wind farm itself.

The figure shows that the increase in nighttime surface temperatures affects the wind farm and only a few miles downwind, meaning that the change is local, not global, in extent.

As for why the surface temperatures would increase (and why they’d increase at night more than during the day), it helps to think first about what happens to the air without a wind farm near by.

If you’ve ever taken an early morning walk (or run, hike, bike ride, etc.) in hilly terrain, you’ve probably experienced how the air near the ground is colder early in the morning than the air is high up off the ground. I’ve got a running route that has hollows where the temperature can be five or more degrees colder than the air up on top of the little ridge 20 feet higher and 50 feet away.

The reason this happens is because at night, the ground cools off fast as it radiates heat away into the air and space. As the ground cools off, it cools off the air right above it, and the cold air sinks because it’s slightly denser than hot air is. If there’s a hollow where the cold air can’t escape, the cold air sits there until a breeze disturbs it or the morning sun heats it up again. And because it’s natural for denser cold air to sit underneath less dense warm air, the cold pockets are very stable so long as they’re not disturbed.

This state of affairs occurs even when there aren’t any hollows to collect the cold air, and even a mass of nighttime wind will tend to have cold air near the ground and warmer air high above the ground.

What the paper says is that wind turbines mix up the cold and warm layers of air by dragging cold air from the ground up high into the air (where it’s normally warmer) and by dragging warm air from high up down to the ground (where it’s normally colder). This redistributes the heat energy held in a given volume of air by roughly equalizing the temperature of a large volume of air. However, because the turbines are only redistributing the energy already present in the air, it doesn’t affect global warming in any way.

In case this isn’t clear, let’s look at an analogy culled from my 21st birthday bar tour – the B-52 shot (pictured at right). Notice that there are three discrete layers of liquor – Kahlua on the bottom, Bailey’s Irish Cream in the middle, and Grand Marnier on the top. The Kahlua is the densest, so if the Bailey’s is poured carefully, it will sit on top of the Kahlua. Similarly, the Grand Marnier is the least dense, so it will essentially float on top of the Bailey’s if it’s poured carefully enough. While you get the beautifully stratified layers of the shot when the three liquors are poured carefully, if the pour is done badly or you covered the shot with your hand and shook it up, you’d end up with a gray-brown cloud that didn’t look nearly as cool.

And regardless of whether you drink it properly stratified or all mixed up, the B-52 contains the same amount of alcohol – merely mixing the layers up doesn’t do anything to the overall alcohol content (we’ll assume that the person ordering the B-52 didn’t want it flaming in this case).

Similarly, at night, cold and dense air settles to the ground just like the Kahlua layer of the B-52, with a layer of warm air (the Bailey’s) on top of that, and (for purposes of this analogy) a layer of even warmer air (Grand Marnier) above that. Adding a wind farm to the area mixes those three layers up just like shaking a B-52 does. What the wind farm doesn’t do, however, is change the amount of alcohol heat energy present in the affected volume of air (more energy in the hot air, less in the cold) – it just mixes all the layers up and makes the heat energy about the same throughout the entire volume.

While it’s clear that the wind farms don’t affect global warming physically, they could affect one of the measurements of global climate disruption. The most common way to measure climate disruption is by measuring the surface temperature multiple times every day and tracking the change of those measurements over the course of years. The problem is that the paper indicates that wind farms increase the nighttime surface temperature, and by a significant amount (about 1.3 °F), simply by mixing up the different layers of air.

If enough of the Earth’s surface, or enough areas near to climate monitoring stations, becomes covered by wind farms, then the wind farms would add an error that would appear to show the surface warming slightly faster than it really is.

Thankfully, however, scientists now know that wind farms might be making nighttime surface temperatures artificially warmer in their immediate vicinity. And since they know this, the scientists at the Goddard Institute for Space Studies (GISS), the Climatic Research Unit (CRU), the Berkeley Earth Surface Temperature project, and NOAA’s National Climate Data Center can correct for the artificial warming in data coming from affected climate monitoring stations.

There are a lot of unanswered questions raised by the paper. The authors conclude that changes in the Earth’s surface reflectivity (aka “albedo”) didn’t have a measurable effect, but it’s not clear that this claim is well supported in the paper. The results apply to the region of Texas that the authors studied, but does it apply to the wind farms along Interstate 80 in Wyoming, or to offshore wind farms off Nantucket? The authors calculated a per-decade trend in nighttime surface temperature based off of nine years of data, but nine years isn’t enough to say whether it will be an actual trend or whether it’ll be a one-time increase that stabilizes after the wind farm is completely built out.

But even with those unanswered questions, it’s clear that the people reporting that wind farms increase global warming are wrong. And in case anyone doesn’t believe the explanations offered above, here’s a statement from the authors themselves:

Overall, the warming effect reported in this study is local and is small compared to the strong background year-to-year land surface temperature changes. Very likely, the wind turbines do not create a net warming of the air and instead only redistribute the air’s heat near the surface (the turbine itself does not generate any heat), which is fundamentally different from the large-scale warming effect caused by increasing atmospheric concentrations of greenhouse gases due to the burning of fossil fuels. [emphasis added]

Image Credits:
Nature Climate Change, DOI: 10.1038/NCLIMATE1505

7 replies »

  1. God, trying to fight the good fight on this one must be like sweeping back the ocean. The idiots just keep coming. Anyone who stayed awake in science class would realize that any warming effects from wind farms would be infintesimal at worst.

    • I’m sure that, if you extended this effect to enough wind farms to power all of human civilization, the impact would be WAY smaller than the effect of CO2-enhancement on the greenhouse effect. By several orders of magnitude.

  2. So are the folks at Reuters climate “deniers” too? The Fox News article is written by Reuters, not Fox News.

    I completely agree with the B-52 example. The amount of alcohol is the same in the whole glass. But if your alcohol sensor isn’t measuring the whole glass at once, but specific areas within the glass, it could lead to false readings. If you took a reading of the Bailey’s with no mix, it is roughly 34 proof. If you poured the drink sloppily (a crime in and of itself), this 34 proof would be mixed with the 80 proof Grand Marnier. So while you are right, mixing the air currents doesn’t make us warmer…if there is a temperature station nearby, it will lead to false results.

    The urban effect of temperature stations has been repeatedly shown. Many of the worlds temperature stations, which used to be in more rural areas, are now in very urban areas. Legions of climate skeptics have taken to the streets with the coordinates of the temperature measurign stations in their areas. These pictures have shown temperature measuring stations not following some, most or any of the guidlines for where they should be located. Some of the funnier pictures are temperature measuring stations located in the middle of a black top parking lot or near the exhaust of heating unit for a building! lol

    Is there global warming? Yes. Does CO2 have a warming effect? Certainly (and has been known for a century or so and is easily verified in a lab). The main debate amongst serious skeptics the effect of the feedbacks. Are the feedbacks positive in warming or negative? This, in essence, IS the debate. All else are side arguments.


    • You’re point about Reuters is a little off base. The article on Fox Nation was from Reuters, yes, but the headlines were radically different.

      Fox Nation (linked in the OP): “New Research Shows Wind Farms Cause Global Warming”

      Reuters News: “Wind farms may have warming effect: research”

      That’s a pretty big difference.

      Also, the Fox Nation article ends with the following sentence:

      “These changes, if spatially large enough, may have noticeable impacts on local to regional weather and climate,” the authors said.

      The Reuters News article has a subheading following the identical sentence and then continues on for an additional nine paragraphs and 364 words after the point at which Fox Nation cut the article off. If Fox Nation had included the rest of the article, I’d have pinned this down as an example of an editor writing an error-filled headline. The original Reuters article had a bunch more information that pretty much contradicted the Fox Nation headline:

      But the researchers said more studies were needed, at different locations and for longer periods, before any firm conclusions could be drawn.

      Although the warming effect shown in that study and the latest research is local, and small compared to overall land surface temperature change, the findings could lead to more in-depth studies. [emphasis added]

      Fox Nation got it wrong with the headline and by leaving out information that countered the claim they made in the headline.

      I already pointed out the exact point you made about “making false results” in the OP:

      While it’s clear that the wind farms don’t affect global warming physically, they could affect one of the measurements of global climate disruption. [emphasis original]

      Thankfully, however, scientists now know that wind farms might be making nighttime surface temperatures artificially warmer in their immediate vicinity. And since they know this, the scientists… can correct for the artificial warming in data coming from affected climate monitoring stations. [emphasis added]

      Finally, the pictures you’re talking about do show that many USHCN climate stations aren’t located ideally. However, at least three studies since 2010 (Menne et al 2010, BEST, and Fall et al 2011) have found that the effects of imperfect locations in the data are small and correctable. Menne et al found that temperature measurement biases were actually mostly related to changes in sensor type and measurement times, and that those changes cooled things, even for poorly placed sensors.

      At this point, the argument that the measurements are unreliable is untenable. If that weren’t the case, then four to five land datasets and two or three satellite datasets wouldn’t all be saying the exact same thing – the temperature increases are real.

      I’m glad to hear that you feel that the real argument is about climate sensitivity. I’d be thrilled if you could convince your fellow travelers to agree with you. Because that, at least, is a reasonable argument to be having.