For more than a decade, National Park Service scientists Kurt Fristrup and Dan Mennit, along with Colorado State University researchers, have been monitoring background noise levels at around 600 sites across more than 90 national U.S. parks. The researchers feared that human-made noise—like the doubling and tripling of cars and airplanes in the U.S. since the ‘70s—was spoiling the parks’ natural soundscapes and disturbing wildlife. Turns out they were right. The growing noise is even affecting human health.
The link between noise pollution and human health issues is well documented. Effects include high blood pressure, poor sleep, and cardiovascular disease. In large cities, sound can often exceed 65 decibels—the threshold where it becomes annoying and can affect our hearing and our hearts. In nature, sound rarely exceeds 40 decibels. That’s where our bodies appear to be most comfortable. But, the researchers found, it’s becoming nearly impossible to find such serenity.
By feeding more than 1.5 million hours of collected acoustic data into a computer algorithm, the National Park Service created a set of maps to give a better picture of average sound levels across the U.S. The first map shows average background sound levels for locations during the summer and looks similar to satellite photo taken of the continent at night:
The second map shows artificial noises set to minimum values as if human activity never had existed:
And the third predicts the difference between the first and second to measure impact of human-made noise on areas around the country:
The first map’s sound scale runs from a low of 20 decibels (the lowest limit that a sound meter can measure) in areas of the West to a high of 67 decibels in some larger cities. Put into context, a typical quiet classroom where no one is speaking registers at about 35 decibels. According to Fristrup, there are many national park settings that are 15 decibels below that.
“Those are the deepest blues on the maps, while the brightest colors are high enough to have a measurable impact on cardiovascular health,” Fristrup said at the annual meeting of the American Association of the Advancement of Science in San Jose, California.
But those sites are dwindling. Every site Fistrup and his colleagues studied—including the remote backcountry—was affected by aircraft noise at the least. Propeller planes flying overhead can create noise at 70 decibels or greater. That’s making it hard for us humans to chill out in the wilderness.
Social scientist Derrick Taff of Penn State University conducted an experiment in which he had folks give impromptu speeches, which expectedly raised subjects’ heart rates and cortisol levels. Then the subjects watched a scene in Yosemite where their heart rates noticeably dropped, only to speed up again at the sound of a motorcycle or propeller airplane.
It’s not just our serenity at stake. According to biologist Clint Francis of California Polytechnic State, the noise reduces the density and reproduction of animals including reptiles, marine mammals and birds. In combination with artificial light, like that from road lights, it can reduce diversity of a given area’s species by a third or more.
(It must be noted that the noise hasn’t been bad for all species. In some areas, black-chinned hummingbirds have benefitted from better nesting environments absent of predators.)
If the objective is to give national park visitors a restorative setting that benefits their minds, stress levels, and cardiovascular health, Taff said, then the evidence suggests we need to work harder to manage sound levels. “They hear human-caused noise, it’s unacceptable, and annoying,” he said.
Some efforts are already underway, including plans to reduce noise from snowmobiles and motorized boats in Yellowstone, reduce aircraft flyovers in areas over the Grand Canyon and Denali National Parks, as well as increasing general use of electric vehicles all around.
But it’s also up to individual park-goers. We need to learn to appreciate natural sounds like bird song and rushing water, Fristrup said. He’s concerned that young people immersed in technology may suffer from a “lost auditory awareness.” So take off those earphones and listen while in the park, he suggests.
Another way to help: assisting in citizen science projects such as monitoring noise levels on an iPhone with WideNoise or mappiness. Your collected data can help researchers study and establish methods to reduce sound and light.
“What we’re learning is that sound and dark skies are becoming more appreciated as part of the experience of national parks. Visitors seek natural sounds, natural quiet, wind, water and bird song,” Taff said. But we all have to do our part to ensure parks stay quiet, so we hear.