In an Aug. 30 rally in Evansville, Indiana, President Donald Trump made three unsubstantiated claims about wind turbines, which he calls “windmills”:

Trump suggested that a single turbine can be responsible for “thousands” of bird deaths. Birds are killed by turbines, but the real death toll from a single turbine is orders of magnitude lower than this. A 2013 study estimated an average of just over five bird deaths per turbine per year.

He repeatedly referred to “problems” when the wind doesn’t blow. It’s true that lack of wind prevents turbines from generating energy, but these pauses do not create problems that power grid operators can’t handle.

Trump also stated that living near turbines is noisy, enough to make someone “go crazy after a couple of years.” Studies indicate that people living near turbines are rarely exposed to average sound levels beyond 45 decibels, which is akin to the hum of a refrigerator. There is no direct evidence that the sound is detrimental to physical or mental health, although it may be annoying to some people.

While each of these claims start with a kernel of truth, Trump’s words misrepresent scientists’ and engineers’ current understanding of wind power and its limitations. We’ll tackle each statement individually, but first, here are his full comments on wind power from his rally:

Trump, Aug. 30: Clean power, right? They want to have windmills all over the place, right? When the wind doesn’t blow, what do we do? Uh, we got problems. When there’s thousands of birds laying at the base of the windmill, what do we do? Isn’t that amazing? The environmentalists, “We like windmills.” Oh, really? What about the thousands of birds they’re killing? Try going to the bottom of a windmill someday. It’s not a pretty picture. But, really, when the wind doesn’t blow, you got problems. If your house is staring at a windmill, not good. When you hear that noise going round and round and round, and you’re living with it, and then you go crazy after a couple of years, not good. And the environmentalists say, oh, isn’t it wonderful?

Bird Deaths

Trump has cited bird deaths before in his complaints about wind power, once falsely claiming that turbines “kill more than 1 million birds a year,” which we’ve previously debunked. According to the U.S. Fish & Wildlife Service, annual bird deaths from turbines range from as low as 21,000 to 679,000 — numbers that are well below the billions of estimated bird deaths from cats or the hundreds of millions from collisions with vehicles or buildings. The median value is 328,000.

This time, Trump implied that a single turbine might kill thousands of birds. Given that there about 58,000 turbines in the United States, even going with the larger estimate, basic math would suggest that each turbine is responsible for about 12 birds a year. And reports suggest the death toll doesn’t go even that high.

A 2013 study by biologists at the Smithsonian Migratory Bird Center and the U.S. Fish and Wildlife Service used data from 68 studies published between 2000 and 2012 to estimate the number of bird deaths from wind turbines. The group found that across the United States, the average number of bird deaths per turbine per year was just over five. That’s slightly more than one bird every season.

Of course, some turbines, whether due to height, design or location, take more avian lives than others. But in the 2013 study, even the worst-offending wind facility was responsible for killing fewer than 21 birds per turbine per year. Therefore, it’s extremely unlikely one would ever come across more than a handful of dead birds at any one time at the base of a turbine — certainly not thousands, as Trump claims.

What Happens When the Wind Doesn’t Blow?

Trump’s statement about there being “problems” when the wind doesn’t blow, which he mentioned twice and has said before in other settings, incorrectly suggests that a quiet day at the wind farm causes some sort of shock to the electrical system.

Because of fluctuations in the weather, and the inability to perfectly predict those changes, wind power does come with the added challenge of extra variability, and has one of the lower so-called capacity factors of all energy sources, since turbines are not always running.

But Trump’s own Department of Energy explains on its website that “power grid operators have always had to deal with variability,” noting that traditional forms of energy generation, which include coal, are also susceptible to breaks in service that the grid must accommodate. Usually, unless there are failures in multiple places, or extremely high demands — or both at once — grid operators can successfully divert energy to where it is needed most and avoid blackouts.

The DOE website continues, “Adding variable renewable power to the grid does not inherently change how this process of balancing electricity supply and demand works. Studies have shown that the grid can accommodate large penetrations of variable renewable power without sacrificing reliability, and without the need for ‘backup’ generation.”

One of the more prominent studies is the Western Wind and Solar Integration Study, which was sponsored by the National Renewable Energy Laboratory. The study concluded that adding up to 30 percent wind energy was completely feasible. In 2017, according to the U.S. Energy Information Administration, wind power was responsible for 6.3 percent of all utility-scale electricity generation, and no single energy source contributed more than 32 percent.

One of the tactics the study identified as improving overall efficiency — which more than compensated for wind or solar variability — was changing how frequently energy resources were scheduled. By evaluating supply and demand every 5 to 15 minutes instead of every 60 minutes, and then dispatching energy resources as needed, the system could make better use of the reserves it had at any moment and reduce the need to bring online additional generators.

Of course, wind energy would be more efficient if air was always gusting, and this is one reason why it’s better to set up your turbine in a windier area. But the lack of constant airflow is anticipated by the electrical grid. As a result, it’s misleading to call these ebbs in generation a “problem,” when it’s possible to appropriately manage them.

Turbine Noise: Loud Enough to Drive Someone Crazy?

Trump’s third claim revolves around the noise associated with wind turbines; he says living near a turbine could cause people to “go crazy after a couple of years.” But there is no evidence for that.

Turbines do emit noise, both from the blades swishing through the air as they rotate, and from the mechanical elements inside the turbine, such as the hum from the internal generator.

These elements can create several different types of sound, which vary based on their frequencies and sound wave characteristics, including:

broadband sound (a mix of different frequencies, might sound like “whooshing”)

infrasonic sound, or infrasound (extremely low frequency sound that’s omnipresent in the environment and travels longer distances but also blends into the background; in many cases inaudible)

impulsive sound (swishing sounds that fluctuate in loudness)

tonal sound (specific pitches)

But as the DOE explains, these sounds are typically less than 40 decibels (dBA) — roughly the noise level of a library, or what experts call “the lowest limit of urban ambient sound” — when measured 437 yards from a turbine. Forty decibels is also the World Health Organization’s maximum recommended average nighttime sound pressure level outside bedrooms. Wind farms are usually located as far from residential homes as possible, and while there are no federal laws dictating the distance, local regulations specify volume limits. A 2017 review notes that “in most studies there are few people, if any, exposed to an average sound level of over 45 dBA,” which is the equivalent of a refrigerator hum.

This doesn’t guarantee a person won’t hear a turbine at all, and these low volumes can still annoy some people. Anecdotally, many people have complained of headaches, dizziness or tinnitus (ringing in ears), among other symptoms, and have attributed them to turbine noise, sometimes calling it wind turbine syndrome.

But numerous scientific reviews, many of them conducted by expert panels on behalf of states and countries investigating the issue, find no evidence that physical or mental health is directly at risk because of turbines. Wind turbine syndrome is not a recognized disease.

For example, a 2013 systematic review from Australia concluded there is “no consistent evidence” that wind turbine noise is associated with health effects, noting that the few associations that have been reported “may be due to confounding, bias or chance.”

The review added that there was “consistent evidence” of annoyance, and “reasonable consistency” that turbines might disrupt sleep, but that “it is unclear whether the observed associations are due to wind turbine noise or plausible confounders.”

In short, scientists can’t definitively rule out health effects, but currently, there is not good evidence that they exist, and even those that are more likely, like sleep disturbances, might be explained by other factors.

Reports by others, including the states of Massachusetts and Oregon, came to similar conclusions.

One of the biggest concerns about wind turbines are the low-frequency sounds, especially the lowest-frequency sound, or infrasound, that turbines give off.

While scientists don’t fully understand infrasound, several lines of evidence indicate these frequencies are not damaging:

As part of testing for the U.S. space program, human subjects found infrasound as loud as 130 decibels “tolerable” for 24 hours. These levels are much higher than anything a person would receive from a turbine, although they were also of a shorter duration.

We are already exposed to infrasound all the time: Our heartbeats and other internal organs — not to mention other natural sources like the ocean — give off amazingly low frequency sound waves all the time.

Other everyday sources of infrasound likely overpower that of turbines anyway. A 2008 Danish report found that traffic on roads next to wind farms was louder than anything the turbines were producing.

Clearly, infrasound is not inherently problematic to humans. Because very low frequencies must have very high amplitudes to be heard, and turbines do not get that loud, any infrasound risk would have to come from inaudible or barely audible sounds. Most researchers do not think these levels are dangerous. A few note that it might be possible for humans to subliminally detect such sounds, although they are unsure of what those effects are, or how damaging they could be.

One of the more plausible mechanisms for adverse effects is sleep disruption. Because poor or inadequate sleep is tied to a variety of health conditions, if someone wakes up more or has trouble staying asleep, it’s possible turbines could be negatively affecting their health. Several studies have looked at this, with some finding a correlation and others not. The studies, however, rely on self-reported measures of sleep, do not always control for confounding factors, like age, and in some cases people exposed to higher levels of turbine noise had fewer difficulties sleeping — the opposite of what one would expect if turbines were causing sleep problems.

Notably, one 2016 study, which was conducted by Health Canada, Canada’s public health department, and published in the Sleep Research Society’s journal, SLEEP, found no relationship between sleep disruption and wind turbine noise. The authors describe their study as “the most comprehensive assessment to date of the potential association between exposure to wind turbine noise (WTN) and sleep,” and “the only study to include both subjective and objective measures of sleep.” Instead, poor sleep was related to how much caffeine residents consumed and other factors, such as health conditions and sleep medication.

The most consistent finding about wind turbines is that some people say they are annoying and that the louder the sound is, the more annoyed people tend to be. This annoyance, however, is not even always driven by noise. Several investigations have found that whether or not someone could see a turbine was more important than the amount of sound they could hear. The degree of annoyance is also often lower if a person receives an economic benefit, such as owning or partially owning the turbine.

An Alternative Explanation

In some cases, as in the sleep results, it’s possible that people who have other health conditions are simply attributing their problems to wind turbines. But some scientists suspect another phenomenon might also be involved: the nocebo effect.

The nocebo effect is when a person develops negative symptoms after they are told something is harmful to them — even when the item is completely innocuous. It’s a kind of reverse placebo effect. Instead of a sugar pill improving your symptoms, it’s a sugar pill making you sick, because you were told it was a poison.

Researchers at the University of Auckland tested whether the nocebo effect could be observed with respect to infrasound. The scientists recruited 54 volunteers and showed half of them a five-minute video in which people complained about various maladies they thought had come from exposure to wind farms. The other half watched a video that included the scientific consensus that wind farms are safe. Everyone was then told they would be exposed to 10 minutes of infrasound, although in reality, half the group wasn’t exposed to anything at all. Afterward, participants were asked whether they felt any symptoms. Regardless of whether they had been exposed to infrasound, the people who had been primed to suspect a problem reported more symptoms. While this experiment doesn’t precisely replicate living near a wind turbine, it indicates the power of suggestion about turbines can be quite strong.

A similar experiment by the same group showed that one could also give positive information about infrasound to get people to believe the opposite. Participants told about therapeutic benefits said they felt better after their infrasound exposure, regardless of whether they actually were exposed to infrasound. In short, people appear to be highly susceptible to both placebo and nocebo effects with respect to turbines.

Other research from 2013 supports the notion that the flurry of health complaints may have more to do with the spread of misinformation about turbines rather than any aspect of the turbines themselves. In the study, which was published in the journal PLoS One, researchers at the University of Sydney analyzed the origin and timing of complaints made to wind farm operators in Australia between 1993 and 2013. Of the 129 people who complained, 73 percent were residents living near the six wind farms the authors described as being “targeted by anti wind farm groups.” In contrast, nearly 65 percent of wind farms had not registered a single complaint. Ninety percent of complainants, the authors added, “made their first complaint after 2009 when anti wind farm groups began to add health concerns to their wider opposition.” The researchers argue that these symptoms are instead a kind of “communicated disease” that comes about because of the nocebo effect.

Whether or not fear over turbines is spreading a disease, the evidence to date does not indicate that turbines themselves directly cause mental illness or disease.

Trump’s comments, therefore, on turbines at his recent rally are inaccurate or misleading on all three counts: He exaggerated the number of birds killed by turbines; he mischaracterized what happens on a wind farm when the wind isn’t blowing, and he overstated the health risks.